Purpose: Determine the antimicrobial resistance and the biofilm forming ability of most prevalent poultry-associated Salmonella serotypes (MPPSTs) isolated specifically from US poultry.
Methods: A total 145 MPPSTs isolated from US poultry including Salmonella Kentucky (57), Enteritidis (41), Typhimurium (14), Heidelberg (13), Mbandaka (10), Seftenberg (4) and three strains each of Montevideo and Infantis were tested for their ability to form biofilms and susceptibility to 15 antibiotics belonging to penicillin, quinolone, cephalosporin, aminoglycoside, sulfonamide and tetracycline classes. Additionally, one strain of each MPPST was tested for its resistance to chlorine (commonly used carcass sanitizer) using a new custom designed laboratory model that uses chicken meat extract (CME) medium and simulates carcass chilling, an important pathogen control step in poultry meat processing.
Results: Overall, 133 out of 145 (92%) isolates were resistant to at least two classes of antimicrobials tested. A total of 81 out of 145 (56%) isolates formed biofilm on polypropylene surface. Irrespective of concentration of CME, the amount of free chlorine decreased from 50 ppm to 3 - 5 ppm in < 5 min. In general, as the CME concentration increased, the pH of the chlorinated water and the survival of different MPPST strains also increased. At lower CME concentrations (3%), serotypes Kentucky and Mbandaka survived until 5 min; serotypes Heidelberg survived until 30 min whereas Montevideo, Typhimurium, Infantis, Seftenberg and Enteritidis survived until 90 min post-inoculation.
Significance: Multi-drug resistance among MPPST is common. Several Salmonella strains produce biofilms which could further enhance resistance to antimicrobials and also to carcass sanitizers and disinfectants during meat processing. MPPSTs also differ in their susceptibility to chlorine and that the level of CME in immersion chilling is an important contributing factor in Salmonella survival.