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Abstract
Peptones, polypeptides obtained from hydrolysis of proteins, are primary protein sources in culture media; traditionally they are derived from animal sources. However, due to concerns expressed by animal rights groups, environmental sustainability, religious beliefs in South Asia and concerns over transmissible spongiform encephalopathy (TSE), especially the bovine form (BSE), vegetable peptones have become an increasingly important alternative. This thesis describes studies of the comparative performance between vegetable peptone (VP)-based and conventional meat peptone (MP)-based culture media, using Salmonella as an analyte and poultry products as food matrices. Productivity and recovery of three strains of Salmonella, in vegetative or injured state, were determined in pre-enrichment broth (buffered peptone water) and selective enrichment broths (Rappaport-Vassiliadis Soy broth, Muller Kauffmann Tetrathionate novobiocin broth), as well as on a range of plating media (XLD, Hektoen Enteric, Bismuth Sulphite and Brilliant green agars), from two commercial manufacturers, one supplying VP-based media (Himedia) and the other supplying MP-based culture media (Oxoid). No statistical differences in growth (P < 0.05) were observed between both brands of liquid and solid culture media for all Salmonella strains. The performance of peptones was also evaluated in five plating media formulated in the laboratory from all the same individual ingredients except peptone, as the solitary variable ingredient. No significant difference (P < 0.05) in performance was observed. Studies were also conducted using naturally and artificially contaminated chicken samples (n = 100), to compare semi-quantitatively the performance of the media for detection of Salmonella from high background matrices, using the ecometric technique, as well as to determine the incidence of Salmonella. Absolute growth indices (AGls) calculated from ecometric streaking on both brands of plating media - XLD, Hektoen Enteric, Bismuth Sulphite and Brilliant Green agars - showed no significant difference in productivity for Salmonella, or specificity, in terms of background micro flora. The overall results of this study underline that VP-based media have equal specificity, productivity and perform similarly to MP-based media. Since, vegetable peptone media are economical with freedom from religious, environmental and BSE concerns, they serve as a suitable replacement for animal peptone-based culture media.