Traditional Fermented Foods as Potential Reservoirs of Antibiotic-Resistant Lactic Acid Bacteria: A Phenotypic Assessment

Abstract

Fermented foods hold significant importance not only in human nutrition but also in maintaining microbial safety, in terms of their rich populations of lactic acid bacteria (LAB). However, their patterns of antibiotic resistance must be rigorously assessed, particularly in light of potential implications for public health. The aim of this study is to characterize the antibiotic susceptibility profiles of LAB strains isolated from kefir, boza, traditional cheese, yogurt, and sourdough samples, and to interpret the findings in terms of safety. A total of 104 LAB isolates were obtained using classical culture methods: kefir (n=16), boza (n=11), artisanal cheese (n=26), yogurt (n=37), and sourdough (n=14). Species-level identification was carried out using Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry (MALDI-TOF MS). Antibiotic susceptibility tests were performed using the Kirby–Bauer disk diffusion method. The test panel included antibiotics representing different groups: ampicillin for the β-lactam group, kanamycin for the aminoglycoside group, erythromycin for the macrolide/lincosamide group, vancomycin for the glycopeptide group, chloramphenicol for the phenicol group, and tetracycline for the tetracycline group. Overall, phenotypic resistance was most prevalent against glycopeptides (vancomycin, 68.3%) and aminoglycosides (kanamycin, 64.4%), whereas higher susceptibility was recorded for beta-lactams (ampicillin, 72.1% susceptible), chloramphenicol (76.0% susceptible), and tetracycline (74.0% susceptible). Of the isolates tested, 23.1% were susceptible to all antibiotics, while 22.1% showed resistance. High susceptibility was generally observed against ampicillin, chloramphenicol, erythromycin, and tetracycline, while resistance to vancomycin and kanamycin was mainly species-dependent. In conclusion, while the majority of isolates displayed a favorable susceptibility profile, the presence of resistance phenotypes highlights the need for molecular validation. Considering the possibility that resistance observed, particularly in the tetracycline and macrolide groups, may be transmitted via mobile genetic elements, genotypic validation analyses are vital. In conclusion, most of the LAB strains obtained from the fermented foods studied showed a safe antibiotic susceptibility profile. Regularly monitoring antibiotic resistance while preserving the microbial diversity inherent in traditional fermented foods is both a scientific obligation and a societal responsibility.