Susceptibility of meat starter cultures to antimicrobials used in food animals in Canada

Antibiotic Susceptibility Profiles of Pediococcus pentosaceus from Various Origins and Their Implications for the Safety Assessment of Strains with Food-Technology Applications

ABSTRACT

In the fight against the spread of antibiotic resistance, authorities usually require that strains "intentionally added into the food chain" be tested for their antibiotic susceptibility. This applies to strains used in starter or adjunct cultures for the production of fermented foods, such as many strains of Pediococcus pentosaceus. The European Food Safety Authority recommends testing strains for their antibiotic susceptibility based on both genomic and phenotypic approaches. Furthermore, it proposes a set of antibiotics to assess as well as a list of microbiological cutoffs (MCs), allowing classification of lactic acid bacteria as susceptible or resistant. Accurate MCs are essential not only to avoid false-negative strains, which may carry antibiotic resistance genes and remain unnoticed, but also to avoid false-positive strains, which may be discarded while screening potential candidates for food-technology applications. Because of relatively scarce data, MCs have been defined for the whole Pediococcus genus, although differences between species should be expected. In this study, we investigated the antibiotic susceptibility of 35 strains of P. pentosaceus isolated from various matrices in the past 70 yr. MICs were determined using a standard protocol, and MIC distributions were established. Phenotypic analyses were complemented with genome sequencing and by seeking known antibiotic resistance genes. The genomes of all the strains were free of known antibiotic resistance genes, but most displayed MICs above the currently defined MCs for chloramphenicol, and all showed excessive MICs for tetracycline. Based on the distributions, we calculated and proposed new MCs for chloramphenicol (16 instead of 4 mg/L) and tetracycline (256 instead of 8 mg/L).

HIGHLIGHTS

Residual antibiotics disrupt meat fermentation and increase risk of infection

Fermented sausages, although presumed safe for consumption, sometimes cause serious bacterial infections in humans that may be deadly. Not much is known about why and when this is the case. We tested the hypothesis that residual veterinary antibiotics in meat can disrupt the fermentation process, giving pathogenic bacteria a chance to survive and multiply. We found that six commercially available starter cultures were susceptible to commonly used antibiotics, namely, oxytetracycline, penicillin, and erythromycin. In meat, statutorily tolerable levels of oxytetracycline and erythromycin inhibited fermentation performance of three and five of the six starter cultures, respectively. In model sausages, the disruption of meat fermentation enhanced survival of the pathogens Escherichia coli O157:H7 and Salmonella enterica serovar Typhimurium compared to successful fermentations. Our work reveals an overlooked risk associated with the presence of veterinary drugs in meat.

Antibiotics have for a long time been used as growth promoters in farm animals, and while they are banned as such in Europe, their clinical use in farm animals still accounts for the majority of consumption. Here, we examined how acceptable levels of antibiotics in meat influence fermentation. Our results show that commonly used bacterial starter cultures are sensitive to residual antibiotics at or near statutorily tolerable levels, and as a result, processed sausages may indeed contain high levels of pathogens. Our findings provide a possible explanation for outbreaks and disease cases associated with consumption of fermented sausages and offer yet another argument for limiting the use of antimicrobials in farm animals.