Presence of CTX-M-1 group extended-spectrum-β-lactamase in dust from Dutch pig farms
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A variety of plasmid-mediated β-lactamases have emerged in gram-negative bacteria in the last ten years, including extended-spectrum β-lactamases (ESBLs). ESBLs are the most influential resistance genes for cephalosporin resistance in Enterobacteriaceae. They represent a public health treat as they limit the choice of effective antimicrobial agents for human treatment, thereby increasing morbidity, mortality, longer hospital stays and higher costs. Among Enterobacteriaceae in livestock CTX-M is the most common ESBL type, and the subtype CTX-M-1 is most common in pigs in Europe. The most relevant human exposure route has not yet been identified. Next to, one possible exposure route could be dust. CTX-M has been already demonstrated in dust from broiler stables, but not in dust from pig stables. The purpose of this study is to determine whether CTX-M-1 genes can be detected in dust, and if so, how strongly EDC CTX-M-1 positive farms are associated with CTX-M-1 positive pig feces farms. In addition, the relevance of CTX-M-1 positive dust as exposure route for humans is evaluated by use of the results from individual human feces cultures. 123 compartment electrostatic dust fall collector (EDC) samples and 34 household EDC samples from fourty different farms were used in this study. After stomaching, freeze drying and DNA extraction, qPCR and gel electrophoresis, ten farms and one household were tested positive. Pig feces culture of these farms shows that twelve farms tested positive by culture and ten farms tested positive by PCR. CTX-M-1 positive EDCs were significantly more often found in farms in which feces was CTX-M-1 positive. Odds ratios of this association were 11.67 (2.22 – 61.28) for culture-positive feces, and 56.00 (6.78 – 462.66) for PCR-positive feces. Similar results were obtained when limiting the analysis to compartments in which both EDC and feces were analyzed. There was also a significant association between CTX-M-1 positive feces from farm inhabitants and farms with positive dust samples (odds ratio 25.96 (2.89 – 233.59)). Thus, an inhalable exposure route seems to be possible. On the other side, the association between CTX-M-1 positive feces from farm inhabitants and farms with positive pig feces samples was also significant (odds ratio 17.41 (1.96 – 155.04)), it is difficult to disentangle the role of direct animal contact from the role of airborne exposure. Further research is warranted to gain more insight into airborne exposure to ESBL.