Serotype distribution, virulence and antibiotic resistance of Streptococcus agalactiae isolated from cultured tilapia Oreochromis niloticus in Lake Volta, Ghana.

Streptococcus agalactiae infection is one of the major factors limiting the expansion of tilapia farming globally. In this study, we investigated the serotype distribution, virulence and antimicrobial resistance of S. agalactiae isolates from tilapia farmed in Lake Volta, Ghana. Isolates from 300 moribund fish were characterised by Gram staining, MALDI-TOF/MS and 16S rRNA sequencing. Serotype identification was based on multiplex polymerase chain reaction (PCR) amplification of the capsular polysaccharide genes. Detection of virulence genes (cfb, fbsA and cspA) and histopathology were used to infer the pathogenicity of the isolates. The susceptibility of isolates to antibiotics was tested using the Kirby-Bauer disk diffusion assay. All 32 isolates identified as S. agalactiae were of serotype Ia. This was notably different from isolates previously collected from the farms in 2017, which belonged to serotype Ib, suggesting a possible serotype replacement. The prevalence of the pathogen was related to the scale of farm operation, with large-scale farms showing higher S. agalactiae positivity. Data from histopathological analysis and PCR amplification of targeted virulence genes confirmed the virulence potential and ability of the isolates to cause systemic infection in tilapia. Except for gentamicin, the majority of the isolates were less resistant to the tested antibiotics. All isolates were fully sensitive to oxytetracycline, erythromycin, florfenicol, enrofloxacin, ampicillin and amoxicillin. This study has improved our understanding of the specific S. agalactiae serotypes circulating in Lake Volta and demonstrates the need for continuous monitoring to guide the use of antimicrobials and vaccines against streptococcal infections in Ghanaian aquaculture systems.

Survival of Salmonella on basil plants and in pesto.

Leafy greens, including fresh herbs, have repeatedly been involved in outbreaks of foodborne disease. Although much effort has been put into studying leafy greens and products such as head lettuce and baby leaves, less is known about fresh leafy herbs, such as basil. The goal of this study was to investigate the survival of Salmonella on basil plants and in pesto. A mix of three Salmonella strains (Reading, Newport, and Typhimurium) was inoculated onto basil leaves and pesto and survived during the experimental period. Whereas the mix of Salmonella survived in pesto stored at 4°C for 4 days, Salmonella was recovered from inoculated leaves for up to 18 days at 20 to 22°C. Although the steady decline of Salmonella on leaves and in pesto suggests a lack of growth, it appears that pesto is a hostile environment for Salmonella because the rate of decline in pesto was faster (0.29 log CFU/g/day) than on leaves (0.11 log CFU/g/day). These findings suggest that the dilution of contaminated ingredients and the bactericidal effect of the pesto environment helped to further reduce the level of enteric organisms during storage, which may have applications for food safety.

Yersinia enterocolitica outbreak associated with ready-to-eat salad mix, Norway, 2011.

In 2011, an outbreak of illness caused by Yersinia enterocolitica O:9 in Norway was linked to ready-to-eat salad mix, an unusual vehicle for this pathogen. The outbreak illustrates the need to characterize isolates of this organism, and reinforces the need for international traceback mechanisms for fresh produce.

Outbreak of Yersinia enterocolitica serogroup O:9 infection and processed pork, Norway.

An outbreak involving 11 persons infected with Yersinia enterocolitica O:9 was investigated in Norway in February 2006. A case-control study and microbiologic investigation indicated a ready-to-eat pork product as the probable source. Appropriate control measures are needed to address consumer risk associated with this product.