Identification of Pathogenic Bacteria in Frozen Mackerel Fish from a Humid Tropical Region

Abstract

Aquaculture products can harbour pathogenic bacteria, which are part of the natural micro-flora of the 
environment. An in-vitro assay was carried out to ascertain and identify major bacterial contaminants of 
frozen fish, which hitherto had constituted an important dietary intake of the people of Nsukka, Nigeria. 
Fish samples collected were identified and bacterial load of the samples determined using agar plate 
method. Differentiations and characterizations of various isolates were based on biochemical reactions 
and gram-staining technique. Frozen mackerel fish (Scomber scombrus) was used for the study. In-vitro 
assay result revealed that the samples were predominantly contaminated by three bacteria species viz: 
Staphylococcus aureus, Escherichia coli and Lactobacillus plantarum. Incidences of the various 
isolates in the culture were found to be 60, 20 and 15%, respectively. The mean bacteria load of the 
isolates was 1.135 x 106 CFU g-1 . This value was found to be markedly higher than the recommended 
public health and safety standard value of between 5.0 x 105 CFU g-1 , approved by Nigerian National 
Agency for Drug Administration and Control (NAFDAC).