Isolation and identification of pathogenic bacteria
associated with frozen mackerel fish (Scomber
scombrus) in a humid tropical environment
Eze, E. I.
, Echezona, B. C.
* and Uzodinma, E. C.
Department of Crop Science, University of Nigeria, Nsukka, Nigeria. 2
Department of Science Laboratory Technology, University of Nigeria, Nsukka, Nigeria. Accepted 8 January, 2010
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. Invitro 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 10
. This value was found to be markedly higher than the recommended public health and safety standard value of between 5.0 x 10
, approved by Nigerian National
Agency for Drug Administration and Control (NAFDAC).
Key words: Isolation, identification, pathogenic bacteria, Scomber scombrus. INTRODUCTION
Fish constitute the cheapest source of animal protein in
Africa (Clucas and Ward, 1996). It is one of the main food
components of humans for many centuries and still
constitutes an important part of the diet of many
countries. The advantage of fish as a food resulted from
its easy digestibility and high nutritional value. Since 70% of the earth’s surface is covered by water, there are
plenty sources to harvest fish from. Fishes are found in
different waters. Some are found in fresh water while
some are found in salt water (sea and oceans). However,
the type of microorganism found associated with a
particular fish depends on the water it was found
(Thatcher and Clark, 1973; Clucas and Ward, 1996).
Freshly harvested aquaculture products, particularly
those from tropical regions may harbour pathogenic
bacteria, which form part of natural micro-flora of fish
*Corresponding author. E-mail: email@example.com.
ponds (Clucas and Ward, 1996). It was further reported
by these workers that harmful microorganism could also
enter seafood processing chain because of inadequate
process control, poor standards of hygiene and sanitation
in processing plants and post-production contamination
during incorrect handling or storage.
Kvenberg (1991) and Rodeick (1991) classified the
bacteria pathogens associated with fish into two: the nonindigenous bacteria pathogen and the indigenous bacteria pathogens. The non-indigenous pathogen
contaminate fish or fish’s habitat in one way or the other and the pathogens include Clostridium botulinum, Listeria
monocytogenes, Staphylococcus aureus, Salmonella
species, Shigalla species, Escherichia coli, etc. The
indigenous bacteria pathogens are those naturally living
in the fish’s habitat. They are the Vibrio species,
Aeromonas species etc. Clucas and Ward (1996) also
listed some organisms likely to cause food-borne
diseases when present in ready-to-eat sea foods. The list
included S. aureus, Salmonella, Vibrio parahaemolyticus,Monocytogenes, Shigalla, Aeromonas, Yersenia and Pseudomonas.
Fishes have high water content and freeze between
temperatures of 0 and 3°C with an average of about 2°C
(Desrosier, 1978). Freezing kills some bacteria, but the
ones not killed will grow upon thawing (Frazier and
Westhoff, 1988). Some bacteria that...
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