Browsing by Author "Jonathan C. Allen, Committee Member"

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Phenotypic and genetic characterization of Listeria monocytogenes from the environment of turkey processing plants
(2009-01-11) Mullapudi, Savitri; Jonathan C. Allen, Committee Member; Lee-Ann Jaykus, Committee Member; Sophia Kathariou, Committee Chair
Resistance of clinical strains of Listeria monocytogenes to heavy metals, especially cadmium and arsenic has been used extensively for subtyping. Furthermore, the three most recent multistate outbreaks of listeriosis in the United States (1998-99 hot dog outbreak, and outbreaks in 2001 and 2002) have involved cadmium resistant strains two of which (1998-99 and 2001) were resistant to the quaternary ammonium disinfectant benzalkonium chloride (BC) as well. In these outbreak strains, genes mediating cadmium and BC resistance were found to be localized in two different gene cassettes on large plasmids (ca. 80 kb). However, limited information has been available on resistance to cadmium, arsenic and BC among L. monocytogenes isolates from the food processing plant environment. It is not known whether resistance to heavy metals (cadmium and arsenic) and BC is plasmid-borne in such strains and whether resistance to cadmium and arsenic may be correlated to resistance to disinfectants commonly used in the processing plant environment. Furthermore, information regarding contamination patterns of turkey processing plants in the United States with regards to different serotypes and strain types of L. monocytogenes is currently inadequate. In this study, we characterized 123 L. monocytogenes isolates (53 of serotype 1/2a or 3a, 39 of serotype 1/2b or 3b, and 27 of the serotype 4b complex, consisting of serotype 4b and the closely related serotypes 4d and 4e, and 4 strains of serotype 1/2c or 3c) from the environment of six turkey processing plants in the United States for cadmium, arsenic and BC resistance. In addition, these isolates were subtyped using pulsed field gel electrophoresis (PFGE). Moreover we investigated the prevalence among these isolates of three different cadmium resistance cadA determinants identified to date in L. monocytogenes: cadA1 (associated with Tn5422), cadA2 (associated with plasmid pLM80, identified in the 1998-99 outbreak strain), and cadA3, associated with the integrated conjugative element (ICE) of L. monocytogenes EGD-e, respectively). We employed plasmid curing protocols to examine if the resistance to heavy metals (cadmium and arsenic) and to BC was plasmid-borne and to assess the stability of cadmium and BC resistance among isolates of L. monocytogenes from the processing plant environment. Resistance to cadmium and BC was more common in serogroup 1/2 strains than 4b, whereas arsenic resistance was more commonly encountered in strains from the serotype 4b complex. We found substantial strain diversity in the turkey processing plants with 104 distinct PFGE types from 123 isolates using both enzymes (AscI and ApaI), resulting in Simpsonâ€™s index of diversity (D) of 0.995. Plant-specific strains were commonly found within each serotype. Heavy metal (cadmium and arsenic) and BC resistance were detected frequently among the serogroup 1 /2 strains. Our investigation has shown that 28% of the L. monocytogenes strains harbored both cadA1 and cadA2 and that the type of determinant (cadA1 vs. cadA2) may vary based on serotype as well as based on BC resistance (cadA2 being found more frequently among BC resistant than BC susceptible strains of the same serotype). The results also showed that the curing of plasmid borne cadmium and BC resistance was possible in certain strains isolated from the environment of turkey processing plants although the rate of plasmid loss was low. These results suggest that the processing plant environment may represent a reservoir for L. monocytogenes having resistance to cadmium and BC. Further studies are needed to elucidate the mechanisms underlying the prevalence of the different determinants, and their possible role in the ecology and evolution of L. monocytogenes in the processing plant environment. In addition, further studies need to be undertaken to confirm the location of the resistance determinants on plasmids, or possibly on the chromosome, especially in strains that failed to lose resistance following exposure to plasmid curing protocols.
Prevalence and Dissemination of Antimicrobial Resistance among Campylobacter jejuni and Campylobacter coli from Meat-Animals
(2009-12-02) Islam, Mohammed Shahidul; Jonathan Olson, Committee Member; Jonathan C. Allen, Committee Member; Sophia Kathariou, Committee Chair
Campylobacter jejuni and C. coli from conventionally grown turkeys have been frequently reported to be resistant to nalidixic acid and ciprofloxacin. To reduce possible contributions of fluoroquinolone use in poultry production to fluoroquinolone resistance in poultry-derived Campylobacter, use of the fluoroquinolone enrofloxacin (trade name, Baytril) was banned in July 2005. However, the impact of this ban on fluoroquinolone resistance in thermophilic campylobacters from turkeys has not been rigorously evaluated yet. In this study, we investigated prevalence of quinolone/fluoroquinolone resistance and multidrug resistance among 1552 Campylobacter isolates (81% C. coli and 19% C. jejuni) derived from 2371 cecal samples of young turkeys (10 days to six weeks of age). The isolates were derived from different flocks and farms, representing three different integrators, from 2002 to 2008. Resistance to ciprofloxacin and nalidixic acid was highly prevalent (585/722, 81%) among isolates from 2002 to August 2005, and prevalence was even higher (779/830, 94%) among isolates from 2006 to 2008, the three surveyed years subsequent to the ban (p<0.0001). Multidrug resistant C. coli (resistant to tetracycline, streptomycin, kanamycin, erythromycin, nalidixic acid and ciprofloxacin) and C. jejuni (resistant to all of the above except erythromycin) represented 46% and 66% of the campylobacters isolated in the periods prior to and subsequent to the enrofloxacin ban, respectively. Multidrug resistance prevalence increased significantly post-ban (p<0.0001) for both C. coli and C. jejuni. Ciprofloxacin MIC determinations suggested that there was no obvious difference in MIC distribution before and after the enrofloxacin ban. Our results suggest that there was no detectable decrease in prevalence of fluoroquinolone resistance among turkey-derived campylobacters within the surveyed three-year period following the enrofloxacin ban. Instead, and for reasons that remain unknown, prevalence values for fluoroquinolone resistance and for multidrug resistance were higher post-ban than pre-ban (p<0.0001). Continued surveys are needed to further evaluate the potential impact of the ban on resistance of campylobacters from turkeys to fluoroquinolones and other antibiotics. Even though fluorioquinolones are no longer permitted for use in poultry, several antimicrobials, for instance tetracycline, continue to be used extensively in conventional production. Naturally competent C. coli C. jejuni are able to acquire foreign DNA from different sources through transformation but the role of transformation in the dissemination of tetracycline resistance in Campylobacter has not been investigated. We therefore investigated transfer of tetracycline resistance from tetracycline resistant C. coli and C. jejuni to tetracycline-susceptible (TS) C. coli and C. jejuni derived from meat animals. Tetracycline-resistant (TR) but kanamycin susceptible (KS) C. coli both from turkey and swine could serve as donors in transformation-mediated transfer of tetracycline resistance to TS C. coli from turkeys. TR and kanamycin-resistant (KR) C. coli from turkeys were unable to serve as donors of tetracycline resistance whereas certain TR KR swine-derived strains successfully transformed tetracycline resistance. None of the TR KR C. jejuni strains could serve as donors and overall C. coli proved to be better donors in transforming tetracycline resistance than C. jejuni. However, a bovine TR KS C. jejuni donors strain was successful in transforming turkey-derived as well as bovine C. jejuni to tetracycline resistance. Further studies are needed to evaluate the impact of transformation in dissemination of tetracycline resistance among C. jejuni and C. coli from animal production systems.
Thermal Processing of Sour Cream using Continuous Flow Microwave Heating - Feasibility Study
(2007-07-26) Settle, David William; Josip Simunovic, Committee Member; Jonathan C. Allen, Committee Member; Leon Boyd, Committee Member; Arthur P. Hansen, Committee Chair
The purpose of this research was to develop a sour cream that could withstand the effect of UHT continuous microwave processing. The major benefit to the manufacturer of the UHT processing would be extended shelf-life, especially in conjunction with asceptic packaging. This would result in less spoilage, thus increased profits. This becomes increasingly important as sour cream increases in popularity and is sold and marketed at greater distances from the point of processing One major problem with UHT processing of acidic dairy products is that high temperatures cause milk proteins to aggregate, especially at pH's around the pI (isoelectric point) of casein. Fouling (or burn-on) of the heat-exchanger tube walls is another factor that excludes the use of UHT processing to sterilize sour cream. The proper formulation of sour cream with the use of stabilizers such as starch and gelatin can also minimize aggregation, reduce syneresis, and increase the viscosity of the final products. The addition of gelatin is often used in sour cream formulations as it increases water binding, whey retention, and adds to mouthfeel, and gives the final product sheen-like appearance. In order to characterize the performance and functionality of sour cream under continuous flow microwave thermal processing conditions, seven sour cream formulations with different gelatin and starch content were produced and processed. Yield stress and viscosity tests were performed and compared to rheological tests performed on commercial brands to determine if they were within the upper and lower commercially accepted limits. Viscosities were dynamically measured with the Stresstech. Dielectric properties of the sour cream samples were also analyzed. Dielectric measurements were taken at 5#176; C intervals. Microwave processing was performed using a 5 kw microwave system. Processing was performed at an output power of 3 kilowatts at 915 MHz at flow rate of 4 liters per minute to determine dielectric properties and estimate the need for formulation adjustments. Rheological analysis of the seven NCSU sour cream formulations showed no correlations between stabilizer levels and yield stress or viscosity. Measurement of time and temperature data showed that variations were present and that processing conditions had an influence on the rheological behavior of the sour creams. Because of this, a single formulation could not be determined as optimal. All seven formulations were more viscous than the commercial brands tested but had lower yield stresses. Also, none of the seven formulations had visual casein aggregation. Rheological analysis of the seven formulations indicated that UHT continuous microwave processing was feasible using any of the formulations. This new process will allow sour cream to be ascetically packaged which had never been done. Aseptic packaging would allow manufactures to increase profit margins by reducing spoilage and eliminate refrigeration costs.