Antimicrobial Susceptibility of Fish Streptococcus Isolated in 2012

TM Huang*, SH Cheng, C Tu

Animal Health Research Institute, Council of Agriculture, Executive Yuan

Abstract

Streptococcosis is an important fish disease resulting in high mortality rates and economical losses. Administration of antimicrobials is widely used to control fish streptococcosis. The objective of the present study was to investigate antimicrobial susceptibility of Streptococcus isolated from diseased fish to commonly used antimicrobial agents. Streptococcus isolated from diseased fish was collected and identified by traditional biochemical characterization and molecular biology methods. Antimicrobial susceptibility was analyzed by disc diffusion method (Kirby-Bauer) and minimum inhibitory concentration (MIC). In total, 51 isolates of streptococcus were collected. Among them, 36 isolates were Streptococcus agalactiae, 11 isolates were S. iniae, and 4 isolates were S. dysgalactiae. According to geographical distribution, 29 Streptococcus isolates were from Chiayi county, 13 isolates were from Tainan city, 5 isolates were from Kaohsiung city and 4 isolates from Yunlin county. All three species of Streptococcus isolates were susceptible to the commonly used antimicrobials, except one isolate of S. agalactiae. This isolate was from Chelon macrolepis in Chiayi county, and possessed resistance to clindamycin and lincomycin. Detection of resistance determinants of clindamycin and lincomycin by polymerase chain reaction showed no ermA, ermB, ermC, or ermTR, while mefA/E genes were found in the clindamycin and lincomycin resistant S. agalactiae isolates. The results of this study indicate that the fish streptococcus isolates are susceptible to the approved antimicrobials for aquaculture use.

Keyword: fish streptococcosis, antimicrobial agent, susceptibility.