Gram-positive cocci – Flashcards

Distinctive Enzymes:  

- Catalase

Growth characteristics:

- grape-like morphology

- wide temp range (18-42°C)

- halophilic

Distribution:

- world-wide

- everyone colonized- skin, mucous membranes, nares

- transmisson is person-person, direct contact, clothing

Pathogenic Species:

- S. aureus

- S. epidermis

- S. saprophyticus

- other coagulase (-) staphylococci

ID:

- catalase (+)

- coagulase (+)

- novobiocin resistant (diff. from S. epidermidis)

- ferments mannitol (diff. from other Staphylococci)

Hemolysis: β or γ

Capsule: yes

Respiration:

- aerobic 

- facultative anaerobe via fermintation of pyruvate (or derivative) to lactate

Other:

- detect catalase via rabbit plasma coagulation

Surface structures & virulence factors:

- capsule (VF)

- peptidoglycan (VF) ~activates complement, stimulates inflammatory cytokines

- Techoic acid~ protective, control enzyme activity, binding receptors and surfaces

- surface protein adhesins

- Protein A~ *virulence factor*, binds Fc portion of Abs → ↓opsonization & clearance; Abs against it non-protective

- β-lactamase, leukocidins, enterotoxins, exfoliative toxins (A & B), Toxic shock syndrome toxin 1 (TSST-1) superantigen → binds MHC class 2 then stimulates T-cell to produce massive amount of IL-2 leading to widespread inflammation

Diseases:

- furuncle/carbuncle

- impetigo

- bacteremia and endocarditis

- bone and joint infectiosn

- wound infections

- pneumonia

- toxic shock syndrome

- staphylococcal scalded skin syndrome (SSSS) aka "Ritter's disease"; toxin attacking desmosomes

Infection routes:

- prosthetic device infection (heart valves, knee joints etc)

- long IV durations

Special Structure:

- capsular polysaccharide adhesin

Disease:

- cause of urinary tract infection in young women

Significant human pathogens:

- Streptococcus pyogenes (group A)

- Streptococcus agalactiae (group B)

- Streptococcus pneumoniae (Pneumococcus)

- virdians streptococci

- mutans streptococci

General characteristics:

- non-motile

- non-spore forming

- divide end-to-end (length depends on medium)

- catalase (-)

Growth:

- facultative anaerobes

- use variety of CHOs needing complex nutrition

- CO₂ enhances growth

- ferment glucose to lactose and no further and makes no gas (homofermentive)

Hemolysis: all

Group and Hemolysis:

- Group A,  β-hemolytic

Culture requirements for identification:

- blood agar with 5% CO₂ 

- bacitracin "A" disk (for ID)

Surface components:

- M-protein (major virulence factor)

- F-protein

- capsule

- lipotechoic acid

Extracellular enzymes:

- C5a peptidase

- streptokinase (includes Streptolysin O & S)

- spreading factors

Diseases:

- localized suppurative diseases

     ~ pharyngitis, tonsilitis, cellulitis, necrotizing  fasciitis, puerperal sepsis, erysipelas

- toxin mediated diseases

     ~ scarlet fever, streptococcal TSS

- autoimmune disease

     ~ rheumatic fever, glomerulonephritis

Function:

- inhibits phagocytosis and intracellular killing via opsonization inhibition

- synergistic with lipotechoic acid in binding to epithelial cells

Disease:

- rheumatic fever (serotypes 1,3,5)

- Abs are protective

Organism:

- S. pyogenes

Diseases:

- scarlet fever

- involved in streptococcal toxic shock syndrome

*Superantigen and carried by bacteriophages

Group and hemolysis:

- Group B and weakly β- or γ-hemolytic

Lab Findings for ID:

- CAMP test~ synergistic β-hemolysis with S. aureus

Diseases:

- puerperal sepsis (childbed fever)

   ~ post-partum endometritis/bacteremia/bacteriuria

- newborn infections

   ~ bacteremia, meningitis, pneumonia

- late-onset neonatal disease

   ~ 1-3 months post-partum bacteremia or meningitis

- infection in compromised host

   ~ diabetes, cirrhosis, renal disease, HIV

**66% not associated with pregnancy or immunocompromise**

Group and Hemolysis:

- non-typable via Lancefield; α-hemolytic

ID:

- Optochin (P-disk) resistant

- catalase (-)

Examples:

- S. salivarius

- S. mitis

- mutans streptococci

- S. sanguis

Disease:

- dental caries

Process:

- has surface adhesins for enamel thus promoting plaque

- converts sucrose to acetic & lactic acid → tooth erosion

Growth, hemolysis, and ID:

- blood agar; α-hemolysis

- ethylhydrocuprine hydrochloride (optochin) on filter paper disk inhibits growth of pneumococci

- bile soluble = activates autolysins of pneumococci → death of pneumococci

- spread by humans only via water/air droplets

Surface structures:

- capsule~ quellung rxn in presence of abs; VIRULENCE FACTOR (serotype 3 esp.)

Enzymes:

- pneumolysin

- IgA protease

- hyaluronidase

- neuraminadase

Diseases:

- pneumococcal pneumonia (50-80% of bacterial pneumonia)

- otitis media

- sinusitis

- endocarditis

Group:

- formerly Lancefield Group D streptococci

- GI, GU, biliary tract

Species:

- E. durans, E. faecium, E. Faecalis (80-90% of infections)

Growth, Hemolysis:

- α-, β-, or γ-hemolytic

- hydrolyzes esculin in presence of 40% bile

- growth in 6.5% NaCl

Surface components:

- lipotechoic acid→ TNF-α and interferon

- extracellular surface protein~ avoid Abs

- aggregation substance

Enzymes:

- cytolysin (toxin)

- bacteriocin (broad spectrum)

- gelatinase (biofilm and cleaves C3)

- hyaluronidase

Infections:

- UTIs

- bacteremia

- endocarditis

- intraabdominal infections

- wound infections

- neonatal sepsis

*not killed by cell wall antibiotics and highly antibiotic resistant