Clinical Microbiology: Staphylococcus and Streptococcus

Comprehensive vocabulary flashcards covering key bacterial characteristics, virulence factors, clinical presentations, and lab diagnostic tests for Staphylococcus, Streptococcus, Enterococcus, and related organisms.

Beta hemolysis

A complete clearing around a bacterial colony on a blood agar plate caused by bacterial exotoxins.

Catalase test

A laboratory test where hydrogen peroxide is added to a bacterial colony, producing visible bubbling if positive.

Staphylococcus sacrolyticus

The only obligate anaerobe species among staphylococci, requiring an anaerobic environment to grow.

Micrococcus

Gram-positive cocci in clusters that are catalase positive, coagulase negative, generally nonpathogenic, and produce small, distinctly yellow colonies.

Staphylococcus epidermidis

A common coagulase-negative staphylococcus species found on normal skin flora that frequently contaminates wound cultures and forms biofilms on catheters and heart valves.

Staphylococcus saprophyticus

A novobiocin-resistant coagulase-negative staphylococcus species that is a major cause of uncomplicated urinary tract infections in young, sexually active females.

Staphylococcus lugdunensis

A bright white, highly virulent coagulase-negative staphylococcus species carrying the mecA gene that can mimic Staphylococcus aureus and tests positive for PYR.

mecA gene

A gene present in staphylococci that confers resistance to oxacillin and methicillin, resulting in MRSA and MRSE strains.

Protein A

A surface virulence factor of Staphylococcus aureus that binds to the Fc portion of IgG antibodies to prevent phagocytosis.

Exfoliative toxins

Staphylococcus aureus toxins (types A and B) that cause the epidermal layer of skin to slough off, resulting in scalded skin syndrome (Ritter's disease) and impetigo.

Toxic Shock Syndrome Toxin (TSST)

A staphylococcal toxin associated with superabsorbent tampon usage that can lead to severe hypotension, shock, and multi-organ failure.

Carbuncles

Deep-seated skin boils that contain multiple lesions and progress into deeper tissues.

Impetigo

A highly contagious skin infection characterized by large pustules surrounded by a small zone of erythema.

Toxic Epidermal Necrolysis (TEN)

A severe, potentially fatal skin-sloughing disease often triggered by drug treatments, characterized by high mortality and treated with steroids.

Slide coagulase test

A test that detects bound coagulase, also known as clumping factor, on the bacterial cell wall.

Tube coagulase test

A test that detects free coagulase secreted by staphylococci.

Latex agglutination test

A rapid staphylococcal test using latex beads coated with human fibrinogen (to bind clumping factor) and IgG antibodies (to bind Protein A).

D-zone test

A disk diffusion test utilizing erythromycin and clindamycin disks to detect inducible clindamycin resistance in staphylococci.

Lancefield classification

A system that categorizes streptococcal species into groups based on specific carbohydrate antigens located on their cell wall.

M protein

An essential cell wall virulence factor of Group A Streptococcus that aids the bacterium in evading phagocytosis.

Scarlet fever

A condition characterized by a spreading red rash appearing $1$ to $2$ days after an untreated streptococcal infection.

Rheumatic fever

An autoimmune post-streptococcal sequela occurring about a month after untreated strep throat, causing joint inflammation and heart valve damage due to cross-reactive antibodies.

Acute glomerulonephritis

A post-streptococcal sequela in which antigen-antibody complexes deposit in the renal glomeruli, resulting in kidney damage.

Group B Streptococcus (Strep agalactiae)

A narrow-zone beta-hemolytic streptococcus that is a leading cause of neonatal sepsis and meningitis, routinely screened in pregnant women at $36$ weeks.

CAMP test

A diagnostic test for Group B Streptococcus that produces an arrowhead-shaped zone of enhanced beta-hemolysis when grown near a streak of Staphylococcus aureus.

Streptococcus pneumoniae

An alpha-hemolytic, lancet-shaped gram-positive diplococcus that is the leading cause of community-acquired pneumonia and forms mucoid colonies with central depressions due to autolysis.

Optochin test

A disk susceptibility test used to presumptively identify Streptococcus pneumoniae, which is optochin susceptible.

Bile solubility test

A test in which the addition of bile salts causes rapid autolysis and dissolution of Streptococcus pneumoniae colonies within $45$ minutes.

Viridans streptococci

A diverse group of alpha-hemolytic normal flora streptococci (e.g., Strep mutans, Strep anginosus) frequently associated with dental infections and subacute bacterial endocarditis.

Enterococcus

Halophilic, bile esculin-positive, PYR-positive gram-positive cocci belonging to Lancefield Group D that inhabit the intestinal tract and cause nosocomial UTIs.

Enterococcus faecium

A species of Enterococcus that commonly carries plasmids conferring vancomycin resistance (VRE) and can transfer resistance to other bacterial species.

Aerococcus

A streptococcus-like organism isolated in urine cultures that forms tiny, crumbly colonies that easily break apart on slides.