Influence of extrinsic stresses on growth and endotoxin profiles of escherichia coli and pseudomonas aeruginosa

Abstract

The threat to the world food supply and the concern for public health as a result of food-borne diseases has been established as a constant global problem. The safety of food, in particular, is of significance to consumers and producers alike. Regarding the diseases related to food-borne pathogens, the disease syndromes affecting the entire human body has become inestimable. The focus of the study was to establish the effect of sanitisers, detergents and household storage temperatures on the growth profiles and toxicity of typical food related organisms. The endotoxin, LPS of these Gram-negative organisms in communal growth as compared to pure culture was the focus of the investigation. Pure and communal samples were grown in the presence of the extrinsic stresses including storage temperature. The change in toxicity was measured using the Limulus amoebocyte lysate test and the possible change in the immune response was determined using the porcine-IL-6 test. The first obvious finding was that the overall sensitivity of organisms was similar for the same sanitiser and the same detergent. The sensitivity of the community varied slightly but in principle followed the same pattern as the individual organisms. The LD50 for all growth samples were as follows: 32 X 104 PPM for sanitiser 1 and sanitiser 2, and 16X 104 PPM for detergent 1 and detergent 2. Growth in community was found not to be the arithmetic sum of the individual growth patterns. The detergents had a marked effect on the growth of all samples throughout the growth cycle. The sub-optimum household storage temperatures inhibited the growth throughout the cycle but growth did not cease entirely. This finding may have revealed that the acceptable refrigeration temperatures still allows for pathogen growth and thus for biofilm formation. Furthermore, the response of the community to the extrinsic stresses appears to be entirely different to the pure culture and therefore needs further exploration to address the problem. Regarding the quantification by LAL, it was found that the enumeration of the food-borne pathogens isolated from households might not be indicative of acclimatisation obtained over short periods of time and the causal stress turning these organisms into more or less toxic pathogens. The sanitisers and detergents induced competition in colonial fashion and the growth varied between feast and famine. The extrinsic stresses had a more observable effect on the older biofilm as this was shown by a decrease in toxicity. The toxicity as quantified by porcine-IL-6 yielded a mixture of stimulation levels for the cytokine. The toxicity change indicated by the test showed a variation between lowering and noticeable elevation for pure cultures. A marked elevation in toxicity was detected in community at storage temperature 4°C. The study would suggest that porcine IL-6 is not an accurate biomarker for pyrogenicity since its sensitivity is questionable and its inability to indicate toxicity if there is a possible change in the LPS structure. It should be said that further elucidation is needed to support this finding. Having said all that, it is no surprise that the validation for the two tests favours the LAL procedure. The large room for pre-test stimulation in pigs’ blood also tends to cast a shadow on the IL-6 findings. The findings of the study contribute to the body of knowledge covering the effects and quantitative analysis of toxins in food. This should add to safety assurance by sensitizing the industry regarding the most suitable analytical methodologies to apply.