E. coli O157:H7 has been found to survive in dry sausages and cause disease. Isothiocyanates have been studied for their capacity to eliminate pathogens from foods and are attractive from the consumer perspective because of their natural origin. There is a need to better understand how isothiocyanates kill microorganisms and their behaviour in food matrices. It was found that glutathione and cysteine naturally present in meat can react with AIT, forming a conjugate with no or low bactericidal activity against an E. coli O157:H7. In addition, AIT presented higher anti-E. coli activity at lower pH values; therefore, it should be more efficient in acid foods. AIT was also found to inhibit the activity of thioredoxin reductase and acetate kinase; hence, enzymatic inhibition may represent a way in which AIT kills E. coli O157:H7. Mustard powder is used as a spice (active myrosinase) and/or binder (inactive myrosinase) in meat products. Both of these powders killed E. coli O157:H7 in dry fermented sausage. This was not expected since the powder lacking myrosinase is not able to produce isothiocyanates. Starter cultures and E. coli were found to consume significant amounts of glucosinolates. Pediococcus pentosaceus UM 121P and Staphylococcus carnosus UM 123M (higher myrosinase-like activity) were compared against P. pentosaceus UM 116P + S. carnosus UM 109M for their ability in reducing E. coli viability in dry sausage. Sausage batches containing powders of hot mustard, cold mustard, autoclaved mustard and no powder were prepared. Both pairs of starters yielded similar results. Reduction >5 log CFU/g of E. coli O157:H7 occurred after 31 d for hot powder and 38 d for cold powder; there was no reduction in the control. E. coli O157:H7 itself has greater effect on glucosinolate degradation than either pair of starters, which may be more important in determining its survival. Autoclaved powder caused >5 log CFU/g reduction after 18 d. This may be the result of synergistic/additive interaction among E. coli O157:H7 myrosinase-like activity, the presence of newly formed/released antimicrobials in the autoclaved powder and the multiple hurdles present in the dry sausage. Autoclaved mustard powder has potential as a novel food ingredient for the meat industry.

The prevalence and antibiotic resistant profiles of shiga-toxin producing Escherichia coli 0157 strains isolated from faeces samples of cattle, pigs and human stool samples were determined. The strains were further characterised by molecular methods for the presence of shiga-toxin virulence genes and antibiotic resistant genes. Seventy-six Escherichia coli 0157 strains were isolated and the prevalence was higher among E. coli isolated from faeces from pigs (44.2% to 50%) than those from cattle faeces (5.4% to 20.0%) or human stool samples (7 .5%). On testing E. coli 0157 isolates for their resistance to 9 antimicrobial agents, multiple antibiotic resistance (MAR) was observed in all of the isolates arising from resistance to three or more antibiotics. Seventy (92.1 %) of the E. coli 0157 isolated from humans, cattle and pigs were resistant to tetracycline. 73 (96.1 %) were resistant to sulphamethoxazole, 63 (82.9%) were resistant to erythromycin. 40 (52.6%) were resistant to streptomycin and 26 (34.2%) were resistant to ampicillin. The highest frequency of resistance was observed among the human isolates (n=3 ), where 3 (I 00%) of the isolates were resistant to tetracycline, sulphamethoxazole, erythromycin and ampicillin. Furthermore, among the pig isolates (n=60), 58 (96. 7%) were resistant to tetracycline, 57 (95%) were resistant to sulphamethoxazole, 47 (78.3%) were resistant to erythromycin. 38 (63.3%) were resistant to streptomycin and 22 (36. 7%) were resistant to ampicillin. The MAR phenotypes S-Smx-T-E, Smx-T-Ap and Smx-T-E were the dorminant phenotypes among the E. coli 0157 isolated from the faeces samples of communal pigs in 30.4%, 21 .7% and 17.4% of these isolates, respectively. However, phenotypes Smx-T -E and S-Smx-T-E-Ne were identified at I6.2% and 10.8%, respectively within the isolates obtained from commercial pig faeces. The phenotype Smx-T-E was the only MAR phenotype identified among the E. coli 0157 isolated from the faecal samples of commercial cattle at Lichtenburg. Furthermore, MAR phenotypes Smx-T-E-C, K-S-Smx-T-E, S-Smx-T-E and Smx-T-E-Ap were obtained at 25%, respectively for the isolates obtained from communal cattle at Mogosane while Smx-T-E-Ap was the dorminant (66.7%) phenotype among the isolates of human origin. The phenotype Smx-T fom1ed the basis of all the MAR phenotypes obtained and this was similar to the percentage antibiotic resistance data. The distribution of the resistant determinants for tetracycline was determined by PCR analysis in resistant isolates. A tetB gene was detected in E. coli 0157 of pig origin. Based on the characterisation of 30 isolates for the presence of STEC virulence genes by PCR, 18 (60%) possessed the hlyA gene, 7 (23.7%) possessed the eae gene and 5 ( 16. 7%,) harboured both genes. The average MAR indices for pig, cattle and human E. coli 0157 isolates were 0.4n2, 0.3419 and 0.4814, respectively. Among the cattle isolates, the group MAR index was highest for the communal (Mogosane) population while the values for the commercial populations at Lichtenburg and Rustenburg were 0.33 and 0.22, respectively. £. coli 0157 isolated from pigs revealed MAR index results that were 0.508 and 0.415 for the commercial and communal populations respectively and 0.1851 for the E. coli control strains. Characterisation by cluster analysis to determine the commonness and resolve differences between the E. coli 0157 isolated from the Various sources revealed a close association between pig (Tlapeng and Mareetsane), cattle (Mogosane) and human isolates. Interestingly, E. coli 0157 isolated from pigs occurred at the highest frequency in all the clusters. which suggested their role in the dissemination of resistant determinants. / MSc. (Agric.) North-West University, Mafikeng Campus, 2006

Refrigeration has been found to cause cell elongation in mesophilic enteric organisms like commensal Escherichia coli and E. coli O157:H7. As elongated cells may divide into multiple daughter cells, they may result in underestimation of pathogen numbers in foods when plate counts are used. When E. coli cultures were incubated at 6°C for ≤10 days, cells grew by elongation, did not divide, and lost viability (LIVE/DEAD vitality stain) at similar rates. Substantial fractions of cells in cultures elongating at 6°C were inactivated by an abrupt shift to 37°C. Direct microscopic observation of cells transferred to 37ºC after 5 days at 6°C showed that few or no cells of normal size (≤4µm) divided, while elongated cells (>4 µm) formed multiple daughter cells. Thus the threat from mesophilic pathogens with a low infective dose may be underestimated in refrigerated foods. It was also found that E. coli O157:H7 cultures containing elongated cells prepared at 6 or 15 °C have greater potential to attach to food contact surfaces than those grown at higher temperatures. Interestingly, at 6°C cell elongation was inhibited by ≥ 100 mg/l cinnamaldehyde and ≥ 200 mg/l cinnamaldehyde was lethal. In contrast, at 37°C 200 mg/l cinnamaldehyde initially delayed multiplication of E. coli cells by causing cell elongation, but from 2 to 4 h, growth resumed and cells reverted to normal length. To understand this transient behaviour, genome-wide transcriptional analysis of E. coli O157:H7 was performed at 2 and 4 h exposure to cinnamaldehyde in conjunction with reverse phase-high performance liquid chromatography analysis for cinnamaldehyde and other cinnamic compounds. At 2 h exposure, cinnamaldehyde induced expression of many oxidative stress-related genes, reduced expression of genes involved in DNA replication, synthesis of protein, O-antigen and fimbriae. At 4 h many repressive effects of cinnamaldehyde on E. coli O157:H7 gene expression were reversed. Data indicated that by 4 h, E. coli O157:H7 was able to convert cinnamaldehyde into the less toxic cinnamic alcohol using alcohol dehydrogenase or aldehyde reductase enzymes (YqhD and DkgA). The results also showed that the antimicrobial activity of cinnamaldehyde was likely attributable to its carbonyl aldehyde group.

Yellow and oriental mustards deodorized by a laboratory autoclave method have been shown to reduce the number of E. coli O157:H7 greater than the mandatory 5 log CFU/g during sausage manufacture. However, E. coli O157:H7 was inconsistently controlled by different deodorized mustards. The antimicrobial action of mustard results from the conversion of naturally present glucosinolates into inhibitory isothiocyanates by plant myrosinase in untreated hot mustard and by bacterial myrosinase-like activity when present in thermally-treated (deodorized) mustard. Variable results with deodorized mustards suggested that plant myrosinase might not have been completely inactivated during laboratory thermal treatment using the autoclave. Results obtained showed that when a 2 cm thick layer of mustard was used during autoclave treatment, plant myrosinase activity periodically remained. However, the completely deodorized mustard failed to reduce bacterial viability as effectively as yellow mustard containing residual or slight amount of myrosinase. As a result, a small amount of myrosinase activity was highly likely contribute to the overall antimicrobial activity of deodorized mustard against E. coli O157:H7 in dry sausage.

E. coli O157:H7 has been found to survive in dry sausages and cause disease. Isothiocyanates have been studied for their capacity to eliminate pathogens from foods and are attractive from the consumer perspective because of their natural origin. There is a need to better understand how isothiocyanates kill microorganisms and their behaviour in food matrices. It was found that glutathione and cysteine naturally present in meat can react with AIT, forming a conjugate with no or low bactericidal activity against an E. coli O157:H7. In addition, AIT presented higher anti-E. coli activity at lower pH values; therefore, it should be more efficient in acid foods. AIT was also found to inhibit the activity of thioredoxin reductase and acetate kinase; hence, enzymatic inhibition may represent a way in which AIT kills E. coli O157:H7. Mustard powder is used as a spice (active myrosinase) and/or binder (inactive myrosinase) in meat products. Both of these powders killed E. coli O157:H7 in dry fermented sausage. This was not expected since the powder lacking myrosinase is not able to produce isothiocyanates. Starter cultures and E. coli were found to consume significant amounts of glucosinolates. Pediococcus pentosaceus UM 121P and Staphylococcus carnosus UM 123M (higher myrosinase-like activity) were compared against P. pentosaceus UM 116P + S. carnosus UM 109M for their ability in reducing E. coli viability in dry sausage. Sausage batches containing powders of hot mustard, cold mustard, autoclaved mustard and no powder were prepared. Both pairs of starters yielded similar results. Reduction >5 log CFU/g of E. coli O157:H7 occurred after 31 d for hot powder and 38 d for cold powder; there was no reduction in the control. E. coli O157:H7 itself has greater effect on glucosinolate degradation than either pair of starters, which may be more important in determining its survival. Autoclaved powder caused >5 log CFU/g reduction after 18 d. This may be the result of synergistic/additive interaction among E. coli O157:H7 myrosinase-like activity, the presence of newly formed/released antimicrobials in the autoclaved powder and the multiple hurdles present in the dry sausage. Autoclaved mustard powder has potential as a novel food ingredient for the meat industry.

Thesis(M.S.)--Auburn University, 2005. / Abstract. Vita. Includes bibliographic references.

Thesis (Ph. D.)--Ohio State University, 2007.

Thesis (M.S.) -- Mississippi State University. Department of Food Science, Nutrition, and Health Promotion. / Title from title screen. Includes bibliographical references.

Thesis (Ph. D.)--University of Missouri-Columbia, 2004. / Typescript. Vita. Includes bibliographical references (leaves 128-42). Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 2004. / Typescript. Vita. Includes bibliographical references (leaves 128-42). Also available on the Internet.