Isolation of Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus from nature: Technological characterisation and antibiotic resistance

Yoghurt fermenting bacteria were isolated from natural sources including plants, dew, and rain samples (total of 300 samples) by the same methods nomadic peoples used for several centuries in Turkey. Inoculation into the reconstituted skim milk followed by planting on specific media and matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry (MALDI-TOF MS) analysis allowed for the identification of 18 Lactobacillus delbrueckii subsp. and 26 Streptococcus thermophilus. A multiplex polymerase chain reaction (PCR) assay applied to lactobacilli enabled the identification of 5 isolates as L. delbrueckii subsp. bulgaricus. The isolates showed a varying range of acidification rates and proteolytic activity in reconstituted skimmed milk (RSM). S. thermophilus isolates showed a broader range of resistance and the most frequent resistance was observed for streptomycin (69.2%), gentamycin (65.3%), clindamycin (61.5%), ampicillin (61.5%), kanamycin (53.8%), and erythromycin (50%). For L. delbrueckii subsp. the highest resistance was determined for vancomycin (38.8%), ciprofloxacin (33.3%), and penicillin (27.8%). The frequency of multiple resistance was tested on 14 different antimicrobials determining that 19 S. thermophilus (73%) and 3 L. delbrueckii subsp. (16.7%) demonstrated resistance to more than three different antibiotics. In contrast to this wide-ranging resistance, five isolates from each genus were found to be susceptible to all tested antibiotics. The present study indicates that lactic acid bacteria (LAB) isolated from nature may have broad-range of resistance to antibiotics and could be a source for the transfer of resistance.