Streptococci & Staphylcocci (24)

Front 1

Streptococci: General

Back 1

-Gram positive cocci
-chains
-catalase negative
-facultative anaerobes

Front 2

Staphylococci: General

Back 2

-Gram positive cocci
-clusters
-catalase positive
-facultative anaerobes

Front 3

Differential Antibody resistance

Back 3

-staph is generally more antibody resistant (MRSA, VRSA)
-due to plasmid transfer

Front 4

Staphylococcus aureus: antigens

Back 4

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

Front 5

Streptococcus pyogenes (Group A Strep): antigens

Back 5

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

Front 6

Streptococcus pneumonia: antigens

Back 6

1) capsular polysaccharides: antiphagocytic, major virulence factor
-used in S. pneumonia speciation and as component of vaccine

Front 7

Coagulase Status of:
S. aureus
S. epidermidis
S. saprophyticus

Back 7

S. aureus: +, major pathogen
S. epidermidis: -, new pathogen, antibody resistant
S. saprophyticus: -, UTI

Front 8

MRSA & SCCmec

Back 8

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)

Front 9

HA-MRSA

Back 9

-Hospital Acquired MRSA: generally larger with more resistance markers
-Transposons encode for macrolide-lincosamide-streptogramin-spectinomycin resistance and tobramycin resistance

Front 10

CA-MRSA

Back 10

-Community Acquired MRSA: generally smaller with fewer resistance markers
-resistance to methicillin "only"
-may produce PVL (Panton-Vanlentine leukocidin) toxin: increased virulence?

Front 11

Lancefield Typing of Streptococci

Back 11

-based on serogroups (cell wall)

Group A = pyogenes
Group B = agalactiae
Group C = Enterococci
Viridans, pneumoniae, anaerobic strep have no Lancefield group

Front 12

Hemolytic Typing of Streptococci

Back 12

Beta: complete clearing of area around a colony (s. pyogenes)
Alpha: partial hemolysis, greening (aerobic s. pneumoniae)
Gamma: no hemolysis

Front 13

Group A Streptococci:
Acute Clinical Manifestations

Back 13

-pharyngitis
-scarlet fever
-impetigo
-erysipelas
-toxic shock
-endocarditis
-necrotizing fascitis

Front 14

Group A Streptococci:
Late Sequelae

Back 14

-rheumatic fever
-glomerulonephritis

Front 15

Staphylococcal Infections

Back 15

-typically localized
-intact skin is major barrier to infection
-skin is the primary site of infection

Front 16

Staphylococcal Infections: examples

Back 16

-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)

Front 17

Staphylococcal Intoxications

Back 17

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

Front 18

Toxic Shock Syndrome Toxin (TSST)

Back 18

-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

Front 19

Superantigens

Back 19

-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

Front 20

CDC: 5 Cs of MRSA Transmission

Back 20

1) Crowding
2) frequent skin to skin Contact
3) Compromised skin
4) Contaminated items
5) lack of Cleanliness

Front 21

Staphylococcus: Drug Resistance

Back 21

-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

Front 22

VRSA

Back 22

Vancomycin Resistance in S. Aureus
-VRE (van resistant enterococci faecalis) transfer mobile resistance markers to VSSA -> VRSA

Front 23

VRE

Back 23

Vancomycin Resistant Enterococci: 2 plasma mediated gene products
1) Van H: reductase
2) Van A: ligase
Together, condensation of Dala-Dlac >> Dala-Dala

Front 24

Steptococci: Epidemiology

Back 24

-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

Front 25

Host Defenses

Back 25

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