Biology subjects

Guldimann, C.

Publications and source records attributed to Guldimann, C..

7 recordsLinked to original sources

bioRxiv2026

Environmental Microbial Community Signatures Associated with Listeria spp. Detection in German Meat Processing Facilities

Listeria monocytogenes can persist in niches of meat processing environments despite routine cleaning and disinfection. Its persistence may depend not only on stress tolerance but also on interactions with resident microbial communities, which may promote or inhibit survival. However, these ecological relationships remain poorly understood. We combined 16S rRNA V3/V4 amplicon sequencing, culture-based detection, and multilocus sequence typing (MLST) to characterize microbial communities in six German meat processing facilities over one year. We examined associations among community structure, sampling sites (drains and food-contact surfaces), and the occurrence of Listeria spp., including L. monocytogenes. Microbial communities were dominated by core genera typical of food-processing environments, particularly Pseudomonas spp. and Acinetobacter spp., but differed significantly among facilities (PERMANOVA, p = 0.001; pairwise R{superscript 2} = 0.023-0.079), indicating facility-specific communities. Culture-based analyses detected Listeria spp. in 51 of 370 environmental samples (13.8%), mainly from drains (44/51, 86.3%). L. monocytogenes was detected in five of six facilities, with 19 of 21 isolates originating from drains (90.5%). MLST of 74 typeable L. monocytogenes isolates revealed high diversity, comprising 21 sequence types across 15 clonal complexes, with lineage II predominating (86.5%). Overall microbial community composition was significantly associated with Listeria spp. and L. monocytogenes presence (PERMANOVA, p = 0.001; R{superscript 2} = 0.0137 and 0.0083). In drains, ASVs assigned to Acinetobacter, Rhizorhapis, and Vagococcus species showed positive associations with Listeria spp.-positive samples. Together these findings suggest that drains are key ecological niches for Listeria spp. and that associated taxa may indicate drain communities linked to Listeria spp. recovery. IMPORTANCEListeria monocytogenes is a major foodborne pathogen that can persist in meat processing environments despite routine cleaning and disinfection. Resident microbial communities may influence its survival, but longitudinal studies linking those communities with culture-based Listeria spp. detection remain limited. Here, we characterized microbial communities in six German meat processing facilities over 1 year using 16S rRNA gene amplicon sequencing and culture-based Listeria spp. detection, and MLST of L. monocytogenes isolates. We identified facility-specific microbial communities, identified floor drains as key niches for Listeria spp., and observed repeated recovery of different L. monocytogenes sequence types across facilities. In drains, ASVs assigned to the genera Acinetobacter, Rhizorhapis, and Vagococcus species were positively associated with culture-positive samples, identifying candidate taxa that may reflect microbial conditions associated with Listeria spp. recovery. These findings highlight the importance of considering not only whether Listeria spp. are detected, but also the resident microbial communities that may support their fitness.

microbiology↗

bioRxiv2026

Identification of genes promoting fitness of a plant-associated Salmonella Choleraesuis strain on alfalfa sprouts during cold storage

Consumption of sprouted seeds, such as alfalfa sprouts, has increased in recent years due to their perceived health benefits. However, these food products have repeatedly been associated with outbreaks of foodborne pathogens, including Salmonella enterica serovars. An S. enterica serovar Choleraesuis strain previously isolated from melon fruit internal tissues was selected as a model to explore plant-pathogen interactions on alfalfa sprouts. Using this strain, we generated a barcoded transposon mutant library comprising approximately 33,000 unique insertions. This library and a collection of individual insertion mutants derived from it were used to identify genetic mechanisms contributing to the fitness of this S. Choleraesuis strain on alfalfa sprouts. The library was screened on sprouts during cold storage at 8{degrees}C. Negative selection for mutants with insertions in eda, fabF, lpp1_2, pnp, stpA, SCHChr_03621 and two intergenic regions were identified. Competition experiments between individual insertion mutants and the wild type confirmed the phenotype of three genes: eda, coding for a keto-hydroxyglutarate-aldolase/keto-deoxy-phosphogluconate aldolase involved in the Entner-Doudoroff pathway, mnmG, encoding the glucose-inhibited division protein, and fabF, involved in fatty acid biogenesis. This study offers a genome-wide perspective on the genes enabling a plant-associated Salmonella strain to persist on alfalfa sprouts. We highlight factors that are critical not only for persistence throughout the entire cold-storage period under conditions that closely simulate real shelf-life conditions in this high-risk food matrix.

microbiology↗

bioRxiv2025

Genomic factors contributing to the resilience of Salmonella enterica on ready-to-eat muskmelon

Salmonella outbreaks have repeatedly been associated with muskmelons. To identify genes under selection in S. enterica growing in this food matrix, barcoded transposon mutant libraries in three S. enterica serovars - Typhimurium, Enteritidis, and Newport - were screened for survival and growth on muskmelon. Applying stringent thresholds, a total of 26 genes in Typhimurium, 34 in Enteritidis, and 50 in Newport were found to significantly influence fitness during muskmelon interaction, with many of these being temperature dependent. Genes whose disruption affected fitness across all three serovars were enriched for functions related to RNA degradation and ribosome biogenesis. Targeted competition assays confirmed the contribution of selected genes, revealing nutrient-dependent phenotypes for most mutants. Remarkably, the polyribonucleotide nucleotidyltransferase gene, pnp, and the D-3-phosphoglycerate dehydrogenase gene, serA, conferred a selective advantage when growing in muskmelon but not under nutrition-rich control conditions. In contrast, the nitrogen regulation response regulator GlnG provided a muskmelon-specific fitness disadvantage. This study provides novel insights into genome-wide adaptation mechanisms of multiple Salmonella serovars to growth on muskmelons, revealing both shared and serovar-specific determinants while illustrating the dynamic genetic responses of S. enterica throughout the interaction period.

genomics↗

bioRxiv2023

Large-scale phenotypic and genomic characterization of Listeria monocytogenes susceptibility to quaternary ammonium compounds

Listeria monocytogenes is a significant concern for the food industry due to its ability to persist in the food processing environment. Decreased susceptibility to disinfectants is one of the factors that contribute to the persistence of L. monocytogenes. The objective of this study was to explore the diversity of L. monocytogenes susceptibility to quaternary ammonium compounds (QACs) using 1,671 L. monocytogenes isolates. This was used to determine the phenotype-genotype concordance and characterize genomes of the QAC sensitive and tolerant isolates for stress resistance, virulence and plasmid replicon genes. Distribution of QAC tolerance genes among 37,897 publicly available L. monocytogenes genomes were also examined. The minimum inhibitory concentration to QACs was determined by the broth microdilution method and non-sequenced isolates (n=1,244) were whole genome sequenced. Genotype-phenotype concordance was 99% for benzalkonium chloride, DDAC and a commercial QAC based sanitizer. Prevalence of QAC tolerance genes was 23% and 28% in our L. monocytogenes collection and in the global dataset, respectively. qacH was the most prevalent gene in our collection (61%), with 19% prevalence in the global dataset. Notably, bcrABC was most common (72%) globally, while 25% in our collection. Prevalence of emrC and emrE was comparable in both datasets, 7% and 2%, respectively. Replicon genes, indicative of plasmid harborage, were detected in 44% of the isolates and associated with the QAC tolerant phenotype. The presented analysis is based on the biggest L. monocytogenes collection in diversity and quantity for characterization of the L. monocytogenes QAC tolerance at both phenotypic and genomic levels. IMPORTANCEContamination of Listeria monocytogenes within the food processing environment is of concern to the food industry due to challenges in eradicating the pathogen once it becomes persistent in the environment. Genetic markers associated with increased tolerance to disinfectants have been identified, which alongside factors favor the persistence of L. monocytogenes in the production environment. By employing a comprehensive large-scale phenotypic testing and genomic analysis our study significantly enhances the understanding of the prevalence of quaternary ammonium compound (QAC) tolerant L. monocytogenes and the genetic determinants associated with the increased tolerance. Furthermore, we report on the prevalence of QAC tolerance genes among 37,897 publicly available L. monocytogenes sequences and their distribution within clonal complexes, isolation sources and geographical locations. As the propagation of QAC tolerance showed not be evenly distributed globally this highlights that understanding the development of L. monocytogenes disinfectant tolerance can be monitored using publicly available WGS data.

microbiology↗

bioRxiv2022

A multidrug-resistant Salmonella enterica serotype Typhimurium DT104 lineage circulating among humans and cattle in the United States lost the ability to produce pertussis-like toxin ArtAB in close temporal proximity to the global DT104 epidemic

Salmonella enterica subspecies enterica serotype Typhimurium definitive type 104 (DT104) can infect both humans and animals and is often multidrug-resistant (MDR). Previous studies have indicated that, unlike most S. Typhimurium, the overwhelming majority of DT104 strains produce pertussis-like toxin ArtAB via prophage-encoded genes artAB. However, DT104 that lack artAB have been described on occasion. Here, we identify a MDR DT104 complex lineage circulating among humans and cattle in the United States, which lacks artAB (i.e., the "U.S. artAB-negative major clade"; n = 42 genomes). Unlike most other bovine- and human-associated DT104 complex strains from the U.S. (n = 230 total genomes), which harbor artAB on prophage Gifsy-1 (n = 177), members of the U.S. artAB-negative major clade lack Gifsy-1, as well as anti-inflammatory effector gogB. The U.S. artAB-negative major clade encompasses human- and cattle-associated strains isolated from [≥]11 U.S. states over a twenty-year period. The clade was predicted to have lost artAB, Gifsy-1, and gogB circa 1985-1987 (95% highest posterior density interval 1979.0-1992.1). When compared to DT104 genomes from other world regions (n = 752 total genomes), several additional, sporadic artAB, Gifsy-1, and/or gogB loss events among clades encompassing [≤]5 genomes were observed. Using phenotypic assays that simulate conditions encountered during human and/or bovine digestion, members of the U.S. artAB-negative major clade did not differ from closely related Gifsy-1/artAB/gogB-harboring U.S. DT104 complex strains (ANOVA raw P-value > 0.05); thus, future research is needed to elucidate the roles that artAB, gogB, and Gifsy-1 play in DT104 virulence in humans and animals. Impact StatementMulti-drug resistant (MDR) Salmonella enterica serotype Typhimurium definitive type 104 (DT104) was responsible for a global epidemic among humans and animals throughout the 1990s and continues to circulate worldwide. Previous studies have indicated that the vast majority of DT104 produce pertussis-like toxin ArtAB via prophage-encoded artAB. Here, we identify a DT104 complex lineage that has been circulating among cattle and humans across [≥]11 U.S. states for over twenty years, which lacks the ability to produce ArtAB (i.e., the "U.S. artAB-negative major clade"). The common ancestor of all U.S. artAB-negative major clade members lost the ability to produce ArtAB in the 1980s; however, the reason for this loss-of-function event within this well-established pathogen remains unclear. The role that ArtAB plays in DT104 virulence remains elusive, and phenotypic assays conducted here indicate that members of the U.S. artAB-negative major clade do not have a significant advantage or disadvantage relative to closely related, Gifsy-1/artAB/gogB-harboring U.S. DT104 complex strains when exposed to stressors encountered during human and/or bovine digestion in vitro. However, ArtAB heterogeneity within the DT104 complex suggests clade-specific selection for or against maintenance of ArtAB. Thus, future studies querying the virulence characteristics of the U.S. artAB-negative major clade are needed. Data SummarySupplementary Data is available under DOI 10.5281/zenodo.7688792, with URL https://doi.org/10.5281/zenodo.7688792.

microbiology↗

bioRxiv2019

Identification of novel mobilized colistin resistance gene mcr-9 in a multidrug-resistant, colistin-susceptible Salmonella enterica serotype Typhimurium isolate using a combination of high-throughput, in silico screening and functional analysis

Mobilized colistin resistance (mcr) genes are plasmid-borne genes that confer resistance to colistin, an antibiotic used to treat severe bacterial infections. To date, eight known mcr homologues have been described (mcr-1 to -8). Here, we describe mcr-9, a novel mcr homologue, detected in a Salmonella enterica serotype Typhimurium (S. Typhimurium) genome using an in silico approach, followed by experimental functional analysis. The amino acid sequence of mcr-9, detected in a multidrug resistant (MDR) S. Typhimurium strain isolated from a human patient in Washington State in 2010, most closely resembled mcr-3, aligning with 64.5% amino acid identity and 99.5% coverage using translated nucleotide blast. The S. Typhimurium strain was tested for phenotypic resistance to colistin and was found to be sensitive at the 2 mg/L European Committee on Antimicrobial Susceptibility Testing breakpoint under the tested conditions. To determine whether it was capable of conferring resistance to colistin when expressed in a heterologous host, mcr-9 was cloned in colistin-susceptible Escherichia coli NEB5 under an IPTG-induced promoter. Expression of mcr-9 conferred resistance to colistin in E. coli NEB5 at 1, 2, and 2.5 mg/L colistin, albeit at a lower level when compared to mcr-3. Pairwise comparisons of the predicted protein structures associated with all nine mcr homologues (Mcr-1 to -9) revealed that Mcr-9, Mcr-3, and Mcr-7 share a high degree of similarity at the structural level. The results of our approach indicate that mcr-9 is capable of conferring phenotypic resistance to colistin in Enterobacteriaceae and should be immediately considered when monitoring plasmid-mediated colistin resistance. Importance: Colistin is a last-resort antibiotic that is used to treat severe infections caused by MDR and extensively drug resistant (XDR) bacteria. The World Health Organization (WHO) has designated colistin as a Highest Priority Critically Important Antimicrobial for human medicine (WHO, Critically Important Antimicrobials for Human Medicine, 5th Revision, 2017), as it is often one of the only therapies available for treating serious bacterial infections in critically ill patients. Plasmid-borne mcr genes that confer resistance to colistin pose a threat to public health at an international scale, as they can be transmitted via horizontal gene transfer and have the potential to spread globally. Therefore, the establishment of a complete reference of mcr genes that can be used to screen for plasmid-mediated colistin resistance is essential for developing effective control strategies.

microbiology↗

bioRxiv2018

Growth potential of Listeria monocytogenes in twelve different types of RTE salads: impact of food matrix, storage temperature and shelf life

Listeriosis is a food borne disease associated with high hospitalization and fatality rates; in 2014, EU member states reported 2194 cases with 98.9% hospitalization rates and 210 fatalities. Proper risk analysis and the development of effective food safety strategies critically depend on the knowledge of the growth characteristics of L. monocytogenes on the product in question. Ready-to-eat (RTE) salads present a challenge in this context due to the absence of a heat treatment step before consumption and the interaction of pathogens with the plant microbial microbiota. This study provides challenge-test based data of the growth characteristics of L. monocytogenes on twelve RTE salads. The food matrix, storage time and storage temperature were factors with a significant impact on the growth of L. monocytogenes. While most tested salads permitted a significant increase of L. monocytogenes in at least one of the tested conditions, no growth was observed on celeriac, carrot and corn salad products. There was a considerable increase in growth at 8 {degrees}C compared to 5 {degrees}C. Our data indicate that the reduction of the storage temperature at retail level to 5 {degrees}C and product shelf life could help mitigate the risk of L. monocytogenes in RTE salads.

microbiology↗