pneumoniae isolate that produced an acquired cephalosporinase
, 3 of the 5 E.
The aim of this study was to describe the presence of the CTX-M-1 phylogenetic subgroup ESBL associated with TEM and SHV genes and the gene encoding cephalosporinase
, CMY-2, in E.
coli Extended-spectrum cephalosporinase
CMY-2 CMY-10 DHA-1 ACC-1 Overexpressed cephalosporinase
Proteus ACC-1 mirabilis E.
In addition, rare chromosome-encoded cephalosporinases
(Ambler class C) produced by Enterobacteriaceae may possess slight extended activity toward carbapenems, but their clinical role remains unknown (2,4).
Strain CEC93, exhibiting a phenotypic profile indicative of a high level of cephalosporinase
expression, was positive for [bla.
Only the use of cloxacillin-containing Mueller-Hinton agar plates (200 [micro]g/mL) to inhibit the activity of the naturally occurring cephalosporinase
(AmpC) allowed detection of a synergy image, signature of the presence of an ESBL (5).
However, a few carbapenem-resistant enterobacterial isolates have been reported; resistance may be caused by production of carbapenemases (2) or by combined mechanisms of an outer membrane permeability defect and extended-spectrum [beta]-lactamases or cephalosporinase
Possible mechanisms for ceftazidime resistance among gram-negative bacilli are alterations in outer membrane proteins, overproduction of cephalosporinase
, or production of an extended-spectrum [beta]-lactamase (ESBL).
A synergy image, signature of the presence of an ESBL, could not be observed between clavulanic acid and cefepime or ceftazidime disks on a routine antibiogram (Figure 3A) unless cloxacillin-containing plates that inhibit cephalosporinase
activity were used (Figure 3B).
Notably, isolates exhibiting this extended-spectrum cephalosporinase
may show a ceftriaxone MIC as low as 2 [micro]g/mL, but MIC to ceftiofur and cefoxitin fall more reliably in the intermediate or resistant range.
Emergence of ceftriaxone-resistant Salmonella isolates and the rapid spread of plasmid-encoded CMY-2-like cephalosporinase
Resistance to carbapenems is rare in Enterobacteriaceae and may be mediated by 3 mechanisms: hyperproduction of an AmpC-type cephalosporinase
combined with decreased drug permeability through the outer membrane, decreased affinity of penicillin-binding proteins that constitute target proteins for carbapenems, and carbapenem-hydrolyzing [beta]-lactamases (1-3).