Enterobacteriaceae Opportunistic Pathogens Flashcards
What are the GENERAL characteristics of Enterobacteriaceae?
- Gram negative bacilli
- Non-spore forming
- All ferment glucose
- Catalase pos (except Shigella dysenteriae)
- Oxidase neg (except Plesiamonas sp.)
- Most reduce nitrate to nitrite (ones causing human infections)
- Peritrichous flagella if motile
- All grow on BA and CHOC
- Grow well at 35-37
Epidemiology of Enterobacteriaceae
E. coli : NF of bowel (human and animal), may inhabit female genital tract
Citrobacter spp, Enterobacter spp, Klebsiella spp, Morganella spp, Proteus spp, Providencia spp and Serratia spp: NF in human GIT
Their mode of transmission?
- Often endogenous and opportunistic
- Person-to-person (often nosocomial)
Virulence factors include:
Endotoxins (fever, vasodilation, inflammation, shock, DIC), capsules, adhesion proteins, multiple antimicrobial resistances
These can cause what in these types of patients?
Nosocomial infections of RT, UT, blood and other sterile sites in hospitalized or debilitated patients
Virulence factors of E.coli causing extraintestinal infections
Endotoxins, pili, capsule
Enterotoxigenis E.coli (ETEC) and their virulence factors
- Potent toxins (serious GI infections)
- Pili, enterotoxins
Enteroinvasive E.coli (EIEC) and their virulence factors
- Invades enterocytes (serious GI infections)
- Similar mechanisms to Shigella
Enteroaggregative E.coli (EAEC) and their virulence factors
- Attach to mucosal cells of GI and change cell surface (serious GI infections)
- Pili, enterotoxins
Enterohemorrhagic E.coli (EHEC/VTEC/STEC) and their virulence factors
- Toxin (life threatening systemic illness)
- SHIGA toxin
Colonial appearance on BA
Large, grey, smooth. glistening, moist, E.coli often B-hemolytic, Kleb + Enterbacter spp. may be mucoid, Proteus spp. often swarm
Gelatin Hydrolysis
- Determines ability to produce gelatinase
Procedure: - Stab 4-5 times, inc in 02 up to 14 days
- Place in 4 degrees daily to check for liquification
- Use uninoculated tube for control, ensure it gels
- Pos= partial/total liquefaction @4deg (control solid)
- Neg= solid at 4deg
Pos QC=Bacillus subtilis
Neg QC=E.coli
4-Methylumbelliferyl-β-D-Glucuronide (MUG) test
- Rapid test to ID E.coli
- Subsrate:4-Methylumbelliferyl-β-D-Glucuronide
Procedure:
- Impreg substrate on paper disc
- Inoc and inc in 2 hrs
- Pos=electric blue fuorescence (E.coli)
- Neg=no fluorescence (Kleb. pnuemoniae)
NOTE: only test oxidase-neg orgs
What are the categories of E.coli?
Uropathogenic (UPEC)
- Pathogenicity islands coding for adhesions and toxins
Meningitis/sepsis-asscosiated (MNEC)
- neonatal meningitis w/ high morbidity and mortality. Spread fr. blood
E.coli are:
- Most are LF, dry (may see precip of bile salts on MAC
- Indole pos
- VP neg
- Citrate neg
- Lysine pos
Klebsiella spp. characteristics
- Klebsiella pnuemoniae, Klebsiella oxytoca
- NF in Nasopharynx and GIT
- UTI, pneumonia, septicemia, liver abcesses
- K.oxytoca: associated w/ self-limiting, antibiotic-associated hemorrhagic colitis
- K.pneumoniae: intrinsically resistant to ampicillan
- Possible multidrug resistance
Kleb spp. are:
Culture:
- Mucoid, Mac-LF &lrg
Tests
- Non-motile
- VP pos
- Ornithine neg
- Urea pos
What test differentiates K.pnuemoniae and K.oxytoca?
Indole
K.pnuemoniae - neg
K.oxytoca - pos
Enterobacter spp. is part of which tribe?
Klebsielleae
NF and infections of Enterobacter spp.
- NF in human GIT (also in soil and water)
- UTI, respiratory and cutaneous infections, nosocomial (contaminated medical devices
Culture and tests of Enterobacter spp
Culture
- Mac: LF; often mucoid (capsule); may have plasmids
Tests
- Motile
- Ornithine pos
Test that differentiates E.aerogenes from E.cloacae
Lysine
E.aerogenes = pos
E.cloasae = neg
Serratia spp., name 2, what tribe are they a part of.
Serratia marcescens
Serratia liquifaciens
Tribe Klebsiella
What can be caused by Serratia spp.?
UTI, pneumonia, septicemia, wound infections
Nosocomial opportunist
