Title: Microbiology — LearnCoachAssist

Q: What is the basic structural difference between Gram-positive and Gram-negative cell walls?
A: 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).

Q: What color do Gram-positive bacteria appear after Gram staining?
A: Purple/violet (retain crystal violet-iodine complex).

Q: What color do Gram-negative bacteria appear after Gram staining?
A: Pink/red (crystal violet is washed out by decolorizer; counterstained with safranin).

Q: What are the four main steps of the Gram stain procedure, in order?
A: 1) Crystal violet (primary stain) 2) Gram's iodine (mordant) 3) Alcohol/acetone decolorizer 4) Safranin (counterstain).

Q: What molecule in the outer membrane of Gram-negative bacteria acts as an endotoxin?
A: Lipopolysaccharide (LPS), specifically its lipid A component.

Q: What is teichoic acid and where is it found?
A: A polymer unique to Gram-positive cell walls that extends through the peptidoglycan and contributes to virulence and immune stimulation.

Q: Name the polymer that gives bacterial cell walls their rigidity.
A: Peptidoglycan (murein), made of alternating NAG and NAM sugars cross-linked by peptide chains.

Q: Which enzyme, found in tears and saliva, breaks down peptidoglycan?
A: Lysozyme.

Q: What bacterial genus lacks a cell wall entirely and is therefore resistant to penicillin?
A: Mycoplasma.

Q: What special cell wall component makes Mycobacterium species acid-fast?
A: Mycolic acid, a waxy lipid layer.

Q: What staining technique is used to identify Mycobacterium tuberculosis?
A: Ziehl-Neelsen (acid-fast) stain, which appears bright red/pink against a blue background.

Q: What is the function of bacterial flagella?
A: Motility/locomotion, propelled by rotation of the flagellar motor.

Q: What is the difference between a bacterial capsule and a slime layer?
A: A capsule is a well-organized, tightly bound polysaccharide layer; a slime layer is loosely attached and diffuse. Both aid adherence and immune evasion.

Q: What is the function of bacterial pili (fimbriae)?
A: Adherence to surfaces/host cells; sex pili also mediate conjugation (DNA transfer).

Q: What is a bacterial endospore and which genera commonly form them?
A: A dormant, highly resistant structure formed under stress; formed by Bacillus and Clostridium species.

Q: Which stain is used to visualize bacterial endospores?
A: Malachite green (Schaeffer-Fulton stain).

Q: What is the difference between the bacterial nucleoid and a plasmid?
A: The nucleoid is the single circular chromosome; a plasmid is a small, extrachromosomal, self-replicating circular DNA fragment often carrying antibiotic resistance genes.

Q: What are the three basic bacterial shapes?
A: Cocci (spherical), bacilli (rod-shaped), and spirilla/spirochetes (spiral).

Q: Differentiate diplococci, streptococci, and staphylococci arrangements.
A: Diplococci = pairs; streptococci = chains; staphylococci = grape-like clusters.

Q: What is the function of the bacterial cell (cytoplasmic) membrane?
A: Selective permeability, transport, energy production (site of electron transport chain), and biosynthesis; lacks sterols (except Mycoplasma).

Q: What is horizontal gene transfer, and name its three main mechanisms.
A: Transfer of genetic material between bacteria (not parent to offspring) via transformation, transduction, and conjugation.

Q: Define bacterial transformation.
A: Uptake of free/naked DNA from the environment by a competent bacterial cell.

Q: Define bacterial transduction.
A: Transfer of bacterial DNA from one cell to another via a bacteriophage.

Q: Define bacterial conjugation.
A: Direct transfer of DNA (often a plasmid) between bacteria through a sex pilus/mating bridge.

Q: What is the difference between obligate aerobes and obligate anaerobes?
A: Obligate aerobes require oxygen for growth; obligate anaerobes are killed or cannot grow in the presence of oxygen.

Q: What are facultative anaerobes?
A: Organisms that can grow with or without oxygen, preferring aerobic respiration when oxygen is available.

Q: What is an aerotolerant anaerobe?
A: An organism that does not use oxygen but can survive and grow in its presence.

Q: What is a capnophile?
A: An organism that grows best with increased carbon dioxide concentration (e.g., Neisseria gonorrhoeae).

Q: What are extremophiles? Give an example category.
A: Organisms adapted to extreme environments; examples include thermophiles (heat), psychrophiles (cold), halophiles (high salt), and acidophiles (low pH).

Q: What is the oxidase test used to detect?
A: Presence of cytochrome c oxidase; used to differentiate Pseudomonas (positive) from Enterobacteriaceae (negative).

Q: What is the catalase test used to detect?
A: Presence of catalase enzyme (breaks H2O2 into water and oxygen bubbles); differentiates Staphylococcus (positive) from Streptococcus (negative).

Q: What is the coagulase test used for?
A: Differentiates Staphylococcus aureus (coagulase-positive) from coagulase-negative staphylococci like S. epidermidis.

Q: What does a positive oxidative-fermentative (O-F) test with acid production indicate?
A: The organism ferments the sugar rather than merely oxidizing it.

Q: What is selective media used for? Give an example.
A: Media that inhibits growth of unwanted organisms while allowing target organisms to grow; e.g., MacConkey agar selects for Gram-negatives.

Q: What is differential media used for? Give an example.
A: Media that allows visual distinction between organisms based on biochemical reactions; e.g., MacConkey agar differentiates lactose fermenters (pink) from non-fermenters.

Q: What does blood agar with beta-hemolysis look like, and what does it indicate?
A: A clear zone of complete hemolysis around colonies, indicating complete lysis of red blood cells (e.g., Streptococcus pyogenes).

Q: What is alpha-hemolysis on blood agar?
A: Partial/incomplete hemolysis producing a greenish discoloration around colonies (e.g., Streptococcus pneumoniae, viridans streptococci).

Q: What are the four phases of the bacterial growth curve?
A: Lag phase, log (exponential) phase, stationary phase, and death (decline) phase.

Q: What happens during the lag phase of bacterial growth?
A: Cells adapt to the environment and synthesize enzymes/metabolites; little to no cell division occurs.

Q: What defines the log (exponential) phase of bacterial growth?
A: Cells divide at a constant maximal rate; population doubles at regular intervals (generation time).

Q: Why does the stationary phase occur?
A: Nutrient depletion and waste accumulation cause growth rate to equal death rate, so population size plateaus.

Q: What is generation (doubling) time?
A: The time required for a bacterial population to double in number.

Q: What are the essential nutritional requirements for most bacterial growth?
A: Carbon source, nitrogen source, energy source, water, minerals, and appropriate pH/temperature/osmotic conditions.

Q: Differentiate autotrophs and heterotrophs.
A: Autotrophs synthesize organic compounds from CO2; heterotrophs obtain organic carbon from other organisms.

Q: What temperature range defines mesophiles, and why are they medically important?
A: Roughly 20-45 degrees C; most human pathogens are mesophiles because this range includes body temperature (37 degrees C).

Q: What is fermentation in bacterial metabolism?
A: Anaerobic breakdown of substrates (often glucose) using an organic molecule as the final electron acceptor, without an electron transport chain.

Q: What is biofilm formation and why is it clinically important?
A: 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).

Q: What is the difference between sterilization and disinfection?
A: Sterilization kills all microbial life including spores; disinfection reduces pathogens to a safe level but may not kill spores.

Q: What is autoclaving and what conditions does it typically use?
A: Sterilization using pressurized steam, typically 121 degrees C at 15 psi for about 15-20 minutes; kills endospores.

Q: What is pasteurization?
A: 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.

Q: What is the mechanism of action of alcohols (ethanol, isopropanol) as disinfectants?
A: Denature proteins and disrupt lipid membranes; most effective at 60-90% concentration in water.

Q: What is the mechanism of action of chlorine-based disinfectants (bleach)?
A: Oxidize and disrupt proteins/enzymes and damage nucleic acids via hypochlorous acid formation.

Q: What is an antiseptic versus a disinfectant?
A: Antiseptics are chemicals safe for use on living tissue; disinfectants are used on inanimate objects/surfaces and may be too harsh for tissue.

Q: What is HEPA filtration used for in microbiology/healthcare?
A: Removing airborne particles including bacteria from air, e.g., in operating rooms and biosafety cabinets.

Q: What is the mechanism of ionizing radiation (e.g., gamma rays) in sterilization?
A: Damages DNA directly and generates free radicals that destroy cellular components; used for sterilizing disposable medical supplies.

Q: What is ethylene oxide gas sterilization used for?
A: Sterilizing heat-sensitive medical equipment by alkylating proteins and nucleic acids.

Q: Define -cidal versus -static suffixes in antimicrobial terms.
A: -cidal (e.g., bactericidal) means it kills the organism; -static (e.g., bacteriostatic) means it inhibits growth/reproduction without necessarily killing.

Q: What is the mechanism of action of penicillins and cephalosporins?
A: Beta-lactam antibiotics that inhibit peptidoglycan cross-linking by binding penicillin-binding proteins, weakening the cell wall and causing lysis.

Q: What is the mechanism of action of vancomycin?
A: Binds D-Ala-D-Ala terminus of peptidoglycan precursors, blocking cell wall synthesis; effective mainly against Gram-positives.

Q: What is the mechanism of action of aminoglycosides (e.g., gentamicin)?
A: Irreversibly bind the 30S ribosomal subunit, causing misreading of mRNA and inhibiting protein synthesis.

Q: What is the mechanism of action of tetracyclines?
A: Bind the 30S ribosomal subunit and block aminoacyl-tRNA attachment, inhibiting protein synthesis.

Q: What is the mechanism of action of macrolides (e.g., erythromycin, azithromycin)?
A: Bind the 50S ribosomal subunit and block translocation, inhibiting protein synthesis.

Q: What is the mechanism of action of fluoroquinolones (e.g., ciprofloxacin)?
A: Inhibit bacterial DNA gyrase and topoisomerase IV, blocking DNA replication.

Q: What is the mechanism of action of sulfonamides?
A: Competitively inhibit dihydropteroate synthase, blocking folic acid synthesis needed for nucleotide production.

Q: What is the mechanism of action of rifampin?
A: Inhibits bacterial DNA-dependent RNA polymerase, blocking transcription.

Q: What is the mechanism of action of metronidazole?
A: Forms toxic free radicals in anaerobic/microaerophilic organisms that damage DNA; used for anaerobes and protozoa.

Q: What enzyme confers resistance to penicillins by hydrolyzing the beta-lactam ring?
A: Beta-lactamase (penicillinase).

Q: What is a beta-lactamase inhibitor and give an example combination.
A: A drug that blocks beta-lactamase enzymes to protect the antibiotic; e.g., clavulanic acid combined with amoxicillin (Augmentin).

Q: What does MRSA stand for and what confers its resistance?
A: Methicillin-resistant Staphylococcus aureus; resistance from altered penicillin-binding protein (PBP2a) encoded by the mecA gene.

Q: What are the four general mechanisms of antibiotic resistance?
A: 1) Enzymatic drug inactivation 2) Altered target site 3) Decreased drug uptake/permeability 4) Increased efflux pump activity.

Q: What is the vancomycin-resistant Enterococcus (VRE) resistance mechanism?
A: Altered peptidoglycan precursor terminus (D-Ala-D-Lac instead of D-Ala-D-Ala) that vancomycin cannot bind.

Q: What is an extended-spectrum beta-lactamase (ESBL)?
A: A bacterial enzyme that confers resistance to a broad range of beta-lactam antibiotics including penicillins and cephalosporins.

Q: What is the difference between bactericidal and bacteriostatic antibiotics in terms of immune system reliance?
A: Bacteriostatic drugs inhibit growth and rely on the host immune system to clear the infection; bactericidal drugs directly kill the organism.

Q: What is antibiotic synergy? Give an example.
A: Combined effect of two drugs greater than the sum of their individual effects; e.g., trimethoprim-sulfamethoxazole sequentially blocking folate synthesis.

Q: What is horizontal transfer of resistance genes commonly mediated by?
A: Plasmids (R factors), transposons, and integrons transferred via conjugation.

Q: Which bacterium is the most common cause of bacterial pharyngitis (strep throat)?
A: Streptococcus pyogenes (Group A Streptococcus).

Q: What post-infectious complications can follow untreated Streptococcus pyogenes infection?
A: Rheumatic fever and post-streptococcal glomerulonephritis.

Q: Which bacterium causes scarlet fever and what toxin is responsible for the rash?
A: Streptococcus pyogenes, via erythrogenic (pyrogenic) exotoxin.

Q: Which bacterium is a leading cause of bacterial meningitis and pneumonia, alpha-hemolytic, and lancet-shaped?
A: Streptococcus pneumoniae.

Q: Which bacterium causes neonatal meningitis/sepsis and is classified as Group B Streptococcus?
A: Streptococcus agalactiae.

Q: Which coagulase-positive, catalase-positive, Gram-positive cocci causes skin infections, toxic shock syndrome, and food poisoning?
A: Staphylococcus aureus.

Q: What toxin produced by Staphylococcus aureus causes toxic shock syndrome?
A: Toxic shock syndrome toxin-1 (TSST-1), a superantigen.

Q: Which coagulase-negative staphylococcus commonly causes infections of prosthetic devices and catheters?
A: Staphylococcus epidermidis.

Q: Which bacterium causes anthrax and what are its three toxin components?
A: Bacillus anthracis; protective antigen, edema factor, and lethal factor.

Q: Which spore-forming bacterium causes tetanus, and what toxin is involved?
A: Clostridium tetani, producing tetanospasmin, which blocks inhibitory neurotransmitter release causing spastic paralysis.

Q: Which spore-forming bacterium causes botulism, and how does its toxin act?
A: Clostridium botulinum; botulinum toxin blocks acetylcholine release at the neuromuscular junction, causing flaccid paralysis.

Q: Which bacterium causes gas gangrene?
A: Clostridium perfringens, via alpha toxin (a lecithinase).

Q: Which bacterium causes pseudomembranous colitis, often after antibiotic use?
A: Clostridioides difficile (formerly Clostridium difficile).

Q: Which bacterium causes diphtheria and how does its exotoxin work?
A: Corynebacterium diphtheriae; diphtheria toxin inhibits protein synthesis by ADP-ribosylating elongation factor-2 (EF-2).

Q: Which acid-fast bacterium causes tuberculosis?
A: Mycobacterium tuberculosis.

Q: What is a Ghon complex?
A: A calcified granuloma (tubercle) with associated lymph node involvement seen in primary tuberculosis infection.

Q: Which acid-fast bacterium causes Hansen's disease (leprosy)?
A: Mycobacterium leprae.

Q: Which Gram-negative diplococcus causes gonorrhea?
A: Neisseria gonorrhoeae.

Q: Which Gram-negative diplococcus causes bacterial meningitis and meningococcemia, notable for a petechial rash?
A: Neisseria meningitidis.

Q: Which Gram-negative bacterium causes most community-acquired urinary tract infections?
A: Escherichia coli (uropathogenic strains).

Q: Which E. coli strain produces Shiga-like toxin and causes hemolytic uremic syndrome?
A: Enterohemorrhagic Escherichia coli (EHEC), especially serotype O157:H7.

Q: Which Gram-negative rod causes typhoid fever?
A: Salmonella typhi.

Q: Which Gram-negative bacterium is a common cause of gastroenteritis from contaminated poultry/eggs (non-typhoidal)?
A: Salmonella enteritidis (non-typhoidal Salmonella).

Q: Which Gram-negative rod causes bacillary dysentery?
A: Shigella species.

Q: Which curved, Gram-negative bacterium causes cholera, and how does its toxin work?
A: Vibrio cholerae; cholera toxin activates adenylate cyclase, increasing cAMP and causing massive watery diarrhea via chloride/water secretion.

Q: Which curved Gram-negative bacterium is a leading cause of bacterial gastroenteritis from undercooked poultry?
A: Campylobacter jejuni.

Q: Which Gram-negative bacterium causes peptic ulcers and gastritis?
A: Helicobacter pylori.

Q: Which Gram-negative rod is a major opportunistic pathogen in cystic fibrosis and burn patients, producing a blue-green pigment?
A: Pseudomonas aeruginosa.

Q: Which Gram-negative bacterium causes whooping cough (pertussis)?
A: Bordetella pertussis.

Q: Which Gram-negative coccobacillus causes Legionnaires' disease?
A: Legionella pneumophila, often from contaminated water systems (e.g., cooling towers).

Q: Which Gram-negative bacterium is a common cause of community-acquired pneumonia and forms mucoid colonies?
A: Klebsiella pneumoniae.

Q: Which small Gram-negative coccobacillus causes epiglottitis and meningitis, especially in unvaccinated children?
A: Haemophilus influenzae type b (Hib).

Q: Which zoonotic Gram-negative bacterium causes plague and is transmitted by fleas?
A: Yersinia pestis.

Q: Which spirochete causes syphilis?
A: Treponema pallidum.

Q: What are the stages of untreated syphilis?
A: Primary (chancre), secondary (rash, systemic symptoms), latent, and tertiary (gummas, cardiovascular and neurological disease).

Q: Which spirochete causes Lyme disease, and what is its vector?
A: Borrelia burgdorferi, transmitted by Ixodes ticks.

Q: What is the classic early skin finding in Lyme disease?
A: Erythema migrans, a bullseye-shaped rash.

Q: Which spirochete causes leptospirosis?
A: Leptospira interrogans, often from water contaminated with animal urine.

Q: Which obligate intracellular bacterium causes trachoma and the most common bacterial STI worldwide?
A: Chlamydia trachomatis.

Q: Which obligate intracellular bacterium causes atypical pneumonia along with Mycoplasma pneumoniae?
A: Chlamydophila (Chlamydia) pneumoniae.

Q: Which cell-wall-deficient bacterium is a common cause of atypical (walking) pneumonia, especially in young adults?
A: Mycoplasma pneumoniae.

Q: Which tick-borne Rickettsia causes Rocky Mountain spotted fever?
A: Rickettsia rickettsii.

Q: What is the characteristic feature of Rickettsial infections regarding growth requirements?
A: They are obligate intracellular bacteria that cannot be cultured on standard artificial media.

Q: Which bacterium causes Q fever and can survive outside host cells due to a spore-like form?
A: Coxiella burnetii.

Q: Which Gram-positive rod causes listeriosis and is notable for causing meningitis in neonates, elderly, and immunocompromised?
A: Listeria monocytogenes, notable for growth at refrigeration temperatures and transplacental transmission.

Q: Which bacterium causes relapsing fever, transmitted by lice or ticks?
A: Borrelia recurrentis (lice-borne) or other Borrelia species (tick-borne).

Q: Which Gram-negative bacterium causes tularemia (rabbit fever)?
A: Francisella tularensis.

Q: Which Gram-negative bacterium causes brucellosis, often from unpasteurized dairy?
A: Brucella species.

Q: Which bacterium is the classic cause of cat scratch disease?
A: Bartonella henselae.

Q: Which anaerobic Gram-negative rod is part of normal oral/GI flora but causes abscesses when it enters sterile sites?
A: Bacteroides fragilis.

Q: What toxin type do Gram-negative bacteria release upon cell lysis, and what is its chemical nature?
A: Endotoxin, which is lipopolysaccharide (LPS), specifically the lipid A portion.

Q: What is the difference between exotoxins and endotoxins?
A: 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.

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

Q: Which bacterium is the classic cause of traveler's diarrhea via a heat-labile/heat-stable enterotoxin?
A: Enterotoxigenic Escherichia coli (ETEC).

Q: What is the Quellung reaction used to identify?
A: Capsule swelling reaction used to serotype encapsulated bacteria such as Streptococcus pneumoniae.

Q: Which bacterial genera are common causes of nosocomial (hospital-acquired) UTIs associated with catheters, aside from E. coli?
A: Enterococcus species and Klebsiella species.

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

Q: What are the two main capsid symmetries seen in viruses?
A: Icosahedral and helical (some viruses, like poxviruses, have complex symmetry).

Q: What is a virion?
A: A complete, infectious virus particle outside a host cell.

Q: Differentiate DNA and RNA viruses in terms of where replication typically occurs.
A: DNA viruses typically replicate in the nucleus (exception: poxviruses); RNA viruses typically replicate in the cytoplasm (exception: influenza and retroviruses use the nucleus).

Q: What is the difference between the lytic and lysogenic cycles of bacteriophages?
A: 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.

Q: What enzyme do retroviruses use to convert RNA into DNA?
A: Reverse transcriptase.

Q: Which virus is the classic example of a retrovirus and causes AIDS?
A: Human immunodeficiency virus (HIV).

Q: What are the main target cells of HIV?
A: CD4+ T helper lymphocytes (also macrophages and dendritic cells) via binding to CD4 and CCR5/CXCR4 co-receptors.

Q: What laboratory value is used to monitor HIV disease progression and AIDS diagnosis threshold?
A: CD4+ T cell count; AIDS is diagnosed when CD4 count falls below 200 cells/microliter or an AIDS-defining illness occurs.

Q: Which virus family causes the common cold most frequently?
A: Rhinovirus (Picornaviridae).

Q: Which virus causes seasonal influenza, and what are its two major surface antigens?
A: Influenza virus; hemagglutinin (HA) and neuraminidase (NA).

Q: What is the difference between antigenic drift and antigenic shift in influenza?
A: Antigenic drift is gradual point mutation in HA/NA causing seasonal epidemics; antigenic shift is abrupt reassortment of gene segments between strains, capable of causing pandemics.

Q: Which virus causes measles and what is its characteristic oral finding?
A: Measles virus (Paramyxoviridae); Koplik spots (small white spots on buccal mucosa).

Q: Which virus causes mumps?
A: Mumps virus (Paramyxoviridae), causing parotitis (swollen salivary glands).

Q: Which virus causes chickenpox (varicella) and, upon reactivation, shingles (zoster)?
A: Varicella-zoster virus (VZV), a herpesvirus.

Q: Which herpesvirus causes infectious mononucleosis?
A: Epstein-Barr virus (EBV), also linked to Burkitt lymphoma and nasopharyngeal carcinoma.

Q: Which herpesvirus is associated with congenital infection causing hearing loss and is a common cause of disease in immunocompromised transplant patients?
A: Cytomegalovirus (CMV).

Q: Which herpesvirus types most commonly cause oral and genital herpes lesions, respectively?
A: HSV-1 typically causes oral herpes (cold sores); HSV-2 typically causes genital herpes (though both can cause either).

Q: What is unique about herpesviruses regarding their infection pattern?
A: They establish lifelong latency in host cells (e.g., neurons) with potential for reactivation.

Q: Which virus causes hepatitis A and how is it transmitted?
A: Hepatitis A virus (Picornaviridae), transmitted fecal-oral, typically self-limited, no chronic carrier state.

Q: Which hepatitis virus is transmitted via blood/body fluids and can become chronic, increasing liver cancer risk?
A: Hepatitis B virus (Hepadnaviridae).

Q: Which hepatitis virus is the most common cause of chronic viral hepatitis in many countries and is transmitted mainly via blood?
A: Hepatitis C virus (Flaviviridae).

Q: Which virus requires co-infection with Hepatitis B to replicate?
A: Hepatitis D virus (delta agent), a defective virus needing HBsAg.

Q: Which hepatitis virus is fecal-oral and particularly dangerous in pregnant women?
A: Hepatitis E virus.

Q: Which virus causes rabies, and what is its characteristic cytoplasmic inclusion body?
A: Rabies virus (Rhabdoviridae); Negri bodies.

Q: Which virus family causes viral gastroenteritis most commonly in children?
A: Rotavirus.

Q: Which virus is the most common cause of outbreak-associated viral gastroenteritis (e.g., on cruise ships)?
A: Norovirus.

Q: Which virus causes poliomyelitis and what cells does it target?
A: Poliovirus (Picornaviridae); targets motor neurons in the anterior horn of the spinal cord, causing flaccid paralysis.

Q: Which arbovirus causes yellow fever, and what is its vector?
A: Yellow fever virus (Flaviviridae), transmitted by Aedes mosquitoes.

Q: Which arbovirus, transmitted by Aedes mosquitoes, causes a triad of fever, rash, and severe joint/bone pain?
A: Dengue virus.

Q: What congenital syndrome is associated with maternal Zika virus infection?
A: Congenital microcephaly and other brain abnormalities in the fetus.

Q: What is the mechanism by which SARS-CoV-2 enters human cells?
A: Binds ACE2 receptor via its spike protein, facilitating membrane fusion and cell entry.

Q: What is the difference between a live-attenuated and an inactivated (killed) vaccine?
A: Live-attenuated vaccines use a weakened but replicating pathogen (stronger, longer immunity, small risk in immunocompromised); inactivated vaccines use a killed pathogen (safer, but often needs boosters/adjuvants).

Q: What is the fundamental structural difference between fungal and bacterial cell walls?
A: Fungal cell walls contain chitin (and sometimes glucans), whereas bacterial cell walls contain peptidoglycan.

Q: What is the key sterol found in fungal cell membranes that is targeted by antifungal drugs?
A: Ergosterol.

Q: Differentiate yeasts and molds morphologically.
A: Yeasts are unicellular, round to oval, reproduce by budding; molds are multicellular, form branching filaments called hyphae.

Q: What is dimorphism in fungi?
A: The ability to switch between yeast and mold forms depending on temperature (e.g., mold at room temp, yeast at body temp).

Q: Which yeast is part of normal flora but causes opportunistic infections like thrush and vaginal candidiasis?
A: Candida albicans.

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

Q: What special stain is used to visualize the capsule of Cryptococcus neoformans?
A: India ink stain.

Q: Which dimorphic fungus, found in soil with bird/bat droppings (Ohio/Mississippi river valleys), causes histoplasmosis?
A: Histoplasma capsulatum.

Q: Which dimorphic fungus, endemic to the southwestern US deserts, causes Valley fever (coccidioidomycosis)?
A: Coccidioides immitis.

Q: Which dimorphic fungus causes blastomycosis, endemic to the Great Lakes and Mississippi/Ohio river valleys?
A: Blastomyces dermatitidis.

Q: Which mold genus causes invasive pulmonary infections in immunocompromised patients and is characterized by septate hyphae with acute-angle branching?
A: Aspergillus species.

Q: Which fungal genus causes mucormycosis, characterized by broad, non-septate hyphae with wide-angle branching, common in diabetic ketoacidosis?
A: Mucor or Rhizopus species (Mucorales).

Q: What organism causes Pneumocystis pneumonia (PCP), a classic AIDS-defining opportunistic infection?
A: Pneumocystis jirovecii.

Q: What are dermatophytes and what infections do they cause?
A: Fungi (e.g., Trichophyton, Microsporum, Epidermophyton) that infect keratinized tissue (skin, hair, nails), causing tinea (ringworm) infections.

Q: What is the mechanism of action of azole antifungals (e.g., fluconazole)?
A: Inhibit lanosterol 14-alpha-demethylase, blocking ergosterol synthesis and disrupting the fungal cell membrane.

Q: What is the mechanism of action of amphotericin B?
A: Binds ergosterol in the fungal cell membrane, forming pores that cause leakage of cell contents.

Q: What is the mechanism of action of echinocandins (e.g., caspofungin)?
A: Inhibit beta-(1,3)-D-glucan synthase, blocking fungal cell wall glucan synthesis.

Q: What is the mechanism of action of griseofulvin?
A: Interferes with fungal microtubule function, disrupting mitosis; used for dermatophyte infections.

Q: What are conidia?
A: Asexual fungal spores produced at the tips of specialized hyphae, used for identification and reproduction.

Q: What condition is caused by ingestion of aflatoxins produced by Aspergillus flavus?
A: Liver damage and increased risk of hepatocellular carcinoma.

Q: What is the causative agent of malaria and what is its vector?
A: Plasmodium species (e.g., P. falciparum, P. vivax), transmitted by female Anopheles mosquitoes.

Q: Which Plasmodium species causes the most severe and deadly form of malaria?
A: Plasmodium falciparum.

Q: What is the causative agent of toxoplasmosis, and what is a common source of infection?
A: Toxoplasma gondii; sources include cat feces and undercooked meat; dangerous in pregnancy (congenital toxoplasmosis) and immunocompromised patients.

Q: Which protozoan causes African sleeping sickness and what is its vector?
A: Trypanosoma brucei, transmitted by the tsetse fly.

Q: Which protozoan causes Chagas disease and what is its vector?
A: Trypanosoma cruzi, transmitted by triatomine (kissing) bugs.

Q: Which protozoan causes amoebic dysentery and liver abscesses?
A: Entamoeba histolytica.

Q: Which flagellated protozoan causes a foul-smelling, greasy diarrhea and is transmitted via contaminated water (common in hikers)?
A: Giardia lamblia (intestinalis).

Q: Which protozoan is a common sexually transmitted parasite causing vaginitis?
A: Trichomonas vaginalis.

Q: Which protozoan causes cryptosporidiosis, a common cause of waterborne diarrhea especially in immunocompromised patients?
A: Cryptosporidium parvum.

Q: Which protozoan causes visceral and cutaneous leishmaniasis, transmitted by sandflies?
A: Leishmania species.

Q: What is the causative agent of trichinosis, typically acquired from undercooked pork?
A: Trichinella spiralis (a roundworm/nematode).

Q: What is the most common helminth (worm) infection in the US, especially among children?
A: Enterobius vermicularis (pinworm).

Q: Which large roundworm is one of the most common helminthic infections worldwide, acquired via fecal-oral ingestion of eggs?
A: Ascaris lumbricoides.

Q: Which hookworm species infect humans via skin penetration from contaminated soil?
A: Necator americanus and Ancylostoma duodenale.

Q: Which tapeworm is acquired from undercooked pork and can cause cysticercosis?
A: Taenia solium.

Q: Which tapeworm is acquired from undercooked beef?
A: Taenia saginata.