Detection of carbapenem-resistant Enterobacterales in food producing animals and human patients: A "One Health" perspective

Abstract

In past decades, antimicrobial-resistant (AMR) bacteria became a growing public health concern. Over time, this phenomenon has become a significant problem on a global scale, particularly for those pathogens showing resistance against molecules of primary interest in the medical treatment of bacterial infections in humans, such as carbapenems. Carbapenems, which belong to the macro-class of β-lactams, are considered by the World Health Organization (WHO) to be “Critically Important Antimicrobials” (CIAs), i.e., drugs used only in extreme cases and as a last line of defense against infections caused by multidrug-resistant Gram- negative microorganisms. The strategies used by bacteria to develop effective resistance to antimicrobials involve many cellular functions, and the main mechanism of resistance to carbapenems is the production of specific enzymes belonging to the β-lactamase class, called carbapenemases. Among these enzymes, those that pose the greatest threat to public health are KPC (Klebsiella pneumoniae carbapenemase), NDM (New Delhi metallo-beta-lactamase), VIM (Verona integron-encoded-metallo-β-lactamase), IMP (Imipenemase) and OXA-48 (oxacillinase). Although the use of carbapenems is banned in veterinary medicine, bacteria resistant to these antimicrobials have been increasingly isolated from food-producing animals in recent years. This phenomenon is probably due to two factors: the selective pressure resulting from the misuse/abuse of antimicrobials, especially other β-lactams, in veterinary medicine, and the contamination from wastewaters, especially those coming from hospitals or highly urbanized environments. Since humans, animals and the environment are closely interlinked, a “One Health” approach is essential to address the problem. For this reason, this study included samples of both human and animal origin. The samples of human origin consisted of 199 urine samples collected from patients hospitalized at the Parma University-Hospital. The samples of animal origin included 691 rectal swabs collected from cows at slaughter, 317 bovine milk filters and 231 fecal samples collected from slaughtered pigs in Parma province.

Since infections caused by carbapenem-resistant bacteria are mainly associated with healthcare settings and are often caused by bacteria belonging to the Enterobacterales family, especially K. pneumoniae and E. coli, human and animal samples were tested for the presence of carbapenem- resistant Enterobacterales. Genotypic methods were used to identify carbapenemases in the isolates that shew signs of resistance to carbapenems in the antimicrobial susceptibility tests (Kirby-Bauer test and Minimal Inhibitory Concentration assay). A total of 53 Enterobacterales strains phenotypically resistant to carbapenems were isolated from the four matrices. Of these, 18 strains (33.96%) were isolated from the human urine samples, 16 (30.19%) from the bovine milk filters, 10 (18.87%) from the bovine rectal swabs and 9 (16.98%) from the pig stools samples. Genes encoding for carbapenemases were found in 7 (13.21%) of these isolates: 2 (3.77%) from human samples, 2 (3.77%) from milk filters and 3 (5.66%) from pig samples. None of the bovine rectal swab isolates were found positive. The genes found in this study belonged to the KPC, VIM and OXA-48-like families. This project was a collaboration between the Inspection of Food of Animal Origin Unit and the Infectious Diseases Unit of the Department of Veterinary Science and the Nephrology Unit of the Department of Medicine and Surgery of the University of Parma.