African Journal of Food, Agriculture, Nutrition and Development Rural Outreach Program ISSN: 1684-5358 EISSN: 1684-5374 Vol. 10, Num. 8, 2010, pp. 3047-3064

African Journal of Food Agriculture, Nutrition and Development, Vol. 10, No. 8, August, 2010, pp. 3047-3064

Original Article

Microbiological, proximate and heavy metal concentration in Penaeus sp. (shrimp) and Calllinectes sp. (crab) from creeks in Niger delta Nigeria

BC Adebayo-Tayo¹, MA Okpo²

¹ Department of Microbiology, University of Ibadan. Ibadan, Oyo State, Nigeria
² Department of Microbiology, University of Uyo, Uyo Akwa Ibom State, Nigeria

Correspondence Address:B C Adebayo-Tayo, Department of Microbiology, University of Ibadan. Ibadan, Oyo State , Nigeria, bukola_tayo@yahoo.com

Code Number: nd10087

Abstract

Keywords: Microbial, Penaeus sp., Callinectes sp., Metals, Proximate

Introduction

Crustacean constitutes an important food component for a large section of the world population, more so in developing countries where shellfish forms a cheap source of protein ^[1] . Among the range of shellfish, shrimps and crabs are the most important thereby accounting for more than 70% of the total earnings of marine export products ^[2] . Shellfish are nutritionally balanced, an excellent source of proteins, a good source of minerals and some vitamins and are also low in fats and cholesterol ^[3] . Crabs and shrimps have been used by riverine dwellers in Niger Delta as food condiments and are recommended for pregnant women and protein malnourished cases. They are also known to reduce the risk of coronary heart disease. They are used in weight control and other disorders including cancer ^[4],[1],[5] .

A survey of the microbiological quality of some shellfish has shown shellfish to harbor pathogenic organisms ^[6],[7] .These pathogenic organisms have been implicated in the outbreak of food-borne diseases in many parts of the world. These illnesses include typhoid fever, hepatitis and similar disorders of the digestive system ^[8],[9] .

Aquatic organisms, in general, accumulate contaminants from the environment and; therefore, have been extensively used in marine pollution monitoring programmes ^[10],[11] . Heavy metals discharged into the marine environment can damage both marine species diversity and ecosystem, due to toxicity and accumulative nature of the metals. The consequence of heavy metal pollution can be hazardous to man, based on the level of consumption of shellfish in riverine area, which is relatively high. There is need to check microbial and chemical contaminants in foods from the aquatic environment in order to understand their hazard levels and thus creating awareness to the public on health risks in consuming raw or undercooked and under -processed shellfish.

This study was undertaken to enumerate the microbial quantity as well as proximate, mineral composition and heavy metal concentration in edible portion of Peanaeus sp. and Callinectes sp. from two creeks in Niger Delta Nigeria in order to evaluate their hazard level in relation to the maximum residual limit for human consumption.

Methodology

Collection of Samples

A total of one hundred and twenty samples each of shrimp and crab (Peanaeus sp. and Callinectes sp respectively) used in this study were freshly harvested mechanically from Itu and Oron Creeks in Oron and Itu local government area of Akwa Ibom state, Eastern Nigeria both which are famous shellfish producing areas in Niger Delta, Nigeria. The sample was collected in triplicate. It was placed in ice and brought to the laboratory.

Microbiological analysis

The samples were washed and the edible portion of the meat removed, homogenized and about 10g taken for microbiological analysis. Standard pour plates were prepared from 10 - fold dilutions into nutrient agar medium for total heterotrophic bacteria counts, MacConkey agar was used for total Coliform counts, Salmonella/Shigella agar for total Salmonella/Shigella counts, Thiosulphate citrate bile salt sucrose agar for total Vibrio counts and Sabouraud dextrose agar for total fungal counts. The bacterial plates were incubated at 37 ^o C for 24-48 hours, while fungal plates were incubated at room temperature (28 ± 2 ^o C) for 3-5 days. Colonies were selected randomly and were characterized using morphological and biochemical test such as gram stain, spore stain, motility, catalase, oxidize, coagulase, indole, MR-VP and Urease and sugar fermentation tests. Bacterial isolates were identified with reference to Cowan and Steel′s Manual for the identification of Medical Bacteria ^[12] and Bergey′s Manual of Determinative Bacteriology ^[13] . Fungal isolates were identified based on their morphological and cultural characteristics as recommended by Sampson et al., ^[14] .

Proximate and mineral analysis

Proximate composition was determined according to the method of A.O.A.C. ^[15] . This includes determination of Ash content, Crude protein, Dry matter, Moisture content and Crude fiber. The mineral contents were also determined using Jenway Digital flame photometer (PFP 7 Model).

Metal concentration analysis

The edible portions of the meat from the samples were removed, homogenized and about 2.5g taken for analysis. Ten milliliters of nitric acid - perchloric acid (10:4) mixture were added to the sample, covered and left overnight at room temperature. The samples were digested, allowed to cool to room temperature, filtered using glass wool and made up to 50ml. The filtered samples were analyzed in triplicate, using Buck 2000 Atomic Absorption spectrophotometer (AAS) as per standard conditions [Table - 1]. The blanks and calibration standard solutions were also analyzed in the same way as for the samples. All the chemical analyses were carried out in duplicate.

Results

The levels of microbial load in the shrimps and crabs from the two creeks in Niger Delta are shown in [Table - 2]. The total bacteria population of samples varied from 8.50 x 10 ⁷ - 9.70 x 10 ⁸ cfu/g and 1.60 x 10 ⁷ - 1.45 x 10 ⁸ cfu/g for Penaeus sp. from Itu and Oron creeks, 7.00 x 10 ⁷ - 8.90 x 10 ⁸ cfu/g and 1.03 x 10 ⁷ - 1.10 x10 ⁸ cfu/g for Callinectes sp. from Itu and Oron creeks.

Penaeus sp.from Itu creek therefore had the highest level of bacterial contamination. The coliform count ranged from 6.20 - 6.80 x 10 ⁷ cfu/g and 8.90 - 9.40 x 10 ⁷ cfu/g for Penaeus sp. from Itu and Oron creeks, 5.30 - 6.40 x 10 ⁷ cfu/g and 7.30 - 8.40 x x 10 ⁷ cfu/g for Callinectes sp. from Itu and Oron creeks.

The Salmonellae / Shigella count ranged from 5.20 x 10 ⁷ -5.50 x 10 ⁸ cfu/g and 6.90 x 10 ⁷ - 7.20 x 10 ⁸ cfu/g for Penaeus sp. from Itu and Oron creeks, 7.00 - 7.50 x 10 ⁷ cfu/g and 6.20 - 6.80 x 10 ⁷ cfu/g for Callinectes sp. from Itu and Oron creeks.

The Vibro count varied from 6.90 x 10 ⁷ - 7.20 x 10 ⁸ and 8.00 x 10 ⁷ - 8.20 x 10 ⁸ cfu/g for Penaeus sp. from Itu and Oron creeks, 5.20 - 5.30 x 10 ⁷ and 5.60 - 5.90 x 10 ⁷ for Callinectes sp. from Itu and Oron creeks.

The fungi count ranged from 3.10 - 3.40 x 10 ⁷ cfu/g and 3.50 - 3.70 x 10 ⁷ cfu/g for Penaeus sp. from Itu and Oron creeks, 3.20 - 3.50 x 10 ⁷ cfu/g and 3.70 - 4.00 x 10 ⁷ cfu/g for Callinectes sp. from Itu and Oron creeks.

Morphological and biochemical characteristic of the bacteria and fungi isolated from the samples from the two creeks are shown in [Table - 3] and [Table - 4].

The organisms isolated from the samples were, Escherichia coli, Salmonella sp., vibrio sp., shigella sp., Serratia marcesens, Bacillus sp., and Streptococcus sp. for bacteria and Aspergillus flavus, Aspergillus niger, and Aspergillus terreus for fungi [Table - 5].

The percentage proximate and mineral composition of the samples is shown in [Table - 6]. The crude protein ranged from 29.85 ^d - 54.13 ^a % in which the highest was obtained from Oron creek. Penaeus sp. and Callinectes sp. from Oron creek has the highest Na, Ca, K and P content.

The concentration of different metals detected in the edible portion of the samples from the two creeks is shown in [Table - 7]. The heavy metal concentrations are found to be significantly higher (P<0.05) in Peaneus sp. from Oron creek except for Pb and Cd than samples from Itu creek. Peaneus sp. from the two creeks had significantly high concentration of metals.

The zinc content in the samples ranged from 24.4 ^d - 94.2 ^a mg/kg in shrimps and in crabs from the two creeks. The highest concentration was detected in shrimp from Oron creek.

Lead was detected in all samples but the highest concentration (0.84 ^a mg/kg) was found in Callinectes sp. (crab) from Itu Creek.

Cadmium was also detected virtually in all the samples. The lowest concentration was detected in shrimp from Oron creek that contained 0.02 ^d mg/kg and the highest was from Crab (0.15 ^a mg/kg) from Itu creek.

The concentration of copper ranged from 3.4 ^d - 7.49 ^a mg/kg in which the highest was found in Peaneus sp. from Oron creek. Manganese was also detected in all the samples and the concentration ranged from 24.2 ^d - 88.6 ^a mg/kg, the highest being detected from Peaneus sp. from Oron creek.

Discussion

The total microbial counts obtained from this work were found to be higher than the specified standard limits (1x10 ⁵ cfu/g) for bacteria and fungi and 1.x10 ² cfu/g for coliforms) by ICMSF ^[16] and USFDA ^[17] . This high level of microbial loads could be as a result of human activities in the rivers where the shellfish are harvested. These activities include; bathing, washing of clothes or other materials, disposal of faecal matters and sewage discharge by municipal authorities and independent oufits.

All these organisms isolated have health implications on man. The presence of E.coli in the Penaeus sp. and Callinectes sp. is an indication of secondary contamination as E.coli are known to be associated with gastrointestinal tracts of warm-blooded animals and are known to be present in the environment as a natural flora. This secondary contamination may be as a result of sewage contamination Penaeus sp. and Callinectes sp. harvesting areas. E. coli is the causative agent of diarrhea, dysentery, hemolytic uremic syndrome, bladder and kidney infection, septicemia, pneumonia and meningitis ^[18] .

Salmonella, one of the most important food-borne pathogens is indication of sewage contamination and appear to be associated with number a of non-human hosts for example, reptiles ^[19] . It has been reported to survive and persist in the aquatic environment. Salmonella has been detected in periwinkles from different creeks ^[7] , in the gut of tilapia and crab ^[20],[21] and causes new-born meningitis and infantile diarrhea. The presence of Streptoccus sp. is also implicated in humans infections like pharyngities, scarlet fever and pneumonia. Shigella sp. and Salmonella sp. are causative agents of illnesses like shigellosis and salmonellosis in human who are the only reservoir of these organisms ^[22]. Bacillus sp. causes a toxin mediated diseases rather than infections such as diarrhea and emetic illness characterized by nausea and vomiting ^[23] .

Serratia marcensens an enteriobacteria, has been implicated in human pulmonary and urinary infection ^[24] . Vibrio sp., a natural habitants of sea water, has been reported by Cash et al., ^[25] that an oral dose of 10 ⁴ + 10 ⁸ Vibrio cholerae organisms can routinely induce cholera infection in humans. A. niger, A. flavus and A. terreus have also been implicated in causing mycetoma in human ^[24] . Aspergullus flavus is involved in allergic aspergillosis (pulmonary aspergillosis) and also produces aflatoxin that is highly carcinogenic ^[26] .

Proximate analysis has shown sample from Oron creek to be nutritionally richer than samples from Itu. This may be attributed to the fact that Oron creek has brackish water, which is often known to be nutritionally richer than fresh water found in Itu creek. The moisture content was found to be higher in Penaeus sp. from Itu creek. Since Itu has fresh water, the shellfish from this water tends to absorb water from the external environment into their cells which are of higher concentration in order to balance the osmotic pressure between the cell and the surrounding water. The fat, fiber and moisture contents in samples from Itu creeks are constituents in shellfish, which provide an energy source to the consumers.

The presence of mineral elements like sodium, calcium, potassium and phosphorus found in brackish water which are major constituents of protein, nucleic acid, co-factors and other cell components, when absorbed into the cells. Shellfish has been reported to serve as a source of protein and mineral elements ^[27] , which helps in the repair of worn-out tissue and body building. The mineral elements analyzed in this work are essential minerals required by humans. The sodium and calcium are essential elements found in human bones phosphorus plays a major role in glucose metabolism and also essential element of the DNA molecule. Iron and Magnesium are essential trace elements; they play a major role in the metabolic processes that take place in human system and regulation of blood. Magnesium may function as a co-factor to some enzymatic activities. Iron is a major component of the hemoglobin found in human blood.

Zinc is an essential element for animals and humans, the recommended daily allowance is 10mg/day in growing children and 15mg/day for adults ^[28] . It has a protective effect against the toxication of both cadmiun and lead ^[29],[30] . A deficiency of zinc is marked by retarded growth, loss of taste and hypogonadism, leading to decrease fertility. Zinc toxicity is rare, but, at concentrations in water up to 40mg/kg, may induce toxicity, characterized by symptoms of irritability, muscular stiffness and pain, loss of appetite, and nausea ^[28] .

Lead was detected in all samples; however, all the Peaneus sp. from the two different creeks contained lead below 0.5mg/kg ^[31] and 1.0 mg/kg ^[32] and Crab from the two different creeks contained lead, the concentration (0,62 ^d - 0.84 ^a mg/kg) of which is above the standard limit of EC ^[31] and not above that of FAO ^[32] . Lead causes renal failure and liver damage in humans ^[33],[34] .

The concentration of cadmium in these shellfishes was below standard limit of EC ^[31] (0.5mg/kg) and 2.0 mg/kg of FAO ^[35] . Humans are exposed to cadmium through food and the average daily intake for adults has been estimated to be approximately 50mg ^[29] . The standard threshold for acute cadmium toxicity would appear to be a total ingestion of 3 -15mg. Severe symptoms have been reported to occur with ingestions of 10 - 326mg, while ingestions exceeding 350mg can result in shock and acute renal failure ^[36] .

The concentrations of copper in the samples were much below the limit of 10mg/kg ^[32] , Copper is an essential part of several enzymes and it is necessary for the synthesis of hemoglobin. Shellfish is the richest sources of copper especially oysters and Crustaceans ^[37] . Underwood ^[37] reported that deficiencies of copper in infants can lead to anemia and hypoproteinemia and no deficiency of copper in adult has been reported.

Manganese was also detected in all the samples, the highest being detected in Peaneus sp. from Oron creek. Manganese deficiencies can lead to severe skeletal and reproductive abnormalities in mammals. It is widely distributed throughout the body with little variation and does not accumulate with age. Total daily intake varies from 2.5 to 7.0mg ^[38] .

Conclusion

The present study revealed that shrimps and crabs from creeks in Niger Delta Nigeria contain unacceptable levels of microorganisms (as laid down by ICMSF [16] and USFDA [17] ). Though nutritionally richer, the heavy metals analyzed from this work provide information about the concentration of metals in crustaceans, which can be related to the industrial activity and other human activities taking place in these two areas (Itu and Oron). Majority of the metal level remain within their permissible safe levels for human consumption as laid down recently by EC ^[31] and FAO ^[32] except in few cases.

The study on the whole evidenced the microbial, nutritional and metal status of shrimps and crabs from Niger Delta. However, it did bring out the probable hazards associated with their consumption.

References

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