Extended spectrum (3-lactamases (ESBLs) were characterized in Salmonella spp. isolates from a pediatric ward of a hospital in Durban. Forty one Salmonella spp. were subjected to serotyping, antibiotic susceptibility testing, E-Tests for ESBL detection, iso-electric focusing, polymerase chain reaction for detection of genes and sequencing. Isolates were screened for the presence of WaTEM, WaSHV, WaCTX-M, WaOXA , WaCMY, WaDHA and WaACC genes. The most common serotype was Salmonella Typhimurium. Isolates were multi-drug resistant with 100% susceptibility only to meropenem and ciprofloxacin. Tazobactam was the most effective inhibitor. Forty-one percent of the isolates were resistant to ceftriaxone, thus limiting therapeutic options for Salmonella infections.TEM-1 was the most predominant (3-lactamase found in 51% of isolates while SHV-12 found in 39 % was the most common ESBL. TEM-63 was evident in 29 %, TEM-116 in 10 % and TEM-131 was found in one isolate. The high ceftazidime MICs of isolates expressing only TEM-63 were indicative of R164S substitution which widens the binding cavity to accommodate the bulky side chains of oxyiminoaminothiazolyl cephalosporins. The identification of TEM-131 which differs from TEM-63 by 1 amino acid reiterates the evolutionary potential of the TEM-type plactamase. Other ESBLs identified included SHV-2, CTX-M-3, CTX-M-15 and CTX-M-37. CMY-2 and the OXA-1 p-lactamase were also detected. This is the first report of TEM-116, CTX-M-3, -15 and -37 in Salmonella spp. in South Africa. All isolates with nalidixic acid MICs > 48 ug/ml had the mutation D87N, or D87G in the QRDR of the gyrA gene. This study showed that Salmonella spp. may be multi-drug resistant with the propensity to harbour p-lactamases in unique combinations. The diversity of ESBLs and the co-expression of quinolone resistance suggests that their incidence in salmonellae needs to be monitored. / Thesis (Ph.D.)-University of KwaZulu-Natal, 2008.

Radiation sensitivity of E. coli O157:H7, non-O157 VTEC and Salmonella to low-dose ionizing irradiation was evaluated. Buffer-suspended E. coli O157 and non-O157 VTEC strains showed similar resistance to 300 Gy X-ray treatments, while Salmonella strains were more resistant. A dose of 1 kGy E-beam radiation reduced two groups of non-O157 E. coli mixtures and one E. coli O157:H7 group inoculated in meat by at least 4 log CFU/g. Salmonella showed only a <2 log CFU/g reduction. Sensory attributes of cooked ground beef patties were not affected (p >0.05) by irradiation. However, irradiated raw carcass muscles were more brown (p < 0.05) but displayed less intense off-aroma (p < 0.05) compared to the control during storage. Therefore, a 1 kGy treatment has the potential to improve microbiological safety with minimal effects on sensory properties of beef; it would be a suitable method for treating carcass trim before preparing ground beef.

Two outbreaks of salmonellosis were linked to the consumption of raw California almonds in 2001 and 2004. Current federal regulations mandate that all almonds grown in California are to be treated with a process that results in a 4-log reduction of Salmonella. Since four out of the five approved technologies to pasteurize almonds rely on the application of heat to control Salmonella, the evaluation of alternative technologies against heat resistant Salmonella Senftenberg was imminent. In this study, almonds that were inoculated with S. Enteritidis PT 30 and S. Senftenberg, were treated with electron beam irradiation (e-beam), blanching and oil roasting. The thermal death time (D-value) for S. Enteritidis PT 30 when treated with e-beam was 0.90 kGy, 15 s when subjected to blanching at 88 degrees C, and 13 s when treated with oil at 127 degrees C. Irradiation and thermal resistance of S. Senftenberg was not significantly different (P > 0.05) from S. Enteritidis PT 30. The commercial application of e-beam as a pathogen intervention was assessed through Monte Carlo simulations (MCS) and experimental measurements. The sensory characteristics of almonds commercially treated by e-beam, blanching and roasting were assessed by a consumer panel. Irradiated and blanched almonds did not differ in consumer overall like (P > 0.05). Bitterness and rancidity attributes of irradiated almonds were between a "dislike slightly" and "dislike moderately", whereas blanched and roasted almonds were between "neither like nor dislike" and "like slightly". Almonds commercially irradiated, blanched and roasted were subjected to an accelerated shelf-life test (ASLT) evaluating percentage free fatty acids, peroxide value, and 2-thiobarbituric acid reactive substances (TBARs). No clear differences between treatments were observed at any given point in time in any of the chemical tests. A gas chromatography-mass-spectrometry-olfactometry (MDGC-MS-O) technology was used to compare full aroma and flavor profiles from raw and e-beam irradiated almonds. Differences in the aroma/odor profile and the taste analysis revealed that the difference between raw and irradiated almonds is extremely subtle. In conclusion, e-beam may be a feasible technology to control Salmonella in almonds if used at low doses, as a part of a series of interventions.

Radiation sensitivity of E. coli O157:H7, non-O157 VTEC and Salmonella to low-dose ionizing irradiation was evaluated. Buffer-suspended E. coli O157 and non-O157 VTEC strains showed similar resistance to 300 Gy X-ray treatments, while Salmonella strains were more resistant. A dose of 1 kGy E-beam radiation reduced two groups of non-O157 E. coli mixtures and one E. coli O157:H7 group inoculated in meat by at least 4 log CFU/g. Salmonella showed only a <2 log CFU/g reduction. Sensory attributes of cooked ground beef patties were not affected (p >0.05) by irradiation. However, irradiated raw carcass muscles were more brown (p < 0.05) but displayed less intense off-aroma (p < 0.05) compared to the control during storage. Therefore, a 1 kGy treatment has the potential to improve microbiological safety with minimal effects on sensory properties of beef; it would be a suitable method for treating carcass trim before preparing ground beef.

Public health concerns associated with high prevalence of foodborne salmonellosis, the emergence of antibiotic-resistant organisms and the identification of poultry meat and products as one of the most common sources of Salmonella support the need for new pathogen control strategies in the poultry industry. Scientific research has focused on the use of bacteriophages as therapeutic agents for humans and animals; however, limited studies have been conducted on bacteriophage application on food safety, especially on poultry. Therefore, the objective of this study was to evaluate the phage density and exposure time required to reduce Salmonella load on experimentally inoculated chicken meat. In Experiment 1, serovars of Salmonella were tested for antimicrobial susceptibility and rifampicin-resistant isolates were generated. Cocktails of the serovars Enteritidis, Kentucky and Typhimurium (EKT), and Hadar and Heidelberg (HH), were inoculated on chicken breast samples to a target of 104 CFU/g. A mixture of three lytic bacteriophages, active against multiple Salmonella serovars was applied to chicken samples. A total of 84 samples (25 +/- 2 g) per each cocktail were distributed among a negative control, Salmonella-inoculated positive control, Salmonella-inoculated samples treated with the phage mixture at differing titers (105, 106, 107, 108, and 109 PFU/ml) with two identical samples at 0, 15, 30, 60, 120, 360 min at 4 degrees C. Experiment 2 evaluated nalidixic acid-resistant Salmonella Typhimurium among negative control, Salmonella-inoculated control (positive control), Salmonella with two phage titers (105 and 109 PFU/ml) at 0, 30, 60 and 120 min at 25 degrees C and 4 degrees C. Results showed differences in means for Salmonella cocktail EKT ranged from 0.1 to 0.7 log10 CFU/g with 0.7 log10 for 108 PFU/ml, 30 min, 4 degrees C. For Salmonella cocktail HH, reductions ranged from 0.1 to 0.4 log10 CFU/g with 0.4 log10 on samples treated with 108 PFU/ml, 120 min, 4 degrees C. For the Experiment 2, a higher phage concentration (109 PFU/ml) at 120 min post-inoculation storage at 25 degrees C was required to yield a 0.9 log10 difference in means. These findings showed that higher concentrations of bacteriophage were more effective controlling Salmonella than lower ones at both temperatures. In addition, temperature, time and bacterial attachment may influence phage efficacy.

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"Erratum" [i.e. Errata] inserted / Includes bibliography / iv, 83 leaves, [33] leaves of plates : ill ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Microbiology and Immunology, 1989

Typescript (photocopy) / xiv, 203 leaves, [2] leaves of col. plates : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Microbiology, 1983

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