Presence of insertion sequences (IS elements) in group B streptococci of bovine origin

Abstract

Background & objectives: Streptococcus agalactiae (group B streptococci, GBS) is one of the leading causative agents of human and animal infections. Recently it was demonstrated that integration of different IS elements could inactivate some of the GBS virulence properties. The presence of IS elements in human isolates has been studied while the bovine isolates were not investigated till now. The objective of the study was to perform IS analysis of a large number of bovine GBS and to use the IS elements for classification and molecular epidemiology of GBS strains.

Methods: A total of 101 GBS isolates obtained from the dairy cows were tested. These were analyzed by PCR and multiplex PCR. Southern hybridization was accomplished with the Enzo(TM) DNA Labeling and Detection Kit. The computer techniques were used for selection of the specific primers and for analysis of the sizes of PCR products.

Results: GBS isolates collected at three different dairy farms were studied for the presence of IS elements. Multiplex PCR was used for the fast screening. It was found that IS861 presented in 29 GBS isolates (28.7%), IS1548 in 9 (8.9%), ISSa4 in 48 (47.5%) and IS1381 in 26 isolates (25.7%). A total of 28 bovine GBS isolates (27.7%) did not possess any of the IS elements, 36 (35.6%) possessed, 35 (34.7%) possessed two and 2 (1.9%) possessed three different IS elements. The GBS with four different IS elements were not found. Taken together, 10 different variants of GBS strains were discovered. Two out of 10 variants being specific for 51 isolates (50.5%) were predominant in bovine GBS. The results of the study demonstrated that the presence of IS elements significantly varied in bovine GBS.

Interpretation & conclusion: The present data demonstrated that variants of IS elements present in GBS genome could be used as effective criteria for molecular epidemiology. In future this approach could probably be used as an additional tool for the epidemiological control and prevention of other bacterial infections.