The Emergence of Colistin- and Imipenem-Associated Multidrug Resistance in Escherichia coli Isolates from Retail Meat

Abstract

To determine the prevalence of Escherichia coli and their drug resistance profiles in fresh pork sold at two retail outlets (open-air market and closed retail stores) in Alice, South Africa. Retail meat samples (n = 176) collected from four shops (two from open-air markets and two from closed stores) were analyzed by conventional biochemical and PCR-based molecular confirmatory tests. The confirmed isolates were profiled for antimicrobial susceptibility to a panel of 12 commercial antibiotics: tetracycline, ampicillin, sulphamethoxazole trimethoprim, erythromycin, gentamycin, colistin sulphate, cefotaxime, chloramphenicol, norfloxacin, ciprofloxacin, cefuroxime, and imipenem. Colistin, ampicillin, and erythromycin resistance genes were profiled with the gene-specific primers. Multidrug resistance (MDR) and the association of imipenem and colistin in the MDR profile were determined. A total of 68 (39.08%) E. coli isolates were confirmed by PCR analysis. Resistance was most common to erythromycin (100%), followed by cefotaxime (95.58%), ampicillin (88.23%), cefuroxime (88.23%), trimethoprim-sulphamethoxazole (88.23%), and tetracycline (60.29%). Overall, 27/68 (39.70%) were MDR (≥ 3antibiotics classes). MDR E. coli isolates associated with imipenem resistance (50.00%) and colistin resistance (33.82%) were detected. The resistance genes were detected among the isolates though not in all the phenotypically resistant isolates. The detection of colistin resistance among MDR E. coli isolates from retail meat is troubling as the drug is a last resort antibiotic. Overall, the epidemiological implications of the findings are of public health importance.

Keywords: Escherichia coli; colistin resistance; imipenem resistance; multiple antibiotic resistance; pork; retail outlet; susceptibility.

Fig. 1

Agarose gel electrophoresis for Escherichia coli identification. Line M – 100 bp ladder, Line 1 – negative control, Line 2 – E. coli ATCC® 25922™ as a positive control, Lines 3–12 – the 147 bp PCR amplification product for E. coli isolates.

Fig. 2

The sensitivity pattern of Escherichia coli isolates against antibiotics. AMP – ampicillin, CO10 – colistin sulphate, TS – trimethoprim-sulphamethoxazole, CXM – cefuroxime, E – erythromycin, C30 – chloramphenicol, IMI – imipenem, GM – gentamycin, T– tetracycline, NOR – norfloxacin, CTX – cefotaxime, CIP – ciprofloxacin, S – susceptible, R – resistant, I – intermediate

Fig. 3

Electrophoresis of mrc-1 gene amplification among Escherichia coli isolates. Line 1 – 100 bp ladder, Line 2 – negative control, Line 3–13 – positive isolates

Fig. 4

Electrophoresis of the ermB gene amplification product (350 bp) in Escherichia coli isolates. Line 1 – 100 bp DNA ladder, Line 2 – negative control, Lines 3–12 – the ermB-resistant E. coli isolates

Fig. 5

Gel electrophoresis of the PCR product (690 bp) amplified with blaTEM primers for the detection of β-lactam-resistant Escherichia coli isolates. Line 1 – DNA ladder, Line 2 – negative control, Lines 3–9 – β-lactam-resistant E. coli isolates