Microbiology and Spoilage Trail in Nile Perch (Lates niloticus), Lake ...

eservoir i.e. Salmonella, Shigella, E. coli, and Staphylococcus aureus, (Huss, Dalgaard and
Gram, 1997).
Generally fish and shellfish are common vehicles of transmitting food borne diseases. On
the other hand, pathogenic bacteria (indigenous bacteria) represent part of the natural flora
on particularly fish from coast and estuarine environment. According to Huss, Dalgaard and
Gram, (1997), the indigenous (pathogenic) bacteria include Vibrio spp., C. botulinum (Type
E), L. monocytogenes, Aeromonas spp., and Shewanella alga. However, the level of
contamination is normally quite low and it is unlikely that the numbers which are naturally
present in uncooked seafood are sufficient to cause disease in healthy human being. Hence
fish as food has far better record on safety than the mammalian meat.
It is known that the primary source of cholera is feces of infected persons and transmission
of bacteria with water and food. However, at present it has also been found that in certain
areas the aquatic environment is a natural reservoir (habitat) for Vibrio cholerae 01. This
means that seafood may be contaminated even if harvested in unpolluted waters, (Popovic
et al., (1993), Huss, Dalgaard and Gram, 1997). Aeromonas spp. that is pathogenic to both
fish and human can be present in aquatic environment, on fish or even in tap (drinking)
water (Gibson, 1992). The microbiologists have been taking the criteria to account that the
presence of Escherichia coli in food indicates the probability of contamination of the food
products with the sewage of human or animal origin. Consequently it has been referred as
an indicator for the presence of pathogenic intestinal bacteria. On the other hand, certain E.
coli strains (EnteropathogenicEPEC; Enteroinvasive-EIEC; Enterotoxigenic-ETEC; and
Enterohaemorrhagic-EHEC) are pathogenic and lead to serious human diseases that can
betransmitted with water and food (Doyle, 1990).
The faecal coliforms and E. coli are particularly useful as indicators of faecal contamination
and poor handling of seafood’s. This is because the organisms are absent from the fish at
the time of capture except in grossly polluted waters. The aerobic plate counts (APC) or
total viable count (TPC) is recommended for all fish and fish products because of its
usefulness as an indicator of utility, the condition and length of storage of products prior
preservation processes such as freezing. According to ICMSF, (1986), most aquatic animals
at the time of harvest have counts in the region of 10 2 – 10 5 organisms per gram. While an
increase in APC/TVC to levels >10 6 per gram is an indicative of long storage at chill
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