Extended-spectrum β-lactamase (ESBL)-producing Enterobacteriaceae are classified as serious threats to human health by the U.S. Centers for Disease Control and Prevention. Water used for irrigation of fresh produce can transmit such resistant bacteria directly to edible plant parts. We screened ESBL-producing Escherichia coli, Enterobacter cloacae, and Citrobacter freundii isolated from irrigation water for their potential to transmit resistance to antibiotic-susceptible E. coli. All strains were genome-sequenced and tested in vitro for transmission of resistance to third-generation cephalosporins on solid agar as well as in liquid culture. Of the 19 screened isolates, five ESBL-producing E. coli were able to transfer resistance with different efficiency to susceptible recipient E. coli. Transconjugant strains were sequenced for detection of transferred antibiotic resistance genes (ARGs) and compared to the known ARG pattern of their respective donors. Additionally, phenotypic resistance patterns were obtained for both transconjugant and corresponding donor strains, confirming ESBL-producing phenotypes of all obtained transconjugants.

With the rapid increase of available sequencing data on clinically relevant bacterial species such as S. aureus, the genomic basis of clinical phenotypes can be investigated in much more detail, allowing a much deeper understanding of the mechanisms involved in disease. We characterized in detail the S. aureus genomic island vSaβ and defined a superordinate system to categorize S. aureus strains based on their vSaβ type, providing information about the strains’ virulence-associated genes and clinical potential.

Currently only five (SEA-SEE) out of 27 known staphylococcal enterotoxins can be analyzed using commercially available kits.Six genes (seg, sei, sem, sen, seo, and seu), encoding putative and undetectable enterotoxins, are located on the enterotoxin gene cluster (egc) which is part of the Staphylococcus aureus genomic island vSaβ. These enterotoxins have been described as likely being involved in staphylococcal food poisoning outbreaks.The aim of the present study was to determine if whole genome data can be used for the prediction of staphylococcal egc enterotoxin production, particularly enterotoxin G (SEG) and enterotoxin I (SEI). For this purpose whole genome sequences of 75 Staphylococcus aureus (S. aureus) strains from different origins (food poisoning outbreaks, human, and animal) were investigated applying bioinformatics methods (phylogenetic analysis using the core genome and different alignments). SEG and SEI expression was tested in vitro using a sandwich ELISA method.Strains could be allocated to 14 different vSaβ types, each type being associated with a single clonal complex (CC). In addition the vSaβ type and CC were associated with the origin of the strain (human or cattle derived). The amount of SEG and SEI produced also correlated with the vSaβ type and the CC of a strain. The present results show promising indications that the in vitro production of SEG and SEI can be predicted based on the vSaβ type or CC of a strain.IMPORTANCE Beside the infection properties in human and animals, S. aureus can produce different enterotoxins in food. The enterotoxins can cause vomiting and diarrhea, often involving many people. Most of these outbreaks remain undiscovered as detection methods for enterotoxins are only available for a few enterotoxins, but not for the more recently discovered enterotoxin G (SEG) and I (SEI).In this study we show promising results that in vitro production of SEG and SEI can be predicted based on the whole genome sequencing data of a strain. In addition, this data could be used to find the source (human- or cattle-derived) of an outbreak strain, which is the key for a better understanding of the role SEG and SEI play in foodborne outbreaks caused by S. aureus.

No abstract