A range of ethnic foods was examined for their microbiological content in relation to total viable counts (TVC) of aerobic bacteria, counts of presumptive coliforms, yeast and mould counts; presence of Salmonella spp., Listeria monocytogenes, Escherichia coli O157:H7 and Campylobacter spp.; total enumeration of Clostridium perfringens, Staphylococcus aureus and Bacillus spp.; identification of moulds and the presence of total aflatoxins. Samples, which included cereals, nuts, dried fruits, herbs and spices, were obtained from local retail outlets and distributors. It was established that three samples of pistachio nuts contained significant levels of aflatoxins. The concentration of total aflatoxins in these three nut samples ranged from 15 to 259 microg/kg of sample. Only two other samples contained trace amounts of aflatoxins, all other samples analysed were found to be free of any detectable level of aflatoxins. TVCs, coliform counts and yeast and mould counts varied widely depending on the matrix tested. Generally, rice, wheat and peanuts produced low counts whereas other nuts, gram flour and spices produced much higher counts. Cl. perfringens, Staph. aureus, and Bacillus spp. were common in spices, nuts and gram flour, however, Listeria monocytogenes was only detected in four samples and in no sample could Salmonella spp, E. coli O157:H7 or Campylobacter spp. be detected.

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Forty-nine samples of raw cow's milk and 20 samples of fresh white soft cheese were collected directly from 20 local dairy factories in the north-west of Libya and analysed for the presence of aflatoxin M1 (AFM1). The samples were analysed using a high-performance liquid chromatography technique for toxin detection and quantification. Thirty-five of the 49 milk samples (71.4%) showed AFM1 levels between 0.03 and 3.13 ng ml(-1) milk. Multiple analyses of five milk samples free of AFM1 artificially contaminated with concentrations of AFM1 at 0.01, 0.05, 0.1, 1.0 and 3.0 ng ml(-1) showed average recoveries of 66.85, 72.41, 83.29, 97.94 and 98.25%, with coefficients of variations of 3.77, 4.11, 1.57, 1.29 and 0.54%, respectively. Fifteen of 20 white soft cheese samples (75.0%) showed the presence of AFM1 in concentrations between 0. 11 and 0.52 ng g(-1) of cheese. Multiple assays of five cheese samples free of AFM1 spiked with different concentration of AFM1 (0.1, 0.5, 1.0 and 3.0 ng g(-1)) showed average recoveries of 63.23, 78.14,83.29 and 88.68%, with coefficients of variation of 1.53, 9.90, 4.87 and 3.79%, respectively. The concentrations of AFM1 were lower in the cheese products than in the raw milk samples.

A method using immunoaffinity as a purification step for the determination of aflatoxin M1 in cheese is described. A simple solvent extraction with dichloromethane followed by a washing step with N-hexane gives a prepurified extract. A comparison between two ways of aflatoxin M1 purification, by solid-phase extraction clean-up and by immunoaffinity, was carried out. The use of immunoaffinity columns containing monoclonal antibodies against aflatoxin M1 gives the best result, i.e. a very clean preparation containing purified aflatoxin M1. The quantification of aflatoxin M1 is then performed by high performance liquid chromatography using fluorometric detection. This method was successfully carried out on naturally-contaminated and spiked cheeses. Recoveries are about 75%. The limit of quantification is 0.020 microgram of aflatoxin M1 per kg of cheese. This method seems suitable for use in monitoring programmes for aflatoxin M1 contamination in dairy products such as cheese.

Campylobacter jejuni is a major cause of human diarrhoeal disease, but specific virulence mechanisms have not been well defined. This blinded study was undertaken with 40 C. jejuni isolates from different sources to determine their haemolytic, cytotoxic and adhesion and invasion activities towards mammalian cells. The results were correlated with source of isolation and genetic makeup by amplified fragment length polymorphism (AFLP) typing. The isolates had variable degrees of haemolytic activity against rabbit erythrocytes and cytotoxicity towards CaCo-2, HeLa and Vero cells. The data indicated that the haemolytic and cytotoxic activities were due to separate factors. A range of cytotoxicity was exhibited, whereby some strains had no activity against the target cells and others had activity against all three cell lines. Certain strains had activity against CaCo-2 cells but little or no activity against the other cells, while others exhibited the opposite phenotype. The data suggested that the cytotoxicity assay with the different cell lines may have detected more than one cytotoxin. A wide variation between isolates was observed for both adherence and invasion with all three cell lines, yet, overall, the strains showed a significantly greater invasion capacity for CaCo-2. There was no clear relationship between source of isolation or disease manifestation and possession of statistically significantly higher levels of particular virulence-associated factors although, in some cases, a correlation between cytotoxicity and cell invasion was evident. Five AFLP clusters, each representing two to eleven isolates with similar profiles, were observed at the 90 % similarity level. Some AFLP groups contained isolates with a common serotype, but each group had C. jejuni isolates from more than one source with the exception of group IV, which contained only human isolates. Isolates with high cytotoxic activity against CaCo-2 cells were confined to groups I, III and IV and a group of unrelated strains (U). Group II isolates had uniformly low cytotoxicity. Isolates in groups I, V and U were more invasive for CaCo-2 cells than isolates in groups II, III and IV. The strain differences in cytotoxicity or invasion did not correlate with source of isolation.