Pyogenic Cocci

Bacteriology PYOGENIC COCCI I. STAPHYLOCOCCI Morphology and culture characteristics • Gram-positive cocci, facultative anaerobic, relatively resistant to - heat, drying, and high-salt environments • Growth: grow singly, in pairs, in short chains, or in irregular clusters; cluster formation more often seen in isolates of solid media culture than in clinical specimens. • Three species of medical importance are: a) S. aureus: colonies may appear golden, coagulase-positive, ferments glucose anaerobically, sensitive to novobiocin b) S. epidermidis: colonies appear white, coagulase-negative, ferments glucose anaerobically, sensitive to novobiocin c) S. saprophyticus: coionies appear either yellow or white, coagulase-negative, fails to ferment glucose anaerobically, resistant to novobiocin Transmission Normal component of human flora, carried asymptomatically (S. aureus, S. epidermidis). A human can serve as endogenous source to himself or exogenous source to others. S. saprophyticus is only occasionally found on human skin Clinical disease Staphylococcus aureus causes: Characteristic feature is abscess formation in any part of the body a) CUTANEOUS INFECTIONS-furuncles, carbuncles, impetigo, scalded skin syndrome generalized exfoliative dermatitis, bullous impetigo, staphylococcal scarlet fever) b) OSTEOMYELITIS, septic arthritis, septic bursitis (either as a complication of S. aureus septicemia or secondary to local trauma or injury) c) SEPTICEMIA AND ENDOCARDITIS d) PNEUMONIA (aspiration or hematogenous spread) and pleural empyema e) TOXIC SHOCK SYNDROME (high fever, hypotension, diarrhea, erythroderma, mental confusion, and renal failure)-Staphylococcus aureus, from phage group I, producing enterotoxin F and exotoxin C (may be identical) f) FOOD POISONING-preformed heat-stable enterotoxin B produced by the toxigenic strains growing in contaminated food g) PERICARDITIS (from hematogenous spread or perforating chest injury) Staphylococcus epidermidis a) Endocarditis-native or prosthetic valves b) Intravenous catheter infections; vascular graft infections c) Peritoneal dialysis catheter-associated peritonitis d) Cerebrospinal fluid shunt infections e) Urinary tract infections (usually in hospitalized patients with urinary tract complications) f) Osteomyelitis (sternal osteomyelitis due to infection of the median sternotomy wound after cardiothoracic surgery, bone infection surrounding a prosthetic joint, hematogenous osteomyelitis from hemodialysis shunt infections) g) Ocular infections-commonly endophthalmitis following ocular surgery Staphylococcus saprophyticus Urinary tract infection in young, sexually active females Diagnosis

• Presumptive evidence of staphylococcal infection by smear gram stain, showing gram-positive cocci in clusters • Culture of pus, purulent fluid, blood, sputum, urine, etc. • Coagulase and novobiocin testing Treatment 1. S. Aureus-most produce penicillinase • DRUG OF FIRST CHOICE-penicillinase-resistant penicillin (dicloxacillin, nafcillin) • "METHICILLIN-RESISTANT" S. aureus-initially seen in drug addicts, now more common; Vancomycin is the drug of choice. 2. S. epidermidis-Vancomycin is the drug of choice

II. STREPTOCOCCI Morphology and culture characteristics Gram-positive cocci, cell division in one plane resulting in pairs or chains, most are facultative anaerobic, although some are obligate anaerobes (includes members of the family Peptostreptococcaceae), catalase-negative, nonmotile.

Classification Hemolysis and Lancefield groups. The Lancefield groups are based on the antigenic "C carbohydrate" found in the cell wall of many streptococci. • Alpha hemolytic (incomplete, may produce greenish discoloration) • Beta hemolytic (complete hemolysis of RBC in the medium)-Lancefield group A (S. pyogenes), group B (S. aga/actiae), group C (S. equisimilis, S. zooepidemicus, S. equi), group D (enterococcus and nonenterococcus), group F (S. anginosus), group G, groups E, L, M, P, U, or V, or non-typables • Gamma hemolytic (no hemolysis)-Lancefield group D (enterococcus and nonenterococcus) bileesculin positive, S. pneumoniae (negative bile-esculin reaction; bile soluble, positive zone inhibition around optochin disk), S. viridans (negative bile-esculin reaction, not bile soluble, negative zone of inhibition around optochin disk) Transmission Part of normal human flora, can induce disease from any portal of entry. Clinical disease Streptococcus pyogenes: M protein (in the cell wall) is closely associated with virulence a) More than 20 toxins are elaborated by S. pyogenes

b) c) d) e)

• Streptokinase-activates plasminogen • Hyaluronidase-lyses important component of ground substance, therefore the propensity for spread versus formation • Erythrogenic toxin-causes rash in scarlet fever • Streptolysin O-this antigenic material is the basis of the titer of anti-streptolysin 0 (ASO) as an indication of recent Group A strep infection PHARYNGITIS, scarlet fever, suppurative complications of pharyngitis (peritonsillar cellulitis, peritonsillar abscess, retropharyngeal abscess, bacteremic metastatic spread); unsuppurative complications of pharyngitis (acute rheumatic fever, poststreptococcal glomerulonephritis) ERYSIPELAS PYODERMA (impetigo) OTHER-cellulitis, lymphangitis, perianal cellulitis, puerperal sepsis, meningitis, pneumonia, emphysema.

Treatment Penicillin G, if allergic-erythromycin Streptococcus pneumoniae a) PNEUMONIA (most common cause of bacterial pneumonia); local complications- empyema, lung abscess, and/or pericarditis; bacteremia (in 25-30% patients with pneumococcal pneumonia)

b) UPPER RESPIRATORY TRACT INFECTION-otitis media, mastoiditis, sinusitis c) EXTRAPULMONARY-meningitis, endocarditis (acute, < 1 % of cases, normal or damaged valves, local tissue destruction common), arthritis, peritonitis

Treatment Although there have been reports of sporadic resistance, the overwhelming majority of S. pneumoniae are exquisitely sensitive to penicillin Group D streptococci causes Endocarditis (both enterococcal and nonenterococcal), bacteremia (usually S. faecalis), urinary tract infection (S. faecalis), intra-abdominal abscess (bacteremia less common), soft tissue infection (often present, pathogenicity unclear), neonatal meningitis, pneumonia (rare) Treatment a. Nonenterococci-penicillin

b. Enterococci-requires synergy between penicillin and aminoglycoside Group B streptococci • EARLY-ONSET (first 5 days of life) neonatal infection; bacteremia • LATE-ONSET (7 days-3 months of age) neonatal infection; bacteremia, fulminant meningitis, osteomyelitis, septic arthritis • POSTPARTUM WOMEN- Endometritis, caesarian section wound infection, bacteremia • IMMUNO-COMPROMISED HOSTS- Pyelonephritis, pneumonia, tracheobronchitis, cellulitis, septic arthritis, meningitis, endocarditis, bacteremia Treatment Penicillin G Viridans streptococci (Streptococci viridans) • ENDOCARDITIS (5. mitior, S. sanguis more common) • SUPPURATIVE INFECTlON-(S. mille'; most common); intra- abdominal, brain abscess, meningitis, bone and joint, skin, respiratory, and oral infection Treatment Penicillin Lab Diagnosis of Streptococci Smears and cultures of clinical specimens Group A: ASO, anti-DNase B, anti-hyaluronidase, type-specific antibody Pneumococcus: Quellung reaction, counterimmunoelectrophoresis Group D: Smear and Culture Group B: CIE, latex particle, agglutination, (+) cAMP test