Microbiology Practice Exam — LearnCoachAssist

Question 1 Microbiology

What is the function of bacterial pili (fimbriae)?

Yellow fever virus (Flaviviridae), transmitted by Aedes mosquitoes. Rhinovirus (Picornaviridae). Sterilizing heat-sensitive medical equipment by alkylating proteins and nucleic acids. Adherence to surfaces/host cells; sex pili also mediate conjugation (DNA transfer).

Question 2 Microbiology

What is the mechanism of action of chlorine-based disinfectants (bleach)?

Roughly 20-45 degrees C; most human pathogens are mesophiles because this range includes body temperature (37 degrees C). Oxidize and disrupt proteins/enzymes and damage nucleic acids via hypochlorous acid formation. India ink stain. Capsule swelling reaction used to serotype encapsulated bacteria such as Streptococcus pneumoniae.

Question 3 Microbiology

What is antibiotic synergy? Give an example.

Transfer of bacterial DNA from one cell to another via a bacteriophage. CD4+ T helper lymphocytes (also macrophages and dendritic cells) via binding to CD4 and CCR5/CXCR4 co-receptors. Combined effect of two drugs greater than the sum of their individual effects; e.g., trimethoprim-sulfamethoxazole sequentially blocking folate synthesis. Yeasts are unicellular, round to oval, reproduce by budding; molds are multicellular, form branching filaments called hyphae.

Question 4 Microbiology

What laboratory value is used to monitor HIV disease progression and AIDS diagnosis threshold?

CD4+ T cell count; AIDS is diagnosed when CD4 count falls below 200 cells/microliter or an AIDS-defining illness occurs. Bacteroides fragilis. Pseudomonas aeruginosa. Enterohemorrhagic Escherichia coli (EHEC), especially serotype O157:H7.

Question 5 Microbiology

Which hepatitis virus is the most common cause of chronic viral hepatitis in many countries and is transmitted mainly via blood?

Mumps virus (Paramyxoviridae), causing parotitis (swollen salivary glands). Hepatitis C virus (Flaviviridae). Mycoplasma pneumoniae. Toxoplasma gondii; sources include cat feces and undercooked meat; dangerous in pregnancy (congenital toxoplasmosis) and immunocompromised patients.

Question 6 Microbiology

What is an aerotolerant anaerobe?

An organism that does not use oxygen but can survive and grow in its presence. Transfer of genetic material between bacteria (not parent to offspring) via transformation, transduction, and conjugation. Cryptococcus neoformans. Taenia saginata.

Question 7 Microbiology

What is the causative agent of trichinosis, typically acquired from undercooked pork?

A toxin that non-specifically bridges MHC II and T-cell receptors outside the normal antigen-binding groove, causing massive, non-specific T-cell activation and cytokine release. Trichinella spiralis (a roundworm/nematode). Chlamydia trachomatis. Reverse transcriptase.

Question 8 Microbiology

What is a superantigen and how does it differ from a normal antigen in immune activation?

Yellow fever virus (Flaviviridae), transmitted by Aedes mosquitoes. Aspergillus species. A toxin that non-specifically bridges MHC II and T-cell receptors outside the normal antigen-binding groove, causing massive, non-specific T-cell activation and cytokine release. Beta-lactamase (penicillinase).

Question 9 Microbiology

What is the mechanism by which SARS-CoV-2 enters human cells?

Enterobius vermicularis (pinworm). Yeasts are unicellular, round to oval, reproduce by budding; molds are multicellular, form branching filaments called hyphae. Hepatitis D virus (delta agent), a defective virus needing HBsAg. Binds ACE2 receptor via its spike protein, facilitating membrane fusion and cell entry.

Question 10 Microbiology

Define bacterial conjugation.

Removing airborne particles including bacteria from air, e.g., in operating rooms and biosafety cabinets. Taenia solium. Chlamydophila (Chlamydia) pneumoniae. Direct transfer of DNA (often a plasmid) between bacteria through a sex pilus/mating bridge.

Question 11 Microbiology

Which tapeworm is acquired from undercooked beef?

Mycobacterium tuberculosis. Hepatitis D virus (delta agent), a defective virus needing HBsAg. Clostridium perfringens, via alpha toxin (a lecithinase). Taenia saginata.

Question 12 Microbiology

What does blood agar with beta-hemolysis look like, and what does it indicate?

A clear zone of complete hemolysis around colonies, indicating complete lysis of red blood cells (e.g., Streptococcus pyogenes). Coccidioides immitis. Cocci (spherical), bacilli (rod-shaped), and spirilla/spirochetes (spiral). Primary (chancre), secondary (rash, systemic symptoms), latent, and tertiary (gummas, cardiovascular and neurological disease).

Question 13 Microbiology

What is the mechanism of action of echinocandins (e.g., caspofungin)?

Inhibit beta-(1,3)-D-glucan synthase, blocking fungal cell wall glucan synthesis. Forms toxic free radicals in anaerobic/microaerophilic organisms that damage DNA; used for anaerobes and protozoa. Enveloped viruses have a lipid bilayer derived from host membrane surrounding the capsid; non-enveloped viruses have only a protein capsid, making them generally more resistant to desiccation and disinfectants. A capsule is a well-organized, tightly bound polysaccharide layer; a slime layer is loosely attached and diffuse. Both aid adherence and immune evasion.

Question 14 Microbiology

Which protozoan is a common sexually transmitted parasite causing vaginitis?

Nutrient depletion and waste accumulation cause growth rate to equal death rate, so population size plateaus. Trichomonas vaginalis. Salmonella enteritidis (non-typhoidal Salmonella). Brucella species.

Question 15 Microbiology

Which curved Gram-negative bacterium is a leading cause of bacterial gastroenteritis from undercooked poultry?

Enveloped viruses have a lipid bilayer derived from host membrane surrounding the capsid; non-enveloped viruses have only a protein capsid, making them generally more resistant to desiccation and disinfectants. Peptidoglycan (murein), made of alternating NAG and NAM sugars cross-linked by peptide chains. Erythema migrans, a bullseye-shaped rash. Campylobacter jejuni.

Question 16 Microbiology

Which encapsulated yeast causes cryptococcal meningitis, especially in immunocompromised (e.g., HIV/AIDS) patients?

Poliovirus (Picornaviridae); targets motor neurons in the anterior horn of the spinal cord, causing flaccid paralysis. Cryptococcus neoformans. Uptake of free/naked DNA from the environment by a competent bacterial cell. Plasmodium species (e.g., P. falciparum, P. vivax), transmitted by female Anopheles mosquitoes.

Question 17 Microbiology

What is an antiseptic versus a disinfectant?

A complete, infectious virus particle outside a host cell. Antiseptics are chemicals safe for use on living tissue; disinfectants are used on inanimate objects/surfaces and may be too harsh for tissue. Blastomyces dermatitidis. Brucella species.

Question 18 Microbiology

Which protozoan causes visceral and cutaneous leishmaniasis, transmitted by sandflies?

Exotoxins are secreted proteins with specific targets and high toxicity, often from Gram-positive (and some Gram-negative) bacteria; endotoxin (LPS) is a structural component of the Gram-negative outer membrane released on lysis, causing fever and septic shock. Ergosterol. Leishmania species. A capsule is a well-organized, tightly bound polysaccharide layer; a slime layer is loosely attached and diffuse. Both aid adherence and immune evasion.

Question 19 Microbiology

Differentiate DNA and RNA viruses in terms of where replication typically occurs.

Corynebacterium diphtheriae; diphtheria toxin inhibits protein synthesis by ADP-ribosylating elongation factor-2 (EF-2). DNA viruses typically replicate in the nucleus (exception: poxviruses); RNA viruses typically replicate in the cytoplasm (exception: influenza and retroviruses use the nucleus). Combined effect of two drugs greater than the sum of their individual effects; e.g., trimethoprim-sulfamethoxazole sequentially blocking folate synthesis. Oxidize and disrupt proteins/enzymes and damage nucleic acids via hypochlorous acid formation.

Question 20 Microbiology

Which Plasmodium species causes the most severe and deadly form of malaria?

Obligate aerobes require oxygen for growth; obligate anaerobes are killed or cannot grow in the presence of oxygen. Congenital microcephaly and other brain abnormalities in the fetus. Plasmodium falciparum. Transfer of genetic material between bacteria (not parent to offspring) via transformation, transduction, and conjugation.

Question 21 Microbiology

What color do Gram-positive bacteria appear after Gram staining?

Purple/violet (retain crystal violet-iodine complex). Sterilizing heat-sensitive medical equipment by alkylating proteins and nucleic acids. Salmonella typhi. Binds ACE2 receptor via its spike protein, facilitating membrane fusion and cell entry.

Question 22 Microbiology

What is the mechanism of action of metronidazole?

Coccidioides immitis. Forms toxic free radicals in anaerobic/microaerophilic organisms that damage DNA; used for anaerobes and protozoa. They establish lifelong latency in host cells (e.g., neurons) with potential for reactivation. Mycobacterium leprae.

Question 23 Microbiology

Which Gram-negative diplococcus causes gonorrhea?

Neisseria gonorrhoeae. Rotavirus. Norovirus. Purple/violet (retain crystal violet-iodine complex).

Question 24 Microbiology

Which bacterium causes pseudomembranous colitis, often after antibiotic use?

Taenia solium. Brucella species. Clostridioides difficile (formerly Clostridium difficile). They are obligate intracellular bacteria that cannot be cultured on standard artificial media.

Question 25 Microbiology

Which spirochete causes leptospirosis?

Ascaris lumbricoides. Leptospira interrogans, often from water contaminated with animal urine. Neisseria meningitidis. Uptake of free/naked DNA from the environment by a competent bacterial cell.

Question 26 Microbiology

What enzyme do retroviruses use to convert RNA into DNA?

Bacteroides fragilis. Liver damage and increased risk of hepatocellular carcinoma. Trypanosoma brucei, transmitted by the tsetse fly. Reverse transcriptase.

Question 27 Microbiology

What is teichoic acid and where is it found?

Vibrio cholerae; cholera toxin activates adenylate cyclase, increasing cAMP and causing massive watery diarrhea via chloride/water secretion. Cells adapt to the environment and synthesize enzymes/metabolites; little to no cell division occurs. A polymer unique to Gram-positive cell walls that extends through the peptidoglycan and contributes to virulence and immune stimulation. Sterilization using pressurized steam, typically 121 degrees C at 15 psi for about 15-20 minutes; kills endospores.

Question 28 Microbiology

What are the four phases of the bacterial growth curve?

Sterilization kills all microbial life including spores; disinfection reduces pathogens to a safe level but may not kill spores. Pseudomonas aeruginosa. Lag phase, log (exponential) phase, stationary phase, and death (decline) phase. An organism that grows best with increased carbon dioxide concentration (e.g., Neisseria gonorrhoeae).

Question 29 Microbiology

What is a Ghon complex?

Mycoplasma pneumoniae. Obligate aerobes require oxygen for growth; obligate anaerobes are killed or cannot grow in the presence of oxygen. A calcified granuloma (tubercle) with associated lymph node involvement seen in primary tuberculosis infection. Bind the 50S ribosomal subunit and block translocation, inhibiting protein synthesis.

Question 30 Microbiology

What is pasteurization?

Chlamydia trachomatis. Mild heat treatment (e.g., 63 degrees C for 30 min or 72 degrees C for 15 sec) that kills most pathogens and reduces spoilage organisms without sterilizing. Candida albicans. A structured community of bacteria embedded in a self-produced extracellular matrix attached to a surface; biofilms increase antibiotic resistance and are linked to chronic infections (e.g., on catheters, implants).

Question 31 Microbiology

What is the mechanism of action of vancomycin?

Borrelia burgdorferi, transmitted by Ixodes ticks. Bacteriostatic drugs inhibit growth and rely on the host immune system to clear the infection; bactericidal drugs directly kill the organism. Gram-positive bacteria have a thick peptidoglycan layer and no outer membrane; Gram-negative bacteria have a thin peptidoglycan layer plus an outer membrane containing lipopolysaccharide (LPS). Binds D-Ala-D-Ala terminus of peptidoglycan precursors, blocking cell wall synthesis; effective mainly against Gram-positives.

Question 32 Microbiology

What is generation (doubling) time?

Hepatitis A virus (Picornaviridae), transmitted fecal-oral, typically self-limited, no chronic carrier state. The time required for a bacterial population to double in number. CD4+ T helper lymphocytes (also macrophages and dendritic cells) via binding to CD4 and CCR5/CXCR4 co-receptors. Giardia lamblia (intestinalis).

Question 33 Microbiology

Which virus family causes the common cold most frequently?

Haemophilus influenzae type b (Hib). A structured community of bacteria embedded in a self-produced extracellular matrix attached to a surface; biofilms increase antibiotic resistance and are linked to chronic infections (e.g., on catheters, implants). Rhinovirus (Picornaviridae). Rabies virus (Rhabdoviridae); Negri bodies.

Question 34 Microbiology

What is unique about herpesviruses regarding their infection pattern?

A bacterial enzyme that confers resistance to a broad range of beta-lactam antibiotics including penicillins and cephalosporins. They establish lifelong latency in host cells (e.g., neurons) with potential for reactivation. Listeria monocytogenes, notable for growth at refrigeration temperatures and transplacental transmission. Antiseptics are chemicals safe for use on living tissue; disinfectants are used on inanimate objects/surfaces and may be too harsh for tissue.

Question 35 Microbiology

What is selective media used for? Give an example.

Salmonella enteritidis (non-typhoidal Salmonella). Necator americanus and Ancylostoma duodenale. Francisella tularensis. Media that inhibits growth of unwanted organisms while allowing target organisms to grow; e.g., MacConkey agar selects for Gram-negatives.

Question 36 Microbiology

What are the three basic bacterial shapes?

Beta-lactam antibiotics that inhibit peptidoglycan cross-linking by binding penicillin-binding proteins, weakening the cell wall and causing lysis. Listeria monocytogenes, notable for growth at refrigeration temperatures and transplacental transmission. Cocci (spherical), bacilli (rod-shaped), and spirilla/spirochetes (spiral). Mycoplasma.

Question 37 Microbiology

What are dermatophytes and what infections do they cause?

Salmonella enteritidis (non-typhoidal Salmonella). Fungi (e.g., Trichophyton, Microsporum, Epidermophyton) that infect keratinized tissue (skin, hair, nails), causing tinea (ringworm) infections. Antiseptics are chemicals safe for use on living tissue; disinfectants are used on inanimate objects/surfaces and may be too harsh for tissue. Mycolic acid, a waxy lipid layer.

Question 38 Microbiology

What is the difference between bactericidal and bacteriostatic antibiotics in terms of immune system reliance?

Asexual fungal spores produced at the tips of specialized hyphae, used for identification and reproduction. Bacteriostatic drugs inhibit growth and rely on the host immune system to clear the infection; bactericidal drugs directly kill the organism. Ergosterol. A bacterial enzyme that confers resistance to a broad range of beta-lactam antibiotics including penicillins and cephalosporins.

Question 39 Microbiology

What is the mechanism of action of griseofulvin?

Competitively inhibit dihydropteroate synthase, blocking folic acid synthesis needed for nucleotide production. Interferes with fungal microtubule function, disrupting mitosis; used for dermatophyte infections. Chlamydia trachomatis. A bacterial enzyme that confers resistance to a broad range of beta-lactam antibiotics including penicillins and cephalosporins.

Question 40 Microbiology

Which spirochete causes syphilis?

Treponema pallidum. Carbon source, nitrogen source, energy source, water, minerals, and appropriate pH/temperature/osmotic conditions. Chlamydia trachomatis. Bartonella henselae.

Question 41 Microbiology

Which bacterium is the classic cause of cat scratch disease?

Bartonella henselae. Organisms adapted to extreme environments; examples include thermophiles (heat), psychrophiles (cold), halophiles (high salt), and acidophiles (low pH). Capsule swelling reaction used to serotype encapsulated bacteria such as Streptococcus pneumoniae. Toxic shock syndrome toxin-1 (TSST-1), a superantigen.

Question 42 Microbiology

What is the catalase test used to detect?

Irreversibly bind the 30S ribosomal subunit, causing misreading of mRNA and inhibiting protein synthesis. Presence of catalase enzyme (breaks H2O2 into water and oxygen bubbles); differentiates Staphylococcus (positive) from Streptococcus (negative). Lytic cycle: phage replicates and lyses the host cell immediately; lysogenic cycle: phage DNA integrates into the host genome as a prophage and replicates passively until induced. Inhibit bacterial DNA gyrase and topoisomerase IV, blocking DNA replication.

Question 43 Microbiology

What is the mechanism of action of tetracyclines?

Clostridium botulinum; botulinum toxin blocks acetylcholine release at the neuromuscular junction, causing flaccid paralysis. Hepatitis A virus (Picornaviridae), transmitted fecal-oral, typically self-limited, no chronic carrier state. Bind the 30S ribosomal subunit and block aminoacyl-tRNA attachment, inhibiting protein synthesis. Hepatitis E virus.

Question 44 Microbiology

Which bacterial genera are common causes of nosocomial (hospital-acquired) UTIs associated with catheters, aside from E. coli?

Human immunodeficiency virus (HIV). Oxidize and disrupt proteins/enzymes and damage nucleic acids via hypochlorous acid formation. Enterococcus species and Klebsiella species. Enterohemorrhagic Escherichia coli (EHEC), especially serotype O157:H7.

Question 45 Microbiology

What staining technique is used to identify Mycobacterium tuberculosis?

Anaerobic breakdown of substrates (often glucose) using an organic molecule as the final electron acceptor, without an electron transport chain. Asexual fungal spores produced at the tips of specialized hyphae, used for identification and reproduction. Ziehl-Neelsen (acid-fast) stain, which appears bright red/pink against a blue background. Trichomonas vaginalis.

Question 46 Microbiology

What is the most common helminth (worm) infection in the US, especially among children?

Staphylococcus epidermidis. Enterotoxigenic Escherichia coli (ETEC). Enterobius vermicularis (pinworm). Neisseria gonorrhoeae.

Question 47 Microbiology

Which bacterium causes diphtheria and how does its exotoxin work?

Sterilizing heat-sensitive medical equipment by alkylating proteins and nucleic acids. Corynebacterium diphtheriae; diphtheria toxin inhibits protein synthesis by ADP-ribosylating elongation factor-2 (EF-2). Liver damage and increased risk of hepatocellular carcinoma. They establish lifelong latency in host cells (e.g., neurons) with potential for reactivation.

Question 48 Microbiology

What is the basic structural difference between enveloped and non-enveloped (naked) viruses?

Trypanosoma brucei, transmitted by the tsetse fly. Hepatitis D virus (delta agent), a defective virus needing HBsAg. Staphylococcus epidermidis. Enveloped viruses have a lipid bilayer derived from host membrane surrounding the capsid; non-enveloped viruses have only a protein capsid, making them generally more resistant to desiccation and disinfectants.

Question 49 Microbiology

Which virus requires co-infection with Hepatitis B to replicate?

Staphylococcus epidermidis. Hepatitis D virus (delta agent), a defective virus needing HBsAg. Erythema migrans, a bullseye-shaped rash. Coccidioides immitis.

Question 50 Microbiology

What is the mechanism of action of macrolides (e.g., erythromycin, azithromycin)?

Clostridium perfringens, via alpha toxin (a lecithinase). Bind the 50S ribosomal subunit and block translocation, inhibiting protein synthesis. Escherichia coli (uropathogenic strains). Bacillus anthracis; protective antigen, edema factor, and lethal factor.