Question 1

Phage typing is based on the fact that?

Accepted Answer

Answer reason: Phage typing relies on the principle of bacteriophage host specificity—many phages infect only particular bacterial species and often only certain strains within that species. By observing which phages lyse an isolate (its lysis pattern), labs can distinguish and epidemiologically track bacterial strains during outbreaks. The key discriminator is this selective susceptibility, not the general fact that viruses can kill bacteria. Options about viruses causing disease or Staphylococcus infections are unrelated to the typing method itself.

Question 2

The arrangement of organisms into taxa?

Accepted Answer

Answer reason: Modern biological classification (taxonomy/systematics) aims to reflect phylogeny, meaning taxa are organized to represent evolutionary relationships. As organisms share a more recent common ancestry, they are grouped more closely (e.g., same genus vs. different families). This is why classification is not arbitrary and is not simply a historical scheme “designed by Darwin,” even though evolutionary theory underpins it. While “degrees of relatedness” and “common ancestors” describe outcomes of classification, the foundational organizing principle is evolutionary history.

Question 3

Into which group would you place a multicellular organism that has a mouth and lives inside the human liver?

Accepted Answer

Answer reason: Many helminths (parasitic worms) that can inhabit the human hepatobiliary system are multicellular eukaryotes classified in Animalia. Fungi and Plantae are also eukaryotic but do not have a mouth; they obtain nutrients by absorption (fungi) or photosynthesis/absorption (plants). Firmicutes and Proteobacteria are bacterial phyla and therefore unicellular prokaryotes, making them incompatible with the stem’s description.

Question 4

Which of the following provides taxonomic information that includes the information obtained in the others listed?

Accepted Answer

Answer reason: The other options are individual methods that generate specific types of similarity/difference information, but each provides a narrower slice of taxonomic evidence. By contrast, the cladogram is the taxonomic product that can incorporate and display all those inputs in a unified classification framework. This makes it the most inclusive option for taxonomic information among the choices.

Question 5

Which of the following criteria is most useful in determining whether two organisms are related?

Accepted Answer

Answer reason: A core principle of bacterial classification is that cell wall structure and staining characteristics (Gram reaction) reflect major phylogenetic groupings and broad structural similarity. Gram positivity indicates a thick peptidoglycan cell wall and lack of an outer membrane, which is a more fundamental, conserved trait than many metabolic or behavioral features. Lactose fermentation, motility, and oxygen requirements can be shared across unrelated taxa and can also be gained/lost relatively easily compared with cell envelope architecture. Therefore, Gram stain result is typically more useful for determining relatedness at a broad level than the other listed single traits.

Question 6

Fimbriae and pili differ in that?

Accepted Answer

Answer reason: The key distinction is functional: fimbriae primarily mediate adherence to host cells and surfaces, whereas pili (sex pili) mediate bacterial conjugation. Conjugation involves direct cell-to-cell contact and transfer of genetic material (typically plasmid DNA) from a donor to a recipient. While some pili types can contribute to twitching motility, that is not the defining difference versus fimbriae being tested here. Therefore, DNA transfer is the most specific differentiator among the choices.

Question 7

Each of the following statements concerning the gram-positive cell wall is true EXCEPT?

Accepted Answer

Answer reason: The bacterial cell wall primarily prevents osmotic lysis in hypotonic environments by providing rigidity against inward water flux and swelling. In a hypertonic environment, cells lose water and can undergo plasmolysis, and the wall does not “protect” against dehydration in the same way. Gram-positive walls are thick peptidoglycan that helps maintain cell shape, are targets for lysozyme cleavage of peptidoglycan bonds, and are generally more susceptible to beta-lactams that inhibit peptidoglycan cross-linking. Teichoic acids are a characteristic structural component of gram-positive cell walls and support their identification and antigenic properties.

Question 8

Antibiotics that target cell wall synthesis ultimately cause bacterial cell death as a result of?

Accepted Answer

Answer reason: Inhibiting bacterial cell wall synthesis weakens peptidoglycan, which normally protects the cell from bursting under hypotonic conditions. Without an intact wall, water influx driven by osmotic pressure causes the cytoplasmic membrane to rupture, leading to death. This mechanism is characteristic of beta-lactams and other cell wall–active agents and is most effective against actively dividing bacteria. By contrast, plasmolysis and cell shrinkage occur in hypertonic environments and are not the lethal consequence of blocking wall synthesis. Reduced plasma membrane synthesis and transport inhibition are different antimicrobial targets and do not explain the classic bactericidal effect of cell wall inhibitors.

Question 9

Which of the following pairs is mismatched?

Accepted Answer

Answer reason: The centrosome is the major microtubule-organizing center in animal cells and is essential for mitotic spindle formation during cell division, not nutrient or food storage. In contrast, the endoplasmic reticulum participates in intracellular transport, the Golgi apparatus modifies and packages proteins for secretion, mitochondria generate ATP via oxidative phosphorylation, and lysosomes contain hydrolytic enzymes for intracellular digestion. A common confusion is mixing up storage roles, which are more associated with vacuoles (especially in plants) rather than the centrosome.

Question 10

A gram-positive bacterium suddenly acquires resistance to the antibiotic methicillin. This trait most likely occurred due to acquisition of new genetic information through?

Accepted Answer

Answer reason: Antibiotic resistance in bacteria commonly arises via horizontal gene transfer, where preformed resistance genes are acquired from another bacterium. Conjugation transfers plasmids (often R plasmids) through cell-to-cell contact via a sex pilus, making it a highly efficient mechanism for rapid spread of resistance traits. Binary fission only produces clonal offspring and does not introduce new genetic information from other cells, while meiosis does not occur in bacteria. Although transformation and transduction can also move genes, the classic rapid acquisition and dissemination of resistance determinants is most strongly associated with plasmid-mediated transfer through direct bacterial contact.

Question 11

You have isolated a motile, gram-positive cell with no visible nucleus. You can safely assume that the cell?

Accepted Answer

Answer reason: A gram-positive organism is, by definition, a bacterium with a thick peptidoglycan cell wall that retains crystal violet on Gram stain. The absence of a visible nucleus further supports that it is prokaryotic, which also rules out membrane-bound organelles like mitochondria. Motility in bacteria is typically via prokaryotic flagella, not eukaryotic 9+2 microtubule structures or cilia. “Extreme environment” would suggest many archaea, but Gram-positive staining and classic peptidoglycan cell wall architecture point most strongly to a bacterial cell wall.

Question 12

A patient presents with inflammation of the heart valves, fever, malaise, and subcutaneous nodules at joints. The recommended treatment is?

Accepted Answer

Answer reason: The symptom cluster of valvular inflammation with fever, malaise, and subcutaneous periarticular nodules is most consistent with acute rheumatic fever (post–Group A streptococcal immune-mediated disease) rather than an active infection requiring a specific antimicrobial. Management is primarily symptomatic and anti-inflammatory (e.g., rest, NSAIDs/salicylates, and supportive measures), with eradication of any antecedent strep infection typically done with penicillin (not listed). The other options are treatments for different pathogens/conditions (streptomycin for certain bacteria like plague/TB, chloroquine for malaria, hyperbaric oxygen for CO poisoning/gas gangrene, praziquantel for trematodes/cestodes), so they do not match this presentation. Therefore, the best answer among the choices is supportive management.

Question 13

Which of the following statements about toxoplasmosis is FALSE?

Accepted Answer

Answer reason: Toxoplasmosis is typically asymptomatic or a mild, self-limited, mononucleosis-like illness in immunocompetent adults, so describing it as generally severe is inaccurate. Severe disease is more characteristic in immunocompromised patients (e.g., AIDS, transplant) where encephalitis and disseminated infection can occur. The organism is a protozoan (Toxoplasma gondii) with cats as the definitive host that shed oocysts, supporting the reservoir statement. Transmission commonly occurs via ingestion (fecal–oral/foodborne) and the infection can cross the placenta causing congenital disease.

Question 14

Unsanitary and crowded conditions increase the incidence of all of the following diseases EXCEPT?

Accepted Answer

Answer reason: Crowding and poor sanitation particularly increase transmission of arthropod-borne infections linked to human ectoparasites (lice) and rodents/fleas, because these settings promote close contact, infestation, and reservoir proliferation. Epidemic typhus and louse-borne relapsing fever are classic diseases of crowded, unhygienic conditions where body lice spread pathogens between people. Plague and endemic murine typhus are associated with rodent–flea cycles, which are facilitated by poor sanitation that attracts rodents and increases flea exposure. Rocky Mountain spotted fever is primarily a tick-borne infection associated with tick habitats and outdoor exposure rather than specifically with unsanitary, crowded living conditions.

Question 15

Epidemics related to bacterial infection of the digestive system are typically caused by?

Accepted Answer

Answer reason: Enteric bacterial outbreaks most commonly spread via the fecal–oral route when sanitation fails, leading to contaminated drinking water or food handling that allows pathogens to multiply. This mechanism explains community-wide epidemics because many people share the same water source or food distribution chain. Unpasteurized milk can cause outbreaks, but it is a narrower exposure category that falls under foodborne transmission rather than the broader and most typical cause. Respiratory transmission and soil exposure are not the predominant routes for epidemic digestive bacterial infections compared with food/water contamination.

Question 16

Aflatoxin is a(n) ______ associated with ingestion of contaminated ______?

Accepted Answer

Answer reason: They most classically contaminate improperly stored nuts and grains, with peanuts being a high-yield association due to warm, humid storage conditions that favor fungal growth. Ingestion can lead to hepatotoxicity and increased risk of hepatocellular carcinoma, reinforcing the importance of recognizing the toxin’s fungal origin. Rye/cereal grain contamination is more classically tested with ergot alkaloids (Claviceps) rather than aflatoxin in many exam contexts, making that pairing less specific here.

Question 17

Clostridium difficile-associated diarrhea is usually preceded by?

Accepted Answer

Answer reason: Difficile diarrhea classically follows disruption of normal colonic flora, most commonly after recent or prolonged antibiotic exposure (eg, clindamycin, cephalosporins, fluoroquinolones), allowing toxin-producing strains to overgrow. The resulting toxins (A and B) cause watery diarrhea and can progress to pseudomembranous colitis. Foodborne exposures and improper storage more strongly suggest preformed toxin or enteric pathogens like Staphylococcus aureus or Bacillus cereus rather than C. difficile. Travel-related diarrhea typically points to organisms such as ETEC, not antibiotic-associated colitis.

Question 18

Disease-causing exotoxins are produced by all of the following organisms EXCEPT?

Accepted Answer

Answer reason: Exotoxins are typically actively secreted protein toxins, classically produced by many Gram-positive and some Gram-negative bacteria, and are often the primary drivers of specific toxidromes (e.g., botulism, cholera, toxin-mediated food poisoning). Clostridium perfringens, Vibrio cholerae, Staphylococcus aureus, and Clostridium botulinum are well-known for clinically important exotoxins that are central to their disease manifestations. In contrast, Shigella is commonly taught as causing disease largely through invasion and inflammation of the colonic mucosa, rather than being categorized alongside the classic exotoxin-producing organisms in many nursing microbiology frameworks. This makes it the best “EXCEPT” choice among the listed organisms when testing recognition of classic exotoxin producers.

Question 19

Which one of the following diseases of the gastrointestinal system is transmitted by the respiratory route?

Accepted Answer

Answer reason: Mumps virus classically spreads person-to-person through respiratory droplets and saliva, then disseminates systemically and can involve salivary glands and other organs. In contrast, staphylococcal enterotoxicosis is a toxin-mediated food poisoning from ingestion of preformed toxin, and Vibrio gastroenteritis is typically acquired from contaminated seafood/water. Bacillary dysentery and traveler’s diarrhea are primarily fecal–oral infections linked to contaminated food or water rather than droplet spread.

Question 20

Which of the following helminthic diseases is a common infestation found in the southeastern United States?

Accepted Answer

Answer reason: Whipworm is classically associated with the southeastern United States (historically including Appalachia) as an endemic soil-transmitted intestinal helminth. This makes it the best match to a location-based “common infestation” question. By contrast, beef tapeworm and hydatid disease are not typically described as common endemic infestations of the U.S. Southeast.

Question 21

Acute gastroenteritis that occurs after an incubation period of two to three days and commonly affects children is probably caused by?

Accepted Answer

Answer reason: Incubation of about 1–3 days with acute watery diarrhea in young children most strongly matches viral gastroenteritis due to rotavirus. Rotavirus is a leading cause of pediatric gastroenteritis worldwide and classically presents with vomiting followed by watery diarrhea and dehydration risk. By contrast, Staphylococcus aureus food poisoning has a much shorter incubation (hours) due to preformed toxin, and Giardia typically causes more subacute to chronic malabsorptive diarrhea. Salmonella is more associated with inflammatory diarrhea/fever and variable incubation, and Trichinella is linked to undercooked pork with systemic myalgias and eosinophilia rather than isolated acute pediatric gastroenteritis.

Question 22

Which of the following organisms is likely to be transmitted via contaminated shrimp?

Accepted Answer

Answer reason: This organism commonly causes acute watery diarrhea, abdominal cramps, and sometimes nausea/vomiting after ingestion of contaminated seafood. Trichinella is linked to undercooked pork or wild game, not shrimp, and Giardia is typically waterborne from fecal contamination of freshwater sources. Clostridium perfringens and Staphylococcus aureus are toxin-mediated food poisonings more often tied to improperly stored meats, gravies, or prepared foods rather than marine shrimp exposure.

Question 23

Which of the following organisms is likely to be transmitted via undercooked pork and horse?

Accepted Answer

Answer reason: This parasite is classically associated with undercooked pork and can also be acquired from undercooked horse meat, leading to trichinellosis with GI symptoms followed by myalgias, fever, and eosinophilia as larvae invade muscle. The other listed organisms are typically transmitted via fecal–oral contamination (e.g., Shigella, Entamoeba) or preformed toxin/skin contamination (Staphylococcus) rather than via encysted larvae in meat. Salmonella is commonly linked to poultry/eggs and can involve meats, but the specific pork-and-horse association most strongly indicates this parasite.

Question 24

All of the following organisms cause meningitis EXCEPT?

Accepted Answer

Answer reason: Meningitis is most commonly caused by specific bacteria (e.g., encapsulated respiratory pathogens), certain fungi in immunocompromised hosts, and a few other pathogens known to invade the meninges. Neisseria meningitidis, Streptococcus pneumoniae, and Haemophilus influenzae are classic bacterial causes of acute meningitis, and Cryptococcus neoformans is a well-known cause of chronic meningitis especially in advanced immunosuppression. Mycobacterium leprae primarily causes Hansen disease with skin and peripheral nerve involvement rather than typical meningeal infection. A common distractor is confusing it with Mycobacterium tuberculosis, which can cause tuberculous meningitis, but that is a different organism.

Question 25

A pathologist detects Negri bodies while examining a brain section taken at autopsy. What was the cause of death?

Accepted Answer

Answer reason: Their presence on brain histopathology strongly supports rabies encephalitis as the lethal diagnosis. The other options do not produce Negri bodies: meningococcal meningitis is identified by neutrophilic meningitis with gram-negative diplococci, eastern equine encephalitis causes viral encephalitis without this specific inclusion, Hansen's disease targets peripheral nerves, and poliomyelitis primarily affects anterior horn cells with different histologic findings. Therefore the autopsy finding points to fatal rabies infection.

Question 26

Which of the following pairs is mismatched?

Accepted Answer

Answer reason: Labeling it as a respiratory-route infection is therefore a mismatch for the usual epidemiology and infection-control teaching. In contrast, meningococcal meningitis spreads via respiratory droplets/secretions, and listeriosis is classically acquired by ingestion of contaminated foods. Rabies transmission requires inoculation of virus in saliva into tissue (typically bites), which is reasonably captured by direct contact with infected saliva rather than airborne spread.

Question 27

Which of the following vaccines can cause the disease it is designed to prevent?

Accepted Answer

Answer reason: The oral polio vaccine is live-attenuated and has a known (very rare) risk of vaccine-associated paralytic poliomyelitis due to reversion to neurovirulence. In contrast, toxoid vaccines (e.g., tetanus) contain inactivated toxin and cannot cause the disease, and inactivated polio vaccine cannot replicate so it cannot cause poliomyelitis. Conjugate/capsular vaccines for Hib and meningococcus contain purified bacterial polysaccharide (often conjugated) and do not contain live bacteria capable of causing invasive disease.

Question 28

Arboviruses cause ______ and are transmitted by ______?

Accepted Answer

Answer reason: Many clinically important arboviruses (e.g., West Nile, Eastern/Western equine encephalitis, Japanese encephalitis) primarily present as encephalitis due to CNS invasion and inflammation. Dog bites point to rabies rather than arboviral disease, and bees are not a typical arboviral vector. While some infections can involve meningitis or meningoencephalitis, the best single association tested is encephalitis with mosquitoes.

Question 29

The lower respiratory tract is protected by all of the following EXCEPT?

Accepted Answer

Answer reason: A key principle of respiratory host defense is that the lower airways and alveoli are normally kept relatively sterile by mechanical clearance and innate immune mechanisms. Mucus and the mucociliary (ciliary) escalator trap and move inhaled organisms upward for removal, while alveolar macrophages phagocytose particles that reach distal airspaces. Secretory IgA contributes to mucosal immunity by limiting microbial adherence and colonization in the respiratory tract. In contrast, reliance on resident “normal flora” competition is not a major protective mechanism in the lungs because significant colonizing flora is not typically present in the lower respiratory tract.

Question 30

Which one of the following produces small "fried-egg" colonies on medium containing horse serum and yeast extract?

Accepted Answer

Answer reason: Their characteristic colony morphology shows a dense central zone with a lighter peripheral zone, producing the classic “fried-egg” appearance. This feature is most associated with Mycoplasma (e.g., M. pneumoniae) and helps distinguish it from other respiratory pathogens. In contrast, Legionella requires buffered charcoal yeast extract agar and does not produce the fried-egg colony pattern on serum-enriched media.

Question 31

All of the following can lead to a positive tuberculin skin test EXCEPT?

Accepted Answer

Answer reason: A tuberculin skin test (PPD) detects a delayed-type (type IV) hypersensitivity response indicating prior sensitization to mycobacterial antigens, not protective immunity. Active TB infection and prior/latent infection can both produce a positive reaction because memory T cells are already primed. Prior vaccination with BCG can also cause a positive PPD due to antigenic cross-reactivity. Mere proximity to a person with TB does not inherently create “immunity”; it may or may not result in infection/sensitization, so the concept of immunity itself is not what drives PPD positivity.

Question 32

Which of the following is mismatched?

Accepted Answer

Answer reason: Whooping cough (pertussis) is caused by Bordetella pertussis, not by Mycobacterium species. Mycobacterium is classically linked to diseases such as tuberculosis and atypical mycobacterial pulmonary infections, which present differently from pertussis. The other pairings listed are standard matches (e.g., Coxiella burnetii with Q fever and Mycoplasma pneumoniae with atypical “walking” pneumonia). Therefore, the Mycobacterium pairing is the mismatch.

Question 33

Which one of the following produces the most potent exotoxin?

Accepted Answer

Answer reason: This organism produces diphtheria toxin, an A-B toxin that inactivates EF-2 via ADP-ribosylation, abruptly halting host protein synthesis and leading to profound local tissue necrosis and systemic effects (e.g., myocarditis, neuropathy). While Streptococcus pyogenes can produce potent toxins (e.g., pyrogenic exotoxins), they are generally not considered as classically “most potent” as diphtheria toxin in standard microbiology comparisons. Mycobacterium tuberculosis primarily causes disease through cell-mediated immune responses and does not rely on a hallmark secreted exotoxin for virulence.

Question 34

Microscopic examination of a lung biopsy shows thick-walled cysts. What is the etiology of the symptoms?

Accepted Answer

Answer reason: The organism forms cystic structures in alveoli that can be highlighted with special stains (e.g., silver stain), correlating with this description. The other endemic dimorphic fungi listed more typically show characteristic yeasts/spherules rather than the hallmark thick-walled cysts in alveolar spaces. Mycobacterial disease is characterized by acid-fast bacilli and granulomatous inflammation, not cyst forms.

Question 35

A patient has a paroxysmal cough and mucus accumulation. What is the etiology of the symptoms?

Accepted Answer

Answer reason: This leads to accumulation of secretions and repeated cough paroxysms as the patient attempts to clear the airway. Corynebacterium is more associated with pharyngeal pseudomembrane and toxin-mediated systemic effects, not a hallmark paroxysmal cough syndrome. Mycoplasma typically causes atypical “walking” pneumonia with persistent dry cough rather than prominent mucus plugging and paroxysms.

Question 36

A patient who presents with red throat and tonsils can be diagnosed as having?

Accepted Answer

Answer reason: A red throat and erythematous tonsils are nonspecific findings that occur in multiple viral and bacterial upper-respiratory infections. Distinguishing streptococcal pharyngitis from viral pharyngitis typically requires additional clinical features (e.g., fever, tender anterior cervical nodes, absence of cough, tonsillar exudates) and/or confirmatory testing such as a rapid antigen detection test or throat culture. Scarlet fever would also require evidence of the characteristic sandpaper rash and strawberry tongue, while diphtheria classically features an adherent gray pseudomembrane and systemic toxicity, neither of which is provided. Because the stem lacks discriminating signs, symptoms, and test results, a specific diagnosis cannot be made safely from the given information alone.

Question 37

Which of the following is incorrectly matched?

Accepted Answer

Answer reason: Pseudomonas aeruginosa more typically causes severe bacterial keratitis, especially in contact lens wearers, and can also cause aggressive conjunctivitis but it is not the named etiology behind “inclusion” disease. The other pairings are standard microbiology associations: C. trachomatis with trachoma, N. gonorrhoeae with ophthalmia neonatorum, and Acanthamoeba with keratitis. Therefore this mismatch is the single best incorrect pairing.

Question 38

Which of the following pairs is mismatched?

Accepted Answer

Answer reason: Poxviruses classically cause diseases like smallpox (variola) and molluscum contagiosum, making this pairing incorrect. The other pairs match well-known etiologies: Chlamydia trachomatis can cause conjunctivitis, Acanthamoeba is a recognized cause of keratitis (especially in contact lens users), and Pseudomonas is a common cause of otitis externa. Buruli ulcer is caused by Mycobacterium ulcerans, so that pairing is also correct.

Question 39

Which of the following cause(s) ringworm?

Accepted Answer

Answer reason: The classic dermatophyte genera are Microsporum, Trichophyton, and Epidermophyton, making the pairing of Microsporum and Epidermophyton an appropriate cause list among the choices. Mycobacterium are acid-fast bacteria that cause diseases such as tuberculosis and leprosy, not dermatophyte tinea. Therefore the combined option including the two dermatophyte genera is superior to single-genus answers and to options that incorrectly include Mycobacterium.

Question 40

Which of the following pairs is mismatched?

Accepted Answer

Answer reason: The other pairings align with classic microbiology: Neisseria gonorrhoeae are gram-negative diplococci, chancroid is due to Haemophilus ducreyi (a gram-negative coccobacillus/rod), and Gardnerella vaginalis is associated with clue cells in bacterial vaginosis. Syphilis is caused by Treponema pallidum, a spirochete that is structurally gram-negative (though it stains poorly with Gram stain). Therefore the mismatch is the organism type assigned to trichomoniasis.

Question 41

Which of the following is NOT a complication of gonorrhea?

Accepted Answer

Answer reason: Neisseria gonorrhoeae can cause localized mucosal infection as well as disseminated gonococcal infection via bacteremia. Dissemination commonly presents with septic arthritis/tenosynovitis and can also lead to serious metastatic infections. Ascending infection in people with a uterus can cause pelvic inflammatory disease with risks of infertility and ectopic pregnancy. Though less common, bacteremic spread can involve the endocardium or meninges, so these are recognized potential complications rather than exclusions.

Question 42

A patient presents with fever and extensive lesions of the labia minora. Her VDRL test was negative. What is the most likely treatment?

Accepted Answer

Answer reason: A negative VDRL makes syphilis (typically a painless chancre) less likely, shifting management away from antibacterial therapy. Antiviral therapy reduces viral replication, shortens symptom duration, and decreases viral shedding when started early in an outbreak. Metronidazole targets anaerobes/Trichomonas, miconazole treats candidiasis, and cephalosporins are used for bacterial STIs like gonorrhea, none of which match ulcerative febrile lesions.

Question 43

Synthesis of a repressible enzyme is stopped by the?

Accepted Answer

Answer reason: Repressible operons (classically the trp operon) are “on” by default and are turned off when an end product acts as a corepressor. The corepressor binds the repressor protein, causing a conformational change that allows the repressor to bind the operator DNA sequence and block RNA polymerase from transcribing structural genes. This directly stops synthesis of the enzyme(s) encoded by that operon. A common distractor is the idea of the corepressor binding DNA by itself; in repressible systems the DNA-binding form is the repressor only after it has bound the corepressor.

Question 44

An enzyme that catalyzes the cutting and resealing of DNA, and is translated from insertion sequences, is?

Accepted Answer

Answer reason: Insertion sequences are simple transposable genetic elements that encode the enzyme required for their own movement within the genome. That enzyme performs sequence-specific DNA cleavage and then re-ligation to integrate the element into a new site, which is the defining biochemical role of this process. Ligase can seal DNA breaks but does not carry out the targeted cutting and mobilization program encoded by insertion sequences. Polymerases and helicase are replication/transcription enzymes and do not mediate transposition.

Question 45

If cells are grown in media containing amino acids labeled with radioactive nitrogen (15N), most of the radioactivity will be found in the cells'?

Accepted Answer

Answer reason: Amino acids are the direct building blocks used in translation to synthesize polypeptides, so nitrogen from labeled amino acids is incorporated primarily into cellular proteins. Although nucleic acids contain nitrogenous bases, amino-acid–derived nitrogen is not the main immediate precursor pool for nucleotide synthesis compared with dedicated nucleotide biosynthetic pathways. Phospholipids are largely composed of fatty acids and glycerol with a phosphate head group, so they incorporate minimal nitrogen unless considering specific nitrogen-containing head groups, making them a poorer sink for 15N from amino acids. Therefore, the greatest accumulation of radioactivity from 15N-labeled amino acids will be in newly made proteins.

Question 46

During which growth phase will gram-positive bacteria be most susceptible to penicillin?

Accepted Answer

Answer reason: In the exponential growth period, organisms are rapidly dividing, so transpeptidation and cell-wall remodeling are at their highest, making cell-wall inhibition most lethal, especially for gram-positive organisms with thick peptidoglycan. In lag and stationary phases, metabolic activity and division slow, reducing new cell-wall construction and decreasing drug killing. Death phase reflects declining viable cells, but susceptibility is not maximized because active growth processes are no longer prominent.

Question 47

A strictly fermentative bacterium produces energy?

Accepted Answer

Answer reason: Strictly fermentative organisms generate ATP exclusively via substrate-level phosphorylation, which occurs during glycolysis. They do not use an electron transport chain for oxidative phosphorylation, so aerobic respiration is not an energy option for them. Although oxygen may inhibit some fermenters, the defining metabolic feature is the absence of respiratory ATP production, not simply oxygen presence/absence. Therefore the best statement about how they produce energy is that it is limited to glycolysis-derived ATP with fermentation used to regenerate NAD+.

Question 48

Microorganisms that catabolize sugars into ethanol and hydrogen gas would most likely be categorized as?

Accepted Answer

Answer reason: Fermentation is an anaerobic metabolic process in which organisms convert sugars into reduced end products to regenerate NAD+ when an electron transport chain is not being used. Ethanol production from sugars is the hallmark end product profile of alcoholic fermentation, and gas production (e.g., CO2 or sometimes H2 depending on organism/pathway) commonly accompanies fermentative metabolism. Aerobic and anaerobic respiration are defined by use of an electron transport chain with an external terminal electron acceptor (O2 or an alternative such as nitrate), which does not primarily yield ethanol as the characteristic end product. Homolactic fermentation primarily produces lactic acid, and heterolactic fermentation typically yields lactic acid plus ethanol/CO2, making alcoholic fermenters the best match for ethanol-focused end products here.

Question 49

Which microscope is most useful for visualizing a biofilm?

Accepted Answer

Answer reason: Fluorescence methods (e.g., fluorescent dyes/probes for polysaccharides, nucleic acids, or viability) provide high contrast and allow clear visualization of architecture and heterogeneity within the biofilm. A standard compound light microscope often lacks contrast for unstained, hydrated biofilm matrix and tends to show only gross aggregates. Transmission electron microscopy offers ultrastructural detail but requires extensive processing that disrupts native biofilm structure and is less practical for intact biofilm visualization.

Question 50

Which microscope is best used for observing the surfaces of intact cells and viruses?

Accepted Answer

Answer reason: Light microscopes (brightfield, phase-contrast, darkfield) are limited by the diffraction limit of visible light and generally cannot resolve viruses or provide comparable surface detail. Fluorescence microscopy is powerful for detecting labeled structures or organisms, but it does not primarily provide detailed surface morphology of intact specimens. Therefore, SEM is the best choice when the question emphasizes observing surfaces and viruses.

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Phage typing is based on the fact that?

The arrangement of organisms into taxa?

Into which group would you place a multicellular organism that has a mouth and lives inside the human liver?

Which of the following provides taxonomic information that includes the information obtained in the others listed?

Which of the following criteria is most useful in determining whether two organisms are related?

Fimbriae and pili differ in that?

Each of the following statements concerning the gram-positive cell wall is true EXCEPT?

Antibiotics that target cell wall synthesis ultimately cause bacterial cell death as a result of?

Which of the following pairs is mismatched?

A gram-positive bacterium suddenly acquires resistance to the antibiotic methicillin. This trait most likely occurred due to acquisition of new genetic information through?

You have isolated a motile, gram-positive cell with no visible nucleus. You can safely assume that the cell?

A patient presents with inflammation of the heart valves, fever, malaise, and subcutaneous nodules at joints. The recommended treatment is?

Which of the following statements about toxoplasmosis is FALSE?

Unsanitary and crowded conditions increase the incidence of all of the following diseases EXCEPT?

Epidemics related to bacterial infection of the digestive system are typically caused by?

Aflatoxin is a(n) ______ associated with ingestion of contaminated ______?

Clostridium difficile-associated diarrhea is usually preceded by?

Disease-causing exotoxins are produced by all of the following organisms EXCEPT?

Which one of the following diseases of the gastrointestinal system is transmitted by the respiratory route?

Which of the following helminthic diseases is a common infestation found in the southeastern United States?

Acute gastroenteritis that occurs after an incubation period of two to three days and commonly affects children is probably caused by?

Which of the following organisms is likely to be transmitted via contaminated shrimp?

Which of the following organisms is likely to be transmitted via undercooked pork and horse?

All of the following organisms cause meningitis EXCEPT?

A pathologist detects Negri bodies while examining a brain section taken at autopsy. What was the cause of death?

Which of the following pairs is mismatched?

Which of the following vaccines can cause the disease it is designed to prevent?

Arboviruses cause ______ and are transmitted by ______?

The lower respiratory tract is protected by all of the following EXCEPT?

Which one of the following produces small "fried-egg" colonies on medium containing horse serum and yeast extract?

All of the following can lead to a positive tuberculin skin test EXCEPT?

Which of the following is mismatched?

Which one of the following produces the most potent exotoxin?

Microscopic examination of a lung biopsy shows thick-walled cysts. What is the etiology of the symptoms?

A patient has a paroxysmal cough and mucus accumulation. What is the etiology of the symptoms?

A patient who presents with red throat and tonsils can be diagnosed as having?

Which of the following is incorrectly matched?

Which of the following pairs is mismatched?

Which of the following cause(s) ringworm?

Which of the following pairs is mismatched?

Which of the following is NOT a complication of gonorrhea?

A patient presents with fever and extensive lesions of the labia minora. Her VDRL test was negative. What is the most likely treatment?

Synthesis of a repressible enzyme is stopped by the?

An enzyme that catalyzes the cutting and resealing of DNA, and is translated from insertion sequences, is?

If cells are grown in media containing amino acids labeled with radioactive nitrogen (15N), most of the radioactivity will be found in the cells'?

During which growth phase will gram-positive bacteria be most susceptible to penicillin?

A strictly fermentative bacterium produces energy?

Microorganisms that catabolize sugars into ethanol and hydrogen gas would most likely be categorized as?

Which microscope is most useful for visualizing a biofilm?

Which microscope is best used for observing the surfaces of intact cells and viruses?

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Aflatoxin is a(n) associated with ingestion of contaminated ?

Arboviruses cause and are transmitted by ?