Abstract
We report on inapparent infections in adult/commercial tilapia in major tilapia fish farms in Guangdong. A total of 146 suspected isolates were confirmed to be S. agalactiae using an API 20 Strep system and specific PCR amplification. All isolates were identified as serotype Ia using multiplex serotyping PCR. An MLST assay showed single alleles of adhP (10), atr (2), glcK (2), glnA (1), pheS (1), sdhA (3) and tkt (2), and this profile was designated ‘unique ST 7’. The analysis of virulence genes resulted in 10 clusters, of which dltr-bca-sodA-spb1-cfb-bac (62, 42.47%) was the predominant virulence gene profile. The PFGE analysis of S. agalactiae yielded 6 distinct PFGE types (A, B, C, D, F and G), of which Pattern C (103) was the predominant type, accounting for approximately 70.55% (103/146) of the total S. agalactiae strains. Therefore, unlike what has been found in juvenile tilapia, in which PFGE pattern D/F is the major prevalent pattern, we found that pattern C was the major prevalent pattern in inapparent infected adult/commercial tilapia in Guangdong, China. In conclusion, we close a gap in the current understanding of S. agalactiae epidemiology and propose that researchers should be alert for inapparent S. agalactiae infections in adult/commercial tilapia to prevent a potential threat to food safety.
Highlights
Streptococcus agalactiae (Lancefield group B; GBS) was first recognized as an important opportunistic agent of humans in the mid-twentieth century[1,2] since the first report in 19393
To close this gap in our knowledge of S. agalactiae epidemiology, 146 strains were isolated from adult/commercial tilapia that were obtained from major tilapia fish farms in Guangdong from August to December 2014
The continuous outbreaks of S. agalactiae infection in tilapia fish farms seriously threaten the safety of the tilapia industry and the health of occupational workers and consumers
Summary
Streptococcus agalactiae (Lancefield group B; GBS) was first recognized as an important opportunistic agent of humans in the mid-twentieth century[1,2] since the first report in 19393. Continuous outbreaks of streptococci infections by S. agalactiae have been reported in various fishes. Previous studies have reported the partial molecular epidemiological characteristics of this infective agent, most isolates have been obtained from acute infections in juvenile tilapia. It remains unclear whether inapparent infections exist in adult/commercial tilapia. To close this gap in our knowledge of S. agalactiae epidemiology, 146 strains were isolated from adult/commercial tilapia that were obtained from major tilapia fish farms in Guangdong from August to December 2014. The molecular epidemiological characteristics of these strains www.nature.com/scientificreports/
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