Microbiology and Bacteriology Practice Flashcards

Practice questions and answers based on medical microbiology notes, covering bacterial identification, clinical significant pathogens, and laboratory diagnostic tests.

What are the three main morphological shapes of bacteria and an example of each?

Cocci (spherical) like Staphylococcus; Bacilli (rod) like E. coli; and Helical (spiral) like Spirillum.

Which two genera of bacteria are known for lacking a cell wall?

Mycoplasma and Ureaplasma.

What is the function of a bacterial capsule in terms of pathogenesis?

It acts as a virulence factor that helps the pathogen evade phagocytosis.

Describe the Gram reaction and peptidoglycan characteristics of Gram-positive bacteria.

They retain crystal violet (stain blue/purple) and possess a thick peptidoglycan layer containing teichoic acids.

What are the four components of the Gram stain procedure in order?

1. Primary stain: Crystal violet; 2. Mordant: Iodine; 3. Decolorizer: Alcohol/acetone ($95\%$ ethanol); 4. Counterstain: Safranin.

What is the specific counterstain modification used for Legionella?

Safranin is replaced with $0.1\%$ basic fuchsin.

What defines the Acid Fast Staining results for positive and negative organisms?

Acid fast organisms appear bright red or pink; non-acid fast organisms appear blue.

Which test is used to detect Gram-negative endotoxin using the blood of horseshoe crabs?

Limulus Lysate Test (using reagent from Limulus polyphemus).

What are the required conditions for sterilizing spores in an autoclave?

$121^\circ\text{C}$ for $20-30$ minutes.

Define the oxygen requirements for capnophiles and microaerophiles.

Capnophiles require $5-10\%$ oxygen; microaerophiles require $2-10\%$ oxygen.

What occurs during the 'Log' phase of bacterial growth?

Exponential multiplication of bacteria occurs, and this is the stage where antibiotics act most effectively.

Differentiate between bacterial transformation and transduction.

Transformation involves bacteria dying and undergoing lysis; transduction involves two bacteria coming together in one cell (mediated by a virus).

What is the purpose of Thiosulfate Citrate Bile Salts (TCBS) agar?

It is a selective and differential medium for Vibrio species; sucrose fermentation causes colonies to turn yellow.

Which agar is selective for Bordetella pertussis and what is its characteristic appearance?

Regan Lowe Agar; colonies appear like mercury droplets.

Describe the three types of hemolysis seen on Blood Agar (BAP).

Alpha: partial lysis (greenish); Beta: complete lysis (clear/colorless); Gamma: no hemolysis.

How is Staphylococcus aureus distinguished from other Staphylococci using Mannitol Salt Agar (MSA)?

S. aureus is a mannitol fermenter (yellow colonies), while S. epidermidis is a non-fermenter.

What virulence factor associated with Staphylococcus aureus causes Scalded Skin Syndrome?

Exfoliative toxin (Ritter Disease).

Which organism is the second most common cause of UTIs in young, sexually active females?

Staphylococcus saprophyticus.

What test differentiates Staphylococcus from Streptococcus?

The Catalase Test (Staphylococcus is positive; Streptococcus is negative).

Which organism is known as 'Group A Streptococcus' (GAS)?

Streptococcus pyogenes.

What is the clinical significance of the CAMP test in identifying Streptococcus agalactiae?

It produces an 'arrow head' zone of hemolysis when grown near S. aureus.

Describe the Gram stain morphology of Streptococcus pneumoniae.

Gram-positive diplococci that are lancet or bullet-shaped.

Which organism is strongly linked to colon cancer?

Streptococcus bovis (specifically S. gallolyticus).

What is the characteristic 'Medusa head' colony morphology associated with?

Bacillus anthracis.

What type of motility is characteristic of Listeria monocytogenes at room temperature?

Tumbling motility in a direct wet mount or an 'inverted Christmas tree' pattern in semisolid medium.

Which medium is used for the primary recovery of Corynebacterium diphtheriae and shows translucent to gray-white colonies?

Loeffler’s medium.

What are 'clue cells' and what condition are they associated with?

Large, squamous epithelial cells covered in Gram-positive and Gram-negative bacilli; associated with Gardnerella vaginalis (bacterial vaginosis).

Which Gram-negative diplococci resembles coffee or kidney beans and is the agent of gonorrhea?

Neisseria gonorrhoeae.

What is the 'hockey puck' colony characteristic of?

Moraxella catarrhalis.

Which Enterobacterales species is the primary marker of fecal contamination in water?

Escherichia coli.

What are the three antigenic determinants (antigens) for Enterobacterales?

O antigen (Somatic), K antigen (Envelope), and H antigen (Flagellar).

Which organism produces a 'metallic green sheen' on Eosin Methylene Blue (EMB) agar?

Escherichia coli.

In a Triple Sugar Iron (TSI) agar, what does a result of K/A (Red/Yellow) with H2S production signify?

The organism is a non-lactose/sucrose fermenter, a glucose fermenter, and produces Hydrogen Sulfide (e.g., Salmonella).

Which species of Yersinia is the causative agent of the Bubonic plague?

Yersinia pestis.

What is the characteristic appearance of Yersinia pestis on a Wayson stain?

A 'closed safety pin' appearance.

Which organism produces a red pigment called prodigiosin?

Serratia marcescens.

What type of motility is characteristic of Vibrio species?

Rapid darting or 'shooting star' motility.

Which organism is strongly associated with Type B gastritis and peptic ulcers?

Helicobacter pylori.

Name the blue pigment produced only by Pseudomonas aeruginosa.

Pyocyanin.

What are the X and V factor requirements for Haemophilus influenzae?

It requires both X factor (hemin) and V factor (NAD).

What is the 'school of fish' arrangement in a Gram stain indicative of?

Haemophilus ducreyi.

Which organism causes Lyme Disease and what is its primary vector?

Borrelia burgdorferi; transmitted by Ixodes (hard) ticks.

What are the 'Hutchinson’s triad' symptoms of late congenital syphilis?

Hutchinson’s teeth, interstitial keratitis, and $8^{th}$ nerve deafness.

Which organism is the most common cause of preventable blindness (trachoma)?

Chlamydia trachomatis.

Why are Mycobacteria described as 'acid-fast'?

They resist decolorization by acidified alcohol due to a high lipid content (up to $60\%$) consisting of mycolic acids.

What is the 'Ghon Complex' in the context of tuberculosis?

It is the first lesion to appear in primary tuberculosis.

Differentiate the paralysis types caused by Clostridium tetani and Clostridium botulinum.

C. tetani causes rigid paralysis (lockjaw); C. botulinum causes flaccid paralysis.

Which Biosafety Level (BSL) is required for handling exotic viruses with no available vaccine that pose life-threatening risks?

BSL 4.