Identification of selected bacterial isolates obtained from fish farms in different regions of Uganda

Abstract

Aquaculture is a farming system where aquatic plants and animals are grown in a controlled environment, for example, by utilizing ponds. Fish farming refers to a subset of aquaculture and is faced with challenges like fish diseases caused by bacteria, yet it is a readily available source of proteins to people. The major aim of this study was to determine the species of bacterial isolates that were previously isolated from fish farms in different regions of Uganda. This was an experimental study to identify the bacteria to species level by use of VITEK 2. Distribution of the Gram negative genera by region, indicated that ten (33%) were from central, eight (26.6%) from east and six (20%) from west and north respectively. Among the (30) Gram-negative bacterial isolates, Enterobacter cloacae complex was the most common (23%) followed by Klebsiella pneumoniae subsp pneumoniae (17%) and Providencia stuartii (13%), then Acinetobacter pitti (10%); Acinetobacter lwoffi, Serratia marcesens and Moraxella osloensis (all at 7%) and lastly Leclercia adecarboxylata, Acinetobacter baumannii complex, Enterobacter asburiae and Moraxella non-liquifaciens (all at 3%). Most of the Gram-positive genera identified were from the western region thirteen (32.5%), followed by central twelve (30%), eastern region eight (20%) and lastly northern seven (17.5%). Majority (71%) of the (40) isolates were Bacillus spp (B. subtilis - 33%, B cereus - 10%, B licheniformis - 18% and B pumilis - 10%); followed by Staphylococcus spp at 20% (Staph aureus – 10%, Staph pseudintermedius -5% and Staph lentus 5%), then Enterococcus gallinarum (8%) and lastly Kocuria rhizophila (3%). The various bacteria that were identified are associated with the fish ecosystems, either as potential pathogens or as those with probiotic activity. Microbial identification by VITEK 2 depends on phenotypic characteristics and the cards (Vetcard) that were used were purposed for terrestrial animal pathogens, hence further analysis confirming the bacterial identity, such as by 16S gene sequencing; and evaluation of pathogenicity will establish their significance in fish health.