Question 1

Which of the following diseases causes a skin rash, hair loss, malaise, and fever?

Accepted Answer

Answer reason: Patchy “moth-eaten” alopecia can occur along with malaise and fever, aligning closely with the symptom cluster in the stem. Gonorrhea, NGU, and trichomoniasis typically present with urethritis/cervicitis and discharge rather than generalized rash and alopecia. Genital herpes is characterized by painful vesicular lesions and localized symptoms, not diffuse rash with hair loss.

Question 2

The most common reservoir for leptospirosis within the United States is?

Accepted Answer

Answer reason: Leptospirosis is a zoonotic spirochetal infection in which the key epidemiologic concept is the animal reservoir that chronically sheds organisms in urine. In the U.S., rodents—especially rats—are the most important maintenance hosts and commonly contaminate environments through urinary shedding. Humans are typically incidental hosts, and water is a transmission vehicle rather than the true biologic reservoir. Dogs can be infected and can shed organisms, but they are a less common reservoir than rodents at the population level.

Question 3

Pyelonephritis may result from?

Accepted Answer

Answer reason: Pyelonephritis is typically caused by bacterial infection of the renal pelvis and kidney that most often ascends from lower urinary tract infections. Inflammation/infection can start at the urethra and bladder and then progress upward through the ureter, making lower-tract processes plausible antecedents. Kidney infection can also occur via hematogenous spread during bacteremia, so systemic infections can seed the kidneys. Since each listed condition can contribute via ascending or bloodstream routes, the inclusive option is the best answer.

Question 4

The most common reportable disease in the United States is?

Accepted Answer

Answer reason: Nationally notifiable (reportable) conditions are those that must be reported to public health authorities, and among the listed sexually transmitted infections, this one has historically had the highest incidence in the U.S. Routine surveillance systems (e.g., CDC) track it closely because of its high prevalence, potential for outbreaks, and significant complications like pelvic inflammatory disease and neonatal infection. In contrast, cystitis and candidiasis are common but are not typically reportable diseases, and lymphogranuloma venereum is much less common. Syphilis is reportable but has a lower overall case count than this condition in most years.

Question 5

Which of the following is treated with penicillin?

Accepted Answer

Answer reason: Syphilis is caused by the spirochete Treponema pallidum, for which intramuscular benzathine penicillin G is the first-line treatment across most stages. The other options are not treated with penicillin because they are viral (genital herpes—HSV; genital warts—HPV), fungal (candidiasis—Candida species), or protozoal (trichomoniasis—Trichomonas vaginalis). Those conditions require antivirals, antifungals, or antiprotozoals (e.g., metronidazole) rather than penicillin.

Question 6

A positive LE test and 10,000 CFU/ml in urine indicates?

Accepted Answer

Answer reason: Leukocyte esterase indicates pyuria from neutrophils, supporting a bacterial urinary tract infection. A urine culture showing 10,000 CFU/mL can be clinically significant for lower UTI, especially when paired with evidence of inflammation on dipstick. Lower tract infection of the bladder fits this finding best, whereas upper tract disease more strongly correlates with systemic signs and may have additional findings like WBC casts. Sexually transmitted infections such as gonorrhea or genital herpes are not diagnosed by urine colony counts in this way and do not typically produce this culture threshold pattern from a standard urine specimen.

Question 7

The addition of which of the following to a culture medium will neutralize acids?

Accepted Answer

Answer reason: Buffer systems contain conjugate acid–base pairs that accept or donate H+ to minimize pH shifts, effectively neutralizing added acid and stabilizing the environment. Sugars are fermentable substrates that commonly increase acid production rather than counteract it. “pH” is a measurement, not an additive that neutralizes acid, and heat or carbon sources do not specifically provide acid-neutralizing capacity.

Question 8

The source of nutrients in nutrient agar is?

Accepted Answer

Answer reason: Nutrient agar is a general-purpose culture medium where the primary nutrient sources are complex organic digests and extracts that supply amino acids, peptides, vitamins, and growth factors. Peptone provides nitrogenous compounds and amino acids from protein hydrolysis, supporting bacterial biosynthesis and energy needs. Beef extract contributes additional carbon sources, minerals, and vitamins that broaden support for nonfastidious organisms. Agar is mainly an inert solidifying agent, and NaCl primarily maintains osmotic balance rather than serving as a nutrient source.

Question 9

Most fungi grow best at pH?

Accepted Answer

Answer reason: Fungal growth is generally favored by mildly acidic environments, while many bacteria prefer near-neutral pH. A pH around 5 supports optimal activity of many fungal enzymes and cellular transport systems, improving replication and colony formation. Neutral pH (around 7) is more typical for many bacterial pathogens and common laboratory media aimed at bacteria. More extreme pH values (very low like 1 or very high like 9–14) denature proteins and disrupt membranes, limiting growth for most organisms.

Question 10

Which of the following is an organic growth factor?

Accepted Answer

Answer reason: A vitamin such as thiamine functions as a coenzyme precursor required for key metabolic reactions and is classically categorized as a growth factor. Glucose is primarily a carbon/energy source rather than a growth factor, while peptone is a complex nitrogen source. Mg+2 is an inorganic ion and water is a basic requirement, not an organic growth factor.

Question 11

Most bacteria grow best at pH?

Accepted Answer

Answer reason: Most medically important bacteria are neutrophiles, meaning their enzymes and membrane transport systems function optimally near neutral pH. As pH moves far from neutrality, protein structure and proton gradients are disrupted, impairing metabolism and replication. A pH around 1 is strongly acidic (typical of the stomach) and is bactericidal to most organisms. Alkaline extremes such as 9 or 14 also inhibit or kill most bacteria, with only specialized alkaliphiles tolerating them.

Question 12

Which enzyme catalyzes the reaction: H2O2 + 2H+ → 2H2O?

Accepted Answer

Answer reason: The shown reaction consumes protons and converts hydrogen peroxide directly into water, matching a peroxidase-type reduction. Catalase instead disproportionates hydrogen peroxide into water and oxygen (2H2O2 → 2H2O + O2), so it does not fit the given equation. Superoxide dismutase acts on superoxide radicals (O2−) and would not use H2O2 as the substrate in this way.

Question 13

Which enzyme catalyzes the reaction: O2- + O2- + 2H+ → H2O2 + O2?

Accepted Answer

Answer reason: That specific chemistry is the defining function of superoxide dismutase in aerobic organisms to limit oxidative damage. Catalase instead breaks down hydrogen peroxide into water and oxygen, acting downstream after hydrogen peroxide has already been formed. Peroxidase reduces hydrogen peroxide using electron donors rather than generating oxygen as shown in the equation.

Question 14

Which enzyme catalyzes the reaction: 2H2O2 → 2H2O + O2?

Accepted Answer

Answer reason: The enzyme responsible is identified by its hallmark production of visible oxygen bubbles when H2O2 is applied in the catalase test. Peroxidase also uses hydrogen peroxide but reduces it by oxidizing another substrate and typically does not generate O2 as a product. Superoxide dismutase acts on superoxide radicals (O2•−) rather than directly converting hydrogen peroxide into oxygen gas.

Question 15

An experiment began with 4 cells and ended with 128 cells. How many generations did the cells go through?

Accepted Answer

Answer reason: The relationship is N = N0 × 2^g, so 128 = 4 × 2^g. Dividing by the starting count gives 32 = 2^g, which corresponds to g = 5. A common error is to treat the increase (124) as linear rather than recognizing repeated doubling.

Question 16

Most bacteria reproduce by

Accepted Answer

Answer reason: Most bacteria reproduce asexually by replicating their single circular chromosome and then dividing into two genetically identical daughter cells. This process is termed binary fission and is the predominant reproductive method across typical bacterial species. Mitosis is a eukaryotic nuclear division mechanism and does not apply to prokaryotes because they lack a true nucleus and mitotic spindle. Budding and fragmentation can occur in some organisms (e.g., certain yeasts or filamentous forms), but they are not the primary method for most bacteria.

Question 17

Which of the following has bacteriochlorophylls and uses alcohols for carbon?

Accepted Answer

Answer reason: “Heterotroph” indicates the carbon source is organic compounds rather than CO2, which fits using alcohols as the carbon source. Therefore the organism described must be a light-using, organic-carbon-using type. A common distractor is photoautotroph, which uses light for energy but fixes CO2 as its carbon source rather than alcohols.

Question 18

Which of the following uses glucose for carbon and energy?

Accepted Answer

Answer reason: Using glucose as both an energy source (oxidizing an organic molecule) and a carbon source (building biomass from organic carbon) defines a chemoheterotroph. Autotrophs use CO2 as their primary carbon source, so they do not use glucose for carbon. Photoheterotrophs may use glucose for carbon but derive energy primarily from light, so they do not use glucose for both carbon and energy in the way described.

Question 19

Which of the following uses CO2 for carbon and H2 for energy?

Accepted Answer

Answer reason: Using CO2 as the carbon source indicates an autotroph. Using H2 as an energy/electron donor indicates a chemotroph (specifically chemolithotroph), which falls under chemoautotrophs. In contrast, photoautotrophs use light for energy, and heterotrophs require organic carbon rather than CO2.

Question 20

In noncyclic photophosphorylation, O2 is released from?

Accepted Answer

Answer reason: Oxygen released during oxygenic photosynthesis comes from photolysis of water in photosystem II. In noncyclic electron flow, light energy drives splitting of water to replace electrons lost from chlorophyll, producing electrons, protons (supporting the proton gradient for ATP synthesis), and molecular oxygen as a byproduct. Carbon dioxide is reduced later in the Calvin cycle and is not the source of evolved oxygen. Therefore the released O2 originates from water rather than carbon substrates or light itself.

Question 21

Cyanobacteria are a type of?

Accepted Answer

Answer reason: Cyanobacteria obtain energy from sunlight via oxygenic photosynthesis and use carbon dioxide as their primary carbon source. This combination of light as the energy source and CO2 as the carbon source defines photoautotrophy. Chemo- options rely on chemical oxidation for energy rather than light, which does not match cyanobacterial metabolism. Photoheterotrophs use light for energy but require organic carbon, which is not the defining pattern for cyanobacteria.

Question 22

Bacterial smears are fixed before staining to?

Accepted Answer

Answer reason: Fixation (heat or chemical) primarily adheres bacteria to the glass so they are not washed off during staining and rinsing steps. It also kills organisms and helps preserve basic cellular morphology, improving smear integrity for microscopic examination. Making cell walls permeable is mainly achieved by specific staining steps (e.g., mordants, decolorizers, detergents), not by routine fixation alone. The stain provides contrast/visibility, whereas fixation prepares and secures the sample so staining can be performed reliably.

Question 23

What structure does light pass through after leaving the condenser in a compound light microscope?

Accepted Answer

Answer reason: After the condenser, the focused light passes through the specimen, where differential absorption/refraction creates the information that forms the image. The objective lens then collects the transmitted light and produces the primary magnified image, so it occurs after the specimen rather than immediately after the condenser. The illuminator is the light source below the condenser, so it precedes the condenser in the light path.

Question 24

A microorganism measures 5 μm in length. Its length in mm would be?

Accepted Answer

Answer reason: 0.005 mm. Unit conversion is based on metric prefixes: 1 mm = 1000 μm. Converting micrometers to millimeters requires dividing by 1000, so 5 μm = 5/1000 mm. This equals 0.005 mm, matching the correct choice. Larger options (e.g., 0.05 mm) reflect a misplaced decimal and represent 10× the true size.

Question 25

A virus measures 100 nm in length. What is its length in μm?

Accepted Answer

Answer reason: 0.01 μm Unit conversion between nanometers and micrometers is based on metric prefixes: 1 μm equals 1000 nm. Converting 100 nm to μm requires dividing by 1000, giving 0.1 μm? Wait—100/1000 = 0.1, but that would correspond to 100 nm being one-tenth of a micrometer; however 1 μm = 1000 nm, so 100 nm = 0.1 μm is correct. Since the closest option reflecting 100 nm in μm is 0.1 μm, any smaller value (0.01 μm) would correspond to 10 nm, and larger values would correspond to 1000 nm or more. Therefore the correct metric conversion selects the option representing one-tenth of a micrometer.

Question 26

Oxidizing agents include all of the following EXCEPT?

Accepted Answer

Answer reason: Oxidizing disinfectants kill microbes primarily by generating reactive oxygen species or by oxidizing cellular proteins, lipids, and nucleic acids. Chlorine compounds, hydrogen peroxide, and ozone are classic oxidizers, and iodine acts as a halogen antiseptic with oxidative/iodination damage to microbial components. Glutaraldehyde instead is an aldehyde high-level disinfectant that works mainly by alkylation/cross-linking of proteins and nucleic acids rather than oxidation. Therefore it is the exception among the listed oxidizing agents.

Question 27

Which of the following chemical agents is used for sterilization?

Accepted Answer

Answer reason: This agent is a gaseous sterilant that alkylates proteins and nucleic acids and is used for heat- and moisture-sensitive equipment (e.g., some plastics and electronics). Alcohol, phenolics, and chlorine are primarily disinfectants/antiseptics and are not reliably sporicidal under routine use conditions. Soap mainly removes microbes mechanically (degerming) rather than killing them to achieve sterility.

Question 28

Which of the following substances is used for surgical hand scrubs?

Accepted Answer

Answer reason: Chlorhexidine binds to the stratum corneum and continues to suppress bacterial regrowth after application, which is why it is commonly used in preoperative hand antisepsis. In contrast, chlorine bleach and glutaraldehyde are high-level disinfectants/sterilants intended for environmental surfaces or equipment and are too harsh/toxic for routine hand scrubbing. Plain soap mainly removes organisms mechanically and lacks the sustained antiseptic activity expected for surgical scrubs.

Question 29

Which concentration of ethanol is the most effective bactericide?

Accepted Answer

Answer reason: Concentrations around 60%–90% are most bactericidal, with 70% commonly cited as optimal for routine disinfection. Absolute alcohol evaporates too quickly and lacks enough water to sustain effective protein denaturation, reducing overall kill. Lower concentrations such as 30%–50% have insufficient antimicrobial activity for reliable bactericidal effect in typical clinical use.

Question 30

Ringworm is caused by a(n)?

Accepted Answer

Answer reason: Ringworm (tinea) is a superficial dermatophyte infection caused by fungi such as Trichophyton, Microsporum, and Epidermophyton. These organisms invade keratinized tissues (stratum corneum, hair, nails), producing the characteristic annular, scaly lesions. Helminths (cestodes, nematodes, trematodes) are multicellular parasites that cause systemic or intestinal infections rather than superficial “ring” skin lesions. Protozoa typically cause gastrointestinal or blood/tissue infections and do not produce classic tinea presentations.

Question 31

Yeast infections are caused by?

Accepted Answer

Answer reason: Yeast infections in humans are most commonly due to opportunistic overgrowth of Candida species on mucosal surfaces and skin, especially when normal flora is disrupted or host defenses are reduced. This organism characteristically causes vulvovaginal candidiasis and oral thrush, with budding yeast and pseudohyphae on microscopy. Several other listed fungi can cause human disease, but they are not the typical cause of routine “yeast infections” (e.g., aspergillosis is primarily a mold-related respiratory/invasive infection). Saccharomyces is primarily associated with fermentation and is a far less common human pathogen compared with Candida in this context.

Question 32

What do tapeworms eat?

Accepted Answer

Answer reason: Because they live in the host small intestine, their main nutrient source is the luminal chyme produced from the host’s digestion. This makes “intestinal contents” the best description of what they feed on. Options like host tissues or red blood cells better fit parasites that actively invade tissue or hematophagous organisms rather than cestodes.

Question 33

The encysted larva of the beef tapeworm is called a?

Accepted Answer

Answer reason: The key principle is recognizing helminth (cestode) life-cycle stages and the terminology for larval forms that infect intermediate hosts. Taenia saginata (beef tapeworm) forms an encysted larval stage in cattle muscle, which is the infective form for humans when undercooked beef is eaten. Redia and cercaria are trematode larval stages associated with snails and free-swimming forms, not cestode tissue cysts. Proglottids are adult tapeworm segments, not larval cysts.

Question 34

A definitive host harbors which stage of a parasite?

Accepted Answer

Answer reason: That corresponds to the adult stage for most helminths and many other parasites. In contrast, intermediate hosts typically harbor larval or asexual developmental stages (e.g., miracidium development in snails for trematodes). A cyst is usually an infective/transmissible or environmentally resistant form and is not what defines the definitive host.

Question 35

The use of phenol (carbolic acid) as a wound disinfectant was first practiced by?

Accepted Answer

Answer reason: The key principle is the historical development of antiseptic technique in microbiology and infection prevention. Joseph Lister introduced carbolic acid (phenol) to disinfect surgical wounds and instruments, markedly reducing postoperative infections. Semmelweis is associated with handwashing using chlorinated lime to prevent puerperal fever, not phenol wound antisepsis. Pasteur and Koch are foundational for germ theory and bacteriology but are not credited with first practicing phenol as a wound disinfectant.

Question 36

Mycology is the study of?

Accepted Answer

Answer reason: Mycology is the branch of microbiology that studies fungi. Fungi include multicellular filamentous forms (molds), unicellular forms (yeasts), and macroscopic fruiting-body forms (mushrooms). The question asks for the broad domain, so the most complete option that captures the major fungal forms is correct. A common distractor is confusing “mycology” with “mycoplasma,” which are bacteria lacking a cell wall rather than fungi.

Question 37

Proof that a microbe could cause disease was provided by?

Accepted Answer

Answer reason: The core principle is that causation between a specific microorganism and a specific disease requires reproducible experimental criteria. Koch established Koch’s postulates, outlining isolation of the organism from diseased hosts, growth in pure culture, reproduction of the disease in a healthy host, and re-isolation of the same organism. This framework provided the classic proof supporting the germ theory of disease by linking microbes to specific illnesses. By contrast, Semmelweis and Lister advanced infection prevention practices, but they did not formulate the definitive experimental proof criteria for microbial causation.

Question 38

Each of the following organisms would be considered a microbe EXCEPT?

Accepted Answer

Answer reason: Microbes are organisms that are microscopic in size and typically require magnification to be seen. Yeasts are unicellular fungi, bacteria are single-celled prokaryotes, protozoa are microscopic eukaryotes, and viruses are acellular infectious particles—all generally considered microbes. A mushroom is the macroscopic fruiting body of certain fungi and is visible to the naked eye, so it is not classified as a microbe in this context. The key distinction tested is microscopic versus macroscopic organismal form.

Question 39

The term used to describe a disease-causing microorganism is?

Accepted Answer

Answer reason: A pathogen is defined as an organism or agent capable of causing disease in a host. “Microbe” is a broad term that includes many microorganisms, most of which are harmless or beneficial. “Bacterium” and “virus” are specific types of microbes, but not all bacteria/viruses necessarily cause disease in every context, so they are not the general term. “Infection” describes the process/condition of invasion and multiplication, not the causative organism.

Question 40

Common commercial benefits of microorganisms include synthesis of?

Accepted Answer

Answer reason: Microorganisms are widely used in industrial microbiology to produce valuable metabolites and recombinant proteins. Certain bacteria and fungi are used to biosynthesize vitamins such as riboflavin, and microbial fermentation has long been used to produce solvents such as acetone. Recombinant DNA technology enables microbes (e.g., engineered bacteria or yeast) to produce human insulin at commercial scale. Aspirin is primarily synthesized via chemical processes rather than microbial production, making it the least fitting choice among the options.

Question 41

In the name Staphylococcus aureus, aureus is the?

Accepted Answer

Answer reason: Binomial nomenclature uses a two-part scientific name where the first word is the genus and the second word is the specific epithet, commonly referred to as the species name in basic microbiology usage. In this format, “Staphylococcus” identifies the genus grouping of related organisms. The term “aureus” distinguishes the organism within that genus from other Staphylococcus species. Options like domain, kingdom, and family are higher taxonomic ranks and are not represented by the second word of the binomial name.

Question 42

The infectious agent that causes AIDS is a?

Accepted Answer

Answer reason: AIDS results from infection with human immunodeficiency virus (HIV), a retrovirus that targets CD4+ T lymphocytes. Viral replication and progressive CD4 depletion lead to impaired cell-mediated immunity and the opportunistic infections and malignancies that define AIDS. Bacteria, protozoa, yeasts, and molds can cause opportunistic infections in advanced HIV disease, but they are not the primary causative agent of AIDS. Therefore the correct classification of the infectious agent is a virus.

Question 43

Which of the following is NOT a domain in the three-domain system?

Accepted Answer

Answer reason: A domain is broader than a kingdom, and kingdoms are nested within domains. Animalia is a kingdom within the domain Eukarya, not its own domain. Therefore it is the only option that is not one of the three domains.

Question 44

Robert Koch identified the cause of?

Accepted Answer

Answer reason: Koch’s key scientific contribution was proving specific microbes cause specific diseases, foundational to germ theory and his postulates. He demonstrated that Bacillus anthracis is the etiologic agent of anthrax by isolating it, growing it, and reproducing disease after inoculation, then re-isolating the organism. Smallpox and AIDS are viral diseases identified much later through virology and immunology advances. While Koch also identified Mycobacterium tuberculosis, the historically classic “first” disease-causation demonstration associated with him is anthrax.

Question 45

Which physician is first associated with vaccination?

Accepted Answer

Answer reason: Edward Jenner pioneered this by using cowpox exposure to protect against smallpox, establishing the foundational concept of vaccination. By contrast, Koch is primarily associated with germ theory and Koch’s postulates, and Lister with antiseptic surgery rather than immunization. Ehrlich is more closely tied to chemotherapy and immunologic theory, and Escherich to bacteriology (E. coli) rather than vaccine development.

Question 46

Which one of the following does NOT belong with the others?

Accepted Answer

Answer reason: g., intracellular, arthropod-associated Gram-negative organisms versus typical extracellular cocci). Coxiella, Ehrlichia, Rickettsia, and Wolbachia are small Gram-negative organisms classically associated with obligate intracellular biology and/or arthropod vectors/endosymbiosis. In contrast, Staphylococcus are Gram-positive cocci that grow extracellularly and are common skin/mucosal flora and pyogenic pathogens. This makes it the clear outlier among the listed genera.

Question 47

Which of the following lacks a cell wall?

Accepted Answer

Answer reason: This organism uniquely lacks a cell wall and instead relies on a sterol-containing cell membrane, which also explains its pleomorphic shape. In contrast, acid-fast organisms still have a peptidoglycan wall but with a waxy mycolic acid–rich layer. Spirochetes and Gram-positive rods likewise retain cell walls even though their structures differ, so they are not the best fit.

Question 48

Which hepatitis virus is most likely to be transmitted through the fecal–oral route?

Accepted Answer

Answer reason: Hepatitis transmission is classically divided into enteric (fecal–oral) versus parenteral/sexual (blood and body fluids). The enteric hepatitis virus is associated with ingestion of contaminated food or water and outbreaks linked to poor sanitation or close contact settings. In contrast, hepatitis B, C, and D are primarily spread via blood exposure, sexual contact, or perinatal transmission, making them less consistent with fecal–oral spread. This distinction is central for choosing appropriate prevention measures (hand hygiene and safe food/water practices versus blood/body fluid precautions and vaccination where applicable).

Question 49

A newly recognized coronavirus has been identified as the causative agent of which disease?

Accepted Answer

Answer reason: Coronaviruses are enveloped RNA viruses, and the first “newly recognized” coronavirus widely identified as causing a distinct severe human disease was SARS-CoV, responsible for severe acute respiratory syndrome. SARS is characterized by fever and progressive lower-respiratory involvement and can lead to significant hypoxemia and respiratory failure. Influenza is caused by influenza viruses (orthomyxoviruses), not coronaviruses. While coronaviruses can cause respiratory syndromes including pneumonia, the question is asking for the named disease classically linked to a newly recognized coronavirus.

Question 50

The nurse would expect the physician to order which medication as the treatment of choice for scarlet fever?

Accepted Answer

Answer reason: A beta-lactam is first-line because GAS remains predictably susceptible and clinical outcomes are well established. One distractor is an antiviral, which would not treat a bacterial toxin-mediated exanthem. Symptomatic agents like NSAIDs may reduce fever/pain but do not eliminate the pathogen or prevent post-streptococcal sequelae.

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