Identification and characterization of gut lactobacilli of ducks by microbiological and molecular techniques

The study was aimed at isolation and identification of Lactic Acid Bacteria from the gastrointestinal tracts of ducklings reared under intensive farming conditions. Mucosal scrapings from Crops, proventriculi, gizzards and intestines were used for cultivation of Lactobacilli in Rogasa and de Man Rogosa and Sharpe agar plates. The distribution of isolates was highest in crops and intestines (36.66% each) but proventriculi and the gizzards accounted for only 13.33% each of the isolates. Based on the API 20A index (Bio Mérieux, France), isolates were classified as Lactobacillus acidophilus, Lactobacillus salivarius, Lactobacillus johnsonii and Lactobacillus fermentum. Thirty isolates were confirmed as Lactobacillus by genus specific polymerase chain reaction presenting highly specific amplicon of 230 bp in length. All the isolates demonstrated auto-aggregation between 20 and 120 minutes and the highest co-aggregation activity against E. coli and S. typhimurium was obtained with L. salivarius (60% in 20 minutes) which also survived at pH 1.0 for 1 hr. High acid tolerance and the marked inhibitory action of L. salivarius against intestinal pathogens needs further investigation for its use as a probiotic for ducks. The isolates were sensitive to benzyl penicillin (87.75%), cephataxim (86.75%), ampicillin (84.75%), erythromycin (84.50%), nitrofurantoin (83.75%), gentamicin (82.50%) and tetracycline (79.50%) but exhibited resistance towards fusidic acid (82.50%), trimethoprim (73.25%), vancomycin (59.50%), ciprofloxacin (45.25%) and cephalexin (40.00%). SDS PAGE analysis revealed protein bands of 69, 65, 60, 55, 50, 48 and 45 KDa in all the four isolates. Whole cell protein profile of L. johnsonii revealed bands ranging from 150 to 15 kDa and can therefore be used as a reference strain for characterization of Lactobacillus isolates in the laboratories.