Identification and antimicrobial susceptibility of lactic acid bacteria from fecal samples of indigenous and commercial pigs

Lactic acid bacteria (LAB) are currently applied as probiotics due to their benefit to pig performance. This study aimed to identify candidate LAB from pig feces and determine their antimicrobial susceptibility following an international standard recommendation. A total of 204 LAB isolates from 60 fecal samples of 30 antibiotic-free healthy fattening indigenous pigs and 30 antibiotic-free healthy fattening commercial pigs were initially screened for viability in acidic and bile conditions. Thirty-four of the isolates as acid-and bile-tolerant LAB were selected for identification and determination of antimicrobial susceptibility. They were characterized and identified by a set of 26 phenotypic tests, whole-cell protein patterns (SDS-PAGE analysis), and 16S rDNA sequencing analysis. They were identified as Enterococcus faecium (11 isolates), E. hirae (nine isolates), Lactobacillus agilis (three isolates), L. plantarum (four isolates), Pediococcus acidilactici (one isolate) and P. pentosaceus (six isolates). The identification by 16S rDNA sequence analysis was strongly consistent with the whole-cell protein profiles, but not with the biochemical profiles. LAB presenting multidrug resistance could be found in antibiotic-free pigs. Determination of minimum inhibitory concentration (MIC) values showed that among the 34 LAB isolates, only four (P. pentosaceus 77F, and L. plantarum 22F, 25F, 31F) from commercial pigs and one (P. acidilactici 72N) from an indigenous pig were susceptible to all eight antibiotics including ampicillin, chloramphenicol, gentamicin, kanamycin, erythromycin, tetracycline, streptomycin and vancomycin according to EFSA criteria. In conclusion, five LAB strains derived from healthy pigs displayed potential as porcine probiotics and will be screened in further clinical studies.