Characterization of Enterohemorrhagic
            <i>Escherichia coli</i>
            Strains Based on Acid Resistance Phenotypes

Bhagwat, Arvind A.; Chan, L.A.; Han, Rachel; Tan, Jasmine; Kothary, Mahendra H.; Jean-Gilles, Junia; Tall, Ben D.

doi:10.1128/iai.73.8.4993-5003.2005

Cited by 63 publications

(61 citation statements)

References 52 publications

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“…Furthermore, E. coli encodes chaperone proteins, HdeA and HdeB, known to confer protection at low pH (pH Ͻ 3); this protection of periplasmic proteins from the acid-induced damages is particularly important considering the high permeability of outer membrane (25,32,46). It is noteworthy that genes encoding these acid resistance systems and chaperone proteins are well conserved in both EHEC and nonpathogenic strains such as K-12, but distinct differences in acid resistance have been reported between commensal E. coli and E. coli O157:H7, between different serotypes of EHEC strains, between E. coli O157:H7 strains from various environmental origins, or even between natural variants isolated from the same E. coli O157:H7 strain (4,6,7,9,26,36). The enhanced acid resistance in E. coli O157:H7 could be explained in part by its genetic repertoire, since strains of this pathogroup contain the largest genome on average among complete E. coli genomes (30).…”

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confidence: 99%

Evolutionary Silence of the Acid Chaperone Protein HdeB in Enterohemorrhagic Escherichia coli O157:H7

Carter

Louie

Fagerquist

et al. 2012

Appl Environ Microbiol

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The periplasmic chaperones HdeA and HdeB are known to be important for cell survival at low pH (pH < 3) in Escherichia coli and Shigella spp. Here we investigated the roles of HdeA and HdeB in the survival of various enterohemorrhagic E. coli (EHEC) following exposure to pH 2.0. Similar to K-12 strains, the acid protections conferred by HdeA and HdeB in EHEC O145 were significant: loss of HdeA and HdeB led to over 100-to 1,000-fold reductions in acid survival, depending on the growth condition of prechallenge cells. However, this protection was much less in E. coli O157:H7 strains. Deletion of hdeB did not affect the acid survival of cells, and deletion of hdeA led to less than a 5-fold decrease in survival. Sequence analysis of the hdeAB operon revealed a point mutation at the putative start codon of the hdeB gene in all 26 E. coli O157:H7 strains analyzed, which shifted the ATG start codon to ATA. This mutation correlated with the lack of HdeB in E. coli O157:H7; however, the plasmid-borne O157-hdeB was able to restore partially the acid resistance in an E. coli O145⌬hdeAB mutant, suggesting the potential function of O157-HdeB as an acid chaperone. We conclude that E. coli O157:H7 strains have evolved acid survival strategies independent of the HdeA/B chaperones and are more acid resistant than nonpathogenic K-12 for cells grown under nonfavorable culturing conditions such as in Luria-Bertani no-salt broth at 28°C. These results suggest a divergent evolution of acid resistance mechanisms within E. coli.

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confidence: 99%

Evolutionary Silence of the Acid Chaperone Protein HdeB in Enterohemorrhagic Escherichia coli O157:H7

Carter

Louie

Fagerquist

et al. 2012

Appl Environ Microbiol

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“…The second acid resistance system (AR2) is glutamate-dependent acid resistance (GDAR), and it can protect cells from acidic stress below pH 3 (22,46). In spite of the central regulatory role of RpoS, clinical and food-borne isolates of pathogenic E. coli with rpoS mutations have been reported (5,53), suggesting that the pathogen may rely on rpoS-independent induction of acid resistance systems.…”

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confidence: 99%

Functional Heterogeneity of RpoS in Stress Tolerance of Enterohemorrhagic Escherichia coli Strains

Bhagwat

Tan

Sharma

et al. 2006

Appl Environ Microbiol

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The stationary-phase sigma factor (RpoS) regulates many cellular responses to environmental stress conditions such as heat, acid, and alkali shocks. On the other hand, mutations at the rpoS locus have frequently been detected among pathogenic as well as commensal strains of Escherichia coli. The objective of this study was to perform a functional analysis of the RpoS-mediated stress responses of enterohemorrhagic E. coli strains from food-borne outbreaks. E. coli strains belonging to serotypes O157:H7, O111:H11, and O26:H11 exhibited polymorphisms for two phenotypes widely used to monitor rpoS mutations, heat tolerance and glycogen synthesis, as well as for two others, alkali tolerance and adherence to Caco-2 cells. However, these strains synthesized the oxidative acid resistance system through an rpoS-dependent pathway. During the transition from mildly acidic growth conditions (pH 5.5) to alkaline stress (pH 10.2), cell survival was dependent on rpoS functionality. Some strains were able to overcome negative regulation by RpoS and induced higher ␤-galactosidase activity without compromising their acid resistance. There were no major differences in the DNA sequences in the rpoS coding regions among the tested strains. The heterogeneity of rpoS-dependent phenotypes observed for stress-related phenotypes was also evident in the Caco-2 cell adherence assay. Wild-type O157:H7 strains with native rpoS were less adherent than rpoS-complemented counterpart strains, suggesting that rpoS functionality is needed. These results show that some pathogenic E. coli strains can maintain their acid tolerance capability while compromising other RpoS-dependent stress responses. Such adaptation processes may have significant impact on a pathogen's survival in food processing environments, as well in the host's stomach and intestine.

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“…Salmonella enterica Serovar Typhimurium strain SL1344, Escherichia coli O157:H7 EDL933, Escherichia albertii USDA 181, and Citrobacter rodentium ATCC 51459 have been described earlier [2,3,8,11,16]. Bacterial cultures were streaked on Luria-Bertani (LB) agar plates from freezer stocks, and a single colony was inoculated in LB broth and grown at 37 o C in a shaker incubator for 18-20 h.…”

Section: Methodsmentioning

confidence: 99%

Determining RNA quality for NextGen sequencing: some exceptions to the gold standard rule of 23S to 16S rRNA ratio§

Bhagwat¹,

Ying²,

Karns³

et al. 2013

Microbiol Discov

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Background: Using next-generation-sequencing technology to assess entire transcriptomes requires high quality starting RNA. Traditionally, the ratios of 23S to 16S ribosomal RNA bands from agarose gel electrophoresis have been used to judge integrity of RNA. Currently, RNA quality is routinely judged using automated microfluidic gel electrophoresis platforms and associated algorithms. Findings: Here we report that the two most popular automated platforms (i.e., BioAnalyzer and Experion systems of Agilent Technology and Bio-Rad Laboratories respectively) and their associate algorithms are based on limited data sets of model organisms. The systems perform data interpretation with presumption that prokaryotic rRNA molecules are eluted in two unique peaks corresponding to 23S and 16S molecules. However, certain microorganisms carry intervening sequences in their rRNA structural genes that are subsequently excised during ribosome formation. In such instances, the 23S and 16S rRNA components are eluted in multiple peaks. As a result, current algorithms used by microfluidic platforms read such samples as 'degraded' and assign them poor RNA quality scores. We observed RNA isolated from several Citrobacter and Salmonella isolates generated false quality scores and low 23S to 16S ribosomal RNA ratios. Conclusions: For RNA-sequencing projects involving non-model organisms, relying solely on automated algorithms for 'quality control' of RNA could be misleading. Multiple peaks corresponding to 23S or 16S RNA could be due to occurrence of multiple intervening sequences in rRNA genes.

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Characterization of Enterohemorrhagic Escherichia coli Strains Based on Acid Resistance Phenotypes

Cited by 63 publications

References 52 publications

Evolutionary Silence of the Acid Chaperone Protein HdeB in Enterohemorrhagic Escherichia coli O157:H7

Evolutionary Silence of the Acid Chaperone Protein HdeB in Enterohemorrhagic Escherichia coli O157:H7

Functional Heterogeneity of RpoS in Stress Tolerance of Enterohemorrhagic Escherichia coli Strains

Determining RNA quality for NextGen sequencing: some exceptions to the gold standard rule of 23S to 16S rRNA ratio§

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