Shiga toxin-producing Escherichia coli isolates from two 2006 outbreaks were compared to other O157:H7 isolates for virulence genotype, biofilm formation, and stress responses. Spinach- and ...lettuce-related-outbreak strains had similar pulsed-field gel electrophoresis patterns, and all carried both stx₂ and stx₂c variant genes. Cooperative biofilm formation involving an E. coli O157:H7 strain and a non-O157:H7 strain was also demonstrated.
In a previous study, we identified Congo red-binding and -nonbinding phase variants of Escherichia coli serotype O157:H7 strain ATCC 43895. The Congo red-binding variant, strain 43895OR, produced a ...dry, aggregative colony that was similar to the red, dry, and rough (rdar) phenotype characteristic of certain strains of SALMONELLA: In contrast, variant 43895OW produced a smooth and white colony morphology. In this study, we show that, similar to rdar strains of Salmonella enterica serovar Typhimurium, strain 43895OR forms large aggregates in broth cultures, firm pellicles at the air-medium interface on glass, and dense biofilms on glass and polystyrene. However, unlike S. enterica serovar Typhimurium, strain 43895OR does not stain positive for cellulose production. When strain 43895OR was fixed on agar, scanning electron microscopy showed cells expressing extracellular matrix (ECM) containing curli fibers. Strain 43895OW was devoid of any ECM or curli fibers on agar but showed expression of curli fibers during attachment to glass. Strain 43895OR produced >4-fold-larger amounts of biofilm than strain 43895OW on polystyrene, glass, stainless steel, and Teflon; formation was >3-fold higher in rich medium than in nutrient-limited medium. Biofilm-associated cells of both strains showed statistically greater resistance (P < 0.05) to hydrogen peroxide and quaternary ammonium sanitizer than their respective planktonic cells. This study shows that the rdar phenotype of E. coli O157:H7 strain 43895OR is important in multicellular growth, biofilm formation, and resistance to sanitizers. However, the lack of cellulose production by strain 43895OR indicates important differences in the ECM composition compared to that of SALMONELLA:
Single-base-pair csgD promoter mutations in human outbreak Escherichia coli O157:H7 strains ATCC 43894 and ATCC 43895 coincided with differential Congo red dye binding from curli fiber expression. ...Red phenotype csgD::lacZ promoter fusions had fourfold-greater expression than white promoter fusions. Cloning the red variant csgDEFG operon into white variants induced the red phenotype. Substrate utilization differed between red and white variants.
A whole-genome sequence analysis of
Listeria monocytogenes strain F2365 revealed 15 potential members of the Crp/Fnr family of transcriptional regulatory proteins. Each gene and the flanking regions ...were cloned, subjected to in vitro transpositional mutagenesis, and recombined into strain F2365. Mutant strains, produced for 14 of the family members, were compared to strain F2365 for differences in carbon utilization, resistance to oxidative stress, and growth under reduced oxygen conditions that would signal an Fnr- or Crp-like function for these proteins. There were no differences among strain F2365 and the 14 mutant strains in the utilization of the carbon sources readily utilized by
L. monocytogenes. Although strain KO2 had a reduced growth rate compared to strain F2365 and the other mutant strains at 30° but not at 37
°C, there were no differences in growth rates among strain F2365 and the mutant strains when incubated at either 30 or 37
°C under reduced oxygen conditions. However, when compared for differences in response to oxidative stress, mutants KO2 and KO5 showed reduced oxidative stress tolerance compared to the wild-type strain F2365. These results suggest that certain members of the putative Crp/Fnr family in
L. monocytogenes may function in response to oxidative stress similar to the Fnr-like protein (Flp) of other Gram-positive bacteria.
Intimate partner violence (IPV) causes substantial physical and psychological trauma. Restrictions introduced in response to the COVID-19 pandemic, including lockdowns and movement restrictions, may ...exacerbate IPV risk and reduce access to IPV support services. This cross-sectional study examines IPV during COVID-19 restrictions in 30 countries from the International Sexual HeAlth and REproductive Health (I-SHARE) study conducted from July 20th, 2020, to February, 15th, 2021. IPV was a primary outcome measure adapted from a World Health Organization multicountry survey. Mixed-effects modeling was used to determine IPV correlates among participants stratified by cohabitation status. The sample included 23,067 participants from 30 countries. A total of 1,070/15,336 (7.0%) participants stated that they experienced IPV during COVID-19 restrictions. A total of 1,486/15,336 (9.2%) participants stated that they had experienced either physical or sexual partner violence before the restrictions, which then decreased to 1,070 (7.0%) after the restrictions. In general, identifying as a sexual minority and experiencing greater economic vulnerability were associated with higher odds of experiencing IPV during COVID-19 restrictions, which were accentuated among participants who were living with their partners. Greater stringency of COVID-19 restrictions and living in urban or semi-urban areas were associated with lower odds of experiencing IPV in some settings. The I-SHARE data suggest a substantial burden of IPV during COVID-19 restrictions. However, the restrictions were correlated with reduced IPV in some settings. There is a need for investing in specific support systems for survivors of IPV during the implementation of restrictions designed to contain infectious disease outbreaks.
Pasteurella haemolytica FnrP is homologous to Fnr, the global transcriptional regulator of anaerobic respiration in Escherichia coli. To investigate the role of O2 in the expression of P. haemolytica ...leukotoxin, we tested a lktC::lacZ fusion constructed in E. coli for a FnrP-mediated regulatory effect under aerobic and anaerobic growth conditions. Both E. coli Fnr and FnrP suppressed leukotoxin transcription under aerobic conditions. Under anaerobic conditions, Fnr suppressed transcription, while FnrP increased transcription. These results were confirmed using FnrP*, a mutant form of FnrP that activates anaerobically inducible genes under aerobic conditions. In mobility shift assays, partially purified FnrP bound to a potential regulatory site in a P. haemolytica lktC promoter fragment.
A Pasteurella haemolytica A1 gene was identified from a recombinant library clone that expressed hemolysis in host Escherichia coli cells. The gene, designated fnrP, had sequence identity to E. coli ...fnr, a global transcriptional regulator of genes required for conversion to anaerobic growth. FnrP complemented anaerobic deficiencies of a fnr-null mutant strain of E. coli and increased expression of the Fnr-dependent, anaerobic terminal reductase gene, frdA. FnrP was purified, identified by immunoblotting, and shown to be nonhemolytic. When FnrP was expressed in E. coli delta-sheA, a null mutant of the cryptic hemolysin SheA, the transformants were nonhemolytic, indicating that FnrP activates this silent hemolysin.
Biofilm formation in Escherichia coli is a tightly controlled process requiring the expression of adhesive curli fibres and certain polysaccharides such as cellulose. The transcriptional regulator ...CsgD is central to biofilm formation, controlling the expression of the curli structural and export proteins and the diguanylate cyclase adrA, which indirectly activates cellulose production. CsgD itself is highly regulated by two sigma factors (RpoS and RpoD), multiple DNA-binding proteins, small regulatory RNAs and several GGDEF/EAL proteins acting through c-di-GMP. One such transcription factor MlrA binds the csgD promoter to enhance the RpoS-dependent transcription of csgD. Bacteriophage, often carrying the stx1 gene, utilize an insertion site in the proximal mlrA coding region of E. coli serotype O157 : H7 strains, and the loss of mlrA function would be expected to be the major factor contributing to poor curli and biofilm expression in that serotype. Using a bank of 55 strains of serotype O157 : H7, we investigated the consequences of bacteriophage insertion. Although curli/biofilm expression was restored in many of the prophage-bearing strains by a wild-type copy of mlrA on a multi-copy plasmid, more than half of the strains showed only partial or no complementation. Moreover, the two strains carrying an intact mlrA were found to be deficient in biofilm formation. However, RpoS mutations that attenuated or inactivated RpoS-dependent functions such as biofilm formation were found in >70 % of the strains, including the two strains with an intact mlrA. We conclude that bacteriophage interruption of mlrA and RpoS mutations provide major obstacles limiting curli expression and biofilm formation in most serotype O157 : H7 strains.
Shiga toxin-producing Escherichia coli isolates from 2006 outbreaks to other O157:H7 isolates for virulence genotype, biofilm formation, and stress responses are compared. It is observed that amount ...of biofilm produced by strain 06E01767 is constant whether the strain is incubated individually or in presence of 06F00475 strain. The results suggest that the E. coli O157:H7 strains associated with spinach and lettuce in the outbreaks of 2006 are closely related. The strains associated with produce outbreaks do not display unusual stress resistance characteristics or biofilm abilities compared to those of isolates from other sources, suggesting that the produce isolates do not undergo a drastic stress adaptation.
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