lncidence of enterotoxigenic Staphylococcus aureus in relation to the microbial safety of seafood

A detailed study was made on the microbial quality, with special reference to food safety, of the fish and fishery products in the retail trade in Cochin and around. Also, farmed molluscan shellfishes like mussels and oysters were investigated for the microbial quality including the presence of pathogenic bacteria. Special stress has been given to monitor the incidence of coagulase positive as well as coagulase negative Staphylococcus in these products and their relative incidence have been recorded.In the next part, the investigation was centered mainly on toxigenic S.aureus. This is because among the Gram positive toxigenic bacteria, the Saureus with potential to produce thermostable enterotoxins are more relavent in food safety conceming seafoods in comparison with the Gram-negative pathogens like Salmonella and V.cholerae.The incidence, toxigenic potential and conditions of toxin production by S.aureus have been investigated in detail. An attempt has also been made to relate the toxigenisis with the presence of the concerned toxigenic genes in the genomes of S. aureus strains.

Characterization and virulence potential of phenotypically diverse Aeromonas veronii isolates recovered from moribund freshwater ornamental fishes of Kerala, India

In the present study, we investigated the involvement of Aeromonas spp. in eliciting disease outbreaks in freshwater ornamental fishes across the state of Kerala, India. We investigated three incidences of disease, in which the moribund fishes exhibited clinical signs such as haemorrhagic septicemia (in gouramy, Trichogaster sp.), dropsy (in Oscar, Astronotus ocellatus) and tail rot/fin rot (in gold fish, Carassius carassius). Pure cultures (n = 20 from each fish; 60 in total) of Aeromonas spp. were recovered from the abdominal fluid as well as from internal organs of affected fishes, although they could not be identified to species level because of the variations in their phenotypic characters. The molecular fingerprinting of the isolates using Enterobacterial Repetitive Intergenic Consensus PCR proved the genetic diversity of the isolates from the three sites. The phylogenetic trees constructed using concatenated sequences (using 16S rRNA, gyrA, gyrB and rpoD genes) indicated that they were related to Aeromonas veronii. They exhibited marked cytotoxic and haemolytic activity, which were responsible for the pathogenic potential of the isolates. The isolates possessed multiple virulence genes such as enterotoxins (act and alt), haemolytic toxins (aerA and hlyA), genes involved in type III secretion system (ascV, aexT and ascF–ascG), glycerophospholipid-cholesterol acyltransferase (gcat) and a type IV pilus (tapA) gene, as determined by PCR. Virulence of representative isolates to goldfish was also tested, and we found LD50 values of 104.07–105.35 cfu/fish. Furthermore, the organisms could be recovered as pure cultures from the lesions as well as from the internal organs.