Gram+ and Gram- Cocci - Kaul 4/26/16 Flashcards
Gram+ cocci
genera, virulence factors
majority comprise 3 genera:
- Staphyococcus
- Streptococcus
- Enterococcus
major virulence factors
- adhesins/cell surface factors : allow to stick to host ECM
- secreted enzymes/toxins : allow to penetrate/digest host ECM
Staphylococci
- Gram stain : cells in clusters (bunches of grapes)
- normal skin flora (most common bacteria on our skin)
- facultative anaerobes (aerobes, but can also grow anaerobically)
- hardy : resistant to heat/drying → persist on fomites
- wound and nosocomial (hosp-acquired) infections
all are catalase+ (unlike streptococci)
S. aureus (major pathogen) is coagulase+, all others are coagulase- Staph (CoNS; CNS)
Staphylococcus aureus basics
most common human pathogen
- normal flora in ant nares of 1/3 of ppl
predisposition to infection can be due to:
- tissue injury (surgical/battle wounds)
- preexisting primary infection
- diabetes
- immunodef
- poor hygiene and nutrition
infections either localized or systemic
S. aureus
superantigen toxins
non-specifically link MHC to TCR
activate T cells with different specificities
- up to 20% of all T cells activated
- overproduction of cytokines (IL1, IL2, TNF)
- toxic shock syndrome toxin (TSST1)
- enterotoxins
- exfoliatin
Staphylococcus aureus
virulence
- cell surface virulence factors
- protein A : (binds to Fc portion of abs) → opposite orientation req for opsonization → anti-opsonin effect to evade immune system
- adhesins : facilitate adhesion to host cell/ECM
- antiphagocytic polysacch microcapsule
- cytolytic exotoxin
- hemolysin - lyses RBCs
- PVL (Panton-Valentine leukocidin) - lyses leukocytes, specifically PMNs (produced predominantly by CA-MRSA)
- superantigen toxins : nonspecifically crosslink MHC/TCR
* (TSST1, enterotoxin, exfoliatin) - tissue “invasin” enzymes : “spreading factors” - facilitate penetration through extracellular tissue
- staphylokinase
- hyaluronidase
- lipase
Staphylococcus aureus
common clinical manifestations
1. SSTIs (skin and soft tissue infections)
- furuncles : small, pus-filled, local infections
- carbuncles : larger skin abscesses
- impetigo : spreading, crusted skin infection
- cellulitis : deep skin infection
2. infection of other tissues, potentially from metastasis of superficial infections…
- osteomylitis
- septic joint/ septic arthritis (esp in children)
- pneumonia
- bloodstream infections: bacteremia, septicemia
- acute endocarditis (freq assoc with IV drug use)
3. toxinoses
- gasteroenteritis (from enterotoxins) → acute onset of GI distress with char projectile vomiting
- toxic shock syndrome (TSST1 exotoxin) → high fever, sunburn like rash, multiple organ failure
- scalded skin syndrome (exfoliatin toxin) → bullous impetigo → desquamation of epidermix
Staphylococcus aureus
treatment options
- beta-lactamase resistant penicillins (ex. nafcillin)
1. penicillinase-resistant penicillins (ex. oxacillin)
2. clindamycin
**if MRSA, vancomycin is SOC antibiotic
- vancomycin - glycopeptide
- daptomycin - lipopeptide
- linezolid - oxazolidone
- ceftaroline - cephalosporin with affinity for PBP2a
S. aureus antibiotic resistance
1945: penicillin
1955: almost all S. aureus resistant due to penicillinase
enter. ..penicillinase-resistant beta-lactams (methicillin, oxacillin, nafcillin)
* bound to PBP2 (penicillin binding protein 2)
countered by…MRSA! (methicillin-resistant S. aureus)
- made PBP2a
now. ..vancomycin!
but. ..VISA (intermediate), VRSA (resistant) → uncommon but growing in importance
Staphylococcus aureus
diagnostics
- Gram stain: Gram+ cocci in clusters
- culture: golden-yellow colonies
- catalase+
- coagulase+
Staphylococcus epidermidis
basics
major component of normal skin flora
- cause wound infections through broken skin
relatively less virulent
freq involved in nosocomial infections, opportunistic infections
produces cell surface polysacch “slime” → adheres to bioprosthetic material and acts as barrier to antibiotics
most are highly resistant to oxacillins, penicillins
Staphylococcus epidermidis
virulence
- polysaccharide capsule adheres to prosthetic devices
- highly resistant to antibiotics
Staphylococcus epidermidis
most common clinical manifestations
nosocomial infections…
- prosthetic jts and heart valves
- IV lines
- UTIs
Staphylococcus epidermidis
treatment options
vancomycin (resistant to many antibiotics)
Staphylococcus epidermidis
diagnostics
- Gram stain: Gram+ cocci in clusters
- catalase+
- coagulase-
Staphylococcus saprophyticus
most common clinical manifestations
normal vaginal flora (infreq found on skin)
UTIs and cystitis in women
Staphylococcus saprophyticus
treatment options
penicillin G
Staphylococcus saprophyticus
diagnostics
- Gram stain: Gram+ coccie in clusters
- catalase+
- coagulase-
- novobiocin resistant
Streptococcus
Gram+ spherical/ovoid cocci arranged in long chains, commonly in pairs
approx 25 species
catalase-
most parasitic forms are fastidious → require enriched media
sensitive to drying/heat
aerotolerant anaerobes
classified based on:
- hemolysis pattern
- cell wall antigen
hemolysis
beta-hemolysis : complete erythrocyte destruction
alpha-hemolysis : RBCs damaged by peroxide → Hb turns green/brown
gamma-hemolysis : no hemolysis
Streptococcus Lancefield groups
serological classification based on antigenic cell wall polysacch: C substance (carbohydrate substance)
react with specific antisera in slide agglutination assays
- Groups A-U exist
- common human pathogens: Groups A, B, D, none
Strep pathogen classification based on
- hemolysis
- sensitivity/resistance
- C substance group
beta hemolytic
- bacitracin sensitive → S. pyogenes : Group A streptococci
- bacitracin resistant → S. agalactiae : Group B streptococci
alpha hemolytic
- optochin sensitive → S. pneumoniae (“non Lancefield” streptococci)
- optochin resistant → Viridans group, ex. S. mitis (“non Lancefield” streptococci)
gamma hemolytic
- S. bovis : Group D streptococci
S. pyogenes; Group A Streptococci
virulence
M protein (80 types)
- key for virulence
- highly variable
streptolysin O and S (lyse RBCs)
pyrogenic superantigen exotoxins:
invasin: streptokinase (allows to penetrate/colonize host)
S. pyogenes; Group A Streptococci
most common clinical manifestation
-
pharyngitis (“strep throat”) : purulent infl in pharynx
* can be assoc withscarlet fever - skin infections : impetigo, erysypelas → cellulitic or necrotizing fasciitis
- streptococcal toxic shock syndrome : mediated by superantigen pyrogenic toxin → leads to multi organ failure
post-infection sequellae (antibody-mediated)
heart and joint: rheumatic fever
- 2-3 weeks after pharyngitis
- myocarditis, arthritis, fever, chorea
kidney: glomerulonephritis
- 1 week after pharyngitis or skin infection
- hematouria, fluid retention/hypervolemia
S. pyogenes; Group A Streptococci
epidemiology
treatment
inhabits human throat, nasopharynx, occasionally skin
- entry usually through skin or pharynx
transmitted via contact, droplets, food → easily spread in crowded environments
cutaneous/throat infection : mostly children
if not treated quickly, systemic infection and progressive sequellae possible
tx
penicillin G
if skin infection: penicillinase-resistant renicillins (oxacillin) since it may be staphylococci
S. pyogenes; Group A Streptococci
diagnostics
Gram stain: Gram+ cocci in chains
catalase-
beta-hemolytic
bacitracin-sensitive
S. agalactiae; Group B Streptococci
virulence
normal flora of female repro tract
leading cause of neonatal sepsis
- women are routinely screened and treated for GBS colonization prior to deliver
S. agalactiae; Group B Streptococci
most common clinical manifestation
neonatal meningitis
neonatal pneumonia
neonatal sepsis
S. agalactiae; Group B Streptococci
epidemiology and treatment
penicillin G
S. agalactiae; Group B Streptococci
diagnostics
- Gram stain:
- catalase-
- beta-hemolytic
- bacitracin-resistant
Viridans group streptococci
virulence
include many species
barring S. pneumonia, most are lumped together as “Viridans” streptococci (green on agar)
widespread residents of oral cavity : gums and teeth
- dental oral procedures can facilitate entrace (otherwise not too invasive)
clinical manifestations
- dental caries
- subacute endocarditis
Viridans group streptococci
most common clinical manifestation
subacute endocarditis
dental caries
Viridans group streptococci
treatment
penicillin G
Viridans group streptococci
diagnostics
Gram stain:
catalase-
alpha-hemolytic
optochin-resistant
- S. pneumoniae*
- *virulence
causes 30-50% of all pneumonia
small, “lancet-shaped” cells arranged in pairs, short chains
aka pneumococci
normal flora in nasopharynx in carriers, doesn’t survive long out of this environment (infections often endogenous)
predisposed: young, elderly, immunocompromised, smokers, ppl living in close quarters
* esp sickle cell and/or splenectomy!
polysacch capsule (> 85 serotypes)
- antiphagocytic, antigenic
- virulence factor: heavy encapsulation → more freq assoc with severe, invasive disease
pneumolysin, autolysin
- S. pneumoniae*
- *most common clinical manifestations
1. lobar pneumonia : pneumococci aspirated into lungs → induce infl response
2. otitis media : inner ear infection; most common bacterial infection in children
3. meningitis : characterisitic nuchal rigidity
4. bacteremia/sepsis
- high mortality rates in adults (up to 60% in elderly)
- esp hits asplenic patients
S. pneumoniae
treatment
used to be treatable by penicillin → now intermed resistance is common
- resistance mediated by PBP
- resistant strains sensitive to 3gen cephalosporins (cefotaxime, cefriaxone)
S. pneumoniae
diagnostics
green on blood agar
lysis by bile acids
sensitive to optochin
Quellung rxn
- Group D*
- Enterococci*
- E. faecalis
- E. faecium
- 2. non-enterococci*
- S. bovis
- *virulence
enterococcal epidemiology
- component of normal GI flora
- resistant to chemicals, persist on fomites
- opportunistic infections, biliary infections, intra-abd abscesses → lead to endocarditis or bacteremia, sepsis
- inherently resistant to lots of antibiotics!
component of normal GI flora
- can grow in 40% bile
bacteremia caused by S. bovis is assoc with GI malignancy and colon cancer
- Group D*
- Enterococci*
- E. faecalis
- E. faecium
- 2. non-enterococci*
- S. bovis
- *most common clinical manifestations
biliary tract infections
UTI (esp enterococci)
- Group D*
- Enterococci*
- E. faecalis
- E. faecium
- 2. non-enterococci*
- S. bovis
treatment
ampicillin + gentamycin
resistant to penicillin G
resistance to vancomycin on the rise
- due to a transposable element
- resistance very common in E. faecium (less in E. faecalis)
- Group D*
- Enterococci*
- E. faecalis
- E. faecium
- 2. non-enterococci*
- S. bovis
diagnostics
Gram stain:
culture:
- enterococci grow in both 40% bile (hydrolyze esculin), 6.5% NaCl
- non-enterococci grow only in bile
enterococci are salt-resistant!
Gram- cocci
Neisseria
N. gonorhoeae (gonococci)
N. meningitidis (meningococci)
Gram-, kidney shaped diplococci
- often seen within PMNs
aerobic
sensitive to heat/drying (like pneumococci)
N. gonorrhoeae
virulence
unencapsulated
heterogeneous cell surface antigens via gene conversion, phase variation mechanisms
antigenically heterogeneous:
- pili
- Opa (opacity proteins, formerly known as PII proteins)
- LOS (endotoxin; like LPS but shorter, more branched side chains)
addtl virulence factors:
- IgA protease (helps infect mucosa!)
- proteins like lactoferrin, transferrin that can extract Fe from host Fe proteins
N. gonorrhoeae
epidemiology/pathogenesis
clinical manifestations
STD attacking mucous membranes : GU, eye, rectum, throat
suppuration, fibrosis
many infected individuals (esp females) asymptomatic
clinical
1. genitourinary tract infections : urethritis, cervicitis → pelvic infl disease, salpingitis (women) → infertility
2. pharyngitis, rectal infections
3. opthalmia neonatorum
- routine prophylaxis (erythromycin ointment or AgNO3)
4. bacteremia → disseminated infection
- rare (gonococci multiply poorly in bloodstream)
- could cause septic arthritis, scattered skin lesions
N. gonorrhoeae
diagnosis
pus secretion from mucosal surfaces
smears: intracellular Gram- cocci
culture: complex nutritional reqs
- oxidase+
- grow better under enhanced CO2 conditions
- ThayerMartin media (choc agar with antibiotics that suppress normal flora)
nucleic acid amplification
- primary method for diag
N. gonorrhoeae
treatment
resistance is a problem: penicillin, tetracycline, quinolones
- 20-30% of new cases are PPNG, TRNG, QRNG → penicillinase-producing or tetracycline-resistant or quinolone-resistant
current guidelines: IM Ceftriaxone + azithromycin/doxycycline to hit concurrent chlamydia infection
N. meningitidis
virulence
antigenic capsule (13 serogroups)
- antigenic capsule is NOT present in N. gonorrhoeae
- serogroups A, B, C, Y, W-135 cause most; B most common in US
- pili, LOS, Opa*
- IgA protease*
- Fe extraction system*
- *similar to N. gonorrhoeae*
N. meningitidis
epidemiology
epidemic waves in closed communities (schools, dorms, barracks), often winter/early spring - young, healthy individs
- infants 6mo-2yr especially susceptible
carrier rate: 5-10%, mostly in nasopharynx
rapid onset → progression to life-threatening in 12-24hr
vacinne available
N. meningitidis
clinical manifestations
meningococcemia
- bacteria rapidly multiply in bloodstream
- spiking fevers, chills, jt/muscle pain
- petechial rash
progresses either into…
- meningitis
- purulent CSP
- infl response in meninges
- characteristic symptoms: severe headache, stiff neck, light sensitivity, vomiting, AMS/coma
- fulminant septicemia/meningococcemia
- LOS-mediated septic shock
- freq seen in infants
- large purplish blotchy hemorrhages
- DIC
- adrenal collapse (Waterhouse-Friderichsen syndrome)
N. meningitidis
diagnosis
Gram stain CSF, blood, skin, or nasopharyngeal samples…
oxidase+
culture for differentiation…
- N. meningitidis can utilize glucose and maltose
- N. gonorrhoeae can utilize glucose only
rapid latex agglutination test for antigenic capsule
N. meningitidis
vaccine
tetravalent conjugate vaccines (MCV4)
- polysacchs conjugated to diphtheria toxoid
- contains capsular antigens A, C, Y, W-135
2014: first serogroup B vaccine = TRUMENBA
table at end for N. gonorrhoeae and N. meningitidis
