Week 5 Flashcards
All enterobacterales are
- Facultative Anaerobes
- GNB
- Oxidase negative
- Reduce nitrates to nitrites
- Fermenters
- Non-spore forming
- Grow on MAC
What four tube system is used to ID enterobacteriaceae
- I = indole
- M = MR
- V = VP
- C = citrate
E coli is
INDOLE: +
* MR +
* VP -
* CITRATE -
157:57 is NSF on SMAC while others do
Klebsiella pneumoniae is
INDOLE -
* MR -
* VP+
* CITRATE +
MUCOID LF
NON MOTILE
LOOSE LIDS BUT ATTACHED
Enterobacter aerogenes is
INDOLE -
* MR -
* VP +
* CITRATE +
Citrobacter freundii
INDOLE -
* MR +
* VP -
* CITRATE V (75%+)
Serratia marcescens *******
INDOLE -
* MR V (25%+)
* VP V (70%+)
* CITRATE +
*DNAse +
NLF OR LLF
may show red pigment
Providencia stuartii
INDOLE +
* MR +
* VP -
* CITRATE +
PPD +
Morganella morganii
INDOLE +
* MR+
* VP -
* CITRATE -
Difference between P Mirabilis and P vulgaris
SWARMING
M is indole neg and V is indole pos
Both are MR +
Both are VP -
M is citrate pos and V is citrate neg
WILL NOT SWARM ON MAC AND WILL NOT GROW ON CNA
Shigella sonnei
*INDOLE -
*MR +
*VP -
*CITRATE -
SUNNY D
serology is Shigella group D
Not positive for alot
Shigella flexneri
INDOLE V (29%+)
* MR +
* VP -
* CITRATE -
serology is Shigella group B
Yersinia enterocolitica
INDOLE V (50%+)
* MR +
* VP -
* CITRATE -
TRUE NLF not even on OPNG
MOTILITY non motile @ 35°C
* MOTILITY motile @ RT
UREA neg/wk+ @ 35°C
* UREA pos @ RT
Bullseye on CIN
Edwardsiella tarda
NDOLE +
* MR +
* VP -
* CITRATE -
which orgs are urea and PPF positive while all stool pathogens are negative for them
- Proteus spp.
- Morganella spp.
- Providencia spp.
pink urea shows that it is not a stool pathogen
which orgs are Hydrogen Sulfide Positive
- Citrobacter freundii - ONLY ONE LF
- Edwardsiella tarda
- Salmonella spp.
- Proteus vulgaris
- Proteus mirabilis
which orgs are VP positive
- Klebsiella spp.
- Enterobacter spp.
- Serratia spp
which orgs are non motiles at 37
Shigella spp.
Klebsiella spp. (LF)
Yersinia spp. (motile at RT)
which org is both a NLF at 24 hrs and LLF at 48 hrs
Shigella sonnei (onpg and ornithine post)
true for any org that is NF on MAC but ONPG positive
MALDI cant tell the difference between ecoli and shigella
what are methods for AST testing
Vitek, Kirby
-AB groups depend on site of infection
-Enteric pathogens are not treated with antimicrobials but supportive therapy
-some Enterobacteriaceae are susceptible to broad spec cephalosporins
*ESBL
*SPICE
What are extended spectrum beta lactamases
-plasmid meditated concern
-entrobacteriac can produce beta lactamase that is different from the one that causes penicillin and ampicillin resistance
-Class A is the infection control one - ESBL -extended Spectrum Beta Lactamase like Ecoli and Kleb
-these are able to resist cephalasporins, cephamycin, aztreonam, piperacillin
What are class A esbls
- are transferred on plasmids
-this ability to transfer resistance is why it is of most concern because it can cause other infections
-the gene is derived from TEM-1, SHV-1
-inhibited by clavulanic acid which is a beta lactamase inhibitor
-these are able to resist cephalasporins, cephamycin, aztreonam, piperacillin
-Carbapenems are the drug of treatment
-mostly e coli and kleb
What are class C ESBLS
- in some Enterobacteriaceae
- Enzyme (cephalosporinase) hydrolyzes penicillins, cephlalosporins, monobactams , and cephamycins
-Chromosomal –Intrinsic resistance; (may move to plasmids)
-Induced by exposure to βeta-lactam drugs may look S in vitro but the treatment will fail once the pt is exposed to the beta lactam drug
-found in SPICE organisms
What is part of SPICE group **
Serratia spp
Providencia spp
Indole positive Proteus: Morganella, P. vulgaris
Citrobacter freundii
Enterobacter spp
(Hafnia has been added)
Chromosomally mediated natural resistance to beta lactams, cephalosporins, and cephamycins
What is the spice group
-first group of cephalosporin resistant organisms
-have the inducible ampC Beta-lactamase which will look Sus in vitro but the treatment will fail after using beta lactamase AB
-has a predictable resistance
-resistant to B lactamase inhibitors and cephamycin’s like cefoxitin
-not part of infection control concern
how will treatment work
-avoid beta lactam antibiotics
-must test susceptibility for Aminoglycosides, fluoroquinolones, SXT, carbapenems
always reported as resistant to peni, cepha, b lactam inhibitor combos
how can we differentiate if it is a Spice or Class A ESBL
-know the spice orgs
-check for 3rd gen cephalosporin
-for Class A ESBL
* For E. coli, P. mirabilis or Klebsiella sp., check the Ceftazidime result. This result is a screen for Class A ESBLs.
* If it is S -> not a Class A ESBL
* If it is R ->set up a PCT test to determine if it is a Class A ESBL
-if the org is not a SPICE, ESBL or CPE Ceftazidime is used as a marker
what is the phenotypic confirmatory test
-testing to see if the class A B lactam can be inhibited by a b lactam inhibitor
-Class A ESBLs are sensitive to Cefoxitin
-There are five discs
-use a standard disk diffusion at 35 C 16-18 hours
-measure the drug alone against the drug + acid combo with a 5 mm difference the combo drug must be bigger for it to be ESBL positive
≥ 5mm difference between both or one pair of antibiotics + Cefoxitin S = Class A ESBL
What is Carbapenemase Producing
Enterobacteriaceae (CPE)
-also known as Also called Carbapenem Resistant Enterobacteriaceae (CREs) or Carbapenem
Producing Organisms (CPOs)
-the resistance gene is transferable on plasmids
-Resistant to carbapenems (e.g. ertapenem, meropenem, imipenem)
-Resistant to all penicillins, cephalosporins, BL-inhibitory combinations
- resistant to fluoroquinolones
-hard to treat, causing poor patient outcomes like increase hospital stay
-needs to be reported to public health
-infection control issue
-biggest risk factor is being in the hospital
-NOT specific to enterobacteriaceae
NDM - NewDehli
-superbug **
What are Class A CPE
- Serine beta lactamases – hydrolyze all cephalosporins and carbapenems
- KPC (Klebsiella pneumoniae carbapenemase), SME (Serratia marcescens)
What are Class B CPE
Metallo-beta lactamases: hydrolyze beta lactam rings using bound zinc ions
* IMP (imipenemase), VIM (Verona integron-encoded MBL), NDM (New Delhi beta
lactamase)
What are Class D CPE
Oxacillinases: characterized by their hydrolytic activity towards oxacillin
* OXA (OXA-48 most common)
* Shows weak activity against cephalosporins so may test S on Vitek (vs. Class A and B
will test R)
What tests can be done for CPE production
-Modified CIM ** gold standard
-ROSCO disks
-CarbaNO
-PCR
What is the Modified Carbapenem Inactivation Method (mCIM)
-make heavy suspension in saline
-add meropenem disk and incubate for 2 hours at 35.If the organism has a carbapenemase enzyme, it will inactive the antibiotic in the disk.
-after 2 hours streak a known meropenem Sensitive Ecoli for confluent growth on MHA
-remove inactivated disk and put on plate with Sensitive E coli - incubate overnight
-if the sensitive Ecoli grows on the disk the org has inactivated the meropenem meaning that it will have a CPE enzyme. However if the sensitive Ecoli still has a S zone size then there isnt a CPE enzyme in the organism
salmonella typhii
I- NEG
M- POS
NP-NEG
CIT-NEG
LITTLE BIT OF H2S IN THE MIDDLE OF THE TSI
SEROLOGY Vi masks the o antigen
salmonella spp
I- NEG
M- POS
NP-NEG
CIT-POS
SEROLOGY O and H POSITIVE and Vi neg
