07: Streptococcus Flashcards
1
Q
Give a general descripton of streptococci/enterococci.
A
- Pyogenic (pus forming) pathogens
- Nonmotile,non-spore forming, mostly facultatively anaerobic, catalase negative, GPC in chains
- Enterococci established as separate species based on DNA homology studies
2
Q
For s. pneumoniae:
- Sites of colonization
- Sites of infection
- Diseases
- Treatment
A
- Oropharynx, nose
- Lungs, sinuses, middle ear, meninges
- Pneumonia, otitis media, sinusitis, infant/adult meningitis
- PCN (3GC if resistant; vancomycin/levofloxacin if highly resistant)
3
Q
For s. pyogenes (GAS):
- Sites of colonization
- Sites of infection
- Diseases
- Treatment
A
- Oropharynx, rectum
- Pharynx, skin, soft tissue
- Pharyngitis (strep throat), TSS, impetigo, rheumatic fever, pyoderma
- PCN/Amox; Macrolides/1GC if allergic
4
Q
For enterococcal spp.:
- Sites of colonization
- Sites of infection
- Diseases
- Treatment
A
- GI tract
- Urinary and biliary tract, cardiac valves
- Acute bacterial prostatitis, endocarditis, neonatal meningitis
- PCN/Amp; if resistant, vanco; if endocarditis, aminoglycoside for synergy; if vanco resistant (VRE), linez/dapto/streptogramin
5
Q
For s. agalactiae (GBS):
- Sites of colonization
- Sites of infection
- Diseases
- Treatment
A
- GU tract
- Neonatal infections involving blood, meninges, GU tract
- Neonatal miningitis, sepsis
- PCN/amox; macrolides/1GC if allergic
6
Q
For viridans streptococci:
- Sites of colonization
- Sites of infection
- Diseases
- Treatment
A
- Oropharynx
- Cardiac valves, bloodstream
- Endocarditis
4.
7
Q
Describe the hemolysis patterns of strep.
A
- S. pyogenes & agalactiae are beta (complete)
- Viridans & pneumoniae are alpha (partial)
- Enterococci are gamma (none)
8
Q
Describe the disk patterns of strep.
A
- S. pneumoniae is the only optochin susceptible species.
- S. pyogenes (GAS) is the only bacitracin susceptible species.
Mnemonic: OVRPS & BBRAS
9
Q
Describe the structural components of GAS.
A
- Hyaluronic acid capsule: interferes with phagocytosis.
- M protein: major virulence factor; interferes with phagocytosis (inhibits complement activation); implicated in pathogenesis of rheumatic fever.
- Protein F & lipoteichoic acid: mediate binding to fibronecting
- Protein G: binds Fc portion of immunoglobulin
10
Q
Describe the secreted products of GAS.
A
- Enzymes
- Streptolysins O & S
- DNase, hyaluronidase, streptokinase: tissue breakdown, pus formation.
- Toxins
- Pyrogenic exotoxins (SPE A, B, C): produce superantigen-mediated TSS; responsible for scarlet fever.
11
Q
Describe the clinical features of GAS pharyngitis.
A
- Epi: 5-15yo, winter/early spring
- Most common of the streptococcal infections, but only account for a small number of pharyngitis cases
- Sore throat, sudden onset, fever, pain with swallowing, headache, lymphadenitis, tonsillar exudates, soft palate petechiae
- Non-suggestives: conjuctivitis, coryza (nasal discharge), cough, diarrhea
- Sequelae: abscess, sepsis, dissemination
- Diagnose using rapid strep kits (specific but not sensitive; treat if positive, confirm if negative), anti-streptolysin (ASO) test (reflects past, not present, infection)
12
Q
Describe the nonsuppurative sequelae of pharyngitis.
A
-
Rheumatic fever: diagnose via Jones criteria:
- Joints (polyarthitis)
- Heart (carditis)
- Nodules (subcutaneous)
- Erythema marginatum (circular rash)
- Sydenham’s chorea (jerking movements)
- Glomerulonephritis: renal disease by strep antigens deposited in glomerular membrane.
Mnemonic: Pharyngitis can result in phever and glomerulonephritis.
13
Q
Describe the clinical features of impetigo.
A
- Rash on face
- Small pustules that progress to thick honey-crusted lesions
- Large primary lesion and several satellite lesions
- Commonly results from GAS or S. aureus
- Complications rare: lymphadenitis, immune-complex glomerulonephritis
14
Q
Describe the clinical features of streptococcal toxic shock syndrome.
A
- Pyrogenic exotoxins A-C implicated
- Superantigen-mediated
- Differs from S. aureus TSS because of frequent presence of infections
- Necrotizing fascitis linked w/ specific M types
15
Q
Describe the treatment/prevention of s. pyogenes infections.
A
- Penicillin
- Protein synthesis inhibitors (e.g., clindamycin) may improve outcome
- Macrolide-resistance emerging
- Vaccines under development (type-specific epitopes or highly conserved regions of M protein; target proteins mediating epithelial adherence)
16
Q
Describe the microbiology and structure of streptococcus pneumoniae.
A
- Lancet-shaped diplococci; optochin susceptible; alpha hemolytic; encapsulated (no virulence without)
- Polysaccharide capsule inhibits phagocytosis and confers type-specific immunity
- Cell wall (peptidoglycan) helps initiate inflammatory response (recruit PMNs, initiating coagulation, inducing cytokine production).
- Competent: naturally transformable, can acquire DNA from environment, acquire genes conferring antimicrobial resistance
17
Q
Describe the epidemiology of pneumococcal disease.
A
- Extremes of age: <2, >65
- Colonize nasopharynx in 5-10% adults, 20-40% children
- Disease increased in winter
- Immunocompromised more likely to be infected
18
Q
What are the main diseases caused by S. pneumoniae?
A
- Meningitis
- Otitis media
- Pneumonia
- Sinusitis
(MOPS)
19
Q
Describe the pathogenesis of pneumococcal pneumonia.
A
- Colonization: Strains w/ increased phosphoryl choline bind epithelial structures (platelet activating factor receptor (rPAF)).
- Invasion: Respiratory via aspiration of nasopharyngeal secretions; increased capsule expression: IgA protease, reduced mucus entrapment, anti-phagocytic; pneumolysin lyses host cells, inhibits ciliary action, activates inflammation & CD4T recruitment
20
Q
Describe the clinical manifestations of pneumococcal disease.
A
- Sudden onset of fever
- Chills
- Pleuritic chest pain
- Cough associated with rusty-colored sputum
- CXR: infiltrate (usually lobar)
- 1/3rd of infx: bacteremia
- Complications: meningitis, arthritis, endocarditis
21
Q
Describe the treatment and prevention of pneumococcal infections.
A
- Penicillin unless resistance; 3GC; high resistance = vancomycin/levofloxacin
- Poyvalent polysaccharide anticapsular vaccine (23 types) for adults; T cell independent (less immunogenic)
- Polysaccharide protein conjugate vaccine (7 types) for infants 2yo or younger; T cell dependent
NB: Escape strains exist (e.g., 19a).
22
Q
Describe streptococcus agalactiae (GBS).
A
- Narrow band of beta hemolysis; bacitracin resistant; able to hydrolyze hippurate
- Commonly associated with infections in newborns (B for babies): pneumonia, meningits, sepsis
- Colonizes vagina, therefore mothers tested at 35-37 weeks and chemoprophylaxed with penicillin as necessary.
23
Q
Describe viridans streptococci.
A
- Heterogenous group of streptococci including 24 different species
- Sanguis = subacute bacterial endocarditis at damaged valves
- Mutans = dental caries
- Alpha hemolytic, optochin resistant
- Part of oropharyngeal flora, GI tract
24
Q
Describe enterococci.
A
- Nonhemolytic (gamma)
- Normal colonic flora (resistant to bile salts) that are penicillin G resistant and cause UTI, biliary tract infections, subacute endocarditis.
- VRE are important cause of nosocomial infection.
