The Beta-Lactamase Family: Classification, Detection
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Transcript The Beta-Lactamase Family: Classification, Detection
The Beta-Lactamase Family:
Classification, Detection, and Interpretive
Criteria
COL Helen Viscount, PhD, D(ABMM)
LTC Steven Mahlen, PhD, D(ABMM)
Transplant patient
Extremely resistant Klebsiella
pneumoniae recovered
Sensitive only to colistin and
gentamicin
Patient put in isolation
Isolate transmitted to 10 other
patients
Outcomes:
4/5 with bacteremia died
1 other died
2 with renal failure
Only 4/11 discharged without
renal failure
Ampicillin: R
Pip/tazo: R
Ceftazidime: R
Ceftriaxone: R
Cefepime: R
Imipenem: R
Meropenem: R
Aztreonam: R
Amikacin: R
Tobramycin: R
Trimeth/sulfa: R
Fluoroquinolones: R
Gentamicin: S
Colistin: S
Nursing home resident
83 years old
Pneumonia
Admitted to ICU
Started on ceftriaxone and
levofloxacin
Blood cultures +
K. pneumoniae
Based on sensi’s:
No more levo
Kept on ceftriaxone
Patient got worse
Had to be ventilated
Ampicillin: R
Pip/tazo: S
Cefazolin: R
Ceftazidime: I
Ceftriaxone: S
Cefepime: S
Imipenem: S
Aztreonam: S
Tobramycin: S
Trimeth/sulfa: R
Levofloxacin: I
Ciprofloxacin: I
Gentamicin: S
Objectives
At the end of this workshop
the attendee should be able to
distinguish ESBL positive
from carbapenemaseproducing bacteria
At the end of this workshop
the attendee should be able to
describe a method to screen
for ESBLs
At the end of this workshop
the attendee should be able to
interpret the results of the
modified Hodge Test
Beta-lactam antibiotics
Penicillins
Ampicillin
Amoxicillin
Piperacillin
Cephalosporins (generations)
1st gen: cephalothin
2nd gen (cephamycins): cefoxitin, cefotetan
3rd gen: ceftazidime, cefotaxime, ceftriaxone
4th gen: cefepime
Beta-lactam antibiotics
Monobactam: aztreonam
Carbapenems:
Imipenem
Meropenem
Ertapenem
Inhibitors
Sulbactam (ampicillin/sulbactam: Unasyn)
Tazobactam (piperacillin/tazobactam: Zosyn)
Clavulanate (amoxicillin/clavulanate: Augmentin)
Mechanisms of Resistance
Altered target (Gram negative/positive)
Altered permeability (Gram negative)
Production of inactivating enzymes (Gram negative/positive)
Gram-negative cell
Gram-positive cell
Outer membrane
Peptidoglycan
Peptidoglycan
Penicillin
Binding proteins
(PBPs)
Inner (cytoplasmic) membrane
Alteration of Target
Resistance to -lactams via altered penicillin-binding
proteins (PBPs)
MRSA
Vancomycin resistance in enterococci
Fluoroquinolone resistance
Altered Permeability
Passive diffusion of Gram-negative cell wall
Mutate outer membrane proteins
Active efflux
Active Efflux
Production of Inactivating Enzymes
Chloramphenicol acetyltransferase
Aminoglycoside-modifying enzymes
-Lactamases
-Lactamases
Well over 340 different enzymes
Extended spectrum -lactamases (ESBLs)
AmpC -lactamases
Chromosomal
Plasmid-mediated
Carbapenemases
-Lactamases
First -lactamase identified: AmpC beta-lactamase
1940, Escherichia coli
1940, penicillinase, Staphylococcus aureus
First plasmid-mediated -lactamase: TEM-1
1965, Escherichia coli, Greece
-Lactamase Activity
H
H
S
R-CONH
C
C
C
N
-lactam
CH3
CH3
O
COOH
Enzyme-Ser-OH
-Lactamase Activity
H
H
S
R-CONH
O
HOH
C
C
C
N
O
H
Ser
Enzyme
CH3
CH3
COOH
L
L L
L
L
L
L
L
-lactamase
production
L
Types of Beta-Lactamases
ESBLs
AmpCs
Carbapenemases
ESBLs
ESBLs
Extended-spectrum beta-lactamases (ESBLs) are mutant
enzymes with a broader range of activity than their parent
molecules
They:
Hydrolyze 3rd and 4th gen cephalosporins and aztreonam
Do not affect cephamycins (2nd gen ceph) or carbapenems
Remain susceptible to beta-lactamase inhibitors
ESBLs
The most common plasmid-mediated ß-lactamases in
Enterobacteriaceae are TEM-1, TEM-2, and SHV-1
TEM: Escherichia coli
Named after first patient with a urinary tract infection that was not
treatable with ampicillin
Her name: Temorina
SHV: Klebsiella pneumoniae
“Sulfhydryl variant”; amino acids in the enzyme that cross-link with other
molecules
“Classical” ESBLs are derived from TEM and SHV enzymes
“Non-classical” ESBLs are derived from enzymes other than
TEM or SHV
Classical ESBLs
Primarily found in E. coli and Klebsiella spp.
Differ from their parent TEM or SHV enzymes by only 1-4
amino acids
>100 TEM- or SHV-derived beta-lactamases have been
described – most are ESBLs
Non-classical ESBLs
Many described, but less common than classical ESBLs
CTX-M
Found in multiple genera of Enterobacteriaceae
Preferentially hydrolyze cefotaxime
U.S., Europe, South America, Japan, Canada
OXA
Mainly in P. aeruginosa
Primarily hydrolyze ceftazidime
France, Turkey
ESBL Epidemiology
ESBLs first appeared in Europe in the mid-1980s
Worldwide, but prevalence varies widely geographically and
between institutions
U.S. national average for ESBLs in Enterobacteriaceae ~3%
ESBL Epidemiology
ESBL producers especially prevalent in ICUs and long
term care facilities
Becoming more widespread in the community also
Have been associated with outbreaks
Typically arise in ICU
Plasmid transfer between GNRs
Organism transfer between patients
Control of outbreaks
Infection control practice – isolation
Restriction of 3rd and 4th generation cephalosporins
Antimicrobial cycling
Clinical Significance
Despite appearing susceptible to one or more penicillins,
cephalosporins, or aztreonam in vitro, the use of these agents
to treat infections due to ESBL-producers has been associated
with poor clinical outcome
Clinical Significance
ESBL genes are often carried on plasmids that also
encode resistance to multiple classes of antimicrobials
Aminoglycosides, Fluoroquinolones
Trimethoprim/Sulfamethoxazole
Treatment experience is largely based on classical ESBL
producers
Carbapenems
ß-lactam/inhibitor combinations
Typical ESBL Susceptibility Profile
Amp: R
Amp: R
Piperacillin: R
Piperacillin: R
Pip/tazo: S
Pip/tazo: S
Cefazolin: R
Cefazolin: R
Cefoxitin: S
Cefoxitin: S
Ceftazidime: S
Ceftazidime: R
Ceftriaxone: R
Ceftriaxone: R
Cefepime: R
Cefepime: R
Aztreonam: S
Aztreonam: R
Imipenem/meropenem: S
Imipenem/meropenem: S
AmpCs
AmpC: General
Chromosomal
Escherichia coli
Citrobacter freundii
Enterobacter aerogenes, E. cloacae
Serratia marcescens
Morganella morganii
Hafnia alvei
Providencia rettgeri, P. stuartii
Pseudomonas aeruginosa
Aeromonas sp.
AmpC: General
Are not inhibited by -lactamase inhibitors
Normally are repressed, so produced at low levels
Chromosomal: inducible
In all except E. coli
In the presence of certain -lactam antibiotics
Normally, produced at low levels
Plasmid-mediated also
The AmpC of E. coli
Chromosomal, but not
Amp: S
inducible
Normally expressed at low
levels
Regulated by a growth
rate-dependent attenuation
mechanism
Can become highly
expressed with mutations
Amox/clav: S
Piperacillin: S
Pip/tazo: S
Cefoxitin: S
Ceftazidime: S
Ceftriaxone: S
Cefepime: S
Aztreonam: S
Imipenem/meropenem: S
AmpC Induction and Derepression
Is induction clinically relevant?
True danger—mutation in induction pathway
“Derepressed mutant”
150-1000 fold more enzyme produced than normal
Chromosomal AmpC profile
Normal
Amp: R
Amox/clav: R
Piperacillin: S
Pip/tazo: S
Cefoxitin: R
Ceftazidime: S
Ceftriaxone: S
Cefepime: S
Aztreonam: S
Imipenem/meropenem: S
Derepressed profile
Amp: R
Amox/clav: R
Piperacillin: R
Pip/tazo: R
Cefoxitin: R
Ceftazidime: R
Ceftriaxone: R
Cefepime: S
Aztreonam: R
Imipenem/meropenem: S
Plasmid-Mediated AmpCs (pAmpC)
First true proof of AmpC on plasmid: 1988
MIR-1, found in Klebsiella pneumoniae
90% identical to E. cloacae ampC
Some are also inducible (DHA-1)
Most frequently found in K. pneumoniae
Also commonly found in:
K. oxytoca
Salmonella sp.
P. mirabilis
E. coli, E. aerogenes also
pAmpCs: Distribution
World-wide distribution
Africa, Asia, Europe, Middle East, North America, South
America, Central America
CMY-2 is most prevalent globally
Algeria, France, Germany, Greece, India, Pakistan, Taiwan,
Turkey, UK, US
ESBLs vs AmpCs
ESBLs
AmpCs
Inhibitors (pip/tazo,
amp/sulbactam, amox/clav)
S
R
Cefoxitin, cefotetan
S
R
Ceftazidime,
ceftriaxone
R
R
S/R
S
Cefepime
Carbapenemases
Carbapenemases
Carbapenem resistance:
High level production of chromosomal AmpC with decreased
outer membrane permeability (porins)
E. cloacae, E. aerogenes
C. freundii
E. coli
S. marcescens
K. pneumoniae (porins)
Carbapenemases
Carbapenem resistance:
Changes in affinity of PBPs for carbapenems
Carbapenemases
Frequently, bugs that produce a carbapenemase produce
other -lactamases
Carbapenemases
KPC (plasmid, K. pneumoniae)
“Klebsiella pneumoniae carbapenemase”
IMI-1 (plasmid, E. cloacae)
Nmc-A (plasmid, E. cloacae)
Sme-1 (plasmid S. marcescens)
IMP-1 (plasmid, S. marcescens, P. aeruginosa)
L-1 (chromosomal, Stenotrophomonas maltophilia)
Carbapenemases: Profile
R to carbapenems, penicillins, cephalosporins
S or R to aztreonam, depending on enzyme
So the key:
Look for intermediate or R to imipenem or meropenem!
KPC
Infection control emergency!!!
May test sensitive to carbapenems though!
Extensive multidrug resistance (XDR)
Very rapid spread
Empiric therapy: colistin + tigecycline
KPC 1-8
Further reading
Yang, 2007. Ann. Pharmocother. 41:1427-1435
Jacoby, 2009. Clin. Microbiol. Rev. 22:161-182
Black et al, 2005. J. Clin. Microbiol. 43:3110-3113
Livermore et al, 2001. J. Antimicrob. Chemother. 48 Suppl
1: 87-102
Pfaller and Segreti, 2006. Clin. Infect. Dis. 42: S153-163.