what are the most important virulence factors used in S.pneumoniae?

describe the epidemiology of the four most common infections caused by S.pneumoniae

describe two tests that can be used to specifically identify S.pneumoniae.

describe the clinical conditions that predispose a patient to infection with enterococcus.

• In the mitis group, one of the 5 subgroups of the streptococci viridans
• viridans = alpha + gamma hemolytic streptococci

how may S.pneumoniae and enterococcus be reliably distinguished in gram staining appearance?

they cannot be!

both are catalase-negative, gram positive cocci that arrange in pairs and short chains

• oropharynx
• GI tract
• GU tract

• VIRIDANS: NOT FOUND ON SKIN SURFACE

• mitis
• mutans
• salivarius
• anginosus
• bovis

viridans anginosus group  is associated with what disease?

• anginosus: abscess formation

viridans mitis group  is associated with what disease?

mitis:

• septicemia in neutropenic patients with mucositis;
• subacute endocarditis
  • often found in pts on chemotherapy...
    

viridans mutans group  is associated with what disease?

mutans:

• endocarditis
• dental caries

viridans salivarius group  is associated with what disease?

salivarius

• periodontal disease
• endocarditis

viridans bovis group  is associated with what disease?

bovis

• septicemia in patients with colon cancer
• meningitis

what are the most important members of enterococcus genus?

• E. faecium

• E.faecalis

there are also common intestinal flora that are enterococci.they are not responsible for disease:

E. gallinarum, E. casseliflavus

• diagnose with cultures
• treat with penicillins; however there are penicillin-resistant strains among members of the mitis group (around 40% S.pneumoniae could be resistant)
  
  • all viridans are susceptible to vancomycin
  • for serious infections (like endocarditis) a combination therapy is indicated-penicillin+aminoglycosides

where does S.pneumoniae colonize and when does it commonly cause disease?

• colonizes oropharynx of children
• S.pneumoniae causes disease when introduced to normally sterile sites, like:
  • paranasal sinuses-->sinusitis
  • ears --> otitis
  • lungs (lower airway) --> pneumonia
  • CNS-->meningitis
  • bloodstream-->bacteremia
• bacteremia is commonly associated with meningitis and infection of the lungs
  

what are some important virulence factors of S.pneumoniae?

• surface adhesion proteins
  • binds to squamous epithelial cells in oropharynx
• phosphocholine
  • present in the bacterial cell wall
  • binds to receptors on leukocytes, platelets, endothelial cells, other tissues like meninges and lungs
  • post-binding, bacterial can migrate inside cell to avoid host immune response
• polysaccharide capsule
  • anti-phagocytic activity
  • perhaps most important virulence factor because the variability of carbohydrates found on surface so that a reliable Ab attack is not always possible
• pneumolysin
  • cytotoxin
  • creates pores by binding to cholesterol in cell membranes of neutrophils
  • can kill cells via this mechanism

what does the clinical presentation of pneumonia look like?

• caused by bacteria that's migrated from oropharynx into lower airways
• abrupt onset
• shaking, chills, sustained fever
• productive cough and chest pain, common
• lobar pneumonia: localised in lower lung lobes
• resolution occurs when specific anti-capsular Abs develop-->phagocytosis & microbial killing
  

• the elderly
• cancer patients
• asplenic patients

• by direct extension from the sinuses or ears
• following head trauma
• after bacteremia
• find: many intracellular  s.pneumoniae in pairs upon microscopy

• disease is common in all age groups except neonates
• mortality and severe neurological deficits are very common
  

in what s.pneumoniae infections is bacteremia common?

• occurs in 25-30% patients with pneumonia
• 80% patients with sinusitis or otitis
• overwhelming sepsis occurs in patients with nonfunctional spleen

when is microscopy useful in S.pneumoniae infections and what is a trademark look of the bacteria?

• meningitis
• to lesser extent, pneumonia
• GRAM STAIN appears with elongated diplococci surrounded by unstained capsule

antigen detection can sometimes be a useful diagnostic technique for S.pneumoniae infections. what bacterial antigen is being detected and what are the limitations of this test?

• pneumococcal C polysaccharide (species specific carbohydrate) is present in the cell wall
• PCP is released in the urine & CSF. it is  detectable in the CSF in almost all patients with meningitis and the urine of 70% patients with pneumonia
• NOT RELIABLE IN PEDS: there is a high rate of false positives

no. although the bacteria grows well on blood-enriched media, rapid autolysis occurs among the organisms. older cultures may spontaneously die.

what is the best and fasted identification test for s.pneumoniae?

bile solubility test: colonies undergo rapid autolysis after exposure to detergents like bile

test is rapid, specific because no other organism undergoes lysis when exposed to bile

better ID option than optochin susceptibility test, which takes up to 24 hours

penicillin resistance is growing, common problem

serious infections (that are penicillin reistant) are treated with fluoroquinolone or with vancomycin combined with ceftriaxone

what bacterial component are vaccines directed against?

• vaccine vs. the polysaccharide capsule
• directed against the most common pneumococcal serotypes useful for preventing infections
• peds vaccine: 7-valent conjugated vaccine
• adult: 23-valent vaccine

• valency of a vaccine:number of serotypes able to be treated by the vaccine combination; the above vaccines are directed against the most common pneumococcal serotypes * therefore useful in preventing infections

what are the main virulence properties of enterococcus?

• surface adhesion proteins
  • allow them to bind to most cells
• secreted proteins with hemolytic activity (cytolysins) & proteolytic activity (gelatinase, serine proteases)
  • tissue damage
• RESISTANCE TO MANY COMMONLY USED ANTIBIOTICS (oxacillin, cephalosporins, aminoglycosides, vancomycin)

when do most enterococcal infections occur and what are they?

• in hospitalized patients that immuno compromised/have received prolonged therapy with broad-spectrum antibiotics
• enterococci are opportunistic pathogens
• common enterococcal infections:
  • UTIs
  • peritonitis (generally polymicrobic)
  • sepsis
  • endocarditis

1. catalase-negative
2. PYR (l-pyrrolidonyl arylamidase) +
3. LAP (leucine aminopeptidase) +

the above tests are very rapid and reliable

• high resistance:
  • cephalosporins (ceftriaxone, ceftazidime,cefepeme)
  • oxacillin
  • trimethoprim-sulfamethoxazole
• all E.faecium isolates are resistant to ampicillin and many are resistant to vancomycin
• must use combo of:

1. aminoglycoside
2. cell wall-active antibiotic (ampicillin, vancomycin)

• good infection control practices are critical to contain patient to patient spread