Antimicrobial Resistance of Escherichia Coli and Salmonella in Pigs, Greater Accra Region, Ghana

Abstract

Background Food-borne pathogens associated with animal products pose significant threat to individual and population health globally. They cause serious infections in humans which can lead to treatment failures if they develop resistance. Escherichia coli (E. coli) is a commensal bacterium of the human and animal gut but has the ability to cause illnesses. Salmonella is one of the major foodborne pathogens worldwide. The presence of Salmonella and E. coli in food animals at slaughter and the consequent cross-contamination of edible carcass tissues present a significant food safety hazard. In this study, fecal and mesenteric lymph node (MLN) carriage of E. coli and Salmonella, their antimicrobial susceptibility profiles and serogroups of Salmonella among healthy pigs at slaughterhouses were investigated. Methods Fecal and MLN samples were collected from one-hundred and forty (140) pigs from three (3) selected slaughterhouses in the Greater Accra Region. Approximately, 5g of feces and 5g of MLN were aseptically removed from the rectum and mesentery respectively at slaughter line. Fecal and MLN were pre-enriched in a non-selective medium; buffered peptone water (BPW). For E. coli isolates, a loop of the aliquots BPW was cultured on MacConkey agar and incubated at 44o C overnight. For Salmonella isolates, a loop full of the pre-enriched aliquots were transferred into a selective enrichment medium; Tetrathionate broth and incubated at 37o C for 24 hours. Enriched aliquots were cultured on xylose lysine deoxycholate (XLD). Based on their colony morphologies, presumptive E. coli and Salmonella isolates were subjected to biochemical testing for identification. The susceptibility of the pure isolates was tested against ten (10) antibiotics using the Kirby-Bauer disk diffusion method. Salmonella serogrouping was done by slide agglutination testing. Slaughterhouse hygiene and slaughter practices were also observed and recorded. Summary descriptive statistics were performed to characterized antimicrobial susceptibility profiles. Results Of the 280 samples collected, 67.50% (189/280) were E. coli positive and 7.86% (22/280) Salmonella positive. Fecal and MLN E. coli carriage was 72.14% (101/140); and MLN E. coli 62.86% (88/140). Similarly, fecal Salmonella carriage was 2.14% (3/140); and MLN Salmonella carriage 13.57% (19/140). Antimicrobial susceptibility testing indicated that E. coli isolates (fecal and MLN) expressed the most resistance to tetracycline (56.1%), ampicillin (39.2%) and trimethoprim/sulphamethoxazole (35.4%). Salmonella isolates showed resistance mainly to ampicillin (31.8%) only. Multi-drug resistance (MDR) was detected in 30.16% of E. coli isolates, however, there was no MDR among the Salmonella isolates tested. The most frequent MDR profile for both fecal and MLN E. coli isolates was to tetracycline, ampicillin and trimethoprim/sulphamethoxazole. Resistance of a single isolate expressed to eight (8) was seen in feces; and seven (7) antibiotics was seen in MLN. All Salmonella serogroups identified consisted of non-typhoidal Salmonella. Structure design, waste management and hygiene practices were sub-standard per the Ghana Food and Drugs Authority code of practice for slaughterhouses. Conclusions Fecal and MLN carriage of E. coli a and Salmonella are high among pigs in Greater Accra Region. High levels of MDR of E. coli detected pose a great public health concern as these resistant strains have the potential of transferring their resistant genes to pathogenic organisms leading to increased rates of treatment failures. Misuse of antibiotics, inappropriate structure designs, poor hygiene and slaughter practices may have contributed to MDR. This calls for stricter regulation and monitoring of the use of antibiotics in livestock production and hygiene practices at slaughterhouses.