Tetracycline resistance in Lactobacilli isolated from digestive system of Iranian backyard chickens

Identifying the strains carrying acquired tetracycline resistance genes is one of the important points in evaluating the safety of probiotic strains. The aim of the present study is to comprehensively evaluate tetracycline resistance in lactobacillus spp. isolated from the digestive system of Iranian backyard chickens.

In the present study, the phenotypic sensitivity patterns of 36 lactobacillus isolates belonging to four species L. reuteri, L. salivarius, L. crispatus and L. johnsonii were evaluated by measuring the Minimum Inhibitory Concentration (MIC) to tetracycline. After that, four tetracycline resistance genes tet(L), tet(M), tet(W) and tet(O) were detected in isolates with phenotypic resistance to this antibiotic based on the polymerase chain reaction method.

As a result, four isolates of L. reuteri, three isolates of L.salivarius, two isolates of L. crispatus and four isolates of L. johnsonii among the studied lactobacillus spp. showed phenotypic resistance to tetracycline. After the detection of tetracycline resistance genes in isolates with phenotypic resistance, the presence of tet(W) gene was confirmed in all investigated isolates. The simultaneous presence of tet(M), tet(L) and tet(W) genes was observed in three studied L. salivarius isolates. It was also found that the phenotypic resistance observed in three isolates of L. johnsoniiABRIG7, L. johnsoniiABRIG14 and L. johnsoniiABRIG24 is caused by the simultaneous presence of tet(O) and tet(W) genes.

This study showed that tetracycline resistance among Lactobacilli isolated from digestive system of Iranian backyard Chickens is due to the presence of single or multiple resistance genes.. We also found that tet(W) is the most widespread tetracycline resistance gene among investigated Lactobacillus isolates. Therefore, local poultry breeders should refrain from arbitrarily using tetracycline, and when the digestive system of domestic chickens is the source for probiotic microorganism selection, the evaluation of resistance to tetracycline from the phenotypic and molecular point of view should be taken into consideration in order to select safe strains.