Clinical Bacteriology: Staphylococci and Micrococci

Comprehensive vocabulary flashcards covering the general characteristics, virulence factors, clinical infections, and laboratory identification of Staphylococcus and Micrococcus species based on clinical bacteriology lecture notes.

Staphylococcus

A genus of Gram-positive cocci whose name is derived from the Greek words for 'bunches of grapes' and 'berries.'

Staphylococcaceae

The family to which the genus Staphylococcus belongs.

General Characteristics of Staphylococci

Gram-positive cocci in clusters, catalase-positive, non-motile, and non-spore-forming.

Staphylococcus saccharolyticus

The only species of Staphylococcus that is an obligate anaerobe.

Salt Tolerance

The ability of many Staphylococcus species to tolerate high concentrations of NaCl, specifically $7.5\% - 10\%$, which is used in selective media.

Modified Oxidase Test

A test used to differentiate Staphylococci (usually negative) from Micrococci (usually positive).

Micrococcus spp.

Gram-positive, catalase-positive cocci that are generally oxidative, modified oxidase-positive, and often produce brightly pigmented yellow, orange, or pink colonies.

Staphylococcus aureus

The most virulent Staphylococcus species; it is the true coagulase-positive Staphylococcus and a major cause of both healthcare-associated and community-acquired infections.

Coagulase

The primary virulence factor of $S. aureus$; it converts fibrinogen in plasma into fibrin to protect the bacteria from phagocytosis.

Bound Coagulase (Clumping Factor)

A type of coagulase attached to the bacterial cell wall and detected by the slide coagulase test.

Free Coagulase (Staphylocoagulase)

An extracellular enzyme excreted by the bacterial cell and detected by the tube coagulase test.

Hyaluronidase

Also known as Duran-Reynal factor; it breaks down hyaluronic acid in connective tissue to help bacteria spread.

Staphylokinase / Fibrinolysin

An enzyme that dissolves fibrin clots, allowing bacteria to escape localized barriers.

Lipase

An enzyme that degrades lipids on skin surfaces, facilitating bacterial survival in sebaceous areas.

Protein A

A factor in the cell wall of $S. aureus$ that binds to the Fc portion of IgG, preventing opsonization and phagocytosis; it is considered an antiphagocytic factor.

Enterotoxins

Heat-stable toxins responsible for staphylococcal food poisoning; Enterotoxin A is the most common cause.

Toxic Shock Syndrome Toxin-1 (TSST-1)

A chromosomally mediated superantigen that stimulates massive cytokine release, leading to fever, rash, hypotension, and shock.

Panton-Valentine Leukocidin (PVL)

A cytolytic toxin that kills polymorphonuclear cells and macrophages; it is associated with severe skin infections and necrotizing pneumonia.

Exfoliative Toxins A and B

Also called epidermolytic toxins; serine proteases that split epidermal intracellular bridges, causing Staphylococcal Scalded Skin Syndrome.

Folliculitis

Mild inflammation of the hair follicle or sebaceous gland.

Furuncle

A large, raised, superficial abscess, also known as a boil, which may develop from folliculitis.

Carbuncle

A deeper infection involving multiple connected furuncles that extends into deeper tissues, often causing systemic symptoms.

Impetigo

A contagious superficial skin infection, common in children, characterized by crusted lesions or bullae.

Ritter disease

The severe, generalized form of Staphylococcal Scalded Skin Syndrome (SSSS) in children.

Catalase Test

A test differentiating Staphylococci from Streptococci where $3\% H_2O_2$ is broken down into water and oxygen, resulting in effervescence.

Mannitol Salt Agar (MSA)

A selective and differential medium where $S. aureus$ typically produces yellow colonies due to the fermentation of mannitol.

Slide Coagulase Test

A rapid test detecting clumping factor; a positive result shows visible clumping within $10 - 20$ seconds.

Tube Coagulase Test

The definitive test for free coagulase; a positive result is the formation of a clot after $1 - 4$ hours of incubation.

DNase Test

A test used to identify pathogenic staphylococci by detecting the hydrolysis of DNA; a positive result shows a clear zone around growth on DNase agar.

PYR Test

Used to differentiate coagulase-positive staphylococci; $S. aureus$ is PYR-negative while $S. lugdunensis$, $S. schleiferi$, and $S. intermedius$ are PYR-positive.

Voges-Proskauer (VP) Test

Detects acetoin production; $S. aureus$, $S. lugdunensis$, and $S. haemolyticus$ are VP-positive, while $S. intermedius$ is VP-negative.

Staphylococcus epidermidis

A common skin inhabitant and the leading cause of healthcare-acquired infections involving indwelling medical devices due to biofilm production.

Staphylococcus saprophyticus

A CoNS species that is a common cause of community-acquired UTIs in young women; it is notably resistant to Novobiocin.

Novobiocin Susceptibility

A test used to identify $S. saprophyticus$; susceptibility is defined by a zone of inhibition $\ge 16\,mm$, while resistance (typical of $S. saprophyticus$) is $< 16\,mm$.

Staphylococcus lugdunensis

A CoNS that is aggressive and can cause infective endocarditis; it is tube coagulase-negative but may be slide coagulase-positive.

MRSA

Methicillin-Resistant Staphylococcus aureus; resistant to all beta-lactam drugs (except certain anti-MRSA cephalosporins) mediated by the mecA gene.

PBP2a

An altered penicillin-binding protein with low affinity for beta-lactam antibiotics, leading to methicillin resistance.

mecA gene

The gene located on the Staphylococcal Cassette Chromosome (SCCmec) that encodes PBP2a.

Cefoxitin Disk Diffusion

The preferred method for detecting mecA-mediated oxacillin resistance; for $S. aureus$, resistance is indicated by a zone $\le 21\,mm$ using a $30\,\mu g$ disk.

D-Test / Double-Disk Diffusion Test

A test used to detect inducible clindamycin resistance (the erm gene) by placing erythromycin and clindamycin disks $15 - 26\,mm$ apart; a 'D' shaped zone indicates a positive result.

VISA and VRSA

Vancomycin-Intermediate ($MIC = 4 - 8\,\mu g/mL$) and Vancomycin-Resistant ($MIC \ge 16\,\mu g/mL$) $S. aureus$.

Nitrocefin / Cephalosporin Test

A rapid test for beta-lactamase production where a positive result is indicated by a color change to pink.

Penicillin Disk Diffusion Zone Edge Test

A sensitivity test for beta-lactamase; a 'Cliff' edge indicates a positive result (resistant), while a 'Beach' edge indicates a negative result (susceptible).