Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
25 Cards in this Set
- Front
- Back
Streptococci: General
|
-Gram positive cocci
-chains -catalase negative -facultative anaerobes |
|
Staphylococci: General
|
-Gram positive cocci
-clusters -catalase positive -facultative anaerobes |
|
Differential Antibody resistance
|
-staph is generally more antibody resistant (MRSA, VRSA)
-due to plasmid transfer |
|
Staphylococcus aureus: antigens
|
1) Protein A: major component of cell wall, covalently bound to PG
-binds Fc region of IgG 2) Coagulase: activity coats bacteria in fibrin, resists phagocytosis -diagnostic coagulase test: plasma incubated with s. aureus -> clot |
|
Streptococcus pyogenes (Group A Strep): antigens
|
1) M proteins and lipoteichnoic acids mediate adherence and are antiphagocytic
-but too many M epitopes for a comprehensive vaccine 2) hyaluronic acid capsule: indistinguishable from mammalian CT |
|
Streptococcus pneumonia: antigens
|
1) capsular polysaccharides: antiphagocytic, major virulence factor
-used in S. pneumonia speciation and as component of vaccine |
|
Coagulase Status of:
S. aureus S. epidermidis S. saprophyticus |
S. aureus: +, major pathogen
S. epidermidis: -, new pathogen, antibody resistant S. saprophyticus: -, UTI |
|
MRSA & SCCmec
|
MRSA: methicillin resistant S. aureus
-SCCmec: staph. chromosomal cassettes encoding methicillin resistance -SCCmec allotypes defined by differences in sequence, organization, and number of mecA (resistance markers) or ccr (recombinase) |
|
HA-MRSA
|
-Hospital Acquired MRSA: generally larger with more resistance markers
-Transposons encode for macrolide-lincosamide-streptogramin-spectinomycin resistance and tobramycin resistance |
|
CA-MRSA
|
-Community Acquired MRSA: generally smaller with fewer resistance markers
-resistance to methicillin "only" -may produce PVL (Panton-Vanlentine leukocidin) toxin: increased virulence? |
|
Lancefield Typing of Streptococci
|
-based on serogroups (cell wall)
Group A = pyogenes Group B = agalactiae Group C = Enterococci Viridans, pneumoniae, anaerobic strep have no Lancefield group |
|
Hemolytic Typing of Streptococci
|
Beta: complete clearing of area around a colony (s. pyogenes)
Alpha: partial hemolysis, greening (aerobic s. pneumoniae) Gamma: no hemolysis |
|
Group A Streptococci:
Acute Clinical Manifestations |
-pharyngitis
-scarlet fever -impetigo -erysipelas -toxic shock -endocarditis -necrotizing fascitis |
|
Group A Streptococci:
Late Sequelae |
-rheumatic fever
-glomerulonephritis |
|
Staphylococcal Infections
|
-typically localized
-intact skin is major barrier to infection -skin is the primary site of infection |
|
Staphylococcal Infections: examples
|
-folliculitis: hair follicle
-boil: subQ infection -impetigo: mixed skin infection, highly infectious -scalded skin syndrome: exfoliative toxins -pneumonia: compromised host (CF, influenza pt, antibiotic therapy, chemotherapy, immunosuppressant) |
|
Staphylococcal Intoxications
|
1/3 of s. aureus -> preformed enterotoxins -> diarrhea & vomiting
-sx occur within 2-6 hrs of ingestions, recovery within 6-8 hrs -enterotoxins are heat stable |
|
Toxic Shock Syndrome Toxin (TSST)
|
-associated with super absorbent tampons
-s. aureus grows in tampon, produces TSST, released into circulation, distributed systemically -bacteremia, shock, hypotension, and two or more of: ARDSm renal impairment, liver abn, coagulopathy, rash w soft tissue necrosis |
|
Superantigens
|
-bind MHCII and TCR independent of antigen -> stimulate 20% of all T cells -> massive cytokine production, systemic toxicity, suppression of innate immunity
-Strep: enterotoxins and TSST -Staph: pyrogenic exotoxins SpeA, SpeB, SpeC |
|
CDC: 5 Cs of MRSA Transmission
|
1) Crowding
2) frequent skin to skin Contact 3) Compromised skin 4) Contaminated items 5) lack of Cleanliness |
|
Staphylococcus: Drug Resistance
|
-resistance acquired via introduction of new genetic material (conjugation, transduction)
-lots of mobile resistance markers and toxins that can travel via different vectors (plasmids, transposons, phage, chromosomal DNA) -often acquire multi-drug resistance |
|
VRSA
|
Vancomycin Resistance in S. Aureus
-VRE (van resistant enterococci faecalis) transfer mobile resistance markers to VSSA -> VRSA |
|
VRE
|
Vancomycin Resistant Enterococci: 2 plasma mediated gene products
1) Van H: reductase 2) Van A: ligase Together, condensation of Dala-Dlac >> Dala-Dala |
|
Steptococci: Epidemiology
|
-widely distributed in nature, natural flora
-5-15% carry Group A or B in nasopharynx -20-40% carry S. pneumoniae (infects humans only) -15-40% of women are vaginal carriers of Group B -s.pyogenes can spread via respiratory droplets, fomites -enterococci are antibiotic resistant, selective advantage during heavy antibiotic use |
|
Host Defenses
|
1) nonspecific: mucociliary, normal flora, intact skin
2) usually resistant to s. pneumonia 3) complement and opsonophagocytosis -ab to M protein of Group A (too many M types for vaccine to pyogenes) -ab to capsular polysaccharide of s. pneumoniae via multi-valent vaccines -no vaccine for s. aureus |