38. Strep Pneumoniae and Enterococcus Flashcards Preview

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streptococcus pneumoniae microbiology?

catalase -

gram +

cocci in pairs and chains


susceptible to optochin

soluble in bile salts


strep pneumoniae virulence?

- evasion of host immunity (polysaccharide capsule = antiphagocytic esp for ppl w/no spleens, pneumolysin mediates destruction of phagocytic cells)

- adherence to host tissues (phosphocholine binds to receptors on endothelial cells, leuks, platelets, tx; surface adhesion proteins binds to squamous epith cells in orpharynx)

- few toxins


strep pneumo abx resistance?

- some resistance to PCNs (93% susceptible)

- resistance via PBP2

- acquired from other streptococci like S.mitis

- less of a problem w/streptococcus than enterococcus

- some resistance to macrolides (85% susceptible, due to ermB or mefA)

- little to no resistance to fluoroquinolones

-35% resistance to TMP-SMX


strep pneumo pathogenesis

- diseases occur when bug in oropharynx migrates to sterile areas: lower airways (pna), paranasal sinuses (sinusitis), ears (otitis), meninges (meningitis)

- bacteremia assoc w/infections of lungs/meninges (rare in pts w/sinusitis or otitis)

- preceded by viral respiratory infection (can led to trapping of S.pneumo)


strep pneumo epi?

- colonizes nasopharynx (prevalence of colonization 40-60% of adults)
- most cases of pneumococcal bacteremia in adults caused by pna


strep pneumo RFs?

- lack of receipt of pneumoccal vaccine

- splenectomy

- inability to form antibody (multiple myeloma or AIDs)

- rare immune deficiencies

- poorly functioning PMNs (alcoholism, cirrhosis, diabetes, glucocorticoid tx, renal insuffic)

- prior resp infec

- inflammatory conditions (COPD, asthma, smoking)


common clinical presentations of strep pneumo?

otitis, sinusitis, bronchitis, pneumonia, meningitis, bacteremia


otitis media?

strep pneumoniae is the most common bacterial isolate, but can be hemophilus influenzae

Abx not needed initially

if persistant fever, then amoxicillin


acute sinusitis

virus is precipitating factor

- persistant and not improving (>10days)
- severe (>3 days)
- worsening (>3 days)

amoxicillin+clavulanate (covers H.influenza and M.cattarhalis better)

respiratory fluoroquinolones

macrolides - increaseing S.pneumo resistance


pneumococcal meningitis

most common cause of bacterial meningitis (second is neisseria meningitis)

direct extension from sinuses or middle ear or bacteremia

abx of choice: ceftriaxone (good CSF penetration) PLUS vancomycin until susceptibilities

gram stain of CSF makes Dx

must obtain LP

must start Abx ASAP



acute onset

fever, chills, myalgias, pleuritic chest pain, dyspnea, productive cough

typical pathogens: S.pneumo, S.aureus, H.influenzae, M. cattarhalis
.......more likely to be dense lobar or multi-lobar consolidation

atypical pathogens: viruses, mycoplasma, chlamydia, legionella, fungi
......more likely to be patchy or bilateral

empiric tx includes atypical coverage

outpt: macrolide or doxycycline (incl s.pneumo resistance)
...if comorbidities or recent prior abx give respiratory fluroquinolone (not ciprofloxacin re: poor s.pneumo activity) like moxifloxacin

inpt: ceftriaxone (or other beta lactam) + atypical coverage, or respiratory fluoroquinolone


strep pneumo vaccination?

pneumococcal polysaccharide vaccine (pneumovax = PPSV 23)
- ppl 65+

pneumococcal protein-conjugate vaccine (Prevnar 13 = PCV13)
- kids to prevent invasive pneumococcal disease (bacteremic or sequelae)
- ppl 65+


enterococcus microbiology?

catalase -


cocci in pairs and short chains

facultative anaerobes

grows readily on most lab media

PYR positive

live in GI tract


enterococcus virulence?

surface adhesions: binds to host cells

tissue damage by cytolysins and protease (doesn't cut through fascial planes)



enterococcus abx resistance?

abx alter gut flora so increased growth of enterococci and abx-resistant like VRE

inherent resistance to cephalosporins, oxacillin

acquired resistance to aminoglycosides, FQ, vancomycin


enterococcus epidemiology

2nd most common cause of nosocomial infections in the US 9Drains, cental lines, urinary catheters, other prosthetics)

if you use a drain to take a culture, can only do so when you FIRST place it because it will be colonized with enterococcus quickly no matter what

VRE = 30% of above infections


clinical presentations of enterococcus?




intra-abd and pelvic infection


enterococcus bacteremai

usu due to IV catheters

secondary to infeciton at other sites (UTI, drain, etc)

need to differentiate from endocarditis (tx and outcomes are very different, echocardiogram to eval heart valves)

tx: 2 week course


enterococcus endocarditis

fever, malaise, rigors, myalgias, often of prolonged duration

echocardiographic evidence of vegetation

higher concern w/prosthetic valves

sequala of metastatic disesa:
- pulm emboli
- abscess
- janeway lesions, roth spots, osler nodes, splinter hemorrhages


enterococcus UTI

commmon in hospitalized males

urinary tract instrumentization or foley catheter

tx w/single abx


enterococcus intra-abdominal and pelvic infections

enterococci are commensals of GI and GU tracts

frequently isolated from abdominal and pelvic infections/cultures (usually polymicrobial w/GNRs and anaerobes)

role of enterococci in these infections in terms of pathogens is contoversial
- could be colonizer, could be pathogen

in many serious infections, if isolated on culture, abx chosen should cover these bacteria


skin and soft tissue enterococcus infections?

in skin and soft tissue cultures, it is often a colonizer, so DON'T TREAT

if isolated from a deep/sterile culture, eg bone culture in diabetic foot infection, then treat


antibiotic resistance of E.faecalis

abx of choice: ampicillin

ampicillin preferable to vancomycin (re VRE)

for endocarditis need to abx: ampicillin and aminoglycoside

B-lactams used for enterococcus (ampicillin, ampicillin-sulbactam, or piperacillin-tazobactam)

carbapenems and cephalosporins w/limited to NO activity


Abx resistance to E.faecium?

not susceptible to ampicillin!

agent of choice: vancomycin

for endocarditis need 2 abx:
- vancomycin and aminoglycoside (both nephrotoxins but have to use it)


VRE treatment options?

linezolid (oral or IV, covers MRSA or VRE but not cidal drug, but still approved for bacteremia - an exception to the norm)

daptomycin (cidal and covers VRE but expensive)

tigecycline (black box warning because good tissue penetration and not good [ ] in the bloodstream)