Overexpression of the third H-NS paralogue H-NS2 compensates fitness loss in hns mutants of the enteroaggregative Escherichia coli strain 042.

Members of the H-NS protein family play a role both in the chromosome architecture and in the regulation of gene expression in bacteria. The genomes of the enterobacteria encode an H-NS paralogue, the StpA protein. StpA displays specific regulatory properties and provides a molecular backup for H-NS. Some enterobacteria also encode third H-NS paralogues. This is the case of the enteroaggregative E. coli (EAEC) strain 042, which encodes the hns, stpA and hns2 genes. We provide in this paper novel information about the role of the H-NS2 protein in strain 042. A C > T transition in the hns2 promoter leading to increased H-NS2 expression is readily selected in hns mutants. Increased H-NS2 expression partially compensates for H-NS loss. H-NS2 levels are critical for the strain 042 fitness. Under some circumstances, high H-NS2 expression levels dictated by the mutant hns2 promoter can be deleterious. The selection of T > C revertants or of clones harboring insertional inactivations of the hns2 gene can then occur. Temperature also plays a relevant role in the H-NS2 regulatory activity. At 37 °C, H-NS2 targets a subset of the H-NS repressed genes contributing to their silencing. When temperature drops to 25 °C, the repressory ability of H-NS2 is significantly reduced. At low temperature, H-NS plays the main repressory role.

Impact of single-room contact precautions on hospital-acquisition and transmission of multidrug-resistant Escherichia coli: a prospective multicentre cohort study in haematological and oncological wards.

OBJECTIVES: Colonization and infection with third-generation cephalosporin-resistant Escherichia coli (3GCR-EC) are frequent in haematological and oncological patients. In this high-risk setting, German guidelines recommend single-room contact precautions (SCP) for patients with 3GCR-EC that are non-susceptible to fluoroquinolones (F3GCR-EC). However, this recommendation is controversial, as evidence is limited. METHODS: We performed a prospective, multicentre cohort study at four haematology and oncology departments assessing the impact of SCP on hospital-acquired colonization or bloodstream infection (BSI) with F3GCR-EC. Two sites performed SCP for F3GCR-EC patients including single rooms, gloves and gowns (SCP sites), and two did not (NCP sites). Active screening for 3GCR-EC was performed and isolates were characterized with molecular typing methods including whole genome sequencing and core genome multiple locus sequence typing to assess patient-to-patient transmission. Potential confounders were assessed by competing-risk regression analysis. RESULTS: Within 12 months, 1386 patients at NCP sites and 1582 patients at SCP sites were included. Hospital-acquisition of F3GCR-EC was observed in 22/1386 (1.59%) and 16/1582 (1.01%) patients, respectively (p 0.191). There were 3/1386 (0.22%) patients with BSI caused by F3GCR-EC at NCP sites and 4/1582 (0.25%) at SCP sites (p 1.000). Patient-to-patient transmission occurred in three cases at NCP and SCP sites each (p 1.000). The number of patients needed to screen in order to prevent one patient-to-patient transmission of F3GCR-EC was determined to be 3729. CONCLUSIONS: Use of SCP had no significant impact on hospital-acquisition or patient-to-patient transmission of F3GCR-EC in this high-risk setting.