|dc.description.abstract||We determined the limits of survival and transmission of Escherichia coli O157:H7 and methicillin-resistant Staphylococcus aureus (MRSA) on common surfaces found in the cabin of a civil aircraft. The two pathogens were suspended in phosphate buffered saline (PBS), simulated sweat and saliva. A concentration of 105 cells/mL of the three suspensions was inoculated onto coupons (1 x 1 cm2) of the polyurethane armrest, metal toilet handle, plastic tray, plastic window shade, leather seat and pocket cloth. The coupons were exposed to typical airplane cabin conditions of 24° C and 18% humidity. Direct sonication was employed to detach the bacteria right after drying and intermittently every 24 hours. Real-time quantitative PCR (qPCR) in combination with propidium monoazide (qPCR-PMA) and plate counts were performed to monitor the persistence of E. coli O157:H7 in viable but non-culturable (VBNC) state. MRSA survival was quantified by plate counts. A surrogate pigskin contact model was employed to establish the transfer rates of the two pathogens from the contaminated surfaces to skin over time. The general linear mixed effects model with repeated measures was used to analyze the data. The qPCR-PMA method eliminated the amplification from dead cells and was significantly more sensitive than the plate counts to establish the limits of E. coli O157:H7 survival (p < 0.05).
E. coli O157:H7 persisted the longest on armrest, (96h) followed by tray table (72h) and toilet handle (48h) and remained viable longer in PBS, followed by sweat and saliva (p < 0.05). Recovery rates for MRSA decreased over time but more rapidly for non-porous compared to porous fomites (p < 0.05). The organism was culturable significantly longer in PBS, followed by saliva and then sweat suspension (p < 0.05). The pigskin model indicates that transmission rates for both pathogens are significantly higher on non-porous materials when compared to porous surfaces (p < 0.05). Our experiments indicate that E. coli O157:H7 and MRSA can survive for several days on surfaces with different physicochemical properties in the presence and absence of organic matter with different pH. To our knowledge, the current study is the first attempt to elucidate the relative risk of pathogen transmission from contaminated surfaces to the hands of the passengers during a commercial airplane flight.
The last chapter of this dissertation describes the trials performed for the isolation of phage displayed peptides with specificity for Campylobacter jejuni. The isolated clone 17 with displayed peptide QGAQARSGTPVQ showed a high degree of binding to Campylobacter jejuni, but also cross-reacted with two other members of the genus Campylobacter, Campylobacter coli and Campylobacter lari. Given the specificity problems observed, the isolated clone 17 can be used as a test for the detection of the Campylobacter genus.||en_US