Identification of Novel Plasmid Replicons Harboring β-Lactamase Resistant Genes in Ampicillin-Resistant Uropathogenic Escherichia coli

Abstract

Misuse of β-lactam antibiotics in the treatment of urinary tract infections (UTI) may result in the prevalence of β-lactam resistant uropathogenic Escherichia coli (UPEC). This study was undertaken to study the prevalence of β-lactam resistant determinants in ninety-one uropathogenic Escherichia coli strains were isolated from patients with UTI. Twenty-four of the ninety-one isolates were resistant to multiple antibiotics. All twentyfour isolates were resistant to the β-lactam antibiotics such as penicillin and ampicillin and a majority (16/24, 67.0%) of the isolates had a minimum inhibitory concentration (MIC) of 256 μg/mL for both antibiotics. The oligonucleotide primers specific for blatem and blactx-m amplified the 851-bp and 550-bp regions of the genes from the template DNA of 100% and 75% of the isolates, respectively. PCR results also indicated that 75% of the isolates contained both genes. High MIC values (256 μg/mL) were observed in isolates simultaneously harboring both genes compared to isolates containing just one β-lactam resistance determinant. Twenty one of the 24 isolates contained plasmids measuring 2.5 to 16.0 kb and 12 of the 21 strains harbored mega plasmids (above 16.0 kb). PCR based replicon typing (PBRT) was used to screen the template DNA from 24 of these isolates for the presence of 15 major plasmid families. Oligonucleotide primers specific for the detection of I1 plasmid amplified the replicon in 17 of 21 (81.0%) of the isolates. Similarly, PCR protocols specific for the detection of B/O and FIA plasmids detected these plasmids in 46.0% and 75.0% of the isolates. The β-lactam resistance determinants were successfully transferred to Salmonella sp. by conjugation along with I1 and B/O plasmid families but the conjugation protocol failed to transfer the FIC plasmid. Pulsed field gel electrophoresis (PFGE) indicated 16 different XbaI digested macrorestriction profiles (mrps) among the 24 UPECs. Our results indicate that the use of β-lactams in clinical practice may select for UPECs resistant to these drugs.