Streptococci & Enterococci

• heterogenous group bacteria
• classification: hemolytic characteristics
  • "strept throat"
  • cellultis
  • neonatal meningitis
  • brain abscess 
  • endocarditis

Streptococci members

• s. pyogenes "Group A"
• s.pnemococcus

beta hemolytic

• Group A--streptococci pyogenes
• Group B--streptococci agalactiae

alpha hemolytic

• streptococcus viridans
• streptococcus pneumoniae

Streptococus pyogenes

• beta hemolytic
• gram + cocci in chains
• grows on blood agar
• best in anaerobic conditions

Group A Streptococcus

(GAS)

• niche is pharynx
• found on skin & nasopharynx of humans
• carriers usually asymptomatic
• may be colonized for months
• P2P spread is helped by droplets or contact

GAS entry

• binds to mucous membranes of pharynx
• uses lipoteichoic acid (adhesin)
• LTA binds to fibronectin--coats cell of oropharynx
• skin & soft tissue infection need deeper penetration into skin

GAS spread & multiplication

• remain localized to site of infection
• increase in aggressive strains that invade deeper tissues--life threatening diseases

GAS: Virulence & Pathogenesis (1)

• virulence depends on proteins that represent toxins
• M proteins that mimic host macromolecules
• GAS must avoid phagocytosis for infection by these factors:
  • M protein
  • hyaluronic acid capsule

M protein

• important in streptococcal pathogenesis
• prevents opsonization by complement
• antibodies formed vs. M protein effectively opsonize organism--protective against infxn
• > 100 M protein serotypes & protective immunity are specific

How does M protein prevent opsonization by complement?

• binds to fibrinogen & interferes w/alternative pathway of complement deposition by forming a dense layer on bacterial surface

                             (OR)

• binds host complement control proteins & inhibit formation of opsonins by complement cascade

GAS Damage

• intense inflammatory response in tissues
• secreted substances cause considerable damage to host tissues
• digestive enzymes "hyaluronidase" enables spread to deep tissue
• secretes toxins causing systemic effects

GAS has 3 toxins

• streptococcal pyogenic exotoxins:
  • A,B,C
• A & C are superantigens that can nonspecifically activate T-cells
  • release of proinflammatory cytokines (IL-1 & TNF)

GAS site of infxn (1)

• pharynx: pharyngitis
• toxin mediated
  • scarlet fever
  • toxic shock syndrome
• non-suppurative complications:
  • acute rheumatic fever
  • glomerulonephritis

 streptococcus pyogenes

Strept Throat (pharyngitis) Complications

• tonsillar abscess
  • infxn of tonsils
• cervical adenitis
  • spread & infxn of cervical lymph node forming abscess

Pharyngitis RX

• penicillin
  • benzathine PCN
  • PCN VK
• amoxicillin
• macrolide
  • azithromycin
  • clarithromycin

Streptococcus Pyogenes:

Scarlet Fever

• macular papular rash--feels live sandpaper
• desquamation--usually hands & feet during 2nd week of illness
• strawberry--raspberry tongue

(streptococcus pyogenes)

sites of infxn (2)

• skin: erysipelas, impetigo, cellulitis
• soft tissue: fasciitis
• muscle: myositis
• endometrium
• lung--pneumonia
• bacteremia & septic shock

Fasciitis RX

• PENICILLIN G
• severe pain, systemic toxicity, rapid spread, fever, skin necrosis w/bullae, tense edema, discoloration

Streptococcal Toxic Shock Syndrome

 (STSS)

• severe multiorgan system illness--abrupt onset requires findings:
  • Hypotension
  • multisystem involvement=renal, hematologic, hepatic, pulmonary, derm

STSS RX

• clindamycin + penicilllin G
  • inhibits toxin synthesis
• supportive--albumin, massive IV fluids

Streptococcus Agalactiae

(GBS)

• beta hemolytic
• Group B streptococci
• gram + cocci in chains
• aerobic
• B antigen
• capsulated

GBS

• vaginal & GI tracts
• transmission from mother to baby (verticle)
• diseases
  • neonatal
  • pnemonia
  • sepsis/meningitis

GBS RX

• ampicillin
• all high risk moms should receive IV amp at onset of labor & throughout

Streptococcus Pneumoniae

• alpha hemolytic
• gram + diplococcus
• encapsulated bacteria
• faculatative aerobic

streptococcus pneumoniae (Spn):

Epidemiology & Encounter

• nasopharyngeal colonization
• disease caused by local spread or aspiration
• smokers, alcoholics, & viral infxns

Spn Pathogenesis

• community acquired pnemonia
• higher incidence in elderly, closed pop, males, american indians, AIDS
• increased colonization w/young age, crowding, viral URI, fall/winter season
• droplet spread--aspiration

Spn Virulence Factors

• IgA protease: mucosal colonization
• Capsular polysaccharide
  • virulent type III serotype
• Cell wall peptidoglycans, teichoic acid elicit inflammation
• Pneumolysin

Lung infxn

• Pneumonia
  • cough, high fever, sputum, dyspnea
• CNS meningitis

Pneumonia RX

azithromycin + ceftriaxone/cefotaxime

PCN resistance & sensitivity

Macrolide Resistance

• ribosomal methylation
• mef E
  • efflux pump mechanism
  • MIC<32--low level resistance

invasive pneumococcal infxn

• meningitis infxn due to streptococcus pneumonia bacteria

Meningitis RX

• dexamethasone 10-20 min before antibiotic
• vancomycin + ceftriaxone
  • vanco stops flow of organisms off--ceftriaxone kills across BBB
• PCN sensitive (MIC<0.2)=ceftriaxone
• PCN resistanct (MIC>0.2) or beta lactam hypersensitivity= vancomycin

Spn sites of infxn

• sinuses
• middle ear
• bronchi

Rx for Spn for respiratory

• sinusitis & otitis media
  • amoxicillin or amox/clav
• acute exacerbations of chronic bronchitis
  • amoxicillin or doxycycline

Pneumococcal Vaccine

• capsular polysaccharide from 23 serotypes
• prevenar vaccine for kids<2yrs

Questions to ask when designing vaccines

• Which immune system should be activated?
• Is immunologic memory stimulated?

Active Immunity

• protective immunity--immune memory
• natural infxn or artificial
• stimulates antigen reactive to T/B cells

Viridans Streptococci

• Gram + in chains
• alpha hemolytic
• oropharynx/GI tract
• cause of dental infxn
• subacute bacterial endocarditis

Subacute Bacterial Endocarditis

• sx: fever, malaise, chest/back pain, cough, dyspnea, myalgia, arthralgias, neurologic sx, wt loss, night sweats
• RX: AMPICILLIN/SULBACTAM + GENTAMICIN

Enterococci

• aerobic
• gram + cocci short chains
• part of normal colonic, vaginal flora

Enterococci sites of infxn

• bactremia, endocarditis
• polymicrobial intra-abdominal infxn--UTI minor

Enterococci Risk Factors

• prolonged hospitalization
• hemodialysis
• ICU--vancomycin use

Enterococci RX

• endocarditis: prolonged combo high doses of: AMINOGLYCOSIDES & AMPICILLIN or VANCOMYCIN
• dalfopristin+quinupristin
• linezolid
• daptomycin