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Wide-spread antibiotic resistance among bacterial pathogens is now a serious public health issue and multi-antibiotic resistance has been reported in many foodborne pathogens including Salmonella and E. coli. A study to determine antibiotic resistance profiles of a range of Salmonella and Verocytotoxigenic E.coli (VTEC) isolated from Irish foods revealed significant levels of antibiotic resistance in the strains. S. typhimurium DT104 were multiantibiotic resistant with 97% resistant to 7 antibiotics. S. Dublin and S. Agona showed lower levels of antibiotic resistance. Antibiotic resistance among VTEC isolates was generally low but two isolates of E. coli O157:H7 from minced beef were shown to be multi-antibiotic resistant (8 to 10 antibiotics). Studies to determine the relationship between antibiotic resistance and tolerance to heat were conducted. The survival of Salmonella spp. with different antibiotic profiles (antibiotic sensitive, laboratory-developed antibiotic resistant mutants or multi-antibiotic resistant) on chicken heated to 55ºC with or without a prior heat shock at 48ºC was established. The D value (time in minutes to achieve a 90% or 1 log reduction in the Salmonella population) recorded for a multi-antibiotic resistant S. Typhimurium DT104 was significantly higher (P<0.05) than for all other strains tested (antibiotic sensitive or with laboratory-acquired antibiotic resistance). These results suggest that the presence of multi-antibiotic resistance genes increased the heat tolerance of Salmonella. The survival of VTEC, E. coli O157:H7 and E. coli O26 (antibiotic sensitive, laboratory-developed antibiotic resistant mutants or multi-antibiotic resistant) in minced beef heated to 55ºC with or without a prior heat shock at 48ºC was established. The D value recorded for multi-antibiotic resistant E. coli O157:H7 was significantly lower than for the other strains tested. These results indicate that the presence of multi-antibiotic resistant genes rendered the pathogens more sensitive to heat. Studies to determine whether antibiotic resistance could be transferred within species (Salmonella Typhimurium to Salmonella Agona) and between species (Salmonella to E. coli) when co-inoculated into laboratory media, milk or minced beef at different storage temperatures (37, 25, 15 and 4ºC) showed that horizontal antibiotic resistance gene transfer occurred in all substrates at temperatures of 37 and 25ºC. At 15ºC, transfer of resistance occurred only in minced meat. Similar results were reported for transfer of antibiotic resistance both within the Salmonella spp. and between different species (Salmonella to E. coli).
Walsh, C., Duffy, G. (2013) Antibiotic resistance in foodborne pathogens. Teagasc Final Report Project RMIS No. 5036.