ABSTRACT

Aquaculture products can harbour pathogenic bacteria, which are 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 had constituted an important dietary intake of the people of Owerri, Nigeria. Fish samples collected were identified and bacterial load of the samples determined using pour plate method. Differentiations and characterizations of various isolates were based on biochemical reactions and gram-staining technique. Frozen Sardine, Mackerel, and Croaker fish were 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 Pseudomonas specie. Incidences of the various isolates in the culture were found to be 45%, 33% and 22%, respectively. The mean bacteria load of the isolates was1.33x109CFU g-. 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-, approved by Nigerian National Agency for Drugs Administration and Control (NAFDAC).

CHAPTER ONE

INTRODUCTION

Fish constitutes the cheapest source of animal protein in Africa (Ducas 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. It has been widely accepted as a good source of protein and other elements for the maintenance of healthy body. The advantages of fish as a food resulted from its easy digestibility and high nutritional value. Fish is a good source of fluorine and iodine, which are needed for the development of strong teeth and the prevention of goiter in man (enlargement of the thyroid gland situated in the neck). 

        However, availability of these vital nutrients depends to a large extent on the methods of storage such as salting, roasting, drying and freezing. Fish of different types are at great demand by the Nigerian consumers as a relatively cheaper source of animal protein. Storage time and temperature are the major factors affecting the rate of loss of quality and shelf life of a fish. 

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 (seas and oceans). 

However, the types of microorganisms found associated with a particular fish depend on the water it was found (Thatcher and Clark, 1973; Ducas and Ward 1996). Freshly harvested aquaculture products, particularly those from tropical regions may harbour pathogenic bacteria, which form part of natural micro-flora of pond fish (Clucas and ward, 1996). It was further reported by these workers that harmful microorganisms 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.

             Kvenberg (1991) and Roderick (1991) classified the bacteria pathogens associated with fish into two: The non-indigenous bacteria pathogens and the indigenous bacteria pathogens.

The non-indigenous bacteria pathogens contaminate fish or fish’s habitat on one way or the other and the pathogens include; Clostridium botulinum, Listeria monolytogenes, Staphylococcus aureus, Salmonella species, Shigalla specie, Escherichia coli, etc.

The indigenous bacteria pathogens are those naturally living in the fish’s habitat. They are the Vibro specie, Aeromonas specie etc. Clucas and ward (1996) also listed some organisms likely to cause food borne diseases when present in ready-to-eat seafood.

The listed included Staphylococcus aureus, Salmonella, Vibro Parahaemolyticus, monocytogenes, Shigalla, aeromonas, Yersenia and Pseudomonas.

Fishes have high water content and freeze between temperatures of Oo and 30c with an average of about 20c (Desrosier, 1978). Freezing kills some bacteria, but the ones not killed will grow upon thawing (Frazier and West Hoff, 1988). Some bacteria that grow on fish, like pseudomonas species, Moraxella species etc can survive freezing temperature and will resume growth when thawed (Frazier and West Hoff, 1988). 

At a temperature of 3Oc or above, species of Clostridium botulinum can survive freezing and may grow and produce toxins (Frazier and west Hoff, 1988). FAO (1989) report showed that fishes become contaminated at sea prior to freezing due to difficulty in designing the plant that would be able to operate satisfactorily at all times in adverse weather conditions at sea.

            The report further indicated that the method of catching fish contributes to the bacterial load of frozen fish and observed that trawling of fish net along the bottom sediments of water for a long time could result in exposing the fish to a high bacterial contamination.

In view of the various ways fishes could be contaminated with micro-organisms, the present research was therefore aimed at finding out if frozen fish consumed on this locality (Owerri) is contaminated with bacterial pathogens, and if so, to identify the major bacteria contaminants. 

1.1      OBJECTIVE OF THE STUDY

⦁ To ascertain and identify the type of pathogenic bacteria associated with frozen fish commonly consumed by people in this locality (Owerri).

⦁ To assess the incidence of these bacterial pathogens in the fish samples.

1.2     JUSTIFICATION OF THE STUDY

This study is intended to provide basic information about microorganisms likely to cause food-borne disease when present in frozen fish that is ready-to-eat.

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