| The animal production industry is an important component of food production and has experienced rapid growth in the last few years. The economies of scale have led to the intensification of livestock production in developed countries, where a large number of animals are raised in a small area. Antibiotic use in veterinary medicine has become indispensable to the growth of the animal food industry because of the close proximity of a large numbers of animals at these facilities, which increases the potential for spreading diseases. Antibiotics are used in livestock to treat sick animals, to prevent infections, and to . improve feed utilisation. However, antibiotic resistance has been raised as a major concern associated with the widespread use of antibiotics in medicine and veterinary practice and as growth promoters in animal husbandry. Attention has been drawn to the possible role of bacteria used as meat starter cultures to serve as reservoirs for antibiotic resistance genes and the possibility they may transfer these genes to zoonotic pathogens. Coagulase-negative staphylococci (CNS) and lactic acid bacteria (LAB) are the main microorganisms used as starter cultures in meat fermentations. This study examined whether bacterial starter cultures could serve as reservoirs of antibiotic resistance transmissible to zoonotic bacteria by making both phenotypic and genotypic assessments. Thirty of the most common bacterial starter cultures used in food and feed were screened for their resistance to several antimicrobial drugs registered in Canada for veterinary use. Antibiotic susceptibility tests were performed by broth microdilution using Iso-Sensitest broth (90% v/v) and deMan-Rogosa-Sharpe broth (10% v/v), while polymerase chain reaction (PCR) was used to investigate the presence of genetic determinants of antibiotic resistance. The results showed that all 30 isolates exhibited resistance to at least 3 antimicrobials regardless of antimicrobial class while 17% or 30% of strains were resistant to antibiotics in 3 or 6 different classes, respectively. Among the strains tested, the highest incidence of resistance noted was to carbadox (100%), sulfamethazine (83%), monensin (83%), chlortetracycline (80%), and vancomycin (80%). The incidence of antimicrobial resistance was higher among Pediococcus pentosaceus and lower for Staphylococcus carnosus strains, suggesting that the latter might be safer than the former when used as starter cultures, from an industrial point of view. Genetic determinants for the lincosamide, macrolide, and tetracycline antimicrobials were not found using PCR. However, the absence of genetic determinants did not invalidate the phenotypic results since the resistance observed may have been encoded by a gene not included in the tests or occurred by a mechanism related to structural/physical features of resistant cells. Expanding the number of genes which were screened in the genotypic tests would increase the degree of certainty that a genetic element was or was not involved in encoding resistance. |
