Molecular typing, antibiogram type and detection of virulence genes of Stereptococcus iniae strains isolated from golden pompano (Tranchinotus ovatus) in Guangxi Province

To acquire the data of genotype and diversity upon the clinical dominant strains Streptococcus iniae of golden pompano (Tranchinotus ovatus) in Guangxi, a total of 17 bacterial isolates were analyzed by molecular typing, antibiogram type and virulence-related gene which were collected from diseased golden pompano in 7 farms located in Guangxi Province during 2015—2016. By using the random amplified polymorphic DNA (RAPD) and repetitive primer polymerase chain reaction (rep-PCR) method, we successfully differentiated all 17 isolates into two distinct genotypes. Seven virulence-related genes were detected by PCR using specific primer, and the results revealed that the virulence-related genotype of these strains was simA⁺scpI⁺pdi⁺sagA⁺cpsD⁺pgmA⁺cfi⁺. All isolates seemed to show a high virulence. In addition, the antibiotic resistance profiles of 17 strains were tested with 20 common antibiotics using Kirby-Bauer disc diffusion methodology. The antibiogram of the isolates belonging to genetype 1 in rep-PCR analysis was AZT, while the antibiograms of genetype 2 were SIZ/T/S/PEN/AZT/SPE/CAZ/PB, SIZ/T/S/PEN/AZT/SPE/CAZ/CR and SIZ/T/S/PEN/AZT/SPE/CAZ/PB/RIF, respectively. Our research revealed that the two genotypes display significant differences of two antibiogram types and the same genetype isolates have similar antibiogram types. Therefore, a correlation between the genotype and the antibiogram types of S. iniae isolates has been identified. This study provides theoretical foundation and technical support for epidemiological study, vaccine development and disease control of S. iniae in golden pompano.