Successfully reported this slideshow.
We use your LinkedIn profile and activity data to personalize ads and to show you more relevant ads. You can change your ad preferences anytime.

Exposure assessment for Listeria monocytogenes in hot-smoked fish in Ghana


Published on

Presentation by Kennedy Bomfeh, Kwaku Tano-Debrah, Firibu K. Saalia and Betty Bediako-Amoa at the first International Congress on Pathogens at the Human-Animal Interface, Addis Ababa, Ethiopia, 15-17 September 2011.

Published in: Technology
  • Be the first to comment

Exposure assessment for Listeria monocytogenes in hot-smoked fish in Ghana

  1. 1. EXPOSURE ASSESSMENT FOR LISTERIA MONOCYTOGENES IN HOT-SMOKED FISH IN GHANA 74 Kennedy Bomfeh1, Kwaku Tano-Debrah1*, Firibu K. Saalia1, Betty Bediako-Amoa1 1Department of Nutrition and Food Science, University of Ghana, Legon *Corresponding author:; The study sought to determine the occurrence and likelihood of ingestion of Listeria monocytogenes in hot-smoked fish (mackerel, tuna, and herrings) in Ghana. A survey was conducted in two coastal fishing and traditional fish processing communities in Accra to determine the frequencies of consumption of the products, and the quantities (Q) often consumed at an instance. The concentration, C, and prevalence of L. monocytogenes was determined in three (3) samples of each product purchased from four central informal markets in Accra (total of 15 samples). Prevalence was determined as the percentage of samples in which the pathogen was detected, and concentration as the colony forming units of the pathogen per gram of fish (CFU/g). The likely numbers of L. monocytogenes, N, ingested through consumption of each type of smoked fish were determined as N= C x Q. The respective prevalence and concentrations of L. monocytogenes were: hot-smoked mackerel - 100%, 1.60x103 CFU/g; hot-smoked tuna 92%, 1.40x103 CFU/g; and hot-smoked herrings 75%, 4.00x102 CFU/g. The quantity of hot-smoked tuna and mackerel often consumed in both communities was >200g, and the respective values for hot-smoked herrings between the two communities were 151g and 101g. Therefore, the likely numbers of the pathogen ingested were ≥3.20x105 cells in mackerel and ≥2.80x105 cells in tuna for both communities. In herrings, the likely numbers were 6.04x104 cells and 4.04x104 cells between the towns. The results suggest that consumers of hot-smoked fish from informal markets are exposed to possible ingestion of Listeria monocytogenes. INTRODUCTION Table 2: Forms in which in which traditionally hot-smoked fish was consumed Form in which consumed As is Cooked * 1 (%) 2 (%) 1 (%) 2 (%) Product Listeria monocytogenes is a food-borne pathogen known to sporadically cause a fatal disease called listeriosis. The organism is reported to cause the most deaths among all food-borne bacterial pathogens. It is able to grow at very low temperatures (-1.5oC), high salinity (up to 10-12% NaCl), low pH (minimum 4.4), and low water activity (0.83)1. L. monocytogenes has been shown to grow in smoked fish2. Ghana is a heavy consumer of fish3, yet no study had been conducted in the country on the occurrence of the pathogen in the products. Much of the fish consumed is traditionally processed as hot-smoked, salted and/or sundried fish (over 80% of fish landings are processed that way)4. This study therefore sought to determine the occurrence of L. monocytogenes in hot-smoked tuna, mackerel and herrings, and to determine the likelihood of ingestion of the pathogen by consumers. Tuna 100 100 Mackerel 48 60 100 100 Herrings 0 0 100 100 1= Jamestown 2= Tema New Town %= percentage of respondents *=cooked in soups or stews Fish on informal markets contaminated with L. monocytogenes Yes No Fish eaten as is (without heating) METHODS RESULTS 10 Fig. 2: Loading fish in basins for sales Ingestion not likely With semi-structured questionnaires, 300 consumers were interviewed on the frequency and consumption of hot-smoked tuna, mackerel and herrings processed traditionally, the quantities they often consumed at an instance, and the form in which the products were consumed. Three samples of each product were then purchased from five informal markets (including one market each in the two survey communities) where consumers indicated they purchased fish. Samples were transported to the laboratory under aseptic conditions. 25g of each product was homogenized in 225ml of buffered peptone water and plated out on Oxford agar by the spread plate technique and incubated at 37oC for 24-72hrs. Colonies typical of L. Monocytogenes were counted and tested for sugar fermentation and β-haemolysis. 23 No Yes Risk of ingestion N=QxS Lm survives in fish during cooking No Ingestion not likely Yes Risk of ingestion N=QxS Fig. 2: Event tree for risk of ingesting Listeria monocytogenes through consumption of traditionally hot-smoked fish purchased from informal markets Table 1: Likely numbers of L. monocytogenes ingested through consumption of contaminated TPF fish on informal markets in Ghana Cty CONCLUSION Listeria monocytogenes occurs in traditionally processed fish on informal markets in Ghana, suggesting that the products could be vehicles for the transmission of the pathogen to consumers. Given the low counts of the pathogen in the products, the risk of ingestion is low. However, individuals who either consume traditionally processed fish purchased from informal markets as is or do not heattreat the products sufficiently increase their risks of ingestion, and vice versa. Tuna on smoker Fig. 1: Processing environment and some handling practices during traditional fish smoking in Ghana >200 ≥3.20x105 Mackerel 1.60x103 >200 ≥2.80x105 4.00x102 151 6.04x104 1.40x103 >200 ≥3.20x105 1. Montville, T.J. and Matthews, K.R. (2005). Food Microbiology: An Introduction. ASM Press, Washington D.C. pp 159 – 171. Mackerel 1.60x103 >200 ≥2.80x105 Herrings Mackerel on smoker C (CFU/g) 1.40x103 Tuna 2 Product Herrings 1 Thawing mackerel N Although the hygienic conditions of traditional fish smoking environments was generally unsatisfactory (Fig.1&2), in another study, we did not detect Listeria monocytogenes in hot-smoked fish sampled immediately after processing. Therefore, the occurrence of the pathogen in samples from informal markets implicates improper post-processing handling as a source of contamination. Tuna Sanitation of processing environment Q (g) DISCUSSION Consumers are exposed to ingesting Listeria monocytogenes if they consume hot-smoked fish from informal markets as is (which was they case among some, Table 2), or if the pathogen survives in fish during domestic cooking (Fig. 2). The former event is more probable, and under such circumstances the likely number of cells ingested would be as presented in Table 1. 4.00x102 101 4.04x104 2. Lindqvist, R. and Westoo, A. (2000). Quantitative risk assessment f or Listeria monocytogenes in smoked or gravad mackerel and rainbow trout in Sweden. International Journal of Food Microbiology 58 181 – 196. Cty= Community 1= Jamestown 2= Tema New Town C=average counts across five markets Q = Most frequently consumed quantities N=likely number of L. monocytogenes ingested REFERENCES 3. Bank of Ghana. (2008). The Fishing Sub-sector and Ghana’s Economy. Research Department, Bank of Ghana 4. Nketsia-Tabiri, J. and Sefa-Dedeh, S. (2000). Quality attributes and utilization of cured fish products in Ghana. Journal of Applied Science and Technology 5:1 148 – 155 PRESENTED AT THE 1ST INTERNATIONAL CONGRESS ON PATHOGENS AT THE HUMAN-ANIMAL INTERFACE (ICOPHAI) , ADDIS ABABA, SEPT. 15-17 2011