Question 1

Which microscope takes advantage of differences in the refractive indexes of cell structures?

Accepted Answer

Answer reason: This makes unstained, living cells and internal structures easier to visualize without killing or altering them with stains. In contrast, darkfield emphasizes scattered light from specimen edges, fluorescence relies on fluorochromes emitting light, and electron microscopy depends on electron beam interactions rather than refractive index differences. Therefore, the instrument that specifically exploits refractive index differences is the phase-contrast microscope.

Question 2

The purpose of a mordant in the Gram stain is to?

Accepted Answer

Answer reason: In Gram staining, the mordant (iodine) forms a crystal violet–iodine complex that is larger and more tightly retained within the thick peptidoglycan of Gram-positive cell walls. This stabilizes the primary stain so it is not removed during the alcohol/acetone decolorization step. Without a mordant, the primary dye would wash out more easily and the differential staining between Gram-positive and Gram-negative organisms would be unreliable. Options about enlarging cells or visualizing flagella refer to different staining techniques, and Gram-negative visibility is achieved mainly by the counterstain after decolorization.

Question 3

Which microscope can be used to visualize DNA or botulinum toxin?

Accepted Answer

Answer reason: A scanning tunneling microscope provides atomic/nanometer-scale surface imaging by measuring electron tunneling current between a sharp probe and the specimen, enabling visualization of molecules such as DNA under appropriate conditions. In contrast, compound light and phase-contrast microscopes are limited to roughly ~200 nm resolution and cannot directly resolve DNA or toxin molecules. Confocal microscopy improves optical sectioning but remains limited by light resolution, and scanning electron microscopy primarily shows surface topography of larger specimens rather than directly imaging individual molecules like DNA.

Question 4

In using this microscope, the observer does NOT look directly at an image through a lens?

Accepted Answer

Answer reason: In contrast, compound light, phase-contrast, darkfield, and fluorescence microscopes are all light microscopes where the observer typically views the specimen through ocular lenses. The key principle tested is whether direct optical viewing is used versus indirect image detection. A common confusion is fluorescence microscopy, but it still uses a light path with eyepieces even though it detects emitted light from fluorochromes.

Question 5

Which of the following is never useful for observing living cells?

Accepted Answer

Answer reason: This makes it unsuitable for viewing live cells in real time, even though it provides high-resolution surface detail. In contrast, phase-contrast and darkfield microscopy enhance contrast in unstained, living specimens, making them commonly used for live-cell observation. Brightfield can also be used with living cells in wet mounts, but typically with less contrast unless staining is applied.

Question 6

Which microscope uses two beams of light to produce a three-dimensional color image?

Accepted Answer

Answer reason: This interference converts small differences in refractive index/thickness into strong contrast with an apparent relief (pseudo–3D) effect, often rendered with color/tinting depending on the optics and settings. Phase-contrast also enhances refractive index differences but does not rely on two separated beams and typically yields a flatter, haloed appearance rather than pronounced relief. Fluorescence depends on fluorophore excitation/emission, darkfield uses oblique illumination, and electron microscopy produces grayscale images from electrons rather than light beams.

Question 7

Which of the following methods is used to preserve food by slowing the metabolic processes of foodborne microbes?

Accepted Answer

Answer reason: Food preservation by cold primarily works through this metabolic suppression, which is why microbial growth is markedly reduced in frozen products. In contrast, pasteurization and ionizing radiation aim to reduce viable organisms by heat or DNA damage rather than simply slowing metabolism. Lyophilization preserves by removing water (desiccation), a different mechanism than metabolic slowing from cold.

Question 8

All of the following substances are effective against nonenveloped viruses EXCEPT?

Accepted Answer

Answer reason: Nonenveloped viruses lack a lipid envelope, making them relatively resistant to agents that act by dissolving lipids or disrupting membranes. Alcohol-based disinfectants are therefore less reliably virucidal against many nonenveloped viruses compared with oxidizing or alkylating methods. Chlorine and ozone are strong oxidizers that can inactivate viral capsid proteins and nucleic acids, and ethylene oxide sterilizes by alkylating proteins/DNA, making these more effective choices. A common pitfall is assuming hand sanitizer alcohol is broadly effective for all viruses; it is less effective against several nonenveloped viruses (e.g., norovirus).

Question 9

The antimicrobial activity of chlorine is due to which of the following?

Accepted Answer

Answer reason: HOCl penetrates microbial cell walls more effectively than the charged hypochlorite ion and then oxidizes critical cellular components such as proteins, enzymes, and nucleic acids. This oxidative damage rapidly disrupts essential metabolic processes and leads to cell death across a broad range of organisms. Hydrochloric acid is not the main antimicrobial species generated in chlorination, and ozone is a different disinfectant altogether.

Question 10

Application of heat to living cells can result in all of the following EXCEPT?

Accepted Answer

Answer reason: Heat kills cells primarily by disrupting protein structure and other macromolecules, which leads to loss of function and cell death. It can break hydrogen bonds, denature enzymes and structural proteins, and alter membrane permeability; at sufficiently high temperatures it can also damage nucleic acids. Thermal death time is a measurement used to describe how long it takes to kill a population at a given temperature, not a direct cellular effect of heat. While increasing temperature can reduce the measured thermal death time, that is a consequence of experimental conditions rather than a mechanism of heat injury to cells.

Question 11

Which of the following pairs is mismatched?

Accepted Answer

Answer reason: In contrast, Basidiomycota produce basidiospores, and Zygomycota characteristically form sporangiospores in sporangia, so those pairings are consistent. Microsporidia are classically described as lacking typical mitochondria (having highly reduced mitosomes), making that pairing acceptable in standard exam framing. The mismatch is therefore the statement that anamorphs lack spores, since their definition centers on spore-based asexual reproduction.

Question 12

Which of the following pairs is mismatched?

Accepted Answer

Answer reason: Green algae specifically are photosynthetic eukaryotes and are evolutionarily related to land plants. In contrast, prokaryotic photosynthesizers are cyanobacteria (historically called blue-green “algae”), not true algae. The other pairings are standard associations: dinoflagellate blooms can produce neurotoxins linked to shellfish poisoning, and algin/agar are derived from brown/red algae, respectively.

Question 13

In the malaria parasite life cycle, humans are the ______ host, while mosquitoes are the ______ host as well as the vector?

Accepted Answer

Answer reason: In malaria, Plasmodium completes sexual reproduction in the Anopheles mosquito (gametocytes develop into gametes, fertilization occurs, and sporozoites form), making the mosquito the definitive host and also the transmission vector. Humans support the asexual erythrocytic and hepatic stages, so they are the intermediate host. A common error is assuming humans are definitive because they manifest the disease, but host classification is based on the parasite’s reproductive cycle, not symptom severity.

Question 14

Which of the following pairs is mismatched?

Accepted Answer

Answer reason: In contrast, spirochetes characteristically have endoflagella (axial filaments) enabling corkscrew motility. Enteric bacteria (Enterobacterales) are predominantly gram-negative bacilli, and Mycobacterium are acid-fast due to mycolic acids in their cell wall. A common pitfall is confusing gram stain with morphology or oxygen preference, but Pseudomonas does not stain gram-positive under standard classification.

Question 15

Which of the following is the best reason to classify Streptococcus in the Lactobacillales?

Accepted Answer

Answer reason: rRNA gene sequences (notably 16S rRNA) are highly conserved, universally present in bacteria, and provide reliable evolutionary signals for higher-level taxonomy. In contrast, Gram reaction and morphology are broad phenotypic features shared across many unrelated groups and can mislead when used for classification beyond basic grouping. Traits like lactose fermentation or association with dairy are ecological/metabolic characteristics that vary within and across taxa and are not definitive for order-level classification.

Question 16

The crab industry needs female crabs for growing more crabs. What bacterium might be used to ensure development of female crabs and shrimp?

Accepted Answer

Answer reason: Using such a symbiont can therefore shift populations toward female development, which aligns with the industry goal of producing more egg-laying individuals. The other options are not classically associated with consistent, heritable sex-manipulation effects in crustaceans. This makes Wolbachia the best match to the question’s applied microbiology concept.

Question 17

Which of the following is NOT a characteristic of spirochetes?

Accepted Answer

Answer reason: Because of their small diameter, they are poorly visualized on routine brightfield microscopy and are typically better seen with dark-field microscopy, phase-contrast microscopy, or special stains (e.g., silver stain). Their outer envelope is structurally similar to gram-negative organisms, and they are characteristically helical. Some spirochetes are part of normal oral flora, so presence in the human oral cavity can be a true characteristic.

Question 18

Which of the following form conidiospores?

Accepted Answer

Answer reason: Actinomycetes (e.g., Streptomyces and related taxa) grow as branching filaments and can produce chains of conidia on aerial filaments, fitting this spore type. In contrast, endospore-forming gram-positive bacteria produce endospores (a survival structure formed inside the cell), which is a different process and spore type. Rickettsias are obligate intracellular bacteria and do not form conidia, and the remaining bacterial morphologic groups listed are not characterized by conidiospore production.

Question 19

Which of the following do you expect to be MOST resistant to high temperatures?

Accepted Answer

Answer reason: This organism is a classic endospore-forming Gram-positive rod, so it survives high temperatures far better than non–spore-forming species. The other listed organisms are vegetative cells without endospores and are comparatively susceptible to heat denaturation of proteins and membrane disruption. In practical terms, spore-formers are why sterilization requires higher heat/pressure (e.g., autoclaving) rather than simple boiling.

Question 20

Staphylococcus and Streptococcus can be easily differentiated in a laboratory by which one of the following?

Accepted Answer

Answer reason: 5% NaCl), whereas Streptococcus species are inhibited by this salt level. Both genera are Gram-positive cocci, so Gram stain reaction does not reliably distinguish them. They also share similar basic cell shape (cocci), with the more practical differentiation being salt tolerance rather than morphology alone. Traits like “ability to cause disease” and “glucose fermentation” are not consistent genus-level discriminators across the many species in each group.

Question 21

Which encephalitis is found predominantly west of the Mississippi River and occurs most often during the months of June and July?

Accepted Answer

Answer reason: Arboviral encephalitides have characteristic geographic distributions and seasonal peaks based on their mosquito vectors and reservoir hosts. Western equine encephalitis is classically associated with regions west of the Mississippi River and tends to occur in summer, with higher activity in early-to-mid summer. This aligns with the June–July timing described. In contrast, Eastern equine encephalitis is primarily seen in the Atlantic and Gulf Coast regions, not predominantly west of the Mississippi.

Question 22

A client with acquired immunodeficiency syndrome has developed a protozoa infection. Which opportunistic infection will the client most likely develop as a result of the protozoa infection?

Accepted Answer

Answer reason: Pneumocystis most commonly causes pneumonia with progressive dyspnea, nonproductive cough, and hypoxemia in advanced immunosuppression. Tuberculosis is a bacterial infection and histoplasmosis is a fungal infection, so they do not match the protozoal-opportunistic pattern implied by the stem. Kaposi's sarcoma is malignancy driven by HHV-8 rather than an opportunistic infection resulting from a protozoal organism.

Question 23

A 10-year-old child being treated for common warts asks the nurse about the cause. What is the most appropriate response by the nurse?

Accepted Answer

Answer reason: This explains why warts are contagious via direct skin-to-skin contact or fomites and why autoinoculation can occur with scratching. Coxsackievirus is more classically linked to hand-foot-and-mouth disease rather than typical common warts, and HHV causes vesicular lesions such as herpes. HIV is not a direct cause of warts, though immunosuppression can increase susceptibility and severity.

Question 24

Commercial sterilization differs from complete sterilization in that commercial sterilization?

Accepted Answer

Answer reason: Commercial sterilization is a heat-based process aimed at making food safe and shelf-stable by eliminating pathogens and most spoilage organisms, rather than achieving absolute sterility. Because it is not intended to destroy every organism and every endospore, heat-resistant organisms can remain. Thermophiles and their spores are specifically adapted to tolerate elevated temperatures and are classic survivors of insufficient sterilizing conditions, which distinguishes commercial from complete sterilization. In contrast, complete sterilization targets total microbial destruction, including the most resistant spores.

Question 25

What role do lactic acid bacteria play in cheese production?

Accepted Answer

Answer reason: Lactic acid bacteria ferment lactose to lactic acid, lowering pH and promoting coagulation of casein, which supports curd formation. As starter cultures they initiate biochemical changes during aging that drive ripening through proteolysis and lipolysis. Their metabolic products (e.g., organic acids and volatile compounds) contribute importantly to the characteristic flavor and aroma profile of many cheeses. In Swiss-type cheeses, interactions within the fermentation ecosystem can support gas formation leading to “eyes,” so the best answer is the inclusive choice rather than any single isolated effect.

Question 26

Bioreactors are widely used for industrial fermentation. Which of the following conditions must be closely monitored for optimal fermentation?

Accepted Answer

Answer reason: Temperature strongly affects enzyme kinetics and membrane function, so deviation reduces growth rate or denatures key enzymes. pH influences protein activity and transport across membranes; metabolic byproducts can shift pH and inhibit yield if not controlled. Oxygen availability determines whether metabolism proceeds aerobically or anaerobically, altering biomass and the type/amount of fermentation products, making it essential to monitor alongside the other parameters.

Question 27

Which of the following reactions makes wine less acidic, and is important for good flavor when grapes with higher acidity are used?

Accepted Answer

Answer reason: This process is carried out by lactic acid bacteria (e.g., Oenococcus), and is specifically used to soften high-acid wines and improve flavor balance. Converting ethanol to acetic acid would increase acidity and produce vinegar-like spoilage. The other listed reactions do not directly reduce the wine’s organic acid load in a way that improves acidity-related flavor.

Question 28

Which of the following places the steps in the PCR procedure in the correct order? 1) Incubate at 94°C to denature DNA strands; 2) Incubate at 72°C for DNA synthesis; 3) Incubate at 60°C for primer hybridization?

Accepted Answer

Answer reason: At ~94°C the hydrogen bonds between DNA strands break (denaturation), creating single-stranded templates. Cooling to around 50–65°C allows primers to anneal to their complementary sequences (primer hybridization). Raising to 72°C optimizes Taq polymerase activity for strand extension; placing synthesis before annealing would be impossible because the polymerase requires a primer with a free 3' OH end.

Question 29

The use of an antibiotic-resistance gene on a plasmid used in genetic engineering makes?

Accepted Answer

Answer reason: Selectable marker genes allow researchers to identify cells that have taken up a plasmid by applying a selective pressure. When an antibiotic is present in the medium, only bacteria expressing the resistance gene from the plasmid can grow, so transformants are selected directly. Replica plating is a related screening technique but is not the core function that the resistance marker provides in routine cloning workflows. The resistance gene does not inherently make the recombinant cell dangerous, and it generally improves survival under antibiotic exposure rather than preventing survival.

Question 30

Nucleic acid hybridization is based on the fact that?

Accepted Answer

Answer reason: Hybridization relies on the specificity of Watson-Crick base pairing, where nucleic acid strands with matching sequences anneal through hydrogen bonding (A-T/U and G-C). This principle allows a labeled probe to bind only to a target sequence with sufficient complementarity, enabling detection or identification of organisms/genes. Strand separation (denaturation) is a prerequisite step, but it is not the fundamental basis of why the probe binds specifically. Statements about genes, chromosomes, or all cells having DNA do not explain the core mechanism that produces selective binding.

Question 31

Bacteria and Archaea are similar in which of the following?

Accepted Answer

Answer reason: This makes “prokaryotic cells” the best shared classification across the two domains. In contrast, peptidoglycan is characteristic of bacterial cell walls but absent in archaea, and archaea have ether (not ester) membrane linkages. They also differ in translation initiation (bacteria use N-formylmethionine rather than methionine) and archaea are generally less susceptible to many antibacterial antibiotics that target bacterial-specific structures.

Question 32

Into which group would you place a photosynthetic organism that lacks a nucleus and has a thin peptidoglycan wall surrounded by an outer membrane?

Accepted Answer

Answer reason: A thin peptidoglycan layer plus an outer membrane is the defining cell envelope architecture of gram-negative bacteria. Many prokaryotes can be photosynthetic, so photosynthesis does not imply a plant kingdom classification. Firmicutes are gram-positive and therefore lack the outer membrane and typically have a thick peptidoglycan wall, making them inconsistent with the stem.

Question 33

If two organisms have similar rRNA sequences, you can conclude that they?

Accepted Answer

Answer reason: rRNA gene sequences (e.g., 16S/18S) are highly conserved and accumulate mutations slowly, making them reliable markers of evolutionary relatedness. Greater similarity in rRNA implies the organisms diverged more recently from the same lineage, supporting shared ancestry. Habitat overlap or traits like lactose fermentation are phenotypic and can be gained/lost independently, so they do not reliably track phylogeny. GC content can vary within related groups and is not the direct inference from rRNA sequence similarity. Many microbes do not mate in a way analogous to higher organisms, and rRNA similarity does not demonstrate gene exchange between the specific pair.

Question 34

What is the outstanding characteristic of the Kingdom Fungi?

Accepted Answer

Answer reason: Fungi are heterotrophic organisms that obtain nutrients by secreting enzymes into their environment and absorbing the resulting dissolved organic molecules. This absorptive mode of nutrition is a defining feature that distinguishes fungi from plants, which are primarily photosynthetic. Inorganic absorption is more characteristic of autotrophs using CO2 and minerals rather than preformed organic carbon. Fungi also vary widely in size (yeasts vs mushrooms), so neither “all microscopic” nor “all macroscopic” is universally true.

Question 35

A genus can best be defined as?

Accepted Answer

Answer reason: Taxonomic hierarchy in microbiology proceeds from broader to narrower groupings, and genus sits directly below family and above species. A genus is defined by grouping one or more closely related species that share key characteristics and evolutionary relationships. Options describing a grouping of families or classes are at higher ranks (family contains genera; class contains orders). The “most specific taxon” is species, not genus, making that choice incorrect.

Question 36

Which of the following is NOT a typical characteristic of most bacterial plasma membranes?

Accepted Answer

Answer reason: Because bacteria lack mitochondria, their electron transport chain and ATP synthesis are commonly associated with the cytoplasmic membrane, making energy production a typical feature. Cholesterol is generally a eukaryotic membrane component and is not present in most bacteria; instead, many bacteria use hopanoids or other lipids to modulate membrane fluidity. Selective permeability is a core function of bacterial membranes, maintained by the lipid bilayer and transport proteins.

Question 37

Which one of the following pairs is mismatched?

Accepted Answer

Answer reason: Carbon storage in many bacteria is typically in cytoplasmic inclusion bodies such as glycogen granules or polyhydroxyalkanoates (e.g., PHB), which function as reserve materials. In contrast, metachromatic (volutin) granules are well known for polyphosphate storage, and lipid inclusions are a classic energy reserve. Gas vacuoles provide buoyancy in aquatic organisms, and sulfur granules can act as energy reserves in sulfur-oxidizing bacteria.

Question 38

Brucella bacteria are considered a potential agent of bioterrorism because?

Accepted Answer

Answer reason: A key bioterrorism characteristic is the ability to be disseminated efficiently (especially via aerosols) and cause disease after inhalational exposure. Brucella spp. can be aerosolized and have a low infectious dose, making inhalation a realistic route for mass exposure. They are treatable with appropriate combination antibiotics, so lack of antibiotic susceptibility is not the defining reason. Endospore formation and ulcerative skin lesions are not typical features of Brucella and describe other organisms/toxins more than brucellosis.

Question 39

Which of the following statements about tularemia is FALSE?

Accepted Answer

Answer reason: Tularemia is a zoonotic infection caused by Francisella tularensis with a broad geographic distribution, especially across parts of North America, so it is not limited to a single state. The organism is classically associated with rabbits and other small mammals, and these serve as important reservoirs in the natural cycle. Transmission commonly occurs via arthropod vectors such as ticks and deer flies, as well as through direct contact with infected animal tissues (e.g., handling carcasses). Therefore, the claim of occurrence only in California is the false statement compared with the well-established etiologic agent and transmission routes.

Question 40

Which of the following leads to all the others?

Accepted Answer

Answer reason: Endothelial injury triggers inflammation and increased vascular permeability, which can progress to capillary damage and rupture. The resulting microvascular dysfunction can also promote microthrombi and impaired perfusion, clinically described as capillary blockage. Subcutaneous hemorrhaging is therefore a downstream manifestation of endothelial disruption rather than the initiating event, while antibody presence reflects the host response after infection begins.

Question 41

Which of the following CANNOT be transmitted to humans from domestic cats?

Accepted Answer

Answer reason: Humans acquire toxoplasmosis through oocysts shed in cat feces or tissue cysts in undercooked meat. Cats can be involved in plague epidemiology mainly via infected fleas or handling sick cats, and Bartonella henselae is classically spread from cats via scratches contaminated with flea feces. Chagas’ disease is primarily transmitted by triatomine (kissing) bugs and is not considered a disease transmitted to humans from domestic cats in the usual clinical sense tested here.

Question 42

Which of the following pairs regarding the epidemiology of malaria is mismatched?

Accepted Answer

Answer reason: Ixodes is a tick genus classically associated with tick-borne infections (e.g., Lyme disease) rather than Plasmodium transmission. Plasmodium as the etiologic agent is correct, and sporozoites do target the liver early in infection. Laboratory diagnosis is made by identifying asexual blood-stage parasites on smear (often ring forms/trophozoites and can include merozoites), and chloroquine remains appropriate only where sensitivity is known.

Question 43

Which of the following is evidence that the arthritis afflicting children in Lyme, Connecticut, was due to bacterial infection?

Accepted Answer

Answer reason: Penicillin-class antibiotics inhibit bacterial cell wall synthesis, so a condition that reliably responds to them is consistent with infection by a susceptible bacterium. In contrast, being noncontagious, occurring mostly in children, having a rash, or being tick-borne can describe both infectious and noninfectious conditions and does not, by itself, prove the cause is bacterial. Therefore, antibiotic treatability is the strongest evidence for bacterial infection in this scenario.

Question 44

A vaccine to provide active immunity to HBV is prepared from?

Accepted Answer

Answer reason: HBV vaccination uses a recombinant subunit approach in which hepatitis B surface antigen (HBsAg) is produced via genetic engineering, classically in Saccharomyces cerevisiae (yeast). This purified antigen stimulates the recipient’s immune system to generate protective anti-HBs antibodies, which is active immunity. Pooled gamma globulin corresponds to passive immunization (HBIG) and provides immediate, short-lived protection rather than inducing immune memory. Whole-virus growth in tissue culture or eggs is not how current HBV vaccines are manufactured, and using viral particles from patients would be unsafe and nonstandard.

Question 45

Which of the following is mismatched?

Accepted Answer

Answer reason: Red blood cell lysis is classically mediated by specific exotoxins/hemolysins (e.g., pore-forming toxins), not by LPS itself. The other pairings align with well-known toxin effects: aflatoxin is hepatocarcinogenic, ergot alkaloids can cause vasoconstriction leading to ischemia/gangrene, and Vibrio cholerae toxin drives profuse secretory diarrhea via increased intestinal electrolyte and water secretion. Shiga toxin can cause mucosal injury and endothelial damage, consistent with tissue destruction mechanisms in dysentery and related complications.

Question 46

Bacterial intoxications differ from bacterial infections of the digestive system in that intoxications?

Accepted Answer

Answer reason: Foodborne intoxication results from ingestion of preformed bacterial toxin, so symptoms can begin within hours because the organism does not need to colonize and multiply first. In contrast, bacterial infection of the GI tract typically requires replication and often invasion or inflammatory response, producing a longer incubation period (often 1–3 days or more). Antibiotics are generally not helpful for toxin-mediated illness and may be harmful in some toxin-producing infections, making that distractor incorrect. Fever is often absent or low-grade in intoxications because there is less mucosal invasion and systemic inflammatory response than with invasive infections.

Question 47

Microscopic examination of a patient's fecal culture shows spiral bacteria. The bacteria probably belong to the genus?

Accepted Answer

Answer reason: Spiral/curved, “comma-shaped” motile organisms seen in stool culture most strongly suggest curved Gram-negative rods such as Campylobacter. This organism is a classic cause of bacterial gastroenteritis acquired from undercooked poultry or unpasteurized milk and is characteristically curved/spiral on microscopy. In contrast, Escherichia coli, Salmonella typhi, and Shigella spp. are straight Gram-negative rods, not spiral forms. While Vibrio cholerae is curved, the question’s emphasis on spiral bacteria in fecal culture most commonly aligns with Campylobacter in routine GI pathogen identification.

Question 48

Which of the following statements about leprosy is FALSE?

Accepted Answer

Answer reason: Leprosy (Mycobacterium leprae) is a chronic infection with low person-to-person transmissibility, and routine strict isolation is not required in most healthcare/community settings. The main infection-control principle is that effective multidrug therapy rapidly reduces infectivity, so standard precautions are generally sufficient. True statements include that M. leprae is acid-fast and diagnosis is commonly confirmed with skin biopsy showing acid-fast bacilli and characteristic pathology. While prolonged close contact is a risk factor, mandatory isolation as a blanket rule is not supported and is the false statement here.

Question 49

Which one of the following causes the most severe illness in humans, with a mortality rate of 30 percent?

Accepted Answer

Answer reason: This infection is known to cause rapidly progressive encephalitis with high fatality and frequent severe neurologic sequelae among survivors. By contrast, western equine, St. Louis, California, and West Nile encephalitis typically have lower overall mortality rates in most outbreaks (though risk increases with age and comorbidity). Therefore the option that best matches a ~30% mortality and “most severe illness” framing is the one selected.

Question 50

A one-year-old boy was listless, irritable, and sleepy. Capsulated Gram-negative rods were cultured from his cerebrospinal fluid. His symptoms were caused by?

Accepted Answer

Answer reason: The key principle is identifying pathogens by Gram stain morphology and virulence factors in meningitis. Encapsulated gram-negative rods in CSF classically indicate H. influenzae type b, whose polysaccharide capsule promotes invasive disease and meningitis in young children, presenting with lethargy/irritability. Neisseria meningitidis is an encapsulated gram-negative diplococcus (not a rod), making it a common distractor but mismatched to the culture description. Rabies and prion diseases cause encephalopathy without culturable bacteria in CSF, and Clostridium tetani is a gram-positive anaerobic rod causing spasticity rather than meningitis.

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Which microscope takes advantage of differences in the refractive indexes of cell structures?

The purpose of a mordant in the Gram stain is to?

Which microscope can be used to visualize DNA or botulinum toxin?

In using this microscope, the observer does NOT look directly at an image through a lens?

Which of the following is never useful for observing living cells?

Which microscope uses two beams of light to produce a three-dimensional color image?

Which of the following methods is used to preserve food by slowing the metabolic processes of foodborne microbes?

All of the following substances are effective against nonenveloped viruses EXCEPT?

The antimicrobial activity of chlorine is due to which of the following?

Application of heat to living cells can result in all of the following EXCEPT?

Which of the following pairs is mismatched?

Which of the following pairs is mismatched?

In the malaria parasite life cycle, humans are the ______ host, while mosquitoes are the ______ host as well as the vector?

Which of the following pairs is mismatched?

Which of the following is the best reason to classify Streptococcus in the Lactobacillales?

The crab industry needs female crabs for growing more crabs. What bacterium might be used to ensure development of female crabs and shrimp?

Which of the following is NOT a characteristic of spirochetes?

Which of the following form conidiospores?

Which of the following do you expect to be MOST resistant to high temperatures?

Staphylococcus and Streptococcus can be easily differentiated in a laboratory by which one of the following?

Which encephalitis is found predominantly west of the Mississippi River and occurs most often during the months of June and July?

A client with acquired immunodeficiency syndrome has developed a protozoa infection. Which opportunistic infection will the client most likely develop as a result of the protozoa infection?

A 10-year-old child being treated for common warts asks the nurse about the cause. What is the most appropriate response by the nurse?

Commercial sterilization differs from complete sterilization in that commercial sterilization?

What role do lactic acid bacteria play in cheese production?

Bioreactors are widely used for industrial fermentation. Which of the following conditions must be closely monitored for optimal fermentation?

Which of the following reactions makes wine less acidic, and is important for good flavor when grapes with higher acidity are used?

Which of the following places the steps in the PCR procedure in the correct order? 1) Incubate at 94°C to denature DNA strands; 2) Incubate at 72°C for DNA synthesis; 3) Incubate at 60°C for primer hybridization?

The use of an antibiotic-resistance gene on a plasmid used in genetic engineering makes?

Nucleic acid hybridization is based on the fact that?

Bacteria and Archaea are similar in which of the following?

Into which group would you place a photosynthetic organism that lacks a nucleus and has a thin peptidoglycan wall surrounded by an outer membrane?

If two organisms have similar rRNA sequences, you can conclude that they?

What is the outstanding characteristic of the Kingdom Fungi?

A genus can best be defined as?

Which of the following is NOT a typical characteristic of most bacterial plasma membranes?

Which one of the following pairs is mismatched?

Brucella bacteria are considered a potential agent of bioterrorism because?

Which of the following statements about tularemia is FALSE?

Which of the following leads to all the others?

Which of the following CANNOT be transmitted to humans from domestic cats?

Which of the following pairs regarding the epidemiology of malaria is mismatched?

Which of the following is evidence that the arthritis afflicting children in Lyme, Connecticut, was due to bacterial infection?

A vaccine to provide active immunity to HBV is prepared from?

Which of the following is mismatched?

Bacterial intoxications differ from bacterial infections of the digestive system in that intoxications?

Microscopic examination of a patient's fecal culture shows spiral bacteria. The bacteria probably belong to the genus?

Which of the following statements about leprosy is FALSE?

Which one of the following causes the most severe illness in humans, with a mortality rate of 30 percent?

A one-year-old boy was listless, irritable, and sleepy. Capsulated Gram-negative rods were cultured from his cerebrospinal fluid. His symptoms were caused by?

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In the malaria parasite life cycle, humans are the host, while mosquitoes are the host as well as the vector?