Text

theses

Klebsiella pneumoniae is ubiquitous in nature as a commensal bacterium, but can also cause nosocomial infections as an opportunistic pathogen. Extended-spectrum β-lactamase (ESBL)- or carbapenemase-producing bacteria or ESBL- or carbapenemase-encoding genes in raw foods have been more prevalent in recent years; however, limited studies have been conducted on the transfer of ESBL- or carbapenemase-encoding genes in raw foods. Therefore, the goal of this research was to elucidate the transfer of ESBL- or carbapenemase-encoding genes in K. pneumoniae under actual food-related conditions. ESBL-producing Klebsiella pneumoniae ATCC 700603 served as a donor and three recipients (KP342∆KM, KP4∆KM, KP8∆KM) isolated from seed sprouts were used for the mating experiments in TSB, pasteurized milk, unpasteurized milk, alfalfa sprouts, and chopped lettuce at 4◦C, 15◦C, 24◦C, and 37◦C. An investigation on the potential transfer of carbapenemase-encoding gene (blaKPC) in Klebsiella pneumoniae to Salmonella and E. coli O157:H7 was also performed in TSB and alfalfa sprouts. In mating experiments to identify ESBL-encoding gene (blaSHV18) transfer, no transconjugants were detected at 4◦C in liquid media and chopped lettuce, but detected in all media at 15◦C, 24◦C, and 37◦C. At 24◦C, the transfer of the blaSHV18 gene occurred more frequently in alfalfa sprouts (5.15E-04 transconjugants per recipient) than in liquid media (1.08E-05) (p<0.05). On chopped lettuce, no transconjugant was detected at day 1 post-mating at 15◦C, but it was observed on day 2 (1.43E-05). Transconjugants carried the blaSHV18 gene transferred from the donor and virulence gene harbored by the recipient. Moreover, a class 1 integrase gene and resistance to tetracycline, trimethoprim/sulfamethoxazole were co-transferred during the mating. No transfer of blaKPC from Klebsiella pneumoniae to Salmonella and E. coli O157:H7 was confirmed under the conditions evaluated. These quantitative results suggest that the transfer of this antibiotic resistance gene under laboratory conditions underestimates its transfer frequency in fresh produce. Importantly, fresh produce exposed to temperature abuse may serve as vehicles for the spread of antibiotic resistance having a potentially negative impact on human health. While we could not confirm the transfer of blaKPC both in TSB and alfalfa sprouts, more studies aimed at determining favorable conditions for the transfer of carbapenemase-encoding gene in foods should be conducted.

ETD_7085

Ph.D.

Includes bibliographical references

by Yang Jin Jung

doi:10.7282/T3154K5X

ETD doctoral

The author owns the copyright to this work.