Gram-Positive Cocci: Micrococci and Staphylococci

60 vocabulary flashcards covering taxonomy, morphology, enzymes, toxins, diseases, resistance mechanisms, laboratory identification, and control measures for Micrococcus and Staphylococcus species.

Micrococcaceae

Family of Gram-positive cocci that includes the genus Micrococcus; normal flora of skin, mucosa, and oropharynx.

Micrococcus

Tetrad-forming Gram-positive cocci considered common contaminants but opportunistic pathogens in immunocompromised hosts.

Tetrads (Packets)

Microscopic arrangement of Micrococcus cells in groups of four or eight.

Micrococcus luteus

Yellow-pigmented skin commensal nicknamed a “milk micrococcus” because it can spoil milk.

Micrococcus roseus

Pink-pigmented species commonly isolated from airborne dust.

Micrococcus dentrificans

Soil-dwelling Micrococcus species.

Milk micrococci

Collective term for M. luteus, M. varians, and M. freudenreichii that spoil milk.

Staphylococcaceae

Family containing the genus Staphylococcus, catalase-positive Gram-positive cocci.

Staphylococcus

‘Grape-like’ clusters of facultative anaerobic, halotolerant, catalase-positive, glucose-fermenting cocci.

Staphylococcus aureus

Coagulase-positive, most virulent Staphylococcus species; ferments mannitol and produces numerous enzymes and toxins.

Coagulase

Enzyme that converts fibrinogen to fibrin; key marker of S. aureus pathogenicity.

Catalase Test

Biochemical test that detects breakdown of H2O2; differentiates catalase-positive staphylococci from catalase-negative streptococci.

Halotolerant

Ability to grow in 7.5 % NaCl, characteristic of Staphylococcus species.

Coagulase-Negative Staphylococci (CoNS)

Group of staphylococci lacking free coagulase; includes S. epidermidis and S. saprophyticus.

Staphylocoagulase

Cell-bound and free forms of coagulase produced by S. aureus; protects bacteria inside fibrin clots.

Hyaluronidase

‘Spreading factor’ enzyme that degrades connective-tissue hyaluronic acid, aiding tissue invasion by S. aureus.

Staphylokinase (Fibrinolysin)

Enzyme that dissolves fibrin clots, facilitating spread of S. aureus.

Lipase (Staphylococcal)

Fat-splitting enzyme essential for survival in sebaceous areas and formation of boils.

DNase (S. aureus)

Enzyme that lowers exudate viscosity by degrading DNA; detected on DNA-methyl-green agar.

β-Lactamase

Enzyme that hydrolyzes β-lactam antibiotics, conferring penicillin resistance to S. aureus.

Enterotoxin A

Heat-stable toxin most commonly causing S. aureus food poisoning.

Panton-Valentine Leukocidin (PVL)

Pore-forming exotoxin that kills leukocytes, leading to severe skin infections and necrotizing pneumonia.

Exfoliatin (Epidermolytic Toxin)

Superantigen toxins A & B that split epidermal layers, causing staphylococcal scalded skin syndrome.

Alpha-Hemolysin

Major cytotoxin of S. aureus that lyses RBCs, platelets, and macrophages causing tissue damage.

Beta-Hemolysin (Sphingomyelinase C)

Heat-labile enzyme with hot-cold hemolysis that targets sphingomyelin in RBC membranes.

Toxic Shock Syndrome Toxin-1 (TSST-1)

Chromosomal superantigen responsible for menstruation-associated toxic shock syndrome.

Staphylococcal Scalded Skin Syndrome (SSSS)

Exfoliative dermatitis in neonates/children caused by exfoliatin; mild form is pemphigus neonatorum.

Ritter’s Disease

Severe neonatal form of SSSS with widespread epidermal peeling.

Bullous Impetigo

Localized blistering skin infection by exfoliatin-producing S. aureus.

Toxic Epidermal Necrolysis (TEN)

Drug-induced hypersensitivity resembling but pathologically distinct from SSSS; treated with steroids.

Folliculitis

Mild inflammation of hair follicles often caused by S. aureus.

Furuncles (Boils)

Painful pus-filled nodules arising from folliculitis.

Carbuncles

Coalesced furuncles extending into subcutaneous tissue; may cause systemic symptoms.

Impetigo

Superficial skin infection with crusty lesions and red borders; can be staphylococcal.

Osteomyelitis (Staphylococcal)

Bone destruction, especially metaphyses of long bones, due to S. aureus.

Methicillin-Resistant S. aureus (MRSA)

S. aureus strains resistant to methicillin, nafcillin, and oxacillin via mecA-encoded PBP2a.

mecA Gene

Gene encoding altered penicillin-binding protein PBP2a that mediates methicillin resistance.

PBP2a

Low-affinity penicillin-binding protein that renders MRSA resistant to β-lactams.

Healthcare-Associated MRSA (HA-MRSA)

MRSA acquired after prolonged hospital exposure.

Community-Associated MRSA (CA-MRSA)

MRSA acquired outside healthcare settings, often PVL-positive.

Vancomycin Agar Screen

BHIA with 6 µg/mL vancomycin used to detect vancomycin-intermediate or resistant S. aureus.

Cefoxitin Disk Diffusion Test

30 µg cefoxitin disk used as surrogate to detect mecA-mediated oxacillin resistance.

D-Zone Test

Double-disk diffusion method identifying inducible clindamycin resistance in staphylococci.

Slide Coagulase Test

Rapid screen for cell-bound clumping factor; positive within 30 s.

Mannitol Salt Agar (MSA)

7.5 % NaCl medium with phenol red; S. aureus ferments mannitol producing yellow colonies.

Novobiocin Susceptibility

5 µg disk test that distinguishes novobiocin-resistant S. saprophyticus from susceptible CoNS.

Tellurite Glycine Agar

Selective medium where S. aureus produces jet-black colonies.

Staphylococcus epidermidis

Coagulase-negative skin commensal causing device-related biofilm infections; novobiocin susceptible.

Biofilm

Slime layer on medical devices enabling S. epidermidis adherence and immune evasion.

Staphylococcus saprophyticus

Novobiocin-resistant CoNS causing UTIs in young sexually active females.

Staphylococcus lugdunensis

CoNS that mimics S. aureus, can be clumping factor positive and mecA positive; notable in endocarditis.

Microdase Test (Modified Oxidase)

Test detecting cytochrome oxidase; positive (blue) in Micrococcus, negative in Staphylococcus.

Lysostaphin Sensitivity

Enzymatic test that lyses staphylococci but not micrococci, producing a zone of inhibition.

Bacitracin (Taxo A) Test

0.04 U disk where Micrococcus is susceptible, Staphylococcus resistant.

Furazolidone Susceptibility

100 µg disk where Staphylococcus is susceptible (>15 mm), Micrococcus resistant.

MALDI-TOF MS

Mass spectrometry technique for rapid species-level identification of staphylococci from culture.

Intranasal Mupirocin

Topical antibiotic used to eradicate nasal carriage of epidemic S. aureus in healthcare workers.

Rifampin

Systemic antibiotic sometimes used with mupirocin for decolonization of S. aureus carriers.

Phenylethyl Alcohol Agar (PEA)

Selective medium with 5 % sheep blood that supports Gram-positive cocci while inhibiting Gram-negatives.