Gram-Positive Cocci: Micrococci and Staphylococci

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

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59 Terms

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Micrococcaceae

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

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Micrococcus

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

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Tetrads (Packets)

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

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Micrococcus luteus

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

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Micrococcus roseus

Pink-pigmented species commonly isolated from airborne dust.

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Micrococcus dentrificans

Soil-dwelling Micrococcus species.

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Milk micrococci

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

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Staphylococcaceae

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

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Staphylococcus

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

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Staphylococcus aureus

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

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Coagulase

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

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Catalase Test

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

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Halotolerant

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

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Coagulase-Negative Staphylococci (CoNS)

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

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Staphylocoagulase

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

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Hyaluronidase

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

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Staphylokinase (Fibrinolysin)

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

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Lipase (Staphylococcal)

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

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DNase (S. aureus)

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

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β-Lactamase

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

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Enterotoxin A

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

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Panton-Valentine Leukocidin (PVL)

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

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Exfoliatin (Epidermolytic Toxin)

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

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Alpha-Hemolysin

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

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Beta-Hemolysin (Sphingomyelinase C)

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

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Toxic Shock Syndrome Toxin-1 (TSST-1)

Chromosomal superantigen responsible for menstruation-associated toxic shock syndrome.

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Staphylococcal Scalded Skin Syndrome (SSSS)

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

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Ritter’s Disease

Severe neonatal form of SSSS with widespread epidermal peeling.

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Bullous Impetigo

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

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Toxic Epidermal Necrolysis (TEN)

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

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Folliculitis

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

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Furuncles (Boils)

Painful pus-filled nodules arising from folliculitis.

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Carbuncles

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

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Impetigo

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

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Osteomyelitis (Staphylococcal)

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

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Methicillin-Resistant S. aureus (MRSA)

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

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mecA Gene

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

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PBP2a

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

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Healthcare-Associated MRSA (HA-MRSA)

MRSA acquired after prolonged hospital exposure.

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Community-Associated MRSA (CA-MRSA)

MRSA acquired outside healthcare settings, often PVL-positive.

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Vancomycin Agar Screen

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

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Cefoxitin Disk Diffusion Test

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

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D-Zone Test

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

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Slide Coagulase Test

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

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Mannitol Salt Agar (MSA)

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

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Novobiocin Susceptibility

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

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Tellurite Glycine Agar

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

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Staphylococcus epidermidis

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

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Biofilm

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

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Staphylococcus saprophyticus

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

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Staphylococcus lugdunensis

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

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Microdase Test (Modified Oxidase)

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

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Lysostaphin Sensitivity

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

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Bacitracin (Taxo A) Test

0.04 U disk where Micrococcus is susceptible, Staphylococcus resistant.

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Furazolidone Susceptibility

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

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MALDI-TOF MS

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

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Intranasal Mupirocin

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

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Rifampin

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

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Phenylethyl Alcohol Agar (PEA)

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