SOURCE:

Faculty: Biosences
Department: Applied Microbiology And Brewing

CONTRIBUTORS:

Uzokwe, C.M;
Ekwealor, I.A;

ABSTRACT:

Fishes are good sources of dietary protein and are reared in artificial ponds in most countries. Poor sanitary condition predisposes the fishes to infestation by pathogenic microorganisms. This study was aimed at isolating bacteria with pathogenic potentials from fish and fish pond waters in the three senatorial zones in Anambra State and assessing their health implications on fishes. A total of 720 African catfish (Clarias gariepinus) and 480 fish pond water samples were collected from different fish farms during the rainy and dry seasons in the three senatorial zones in Anambra State, Nigeria and were subjected to analysis. Questionnaires developed served as sources of information on the socio-demographic, physical and sanitary conditions of the farms, physiological health conditions of the fishes, as well as the management of the ponds. Physicochemical characteristics of the pond water samples which include temperature, pH, conductivity, turbidity, alkality, nitrite, phosphate, sulphate and biological oxygen demand were determined. Bacteria were isolated and identified based on their morphological and biochemical characteristics. The bacterial counts from the gills and livers of the fishes and water samples of the fish ponds, among the three senatorial zones and during dry and rainy seasons were recorded.
Susceptibility of the isolates to conventional antibiotics was carried out and five most resistant isolates were further characterized based on 16S rRNA sequencing. Pathogenicity tests of the resistant isolates were studied using 740 ten weeks old fishes and three months old adult albino mice. Blood profile (Hb, PCV, WBC, RBC, lymphocyte, monocyte, AST and ALT), histological status and weight of the experimental animals were determined before inoculation, one week and two weeks after inoculation, while the bacterial load and mortality rate were calculated at the end of the experiment. The infected fishes were treated with probiotic (Saccharomyces cerevisiae) and antibiotic (chloramphenicol), and the analysis of the blood profile, histological status, weight of the fishes and bacterial load of fish organs determined after treatment. Information from the questionnaires revealed that all the ponds were made of concrete, used commercial feeds for the fishes and sourced water from bore hole. Variations in the physicochemical characteristics of the pond water samples were observed, however, the results of the parameters studied were within the permissible limit for aquaculture with the exception of turbidity and nitrite. Bacteria isolated from the fish and fish pond water samples belonged to the genera Vibrio, Aeromonas, Pseudomonas, Lactobacillus, Staphylococcus, Microbacterium, Serratia, Proteus, Bacillus, Streptococcus, Citrobacter, Micrococcus, Enterococcus, Enterobacter, Paenalcaligenes, Lysinibacillus, Acinetobacter and Escherichia. The most occurring organisms in the fish and pond water were Bacillus sp. and Staphylococcus sp respectively. Analysis of the bacterial counts shows that there was significant difference between the gills and livers and the fish pond water samples among the three senatorial zones and during the dry and rainy seasons. The bacterial counts from the gills ranged from 1.3 × 103 – 7.9× 103cfu/g in dry season and 1.3× 103 – 9.6× 103cfu/g in rainy season, while the counts obtained in the liver during dry and rainy season ranged from 1.7× 102 – 7.0× 102cfu/g and 2.6 × 102 – 6.3× 102cfu/g respectively. The mean bacterial count of the pond waters ranged from 2.1±0.95 × 106 to 22.6± 0.81×106 cfu/ml during the dry season and 20.6±0.81 × 106 to 44.8±0.49 ×10 cfu/ml in the rainy season in Anambra North. In Anambra South, the range is from 13.3±0.29 ×106 to 22.6±0.81 ×106 cfu/ml and 19.2±1.04 ×106 to 44.8±0.49 ×106 cfu/ml during dry and rainy seasons respectively. For Anambra Central, the range was 10.3±0.42 ×106 to 15.0±1.0 ×106cfu/ml and 22.0±05 ×106 to 38.9±0.25 ×106cfu/ml during dry and rainy seasons respectively. Percentage susceptibility of the isolates to antibiotics was highest with chloramphenicol, vancomycin, ciprofloxacin and trimethoprim (94.4%), and least with erythromycin (72.2%). The five most resistant isolates were identified as Lysinibacillus sphaericus G39, Bacillus subtilis BB1, Serratia marcescens Db11, Pseudomonas aeruginosa PA01 and Paenalcaligenes suwonensis UN24. Pathogenicity study of the isolates showed that there was significant difference (p value < 0.05) in the bacterial load obtained from the fish tissues, during dry and rainy seasons and in the three senatorial zones. The isolates also showed varying differences in the blood profile, bacterial load and weight of the experimental animals. Histological changes such as distortion of the gill architecture, widening of liver sinusoids, and inflammation of the periportal cell were observed in the fish tissues while enlarged sinusoid, loss of stratum corneum, hyperkeratosis and minor erosion of the intestinal mucosa were found in mice tissues. The highest mortality (44.4%) was observed in fishes inoculated with Serratia marcescens Db11, while mortality rate of 66.7% was observed in mice inoculated with Pseudomonas aeruginosa PA01. Treatment of the infected fishes with probiotic and antibiotic showed varying differences in the blood profile, weight and bacterial load of the fish tissues. This study showed high bacterial contamination of the fish pond waters, which may have given rise to the high bacterial load observed in the internal organs of the fishes especially during the rainy seasons. It has also been shown that the use of probiotics may possibly reduce the infection caused by the resistant bacteria isolates from the pond waters and the internal organs of the fishes.