Detailed analysis of Streptococcus agalactiae isolated from environmental samples and fish specimens during a massive fish kill in Kuwait Bay

Abstract

This study was undertaken to identify and characterize bacterial isolates obtained simultaneously from
dead fish samples during a massive fish kill in Kuwait Bay and sewage water samples running into
Kuwait Bay, using conventional and molecular techniques. Of the 71 bacterial isolates studied, 66
isolates were recovered from seven different fish species and five isolates were isolated from sewage
samples. The species-specific identity of the isolates was established by phenotypic characteristics
and by PCR amplification of the 16S rRNA gene, using Streptococcus agalactiae-specific primers. The
genotyping of 12 isolates from fish samples and all five isolates from sewage samples was performed
by random amplification of polymorphic DNA (RAPD) analyses. Culture methods identified 44 of 66
(67%) and 4 of 5 (80%) isolates obtained from fish and sewage samples, respectively, as S. agalactiae.
The PCR amplification of 16S rRNA not only confirmed the results of conventional methods, but also
resulted in additional identification of 14 of 66 (21%) isolates obtained from fish samples and the
remaining isolate recovered from sewage sample as S. agalactiae. A total of nine RAPD patterns were
observed among the 17 isolates studied and the RAPD patterns could be grouped into three clusters.
Interestingly, four of the isolates recovered from sewage samples produced nearly identical RAPD
banding patterns (85 - 100% similarity) with some of the S. agalactiae strains isolated from Mullet
kidney and brain specimens, indicating the possibility of sewage being the source of infection.