Purpose: The purpose of the study is to isolate DNase- and protease-producing bacteria as well as to show their effects on catfish spoilage.
Methods: Six catfish samples were obtained from an aquaculture facility at Delaware State University and from a local retail source for comparison of microbial populations. The catfish were stored for up to 3 weeks at 4°C among various intervals and samples were taken for microbiological analysis. The duplicate samples (20g) were stomached with a saline solution (180ml) and then plated on selective and rich media for analysis of DNase- and protease-producing bacteria and total aerobic plate counts, respectively. The triplicate plates were incubated for 3 days at 28 °C, and then colonies were enumerated for comparison of the population types. DNase- and protease-producing colonies were selected for genus confirmation by Polymerase Chain Reaction (PCR) using universal primers for Pseudomonas.
Results: The total aerobic microbial populations of the catfish obtained from the aquaculture facility took approximately 3 weeks to reach the stationary phase at log 10 CFU/g with limited DNase producing bacteria counts around log 0-1 CFU/g, but high amounts of protease producing bacteria at log 9.8 CFU/g. The catfish purchased from a local retail source took 15 days to reach the stationary phase at log 10 CFU/g with increasing numbers of protease at log 9.6 CFU/g and DNase producing bacteria at log 9.1 CFU/g. PCR confirmations showed that 40/62 DNase- and protease-producing colonies were positive for Pseudomonas species.
Significance: Results obtained in this study suggest that extracellular DNase- and protease -producing bacteria play a large role in catfish spoilage and support the need for further research on bacterial identification isolated from the catfish spoilage.