STEPTRACKERMICROBIOLOGY | GRAM-POSITIVE COCCI | HIGH-YIELD REVIEW

Streptococci II — Pneumococcus, Viridans & Enterococci

α-hemolytic and nonhemolytic streptococci: the leading cause of pneumonia and meningitis, the dental flora that seeds damaged valves, and the gut organisms that resist almost everything.

FOCUS ON
S pneumoniae: lancet-shaped diplococci, α-hemolytic, optochin S, bile soluble, capsule (quellung ⁺), IgA protease. Most common cause of "MOPS": Meningitis, Otitis media, Pneumonia, Sinusitis. Asplenia → overwhelming sepsis. Viridans (S mutans, S sanguinis): optochin R → dental caries, subacute endocarditis (dextrans bind fibrin on damaged valves). S gallolyticus (bovis): bacteremia/endocarditis → colon cancer. Enterococcus: 6.5% NaCl, UTI, biliary, endocarditis; VRE.
ORGANISM · DISEASE
FEATURES
CLINICAL PICTURE
CLUE · TREATMENT
Pneumococcal pneumonia
Capsule, pneumolysin
Abrupt fever, rigors, rusty sputum, lobar consolidation
Most common CAP · ceftriaxone ± macrolide
Pneumococcal meningitis
Most common in adults and children > 3 months (post-Hib vaccine)
Fever, headache, neck stiffness; high mortality
Vancomycin + ceftriaxone (+ dexamethasone)
Otitis media · sinusitis
Most common bacterial cause
Bulging TM, facial pain
Amoxicillin
Asplenia / sickle cell
No splenic clearance of encapsulated bacteria
Overwhelming post-splenectomy sepsis
Pneumococcal, Hib, meningococcal vaccines; penicillin prophylaxis in sickle cell
Pneumococcal vaccines
PCV (conjugated, T-cell dependent) · PPSV23 (polysaccharide)
PCV for infants and adults ≥ 65 / at risk
Conjugation makes a polysaccharide immunogenic in infants
Viridans streptococci
α-hemolytic, optochin R, bile insoluble; normal mouth flora
S mutans/mitis: dental caries · S sanguinis: subacute endocarditis on damaged valves after dental work
Dextrans bind fibrin-platelet aggregates
S anginosus group
Viridans subgroup
Abscesses (brain, liver, lung, dental)
—
S gallolyticus (bovis)
group D, nonenterococcal
Grows in bile, not 6.5% NaCl
Bacteremia and subacute endocarditis
Colonoscopy — associated with colorectal cancer
Enterococcus faecalis / faecium
group D
γ-hemolytic, catalase −, grows in bile + 6.5% NaCl, PYR ⁺; intrinsically resistant to cephalosporins
UTI, biliary infections, subacute endocarditis (after GI/GU procedures), wound and catheter infections
Ampicillin (+ gentamicin for endocarditis)
Vancomycin-resistant enterococci
D-Ala-D-Ala → D-Ala-D-Lac (vanA)
Hospital infections, mostly E faecium
Linezolid, daptomycin, tigecycline

Mechanism — how viridans strep lands on a valve

Damaged valveRheumatic, congenital, MVP
→
Sterile fibrin-platelet nidus
→
Dental work → bacteremia
→
Dextrans adhereSubacute endocarditis

α and γ streptococci compared

ORGANISM
OPTOCHIN
BILE / NaCl
MAIN DISEASE
S pneumoniae
Sensitive
Bile soluble
MOPS
Viridans
Resistant
Insoluble
Caries, SBE
S gallolyticus
—
Bile ⁺ / NaCl −
Endocarditis + colon cancer
Enterococcus
—
Bile ⁺ / NaCl ⁺
UTI, biliary, endocarditis

How it's tested

COMMON CONFUSIONBoth enterococci and S gallolyticus are group D — only S gallolyticus endocarditis demands a colonoscopy.
THE TRAPEnterococci resist all cephalosporins — empiric ceftriaxone misses them; ampicillin is the drug.
YOUR APPROACHα-hemolysis → optochin; γ → salt and bile; then match the site and the predisposing setting.

If you see… think…

Rusty sputum, lancet-shaped diplococci → S pneumoniae
Most common cause of meningitis in adults → S pneumoniae
Splenectomy patient with fulminant sepsis → encapsulated: pneumococcus
Endocarditis weeks after dental extraction on a rheumatic valve → viridans strep (S sanguinis)
Dental caries → S mutans
Endocarditis with S gallolyticus → colon cancer workup
Endocarditis after cystoscopy or colonoscopy → Enterococcus
Grows in 6.5% NaCl → Enterococcus
Vancomycin resistance via D-Ala-D-Lac → VRE
Optochin resistant α-hemolytic strep → viridans group