Extended-Spectrum Beta-Lactamases in Escherichia Coli Carrying an IncF Plasmid

The increasing frequency of extended spectrum beta lactamases (ESBL)-producing E. coli from clinical specimens is causing treatment failure and is of great concern. Association of IncF plasmid with ESBL-producing E. coli had been reported in clinical isolates; however IncF plasmid from environmental samples is not well studied. The objectives of this research were (1) to evaluate antibiograms of environmental Escherichia coli carrying resistance plasmids (R-plasmids) belonging to IncF groups (IncFIA, IncFIB, and/or IncFII) and (2) to determine the prevalence of ESBL-producing E. coli from these samples. We examined 28 E. coli isolates from Orange County for reduced susceptibility or resistance to 12 antibiotics. Plasmids of these wildtype E. coli were purified and transformed into competent cells of E. coli DH10B. Transformants with resistance-plasmids were then acquired from the 28 E. coli isolates using selective media containing ampicillin (AMP), gentamicin (GEN), tetracycline (TET), chloramphenicol (CHL), or sulfamethoxazole (SMX). We obtained 40 transformants, which were carrying resistance plasmids from the wildtypes. Of the 40 transformants, 28 transformants carried a unique IncF plasmid were further analyzed. Antibiograms of both wildtypes and transformants were determined by disk diffusion assays using Clinical Laboratory Standards Institute standards with the following antibiotics: AMP, GEN, TET, CHL, kanamycin (KAN), cefotaxime (CTX), ceftazidime (CAZ), ciprofloxacin (CIP), sulfisoxazole (SXZ), trimethoprim (TMP), CTX with clavulanic acid (CLA), and CAZ with CLA. An increase in the zone diameter of ≥5 mm from CTX and CAZ disks, each alone and in combination with CLA, was used to screen an ESBL-producing E. coli. Of the 28 wildtype isolates tested for resistance to antibiotics, 24 (85.7%) were resistant to AMP and 13 (46%) and 6 (21%) to third generation cephalosporins, CTX and CAZ, respectively. These isolates were also resistant to other antibiotics. Overall, 85.7% of the wildtypes were multidrug-resistant, which were resistant to more than 3 antibiotics. Transformants (n=28) carrying unique IncF groups were found to have resistance to AMP (79%), CTX (36%), and CAZ (18%). Resistance to CTX and CAZ was inhibited by clavulanic acid in 98% and 100% in CTX and CAZ-resistant strains indicating a positive result of ESBLs for both wild types and transformnants. Transformants carrying the IncF plasmid group arising from environmental E. coli were also resistant to other tested antibiotics except CIP. In this experiment, we discovered that environmental E. coli carrying plasmids of IncF group confer multidrug resistance and extended-spectrum beta-lactamases which represent a significant health risk of environmental bacteria.