الفهرس 
Escherichia coli, Mechanism of Antibiotic ResistanceOnly 14 pages are availabe for public view
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Abstract
ESBLs are plasmid-mediated enzymes that hydrolyze the 3rdGCs and the monobactams (aztreonam) but have no effect on the cephamycins (cefoxitin, cefotetan) and the carbapenems. They have been found to be inhibited by clavulanic acid, sulbactam and tazobactam. This is the property which helps their detection in the laboratory. The plasmid mediated ESBLs can be grouped into three main types: TEM, SHV or CTX-M. Another class of β-lactamases, the AmpC β-lactamases, confers resistance to 3rdGCs and cephamycins and they are not inhibited by clavulanic acid. The expression of the AmpC β-lactamases can be generated by chromosomal or plasmid genes.
ESBL and AmpC producing pathogens have increased in hospitals and community settings. Currently, the antimicrobial therapeutic options for treating infections caused by ESBL-AmpC producers are limited. The fecal flora of healthy individuals in hospitals and in the community can represent a reservoir for ESBLs, pAmpC β-lactamases. Therefore, we conducted a study to determine the prevalence of faecal carriage of ESBLs, Ampc producing E. coli among HCWs at Fayoum University Hospital by conventional microbiological methods and on molecular basis.
Stool samples were collected from 200 HCWsand it is found thatthe prevalence of fecal carriage of ESBLs producing E. coli among HCWs was 21% (42/200). The prevalence of fecal carriage of pAmpC
β-lactamases was 1% (2/200) and 2% (4/200) carry combined ESBL and AmpC producing E. coli.
Fecal carriage of ESBLs producing E. coli among HCWs from different wards were as follow; 26.1% (12/46) of HCWs in internal medicine wards and ICUs, followed by 22.5% (9/40) of HCWs in operating theaters, 18.5% (5/27) in outpatient wards, 15.4% (6/39) of HCWs in surgery, 13.6% (3/22) in pediatric wards, 11.8% (2/17) in obstetrics, and 11% (1/9) in laboratory ward.
Fecal carriage of plasmid AmpC producing E. coli was detected in operating theaters.While fecal carriage of combined ESBLs and AmpC β-lactamases producing E. coli detected in internal medicine wards and ICUs.
All 200 isolates were susceptible to imipenem. Also amikacin have an excellent susceptibility to E. coli. Isolates exhibited higher resistance to ceftazidime.
Phenotypic screening for ESBL enzymes detection by disc diffusion test and MICs revealed; 29.5% showed resistance to one or more of 3rdGCs, among the 3rdGCs used in the screening, ceftazdime had a better sensitivity (100%), while cefotaxime lacked sensitivity (52.3%).
Phenotypic AmpC screening test by cefoxitin resistance; detects 8% isolates positive for AmpC β-lactamases with sensitivity 100%, and accuracy 83% when compared with PCR.
Phenotypic conformation for ESBL by combined discs test detected 62.7% of 59 ESBL screening test positive isolates, with sensitivity 86%, high positive predictive value 100% and accuracy 90% when compared with PCR.
DSDT for AmpC and combined ESBL, AmpC enzymes confirmation detected; 22.7% produce AmpC β-lactamases, 18.2% produce both ESBL and Ampc β-lactameses and 59.1% were negative isolates. Sensitivity of DSDT: 100% and accuracy 86% when compared with PCR.
Molecular analysis revealed that; the prevalence of genes encoding ESBLs, AmpC among HCWs as follows: 19% had pure ESBL genes, among these isolates, 94.1% were bla (SHV), 18.4% bla (TEM) and 5.3% bla (CTX-M). Only 7.9% had two types of ESBLs. 1% of isolates had pure AmpC genes (CIT group), while2% of isolates with combined AmpC and ESBL genes. It was found that: bla (SHV) are the dominant ESBLs among the E. coli resistant strains in HCWs.
We recommended detection of ESBLs and AmpC β-lactamases production by confirmatory DSDT (using BA and clavulanic acid as inhibitory for AmpC, ESBL enzymes respectively) which is simple and any microbiology laboratory can do it along with the routine antibiotic susceptibility testing (for screeningESBLs and AmpC β-lactamasesproduction).
Finally, the results imply that ESBL-AmpC producing E. coli are present in alarming prevalence even in healthy populations in hospitals.
A threatening epidemiologicalproblem is the dissemination of these ESBL-AmpC producing organisms to the patients in hospitals and healthy people in the community. This requires sound infection control measures including improving hygiene and regular detection of ESBL- AmpC producing isolates.