Genetic but No Phenotypic Associations between Biocide Tolerance and Antibiotic Resistance in Escherichia coli from German Broiler Fattening Farms.

Biocides are frequently applied as disinfectants in animal husbandry to prevent the transmission of drug-resistant bacteria and to control zoonotic diseases. Concerns have been raised, that their use may contribute to the selection and persistence of antimicrobial-resistant bacteria. Especially, extended-spectrum ß-lactamase- and AmpC ß-lactamase-producing Escherichia coli have become a global health threat. In our study, 29 ESBL-/AmpC-producing and 64 NON-ESBL-/AmpC-producing E.coli isolates from three German broiler fattening farms collected in 2016 following regular cleaning and disinfection were phylogenetically characterized by whole genome sequencing, analyzed for phylogenetic distribution of virulence-associated genes, and screened for determinants of and associations between biocide tolerance and antibiotic resistance. Of the 30 known and two unknown sequence types detected, ST117 and ST297 were the most common genotypes. These STs are recognized worldwide as pandemic lineages causing disease in humans and poultry. Virulence determinants associated with extraintestinal pathogenic E.coli showed variable phylogenetic distribution patterns. Isolates with reduced biocide susceptibility were rarely found on the tested farms. Nine isolates displayed elevated MICs and/or MBCs of formaldehyde, chlorocresol, peroxyacetic acid, or benzalkonium chloride. Antibiotic resistance to ampicillin, trimethoprim, and sulfamethoxazole was most prevalent. The majority of ESBL-/AmpC-producing isolates carried blaCTX-M (55%) or blaCMY-2 (24%) genes. Phenotypic biocide tolerance and antibiotic resistance were not interlinked. However, biocide and metal resistance determinants were found on mobile genetic elements together with antibiotic resistance genes raising concerns that biocides used in the food industry may lead to selection pressure for strains carrying acquired resistance determinants to different antimicrobials.

Backtracking and forward checking of human listeriosis clusters identified a multiclonal outbreak linked to Listeria monocytogenes in meat products of a single producer.

Due to its high case fatality rate, foodborne listeriosis is considered a major public health concern worldwide. We describe one of the largest listeriosis outbreaks in Germany with 83 cases of invasive listeriosis between 2013 and 2018. As part of the outbreak investigation, we identified a highly diverse Listeria monocytogenes population at a single producer of ready-to-eat meat products. Strikingly, the extensive sampling after identification of a first match between a cluster of clinical isolates and a food isolate allowed for a linkage between this producer and a second, previously unmatched cluster of clinical isolates. Bacterial persistence in the processing plant and indications of cross-contamination events explained long-term contamination of food that led to the protracted outbreak. Based on screening for virulence factors, a pathogenic phenotype could not be ruled out for other strains circulating in the plant, suggesting that the outbreak could have been even larger. As most isolates were sensitive to common biocides used in the plant, hard to clean niches in the production line may have played a major role in the consolidation of the contamination. Our study demonstrates how important it is to search for the origin of infection when cases of illness have occurred (backtracking), but also clearly highlights that it is equally important to check whether a contamination at food or production level has caused disease (forward checking). Only through this two-sided control strategy, foodborne disease outbreaks such as listeriosis can be minimized, which could be a real improvement for public health.

Evaluation of a Newly Developed Vacuum Dried Microtiter Plate for Rapid Biocide Susceptibility Testing of Clinical Enterococcus Faecium Isolates.

We investigated the suitability of a newly developed biocide susceptibility test system based on microtiter plates containing vacuum dried biocides as a fast and reliable screening method. The evaluated substances included the cationic biocides benzalkonium chloride (BAC), chlorhexidine dihydrochloride (CHX), cetylpyridinium chloride, didecyldimethylammonium chloride, and octenidine dihydrochloride. Testing a selection of Escherichia coli and enterococci, the biocide microtiter plates provided results comparable to those obtained from broth microdilution according to ISO 20776-1. Broad MIC ranges allowed for testing gram-positive and gram-negative species with the same plate design. In the second part of our study, we applied the established method to analyze the susceptibility of 90 clinical Enterococcus faecium isolates from a German university hospital, as previous studies have indicated a link between reduced susceptibility to substances such as CHX and BAC and vancomycin resistance. We therefore determined MIC and minimum bactericidal concentrations (MBC) for 48 non-clonal vancomycin susceptible and 42 non-clonal vancomycin resistant isolates, but MIC95 and MBC95 were quite similar in both groups. Our easy to handle and ready to use test system enables the routine surveillance of bacterial tolerance towards disinfectants in hospitals. As a result, hygiene measures can be adapted and nosocomial infections controlled despite increasing prevalence of antibiotic-resistant bacteria.