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Authors:Nguyen, Yen Pham Thuy
Contributors:Li, Yong (advisor)
Food Science (department)
Keywords:Food science
Date Issued:2020
Publisher:University of Hawai'i at Manoa
Abstract:Escherichia coli is notoriously known as a common cause of foodborne infections. Pathogenic E. coli serotypes cause approximately 73,480 illnesses, 2,168 hospitalizations, and 61 deaths annually in the United States. The food industry utilizes sanitizers to minimize the risk of foodborne illness outbreaks. Implementing sanitizers to wash fresh produce and meat has been found effective in reducing pathogens. However, there are concerns about bacteria acquiring resistance against sanitizers. Bacteria may utilize the same resistance mechanisms against antibiotics as they do against sanitizers. Thus, it raises the question of cross-resistance against both antimicrobials and the potential risks to food safety and public health. Antibiotics are used therapeutically to treat bacterial infections and to prevent infections during medical procedures. Unfortunately, overuse and misuse of antibiotics have led to the emergence of antibiotic-resistant bacteria. The concern of antibiotic-resistant bacteria is an ongoing global phenomenon. A key factor that has contributed to the rise of multidrug-resistant bacteria is the spread of resistant genes by mobile genetic elements. These genes are commonly located on plasmids, which are self-replicating DNA that can harbor various functional genes. Antibiotic-resistant bacteria are reservoirs of resistance genes that can be mobilized and transmitted between bacteria.
This study aimed to explore the prevalence of antibiotic resistance in E. coli strains isolated from agricultural water used in local farms in Hawaii. Additionally, the susceptibility profiles of tested bacteria were determined against an array of sanitizers. The association between antibiotic resistance and sanitizer susceptibility of the E. coli strains was evaluated. Finally, efforts were made to investigate whether plasmids are involved in the resistance and cross-resistance of tested bacteria against these antimicrobials.
Antibiotic and sanitizer susceptibility profiles of 182 E. coli strains were constructed using the Kirby-Bauber disk diffusion method. Inhibition zones of 15 common antibiotics were measured. The antimicrobial effects of three sanitizers, bleach, peroxyacetic acid, and lactic acid, were determined on tested bacteria. Correlation tests were used to evaluate association between the antibiotic resistance and sanitizer susceptibility. Six E. coli isolates that showed cross-resistance to the antibiotics and sanitizers were subjected to plasmid curing using sublethal concentrations of sodium dodecyl sulfate. Afterwards, derived colonies were randomly selected and tested against the antimicrobials agents they were once resistant to. Finally, polymerase chain reaction (PCR) was used to detect antibiotic resistance genes in parent and plasmid cured strains of the E. coli isolates.
Of the 15 tested antibiotics, E. coli isolates showed a high prevalence of resistance to cefotaxime (61.5%), ampicillin (42.3%), and erythromycin (41.74%). Among all the isolates, 99 (54.3%) showed resistance against two or more antibiotics. One isolate showed resistance against 11 antibiotics. Most of the tested strains demonstrated higher resistance against peroxyacetic acid than bleach. There was a moderate correlation between tetracycline resistance and peroxyacetic acid resistance, with a correlation coefficient of 0.4. In comparison, the association between resistances against different antibiotics was much stronger. The highest correlation coefficient was 0.83 between sulfamethoxazole/trimethoprim (SXT) and kanamycin. After plasmid curing, the six cross-resistant E. coli isolates showed increased inhibition zones in the disk diffusion assay with some antibiotics and sanitizers. The kanamycin resistance gene aphA1 was detected in both the parent and plasmid-cured strains of isolate 32-2. However, the ampicillin resistance gene ampC was only detected in the parent strain of isolate N1, suggesting the gene is located on the plasmid and lost during plasmid curing.
This study has laid the groundwork for understanding the relationship between antibiotic resistance and sanitizer resistance in foodborne pathogens, which pose a severe threat to food safety and public health. To our knowledge, this is the first report illustrating a correlation between tetracycline resistance and peroxyacetic acid resistance in E. coli isolated from water sources. The genetic and physiological characteristics of this kind of cross-resistant strain warrant further investigation.
Pages/Duration:90 pages
Rights:All UHM dissertations and theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission from the copyright owner.
Appears in Collections: M.S. - Food Science

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