Bacteriology Review Flashcards

A comprehensive set of 80 question-and-answer flashcards covering taxonomy, staining, cell structure, virulence factors, toxins, antimicrobial mechanisms, sterilization, biosafety, specimen management, and bacterial genetics based on the lecture notes.

What type of microorganisms are bacteria classified as?

Single-celled prokaryotes that divide by binary fission.

Name the three major groups of prokaryotes in bacterial taxonomy.

Eubacteria, Cyanobacteria, Archaebacteria.

Which bacterial genus lacks a true cell wall and therefore stains Gram-negative?

Mycoplasma (and Ureaplasma).

What is the main structural component of the bacterial cell wall?

Peptidoglycan.

Which dye is the primary stain in the Gram stain?

Crystal violet.

What is the function of Gram’s iodine in Gram staining?

Acts as a mordant to fix crystal violet to cell wall.

Which reagent serves as the decolorizer in a Gram stain?

95 % alcohol or acetone-alcohol.

Why do Gram-negative bacteria lose crystal violet during decolorization?

Their lipid-rich outer membrane is dissolved by alcohol, allowing dye to escape.

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

Violet or purple.

Name two Gram-negative cocci that are exceptions to the ‘all cocci are Gram-positive’ rule.

Neisseria and Moraxella (Branhamella).

What is the Ziehl-Neelsen stain primarily used for?

Detecting acid-fast bacteria such as Mycobacterium spp.

Which waxy cell-wall component makes acid-fast bacteria hard to stain?

Mycolic acid (hydroxymethoxy acid).

List one hot and one cold method for acid-fast staining.

Hot: Ziehl-Neelsen; Cold: Kinyoun.

Which stain differentiates Mycobacterium tuberculosis from M. smegmatis?

Pappenheim stain.

What special stain is used to visualize bacterial capsules microscopically?

India ink or Hiss stain (negative staining).

Name two medically important spore-forming genera.

Bacillus (aerobic) and Clostridium (anaerobic).

What compound gives endospores their resistance to heat and chemicals?

Calcium dipicolinate (dipicolinic acid).

Which surface appendage is primarily responsible for bacterial conjugation?

Pili (sex pili).

What is the purpose of bacterial flagella?

Motility/locomotion.

At what temperature are flagella best demonstrated?

25 °C (flagella of Listeria and Yersinia are inhibited at 37 °C).

Define true motility in a hanging-drop preparation.

Directional movement of bacteria across the field, not just vibration.

What reagent is used in the Limulus lysate test to detect endotoxin?

Amoebocyte lysate from the horseshoe crab (Limulus polyphemus).

Differentiate exotoxin release from endotoxin release.

Exotoxins: actively secreted by living cells; Endotoxins: released upon cell lysis.

Which heat-stable toxin is an exception among exotoxins?

Staphylococcal enterotoxin (food poisoning).

Give one example each of cytotoxin, enterotoxin, and neurotoxin.

Cytotoxin: diphtheria toxin; Enterotoxin: cholera toxin; Neurotoxin: tetanospasmin.

Name the five main target sites of antimicrobial agents.

Cell wall synthesis, protein synthesis, nucleic acid synthesis, cell membrane function, metabolic pathways.

Which antibiotic class inhibits cell wall synthesis via β-lactam ring?

Penicillins, cephalosporins, carbapenems, monobactams.

What is the minimum inhibitory concentration (MIC)?

Lowest antibiotic concentration preventing visible growth.

What culture medium is standard for the Kirby-Bauer disk diffusion test?

Mueller-Hinton agar (4 mm depth, pH 7.2-7.4).

How is the 0.5 McFarland turbidity standard prepared?

99.5 ml of 1 % H₂SO₄ + 0.5 ml of 1 % BaCl₂ (≈1.5 × 10⁸ CFU/ml).

List the four phases of the bacterial growth curve.

Lag, Log (exponential), Plateau (stationary), Decline (death).

Which bacterial growth phase is most susceptible to antibiotics?

Log (exponential) phase.

Define obligate aerobe and give one example.

Requires oxygen (≈21 % O₂) to grow; example: Pseudomonas aeruginosa.

What atmosphere does a capnophilic organism prefer?

Increased CO₂ (5-10 %) with about 15 % O₂.

Which pathogen is classically microaerophilic, requiring 5-10 % O₂?

Campylobacter jejuni.

Name a psychrophilic pathogen that can grow at 4 °C.

Listeria monocytogenes or Yersinia enterocolitica.

What pH range favors growth of Vibrio cholerae?

Alkaline pH 8-10 (e.g., APW).

Which instrument sterilizes by moist heat at 121 °C, 15 psi, for 15 min?

Autoclave (Charles Chamberland).

What biological indicator is used to verify autoclave efficiency?

Geobacillus stearothermophilus spores.

Define tyndallization.

Fractional steaming at 100 °C for 30 min on three consecutive days.

Which method sterilizes heat-labile liquids using membrane filters?

Filtration (cellulose acetate/nitrate).

Name one gas chemical sterilant for heat-sensitive equipment.

Ethylene oxide (ETO).

Which disinfectant concentration of alcohol is most effective?

70 % ethanol or isopropanol.

What is the phenol coefficient used for?

Comparing disinfectant’s bactericidal power to phenol using S. aureus and S. typhi.

Which genus produces streptomycin naturally?

Streptomyces griseus.

Give two essential properties of an ideal chemotherapeutic agent.

Selective toxicity and bactericidal activity without resistance or side effects.

Which genetic exchange process involves uptake of free DNA by a competent bacterium?

Transformation.

What protein mediates homologous recombination in bacteria?

RecA protein.

In transduction, what vehicle transfers donor DNA?

A bacteriophage particle.

What is the difference between F-plasmid and Hfr conjugation?

F-plasmid transfers only plasmid DNA; Hfr transfers chromosomal genes via integrated plasmid.

How many biosafety levels exist for microbiology labs?

Four (BSL-1 to BSL-4).

Which biosafety cabinet class is most common in clinical labs?

Class II biosafety cabinet.

State two general guidelines for specimen collection.

Collect before antibiotics and from the actual infection site under aseptic conditions.

What anticoagulant is used in blood culture bottles?

0.025 % sodium polyanethol sulfonate (SPS).

How much adult blood is recommended per culture set?

20-30 ml (10-15 ml per bottle).

Which CSF tube is routinely sent to Microbiology?

Tube #2 (or #4 if only one sent, after micro first).

Name the most common bacterial meningitis agent in neonates.

Streptococcus agalactiae (Group B strep).

What constitutes an acceptable sputum sample under Gram stain criteria?

25 PMNs and <10 squamous epithelial cells per low-power field.

What loop size is commonly used for urine colony counts of 0.001 ml?

10 µl loop (multiply colonies by 1,000).

Interpret a urine culture yielding 6 × 10⁴ CFU/ml.

Doubtful bacteriuria (10³-10⁵ CFU/ml).

Which transport medium is preferred for Neisseria gonorrhoeae swabs?

Stuart medium (or Transgrow/JEMBEC).

At what temperature should CSF be stored if immediate processing is delayed?

Room temperature (never refrigerate).

List two selective transport media for enteric pathogens.

Cary-Blair and glycerol saline.

Which swab material should be avoided for bacterial culture?

Cotton (use Dacron or calcium alginate).

Name two common streak methods to obtain pure cultures.

Quadrant streak and pour-plate method.

What selective media component suppresses Gram-positive flora in MacConkey agar?

Bile salts and crystal violet.

Which microscopy type visualizes Treponema pallidum motility?

Dark-field microscopy.

What growth factor does Haemophilus influenzae require?

X factor (hemin) and V factor (NAD).

Which bacterial enzyme is nicknamed the “spreading factor”?

Hyaluronidase (Duran-Reynal factor).

Differentiate bacteriostatic from bactericidal agents.

Bacteriostatic inhibit growth; bactericidal kill the organisms.

What is the purpose of superoxide dismutase in bacteria?

Detoxifies superoxide radicals, allowing survival in oxygen.

Which anaerobic genus forms terminal spores resembling drumsticks?

Clostridium tetani.

Name two fungi-like bacteria that are Gram-positive branching rods.

Nocardia (aerobic) and Actinomyces (anaerobic).

Which component of Streptococcus pyogenes cell wall confers antiphagocytic properties?

M protein.

What laboratory test demonstrates capsule swelling?

Quellung reaction.

Which electron microscopy type provides 3-D surface images?

Scanning electron microscopy (SEM).

What is the preferred method for collecting anaerobic specimens from deep tissue?

Needle and syringe aspiration (anaerobic transport).

Which disinfection method uses 63 °C for 30 min?

Batch pasteurization (Low-Temperature Holding).

Name one organism resistant to refrigeration that can still be cultured after 24 h at 4 °C.

Staphylococcus aureus (halophilic and cold tolerant).

State one factor that decreases disinfectant potency.

Lower concentration, improper pH, insufficient contact time, low temperature, or high organic load.