Prevalence of AmpC and SHV β-Lactamases in Clinical Isolates of Escherichia coli From Tehran Hospitals

Abstract

Background: Beta-lactam resistance in Gram-negative bacteria, especially Escherichia coli, is a main clinical problem. It is often caused by the coproduction of β-lactamases, particularly extended-spectrum β-lactamases (ESBLs) and AmpC enzymes. It may lead to a problem for diagnosis via recommended phenotypic tests by the Clinical and Laboratory Standards Institute (CLSI). Conversely, β-lactamase genes have several subfamilies; therefore, using designed primers with high ability could be valuable to detect all of them. Objectives: This investigation focused on evaluating the prevalence of extended-spectrum β-lactamases using disk diffusion method and confirmatory test (Combined Disk), as well as PCR for complete detection of these genes (SHV-and AmpC (CITM, FOX)-type β-lactamase genes). Materials and Methods: 500 clinical samples were collected from different hospitals of Tehran, Iran and 200 E. coli isolates were detected by standard biochemical tests such as IMVIC. These specimens were isolated from urine, stool, blood, and wound. Subsequently, the isolates were screened by disk diffusion method and combined disk assay for β-lactamase production. Resistant isolates were evaluated by PCR for molecular assessing. Results: In disk agar diffusion test, 128(64%) E. coli isolates resistant to ceftazidime (55.5%) and cefotaxime (64%) were selected and followed by combined disk (ceftazidime, cefotaxime, and clavulanic acid) assay. In combined disk assay, among 128 screened isolates, 115 (89.8%) and 13 (10.2%) isolates were detected as ESBLs and AmpC producers, respectively. PCR performed on all 128 selected isolates via phenotypic tests and the results showed that among 115 and 13 isolates, 7 (6.1%) and 13(100%) cases contained blaSHV and blaCITM, respectively. Fox gene was not detected in any sample. Conclusions: Our findings indicate that the prevalence of ESBLs in Tehran is rising. According to CLSI, isolates showing negative confirmatory test are potentially considered as producers of AmpC (the result of CITM PCR was 100% positive). On the other hand, co-production of ESBLs and AmpC may lead to ESBLs false negative. Thus, development of diagnosis methods for complete detection of β-lactamase enzymes is important for resistance control and the treatment with high achievement.

Prevalence of AmpC β-lactamase in Clinical Isolates of Escherichia coli, Klebsiella spp., and Proteus mirabilis in a Tertiary Hospital in Tehran, Iran

“…A study conducted in northern Iran reported a rate of 7.7% based on phenotypic methods (16). In another study in Tehran, 10.2% of E. coli isolates were AmpC-positive according to the PCR method (17). The lower prevalence compared to our results could be due to differences in PCR assay design, as the abovementioned studies did not apply primers for detecting DHA and MOX genes in the assay protocol (17).…”

“…This needs special attention because it may indicate the spread of PMABL-producing strains in the community, as some other studies have suggested (2,8). The prevalence of ESBLproducing isolates was 49% in our study, which is a little lower than the rates of 57% and 52% previously reported in Iran (16,17).…”

“…and E. coli isolates (46.7% and 38%, respectively). In another report, all E. coli isolates were positive for the CIT family (17) and no FOX was detected. Fam et al (10) and Manoharan et al (4) found that the CIT and CIT-FOX genes were more frequent.…”

“…In another study in Tehran, 10.2% of E. coli isolates were AmpC-positive according to the PCR method (17). The lower prevalence compared to our results could be due to differences in PCR assay design, as the abovementioned studies did not apply primers for detecting DHA and MOX genes in the assay protocol (17). Peter-Getzlaff et al (6) reported that 21/51 (41%) of E. coli isolates in their study were AmpC producers, among which 9 (19.6%) carried plasmid-mediated genes (6).…”

Identification of Extended-Spectrum β-Lactamase Genes and AmpC-β-Lactamase in Clinical Isolates of Escherichia coli Recovered from Patients with Urinary Tract Infections in Kerman, Iran

“…The rate of resistance to imipenem was very low; this is similar to the results of others studies conducted in Iran and worldwide. Thus, imipenem is still the most active agent against ESBL and AmpC-β-lactamase-producing E. coli isolates (2,(26)(27)(28). However, in the present study, two isolates were found to be resistant to imipenem; thus, resistance to this antibiotic may increase in the future (2,29).…”