Search for carbapenem-resistant bacteria and carbapenem resistance genes along swine food chains in Central Italy

Abstract

The presence of carbapenem-resistant bacteria and carbapenem resistance genes (CRGs) in livestock is increasing. To evaluate the presence of carbapenemase-producing Enterobacteriaceae (CPE) and the main CRGs along swine food chains of the Marche Region (Central Italy), samples of faeces, feed, and animal-food derived products were collected from seven small/medium, medium, and large-scale pig farms. A total of 191 samples were analysed using a culture-dependent method, with the aim of isolating CPE. Isolates were analysed for their resistance to carbapenems using a modified Hodge test and the microdilution method for the minimum inhibitory concentration (MIC) determination. Moreover, the extraction of microbial DNA from each sample was performed to directly detect selected CRGs via qPCR. Among the 164 presumptive resistant isolates, only one strain from a liver sample, identified as Aeromonas veronii, had an ertapenem MIC of 256 μg/mL and carried a carbapenemase- (cphA) and a β-lactamase- (blaOXA-12) encoding genes. A low incidence of CRGs was found; only nine and four faecal samples tested positive for blaNDM-1 and blaOXA-48, respectively. Overall, the importance of monitoring CPE and CRGs in livestock and their food chains should be stressed to control all potential non-human CPE and CRGs reservoirs and to determine safety levels for human health.

Fig 1. Mean values ± standard deviation of the viable counts obtained on MacConkey agar for each sample type.

Fig 2. Phylogenetic tree created (https://online.phyloviz.net/) by multi-sequence alignment of six alleles’ FASTA input of all Aeromonas veronii isolates (n = 627) deposited in PubMLST.

The Aeromonas strain of this study is identified by the green node. The ST609 (blue node) is also evidenced as the putative founder of the clonal complex in which our strain is included.