Expression of Escherichia coli TehA gives resistance to antiseptics and disinfectants similar to that conferred by multidrug resistance efflux pumps

Increased resistance against tellurite is conferred by a mutation in the promoter region of uncommon tellurite resistance gene tehB in the ter-negative Shiga toxin-producing Escherichia coli O157:H7

Resistance to potassium tellurite (PT) is an important indicator in isolating Shiga toxin-producing Escherichia coli (STEC) O157:H7 and other major STEC serogroups. Common resistance determinant genes are encoded in the ter gene cluster. We found an O157:H7 isolate that does not harbor ter but is resistant to PT. One nonsynonymous mutation was found in another PT resistance gene, tehA, through whole-genome sequence analyses. To elucidate the contribution of this mutation to PT resistance, complementation of tehA and the related gene tehB in isogenic strains and quantitative RT‒PCR were performed. The results indicated that the point mutation not only changed an amino acid of tehA, but also was positioned on a putative internal promoter of tehB and increased PT resistance by elevating tehB mRNA expression. Meanwhile, the amino acid change in tehA had negligible impact on the PT resistance. Comprehensive screening revealed that 2.3% of O157:H7 isolates in Japan did not harbor the ter gene cluster, but the same mutation in tehA was not found. These results suggested that PT resistance in E. coli can be enhanced through one mutational event even in ter-negative strains.

IMPORTANCE

Selective agents are important for isolating Shiga toxin-producing Escherichia coli (STEC) because the undesirable growth of microflora should be inhibited. Potassium tellurite (PT) is a common selective agent for major STEC serotypes. In this study, we found a novel variant of PT resistance genes, tehAB, in STEC O157:H7. Molecular experiments clearly showed that one point mutation in a predicted internal promoter region of tehB upregulated the expression of the gene and consequently led to increased resistance to PT. Because tehAB genes are ubiquitous across E. coli, these results provide universal insight into PT resistance in this species.

Mixed waste contamination selects for a mobile genetic element population enriched in multiple heavy metal resistance genes

Mobile genetic elements (MGEs) like plasmids, viruses, and transposable elements can provide fitness benefits to their hosts for survival in the presence of environmental stressors. Heavy metal resistance genes (HMRGs) are frequently observed on MGEs, suggesting that MGEs may be an important driver of adaptive evolution in environments contaminated with heavy metals. Here, we report the meta-mobilome of the heavy metal-contaminated regions of the Oak Ridge Reservation subsurface. This meta-mobilome was compared with one derived from samples collected from unimpacted regions of the Oak Ridge Reservation subsurface. We assembled 1615 unique circularized DNA elements that we propose to be MGEs. The circular elements from the highly contaminated subsurface were enriched in HMRG clusters relative to those from the nearby unimpacted regions. Additionally, we found that these HMRGs were associated with Gamma and Betaproteobacteria hosts in the contaminated subsurface and potentially facilitate the persistence and dominance of these taxa in this region. Finally, the HMRGs were associated with conjugative elements, suggesting their potential for future lateral transfer. We demonstrate how our understanding of MGE ecology, evolution, and function can be enhanced through the genomic context provided by completed MGE assemblies.

Detection of an IMI-2 carbapenemase-producing Enterobacter asburiae at a Swedish feed mill

Occurrence of multidrug resistant Enterobacteriaceae in livestock is of concern as they can spread to humans. A potential introduction route for these bacteria to livestock could be animal feed. We therefore wanted to identify if Escherichia spp., Enterobacter spp., Klebsiella spp., or Raoutella spp. with transferable resistance to extended spectrum cephalosporins, carbapenems or colistin could be detected in the environment at feed mills in Sweden. A second aim was to compare detected isolates to previous described isolates from humans and animals in Sweden to establish relatedness which could indicate a potential transmission between sectors and feed mills as a source for antibiotic resistant bacteria. However, no isolates with transferable resistance to extended-cephalosporins or colistin could be identified, but one isolate belonging to the Enterobacter cloacae complex was shown to be carbapenem-resistant and showing carbapenemase-activity. Based on sequencing by both short-read Illumina and long-read Oxford Nanopore MinIon technologies it was shown that this isolate was an E. asburiae carrying a bla_IMI-2 gene on a 216 Kbp plasmid, designated pSB89A/IMI-2, and contained the plasmid replicons IncFII, IncFIB, and a third replicon showing highest similarity to the IncFII(Yp). In addition, the plasmid contained genes for various functions such as plasmid segregation and stability, plasmid transfer and arsenical transport, but no additional antibiotic resistance genes. This isolate and the pSB89A/IMI-2 was compared to three human clinical isolates positive for bla_IMI-2 available from the Swedish antibiotic monitoring program Swedres. It was shown that one of the human isolates carried a plasmid similar with regards to gene content to the pSB89A/IMI-2 except for the plasmid transfer system, but that the order of genes was different. The pSB89A/IMI-2 did however share the same transfer system as the bla_IMI-2 carrying plasmids from the other two human isolates. The pSB89A/IMI-2 was also compared to previously published plasmids carrying bla_IMI-2, but no identical plasmids could be identified. However, most shared part of the plasmid transfer system and DNA replication genes, and the bla_IMI-2 gene was located next the transcription regulator imiR. The IS3-family insertion element downstream of imiR in the pSB89A was also related to the IS elements in other bla_IMI-carrying plasmids.

Multi-omics of the esophageal microenvironment identifies signatures associated with progression of Barrett's esophagus

BACKGROUND

The enrichment of Gram-negative bacteria of oral origin in the esophageal microbiome has been associated with the development of metaplasia. However, to date, no study has comprehensively assessed the relationships between the esophageal microbiome and the host.

METHODS

Here, we examine the esophageal microenvironment in gastro-esophageal reflux disease and metaplasia using multi-omics strategies targeting the microbiome and host transcriptome, followed by targeted culture, comparative genomics, and host-microbial interaction studies of bacterial signatures of interest.

RESULTS

Profiling of the host transcriptome from esophageal mucosal biopsies revealed profound changes during metaplasia. Importantly, five biomarkers showed consistent longitudinal changes with disease progression from reflux disease to metaplasia. We showed for the first time that the esophageal microbiome is distinct from the salivary microbiome and the enrichment of Campylobacter species as a consistent signature in disease across two independent cohorts. Shape fitting and matrix correlation identified associations between the microbiome and host transcriptome profiles, with a novel co-exclusion relationship found between Campylobacter and napsin B aspartic peptidase. Targeted culture of Campylobacter species from the same cohort revealed a subset of isolates to have a higher capacity to survive within primary human macrophages. Comparative genomic analyses showed these isolates could be differentiated by specific genomic features, one of which was validated to be associated with intracellular fitness. Screening for these Campylobacter strain-specific signatures in shotgun metagenomics data from another cohort showed an increase in prevalence with disease progression. Comparative transcriptomic analyses of primary esophageal epithelial cells exposed to the Campylobacter isolates revealed expression changes within those infected with strains with high intracellular fitness that could explain the increased likelihood of disease progression.

CONCLUSIONS

We provide a comprehensive assessment of the esophageal microenvironment, identifying bacterial strain-specific signatures with high relevance to progression of metaplasia.

Vaginal tablets of dequalinium chloride 10 mg versus clotrimazole 100 mg for vaginal candidiasis: a double-blind, randomized study

PURPOSE

To compare the clinical response, microscopic examination and fungal culture between dequalinium chloride (DQC) and clotrimazole (CT) for treating vaginal candidiasis (VC).

METHODS

The double-blind, randomized study was conducted from September 2014 to September 2016 at Siriraj Hospital, Thailand. Eligible participants were Thai women diagnosed with VC by microscopic examination. The exclusion criteria included immunocompromised conditions, consumption of antifungal drugs, and having recurrent VC. Each participant was randomized with a 1:1 allocation to receive six vaginal tablets of 100 mg CT or 10 mg DQC. Two visits included 10 ± 2 days (C1) and 38 ± 4 days (C2). Outcome measures were improvement of VC symptoms, microscopic examination, culture, satisfaction and tolerability.

RESULTS

Of 155 eligible participants, 150 were randomized and allocated into CT (N = 76) and DQC (N = 74). The average age was 31.1 ± 7.2 years. Comparable improvement of clinical response was demonstrated (OR at C1 0.79, 95% CI 0.56-1.10, p = 0.197; and OR at C2 0.99, 95% CI 0.69-1.43, p = 0.985). Of CT and DQC groups, the microscopic examination was positive at 11/75 (14.9%) vs 18/72 (25.3%) at C1 and 18/74 (24.3%) vs 28/66 (42.4%) at C2. And the culture was positive at 25/75 (33.8%) vs 46/72 (65.7%) at C1 and at 26/74 (36.6%) vs 46/66 (69.7%) at C2. Most participants had high satisfaction and tolerability and none reported any side effects.

CONCLUSION

DQC and CT show comparable clinical response but CT results in greater improvement of microscopic examination and fungal culture.

CLINICAL TRIAL REGISTRATION

The Clinical Trial Registry number was NCT02242695. (September 17, 2014).

Development of Escherichia coli-based gene expression profiling of sewage sludge leachates

AIMS

The impact of municipal waste on pathogenic micro-organisms released into the environment is a public health concern. This study aims to evaluate the effects of sewage sludge and antibiotic contaminants on stress response, virulence and antibiotic resistance in a pathogenic Escherichia coli.

METHODS AND RESULTS

The effects of sewage sludge leachates on uropathogenic E. coli CFT073 were determined by monitoring the expression of 45 genes associated with antibiotic/metal resistance, stress response and virulence using RT-qPCR. The E. coli gene expression was validated using subinhibitory concentrations of tetracycline and ciprofloxacin. E. coli exposed to sewage sludge or sewage sludge+fly ash leachates altered the expression of five antibiotic and metal resistance, three stress response and two virulence-associated genes. When antibiotics were combined with sludge or sludge+fly ash the antibiotic-associated gene expression was altered.

CONCLUSIONS

E. coli treated with two sludge leachates had distinct gene expression patterns that were altered when the sludge leachates were combined with tetracycline, although to a lesser extent with ciprofloxacin.

SIGNIFICANCE AND IMPACT OF THE STUDY

The E. coli multigene expression analysis is a potential new tool for assessing the effects of pollutants on pathogenic microbes in environmental waters for improved risk assessment.

Comparative Genomics Analysis of Plasmid pPV989-94 from a Clinical Isolate of Pantoea vagans PV989

Pantoea vagans, a gram-negative bacterium from the genus Pantoea and family Enterobacteriaceae, is present in various natural environments and considered to be plant endophytes. We isolated the Pantoea vagans PV989 strain from the clinic and sequenced its whole genome. Besides a chromosome DNA molecule, it also harboured three large plasmids. A comparative genomics analysis was performed for the smallest plasmid, pPV989-94. It can be divided into four regions, including three conservative regions related to replication (R1), transfer conjugation (R2), and transfer leading (R3), and one variable region (R4). Further analysis showed that pPV989-94 is most similar to plasmids LA637P2 and pEA68 of Erwinia amylovora strains isolated from fruit trees. These three plasmids share three conservative regions (R1, R2, and R3). Interestingly, a fragment (R4′) in R4, mediated by phage integrase and phage integrase family site-specific recombinase and encoding 9 genes related to glycometabolism, resistance, and DNA repair, was unique in pPV989-94. Homologues of R4′ were found in other plasmids or chromosomes, suggesting that horizontal gene transfer (HGT) occurred among different bacteria of various species or genera. The acquired functional genes may play important roles in the adaptation of bacteria to different hosts or environmental conditions.

Pacing across the membrane: the novel PACE family of efflux pumps is widespread in Gram-negative pathogens

The proteobacterial antimicrobial compound efflux (PACE) family of transport proteins was only recently described. PACE family transport proteins can confer resistance to a range of biocides used as disinfectants and antiseptics, and are encoded by many important Gram-negative human pathogens. However, we are only just beginning to appreciate the range of functions and the mechanism(s) of transport operating in these proteins. Genes encoding PACE family proteins are typically conserved in the core genomes of bacterial species rather than on recently acquired mobile genetic elements, suggesting that they confer important core functions in addition to biocide resistance. Three-dimensional structural information is not yet available for PACE family proteins. However, PACE proteins have several very highly conserved amino acid sequence motifs that are likely to be important for substrate transport. PACE proteins also display strong amino acid sequence conservation between their N— and C-terminal halves, suggesting that they evolved by duplication of an ancestral protein comprised of two transmembrane helices. In light of their drug resistance functions in Gram-negative pathogens, PACE proteins should be the subject of detailed future investigation.

Quaternary ammonium-based biomedical materials: State-of-the-art, toxicological aspects and antimicrobial resistance

Microbial infections affect humans worldwide. Many quaternary ammonium compounds have been synthesized that are not only antibacterial, but also possess antifungal, antiviral and anti-matrix metalloproteinase capabilities. Incorporation of quaternary ammonium moieties into polymers represents one of the most promising strategies for preparation of antimicrobial biomaterials. Various polymerization techniques have been employed to prepare antimicrobial surfaces with quaternary ammonium functionalities; in particular, syntheses involving controlled radical polymerization techniques enable precise control over macromolecular structure, order and functionality. Although recent publications report exciting advances in the biomedical field, some of these technological developments have also been accompanied by potential toxicological and antimicrobial resistance challenges. Recent evidenced-based data on the biomedical applications of antimicrobial quaternary ammonium-containing biomaterials that are based on randomized human clinical trials, the golden standard in contemporary medicinal science, are included in the present review. This should help increase visibility, stimulate debates and spur conversations within a wider scientific community on the implications and plausibility for future developments of quaternary ammonium-based antimicrobial biomaterials.

Use of locally delivered dequalinium chloride in the treatment of vaginal infections: a review

Background

Vaginal infections are responsible for a large proportion of gynaecological outpatient visits. Those are bacterial vaginosis (BV), vulvovaginal candidosis (VVC), aerobic vaginitis (AV) associated with aerobic bacteria, and mixed infections. Usual treatments show similar acceptable short-term efficacy, but frequent recurrences and increasing microbial resistance are unsolved issues. Furthermore, vaginal infections are associated with a variety of serious adverse outcomes in pregnancy and generally have a major impact on quality of life. Identifying the correct therapy can be challenging for the clinician, particularly in mixed infections.

Findings

Dequalinium chloride (DQC) is an anti-microbial antiseptic agent with a broad bactericidal and fungicidal activity. Systemic absorption after vaginal application of DQC is very low and systemic effects negligible. Vaginal DQC (Fluomizin^®vaginal tablets) has been shown to have equal clinical efficacy as clindamycin in the treatment of BV. Its broad antimicrobial activity makes it appropriate for the treatment of mixed vaginal infections and in case of uncertain diagnosis. Moreover, resistance of pathogens is unlikely due to its multiple mode of action, and vaginal DQC provides also a reduced risk for post-treatment vaginal infections.

Conclusions

Vaginal DQC (10 mg) as 6-day therapy offers a safe and effective option for empiric therapy of different vaginal infections in daily practice. This review summarizes the available and relevant pharmacological and clinical data for the therapy of vaginal infections with vaginal DQC and provides the rationale for its use in daily gynaecologic practice.

Homologs of the Acinetobacter baumannii AceI transporter represent a new family of bacterial multidrug efflux systems

Multidrug efflux systems are a major cause of resistance to antimicrobials in bacteria, including those pathogenic to humans, animals, and plants. These proteins are ubiquitous in these pathogens, and five families of bacterial multidrug efflux systems have been identified to date. By using transcriptomic and biochemical analyses, we recently identified the novel AceI (Acinetobacter chlorhexidine efflux) protein from Acinetobacter baumannii that conferred resistance to the biocide chlorhexidine, via an active efflux mechanism. Proteins homologous to AceI are encoded in the genomes of many other bacterial species and are particularly prominent within proteobacterial lineages. In this study, we expressed 23 homologs of AceI and examined their resistance and/or transport profiles. MIC analyses demonstrated that, like AceI, many of the homologs conferred resistance to chlorhexidine. Many of the AceI homologs conferred resistance to additional biocides, including benzalkonium, dequalinium, proflavine, and acriflavine. We conducted fluorimetric transport assays using the AceI homolog from Vibrio parahaemolyticus and confirmed that resistance to both proflavine and acriflavine was mediated by an active efflux mechanism. These results show that this group of AceI homologs represent a new family of bacterial multidrug efflux pumps, which we have designated the proteobacterial antimicrobial compound efflux (PACE) family of transport proteins.

Bacterial multidrug efflux pumps are an important class of resistance determinants that can be found in every bacterial genome sequenced to date. These transport proteins have important protective functions for the bacterial cell but are a significant problem in the clinical setting, since a single efflux system can mediate resistance to many structurally and mechanistically diverse antibiotics and biocides. In this study, we demonstrate that proteins related to the Acinetobacter baumannii AceI transporter are a new class of multidrug efflux systems which are very common in Proteobacteria: the proteobacterial antimicrobial compound efflux (PACE) family. This is the first new family of multidrug efflux pumps to be described in 15 years.

Elucidating the genetic basis of crystalline biofilm formation in Proteus mirabilis

Proteus mirabilis forms extensive crystalline biofilms on urethral catheters that occlude urine flow and frequently complicate the management of long-term-catheterized patients. Here, using random transposon mutagenesis in conjunction with in vitro models of the catheterized urinary tract, we elucidate the mechanisms underpinning the formation of crystalline biofilms by P. mirabilis. Mutants identified as defective in blockage of urethral catheters had disruptions in genes involved in nitrogen metabolism and efflux systems but were unaffected in general growth, survival in bladder model systems, or the ability to elevate urinary pH. Imaging of biofilms directly on catheter surfaces, along with quantification of levels of encrustation and biomass, confirmed that the mutants were attenuated specifically in the ability to form crystalline biofilms compared with that of the wild type. However, the biofilm-deficient phenotype of these mutants was not due to deficiencies in attachment to catheter biomaterials, and defects in later stages of biofilm development were indicated. For one blocking-deficient mutant, the disrupted gene (encoding a putative multidrug efflux pump) was also found to be associated with susceptibility to fosfomycin, and loss of this system or general inhibition of efflux pumps increased sensitivity to this antibiotic. Furthermore, homologues of this system were found to be widely distributed among other common pathogens of the catheterized urinary tract. Overall, our findings provide fundamental new insight into crystalline biofilm formation by P. mirabilis, including the link between biofilm formation and antibiotic resistance in this organism, and indicate a potential role for efflux pump inhibitors in the treatment or prevention of P. mirabilis crystalline biofilms.

Combining quantitative genetic footprinting and trait enrichment analysis to identify fitness determinants of a bacterial pathogen

Strains of Extraintestinal Pathogenic Escherichia c oli (ExPEC) exhibit an array of virulence strategies and are a major cause of urinary tract infections, sepsis and meningitis. Efforts to understand ExPEC pathogenesis are challenged by the high degree of genetic and phenotypic variation that exists among isolates. Determining which virulence traits are widespread and which are strain-specific will greatly benefit the design of more effective therapies. Towards this goal, we utilized a quantitative genetic footprinting technique known as transposon insertion sequencing (Tn-seq) in conjunction with comparative pathogenomics to functionally dissect the genetic repertoire of a reference ExPEC isolate. Using Tn-seq and high-throughput zebrafish infection models, we tracked changes in the abundance of ExPEC variants within saturated transposon mutant libraries following selection within distinct host niches. Nine hundred and seventy bacterial genes (18% of the genome) were found to promote pathogen fitness in either a niche-dependent or independent manner. To identify genes with the highest therapeutic and diagnostic potential, a novel Trait Enrichment Analysis (TEA) algorithm was developed to ascertain the phylogenetic distribution of candidate genes. TEA revealed that a significant portion of the 970 genes identified by Tn-seq have homologues more often contained within the genomes of ExPEC and other known pathogens, which, as suggested by the first axiom of molecular Koch's postulates, is considered to be a key feature of true virulence determinants. Three of these Tn-seq-derived pathogen-associated genes--a transcriptional repressor, a putative metalloendopeptidase toxin and a hypothetical DNA binding protein--were deleted and shown to independently affect ExPEC fitness in zebrafish and mouse models of infection. Together, the approaches and observations reported herein provide a resource for future pathogenomics-based research and highlight the diversity of factors required by a single ExPEC isolate to survive within varying host environments.

Role of a TehA homolog in Vibrio cholerae C6706 antibiotic resistance and intestinal colonization

Vibrio cholerae is the causative agent of the devastating diarrheal disease cholera. A number of regulatory pathways are involved in V. cholerae pathogenesis and antibiotic resistance. For example, there are over 40 LysR-family proteins in the V. cholerae genome, but most of their functions are unknown. In this study, we examine the role of VC2323 (TehAVc) and its divergently transcribed LysR-family regulator VC2324 (TehRVc) in V. cholerae pathogenesis. We found that in V. cholerae C6706, the expression of tehAVc is dependent on TehRVc. VC2323 (TehAVc), homologous to the Escherichia coli tellurite resistance protein (TehAEc), differs from TehAEc in that TehAVc has no noticeable role in tellurite resistance but instead contributes to chloramphenicol resistance. Interestingly, both tehAVc and tehRVc mutants were defective in colonization of infant mice. Though the expression of a key virulence gene tcpA was not affected in either of these mutants, tehAVc mutants failed to attach to mouse intestinal surfaces in the presence of crude bile, suggesting a new role of the TehAVc-TehRVc pair in V. cholerae pathogenesis.

Emergence of resistance to antibacterial agents: the role of quaternary ammonium compounds--a critical review

Quaternary ammonium compounds (QACs) are widely distributed in hospitals, industry and cosmetics. Little attention has been focused on the potential impact of QACs on the emergence of antibiotic resistance in patients and the environment. To assess this issue, we conducted a literature review on QAC chemical structure, fields of application, mechanism of action, susceptibility testing, prevalence, and co- or cross-resistance to antibiotics. Special attention was paid to the effects of QACs on microflora; in particular, the issue of the potential of QACs for applying selective pressure on multiple-antibiotic-resistant organisms was raised. It was found that there is a lack of standardised procedures for interpreting susceptibility test results. QACs have different impacts on the minimum inhibitory concentrations of antibacterials depending on the antibacterial compound investigated, the resistance genes involved, the measuring methodology and the interpretative criteria. The unmet needs for adequate detection of reduced susceptibility to QACs and antibiotics include (i) a consensus definition for resistance, (ii) epidemiological cut-off values and (iii) clinical resistance breakpoints. This review advocates the design of international guidelines for QAC use.

Crystallization and initial X-ray diffraction analysis of the tellurite-resistance S-adenosyl-L-methionine transferase protein TehB from Escherichia coli

TehB is an S-adenosyl-L-methionine (SAM) dependent methyltransferase that detoxifies tellurite in bacteria. The Escherichia coli TehB protein was purified and crystallized in the presence of both SAM and sinefungin. The TehB-SAM and TehB-sinefungin crystals both diffracted X-rays to 1.9 Å resolution. The TehB-SAM crystals belonged to space group C2, with unit-cell parameters a = 60.0, b = 56.1, c = 130.6 Å, β = 97.9°. The TehB-sinefungin crystals belonged to space group P2(1), with unit-cell parameters a = 59.1, b = 55.5, c = 129.7 Å, β = 95.9°.

Characterization of the Haemophilus influenzae tehB gene and its role in virulence

The Haemophilus influenzae ORF designated HI1275 in the Rd KW20 genomic sequence encodes a putative S-adenosyl methyltransferase with significant similarity to tellurite-resistance determinants (tehB) in other species. While the H. influenzae tehB can complement an Escherichia coli tehB mutation, thus restoring tellurite resistance, its role in H. influenzae is unknown. In a previous study defining the iron and haem modulon of H. influenzae, we showed that transcription of this gene in H. influenzae Rd KW20 increases during growth in iron- and haem-restricted media. Since iron and haem uptake genes, and other known virulence factors, constitute the majority of the iron- and haem-regulated gene set, we postulated that tehB may play a role in nutrient acquisition and/or the virulence of H. influenzae. A tehB mutant was constructed in the H. influenzae type b strain 10810 and was evaluated for growth defects in various supplemented media, as well as for its ability to cause infection in rat models of infection. Deletion of tehB leads to an increase in sensitivity both to tellurite and to the oxidizing agents cumene hydroperoxide, tert-butyl hydroperoxide and hydrogen peroxide. The tehB mutant additionally showed a significantly reduced ability to utilize free haem as well as several haem-containing moieties including haem-human serum albumin, haemoglobin and haemoglobin-haptoglobin. Examination of the regulation kinetics indicated that transcription of tehB was independent of both tellurite exposure and oxidative stress. Paired comparisons of the tehB mutant and the wild-type H. influenzae strain 10810 showed that tehB is required for wild-type levels of infection in rat models of H. influenzae invasive disease. To our knowledge this is the first report of a role for tehB in virulence in any bacterial species. These data demonstrate that H. influenzae tehB plays a role in both resistance to oxidative damage and haem uptake/utilization, protects H. influenzae from tellurite exposure, and is important for virulence of this organism in an animal model of invasive disease.

A transcriptional "Scream" early response of E. coli prey to predatory invasion by Bdellovibrio

We have transcriptionally profiled the genes differentially expressed in E. coli prey cells when predatorily attacked by Bdellovibrio bacteriovorus just prior to prey cell killing. This is a brief, approximately 20–25 min period when the prey cell is still alive but contains a Bdellovibrio cell in its periplasm or attached to and penetrating its outer membrane. Total RNA was harvested and labelled 15 min after initiating a semi-synchronous infection with an excess of Bdellovibrio preying upon E. coli and hybridised to a macroarray spotted with all predicted ORFs of E. coli. SAM analysis and t-tests were performed on the resulting data and 126 E. coli genes were found to be significantly differentially regulated by the prey upon attack by Bdellovibrio. The results were confirmed by QRT-PCR. Amongst the prey genes upregulated were a variety of general stress response genes, potentially “selfish” genes within or near prophages and transposable elements, and genes responding to damage in the periplasm and osmotic stress. Essentially, the presence of the invading Bdellovibrio and the resulting damage to the prey cell elicited a small “transcriptional scream”, but seemingly no specific defensive mechanism with which to counter the Bdellovibrio attack. This supports other studies which do not find Bdellovibrio resistance responses in prey, and bodes well for its use as a “living antibiotic”.

The bacterial response to the chalcogen metalloids Se and Te

Microbial metabolism of inorganics has been the subject of interest since the 1970s when it was recognized that bacteria are involved in the transformation of metal compounds in the environment. This area of research is generally referred to as bioinorganic chemistry or microbial biogeochemistry. Here, we overview the way the chalcogen metalloids Se and Te interact with bacteria. As a topic of considerable interest for basic and applied research, bacterial processing of tellurium and selenium oxyanions has been reviewed a few times over the past 15 years. Oddly, this is the first time these compounds have been considered together and their similarities and differences highlighted. Another aspect touched on for the first time by this review is the bacterial response in cell-cell or cell-surface aggregates (biofilms) against the metalloid oxyanions. Finally, in this review we have attempted to rationalize the considerable amount of literature available on bacterial resistance to the toxic metalloids tellurite and selenite.

NsrR: a key regulator circumventing Salmonella enterica serovar Typhimurium oxidative and nitrosative stress in vitro and in IFN-gamma-stimulated J774.2 macrophages

Over the past decade, the flavohaemoglobin Hmp has emerged as the most significant nitric oxide (NO)-detoxifying protein in many diverse micro-organisms, particularly pathogenic bacteria. Its expression in enterobacteria is dramatically increased on exposure to NO and other agents of nitrosative stress as a result of transcriptional regulation of hmp gene expression, mediated by (at least) four regulators. One such regulator, NsrR, has recently been shown to be responsible for repression of hmp transcription in the absence of NO in Escherichia coli and Salmonella, but the roles of other members of this regulon in Salmonella, particularly in surviving nitrosative stresses in vitro and in vivo, have not been elucidated. This paper demonstrates that an nsrR mutant of Salmonella enterica Serovar Typhimurium expresses high levels of Hmp both aerobically and anaerobically, exceeding those that can be elicited in vitro by supplementing media with S-nitrosoglutathione (GSNO). Elevated transcription of ytfE, ygbA, hcp and hcp is also observed, but no evidence was obtained for tehAB upregulation. The hyper-resistance to GSNO of an nsrR mutant is attributable solely to Hmp, since an nsrR hmp double mutant has a wild-type phenotype. However, overexpression of NsrR-regulated genes other than hmp confers some resistance of respiratory oxygen consumption to NO. The ability to enhance, by mutating NsrR, Hmp levels without recourse to exposure to nitrosative stress was used to test the hypothesis that control of Hmp levels is required to avoid oxidative stress, Hmp being a potent generator of superoxide. Within IFN-gamma-stimulated J774.2 macrophages, in which high levels of nitrite accumulated (indicative of NO production) an hmp mutant was severely compromised in survival. Surprisingly, under these conditions, an nsrR mutant (as well as an nsrR hmp double mutant) was also disadvantaged relative to the wild-type bacteria, attributable to the combined oxidative effect of the macrophage oxidative burst and Hmp-generated superoxide. This explanation is supported by the sensitivity in vitro of an nsrR mutant to superoxide and peroxide. Fur has recently been confirmed as a weak repressor of hmp transcription, and a fur mutant was also compromised for survival within macrophages even in the absence of elevated NO levels in non-stimulated macrophages. The results indicate the critical role of Hmp in protection of Salmonella from nitrosative stress within and outside macrophages, but also the key role of transcriptional regulation in tuning Hmp levels to prevent exacerbation of the oxidative stress encountered in macrophages.

Antibiotic stress, genetic response and altered permeability of E. coli

Background

Membrane permeability is the first step involved in resistance of bacteria to an antibiotic. The number and activity of efflux pumps and outer membrane proteins that constitute porins play major roles in the definition of intrinsic resistance in Gram-negative bacteria that is altered under antibiotic exposure.

Methodology/Principal Findings

Here we describe the genetic regulation of porins and efflux pumps of Escherichia coli during prolonged exposure to increasing concentrations of tetracycline and demonstrate, with the aid of quantitative real-time reverse transcriptase-polymerase chain reaction methodology and western blot detection, the sequence order of genetic expression of regulatory genes, their relationship to each other, and the ensuing increased activity of genes that code for transporter proteins of efflux pumps and down-regulation of porin expression.

Conclusions/Significance

This study demonstrates that, in addition to the transcriptional regulation of genes coding for membrane proteins, the post-translational regulation of proteins involved in the permeability of Gram-negative bacteria also plays a major role in the physiological adaptation to antibiotic exposure. A model is presented that summarizes events during the physiological adaptation of E. coli to tetracycline exposure.

The genome sequence of Mannheimia haemolytica A1: insights into virulence, natural competence, and Pasteurellaceae phylogeny

The draft genome sequence of Mannheimia haemolytica A1, the causative agent of bovine respiratory disease complex (BRDC), is presented. Strain ATCC BAA-410, isolated from the lung of a calf with BRDC, was the DNA source. The annotated genome includes 2,839 coding sequences, 1,966 of which were assigned a function and 436 of which are unique to M. haemolytica. Through genome annotation many features of interest were identified, including bacteriophages and genes related to virulence, natural competence, and transcriptional regulation. In addition to previously described virulence factors, M. haemolytica encodes adhesins, including the filamentous hemagglutinin FhaB and two trimeric autotransporter adhesins. Two dual-function immunoglobulin-protease/adhesins are also present, as is a third immunoglobulin protease. Genes related to iron acquisition and drug resistance were identified and are likely important for survival in the host and virulence. Analysis of the genome indicates that M. haemolytica is naturally competent, as genes for natural competence and DNA uptake signal sequences (USS) are present. Comparison of competence loci and USS in other species in the family Pasteurellaceae indicates that M. haemolytica, Actinobacillus pleuropneumoniae, and Haemophilus ducreyi form a lineage distinct from other Pasteurellaceae. This observation was supported by a phylogenetic analysis using sequences of predicted housekeeping genes.

Combination of cell-free expression and NMR spectroscopy as a new approach for structural investigation of membrane proteins

Despite major technical advance in methods used for structural investigations of proteins structure determination of membrane proteins still poses a significant challenge. Recently, the application of cell-free expression systems to membrane proteins has demonstrated that this technique can be used to produce quantities sufficient for structural investigations for many different membrane proteins. In particular for NMR spectroscopy, cell-free expression provides major advantages since it allows for amino acid type selective and even amino acid position specific labeling. In this mini-review we discuss the combination of cell-free membrane protein expression and liquid state NMR spectroscopy.

The yjeB (nsrR) gene of Escherichia coli encodes a nitric oxide-sensitive transcriptional regulator

Microarray studies of the Escherichia coli response to nitric oxide and nitrosative stress have suggested that additional transcriptional regulators of this response remain to be characterized. We identify here the product of the yjeB gene as a negative regulator of the transcription of the ytfE, hmpA and ygbA genes, all of which are known to be upregulated by nitrosative stress. Transcriptional fusions to the promoters of these genes were expressed constitutively in a yjeB mutant, indicating that all three are targets for repression by YjeB. An inverted repeat sequence that overlaps the -10 element of all three promoters is proposed to be a binding site for the YjeB protein. A similar inverted repeat sequence was identified in the tehA promoter, which is also known to be sensitive to nitrosative stress. The ytfE, hmpA, ygbA, and tehA promoters all caused derepression of a ytfE-lacZ transcriptional fusion when present in the cell in multiple copies, presumably by a repressor titration effect, suggesting the presence of functional YjeB binding sites in these promoters. However, YjeB regulation of tehA was weak, as judged by the activity of a tehA-lacZ fusion, perhaps because YjeB repression of tehA is masked by other regulatory mechanisms. Promoters regulated by YjeB could be derepressed by iron limitation, which is consistent with an iron requirement for YjeB activity. The YjeB protein is a member of the Rrf2 family of transcriptional repressors and shares three conserved cysteine residues with its closest relatives. We propose a regulatory model in which the YjeB repressor is directly sensitive to nitrosative stress. On the basis of similarity to the nitrite-responsive repressor NsrR from Nitrosomonas europaea, we propose that the yjeB gene of E. coli be renamed nsrR.

Efficient strategy for the rapid backbone assignment of membrane proteins

Investigations of membrane proteins pose one of the biggest current challenges in structural biology. Recent advances in protein production techniques based on cell-free transcription/translation methods have, however, opened new opportunities in this area. Here, we report an efficient protocol for the backbone assignment of membrane proteins as the first step of NMR-based structure determination.

Inducement and reversal of tetracycline resistance in Escherichia coli K-12 and expression of proton gradient-dependent multidrug efflux pump genes

Expression of eight transporter genes of Escherichia coli K-12 and its DeltaacrAB mutant prior to and after induction of both strains to tetracycline resistance and after reversal of induced resistance were analyzed by quantitative reverse transcriptase PCR. All transporter genes were overexpressed after induced resistance with acrF being 80-fold more expressed in the DeltaacrAB tetracycline-induced strain.

Efflux pumps in bacteria: overview, clinical relevance, and potential pharmaceutical target

Trends in microbial resistance suggest a dramatic increase in the frequency of reports of multi-drug efflux pumps in bacteria and fungi. Although it is difficult to determine whether this increase is due to the increased attention given to this resistance mechanism, or an increase in frequency, efflux pumps are becoming an important consideration in resistance emergence. These efflux pumps comprise at least four different classes in Gram-positive and Gram-negative bacteria, as well as in Streptomyces and fungi. As more efflux pumps are characterised and studied, both biochemically and structurally, the opportunity for intervention may arise.

In vivo 31P nuclear magnetic resonance investigation of tellurite toxicity in Escherichia coli

Here we compare the physiological state of Escherichia coli exposed to tellurite or selenite by using the noninvasive technique of phosphorus-31 nuclear magnetic resonance (NMR) spectroscopy. We studied glucose-fed Escherichia coli HB101 cells containing either a normal pUC8 plasmid with no tellurite resistance determinants present or the pTWT100 plasmid which contains the resistance determinants tehAB. No differences could be observed in intracellular ATP levels, the presence or absence of a transmembrane pH gradient, or the levels of phosphorylated glycolytic intermediates when resistant cells were studied by 31P NMR in the presence or absence of tellurite. In the sensitive strain, we observed that the transmembrane pH gradient was dissipated and intracellular ATP levels were rapidly depleted upon exposure to tellurite. Only the level of phosphorylated glycolytic intermediates remained the same as observed with resistant cells. Upon exposure to selenite, no differences could be observed by 31P NMR between resistant and sensitive strains, suggesting that the routes for selenite and tellurite reduction within the cells differ significantly, since only tellurite is able to collapse the transmembrane pH gradient and lower ATP levels in sensitive cells. The presence of the resistance determinant tehAB, by an as yet unidentified detoxification event, protects the cells from uncoupling by tellurite.

Efflux-mediated drug resistance in bacteria

Drug resistance in bacteria, and especially resistance to multiple antibacterials, has attracted much attention in recent years. In addition to the well known mechanisms, such as inactivation of drugs and alteration of targets, active efflux is now known to play a major role in the resistance of many species to antibacterials. Drug-specific efflux (e.g. that of tetracycline) has been recognised as the major mechanism of resistance to this drug in Gram-negative bacteria. In addition, we now recognise that multidrug efflux pumps are becoming increasingly important. Such pumps play major roles in the antiseptic resistance of Staphylococcus aureus, and fluoroquinolone resistance of S. aureus and Streptococcus pneumoniae. Multidrug pumps, often with very wide substrate specificity, are not only essential for the intrinsic resistance of many Gram-negative bacteria but also produce elevated levels of resistance when overexpressed. Paradoxically, 'advanced' agents for which resistance is unlikely to be caused by traditional mechanisms, such as fluoroquinolones and beta-lactams of the latest generations, are likely to select for overproduction mutants of these pumps and make the bacteria resistant in one step to practically all classes of antibacterial agents. Such overproduction mutants are also selected for by the use of antiseptics and biocides, increasingly incorporated into consumer products, and this is also of major concern. We can consider efflux pumps as potentially effective antibacterial targets. Inhibition of efflux pumps by an efflux pump inhibitor would restore the activity of an agent subject to efflux. An alternative approach is to develop antibacterials that would bypass the action of efflux pumps.

High level cell-free expression and specific labeling of integral membrane proteins

We demonstrate the high level expression of integral membrane proteins (IMPs) in a cell-free coupled transcription/translation system using a modified Escherichia coli S30 extract preparation and an optimized protocol. The expression of the E. coli small multidrug transporters EmrE and SugE containing four transmembrane segments (TMS), the multidrug transporter TehA with 10 putative TMS, and the cysteine transporter YfiK with six putative TMS, were analysed. All IMPs were produced at high levels yielding up to 2.7 mg of protein per mL of reaction volume. Whilst the vast majority of the synthesized IMPs were precipitated in the reaction mixture, the expression of a fluorescent EmrE-sgGFP fusion construct showed evidence that a small part of the synthesized protein 'remained soluble and this amount could be significantly increased by the addition of E. coli lipids into the cell-free reaction. Alternatively, the majority of the precipitated IMPs could be solubilized in detergent micelles, and modifications to the solubilization procedures yielded proteins that were almost pure. The folding induced by formation of the proposed alpha-helical secondary structures of the IMPs after solubilization in various micelles was monitored by CD spectroscopy. Furthermore, the reconstitution of EmrE, SugE and TehA into proteoliposomes was demonstrated by freeze-fracture electron microscopy, and the function of EmrE was additionally analysed by the specific transport of ethidium. The cell-free expression technique allowed efficient amino acid specific labeling of the IMPs with 15N isotopes, and the recording of solution NMR spectra of the solubilized EmrE, SugE and YfiK proteins further indicated a correctly folded conformation of the proteins.

Cross-resistance to antibiotics of Escherichia coli adapted to benzalkonium chloride or exposed to stress-inducers

AIMS

To study the effects of adaptation and stress on the resistance to benzalkonium chloride (BC) and cross-resistance to antibiotics in Escherichia coli.

METHODS AND RESULTS

Precultivation of E. coli ATCC 11775 and E. coli DSM 682 in the presence of subinhibitory concentrations of BC or stress inducers (salicylate, chenodeoxycholate and methyl viologen) resulted in higher minimum inhibitory concentration (MIC) of BC and chloramphenicol (CHL). Adaptation to growth in sixfold of the initial MIC of BC resulted in stable BC resistance and enhanced tolerance to several antibiotics and ethidium bromide (EtBr). The MIC of CHL increased more than 10-fold for both strains. Enhanced efflux of EtBr in adapted E. coli ATCC 11775 indicated that the observed resistance was due to efflux. Changes in outer membrane protein profiles were detected in the BC-adapted cells. There were no indications of lower membrane permeability to BC.

CONCLUSIONS

Induction of stress response or gradual adaptation to BC or CHL results in acquired cross-tolerance between BC and antibiotics in E. coli. Enhanced efflux was one of the observed differences in adapted cells.

SIGNIFICANCE AND IMPACT OF THE STUDY

Provided not taking due precautions, extensive use of disinfectants could lead to emergence of antibiotic-resistant isolates.

Tellurite uptake by cells of the facultative phototrophRhodobacter capsulatusis a ΔpH-dependent process

The uptake by light-grown cells of Rhodobacter capsulatus of the highly toxic metalloid oxyanion tellurite (TeO(3)(2-)) was examined. We show that tellurite is rapidly taken up by illuminated cells in a process which is inhibited by the protonophore carbonyl cyanide-p-trifluoromethoxyphenyl-hydrazone (FCCP) and by the K(+)/H(+) exchanger nigericin. Notably, the light-driven membrane potential (Delta psi) is enhanced by K(2)TeO(3)> or =200 microM. Further, tellurite uptake is largely insensitive to valinomycin, strongly repressed by the sulfhydryl reagent N-ethylethylmaleimide (NEM) and competitively inhibited by phosphate. We conclude that tellurite is transported into cells by a Delta pH-dependent, non-electrogenic process which is likely to involve the phosphate transporter (PiT family).

DNA microarray analysis of the expression profile of Escherichia coli in response to treatment with 4,5-dihydroxy-2-cyclopenten-1-one

We carried out DNA microarray-based global transcript profiling of Escherichia coli in response to 4,5-dihydroxy-2-cyclopenten-1-one to explore the manifestation of its antibacterial activity. We show that it has widespread effects in E. coli affecting genes encoding proteins involved in cell metabolism and membrane synthesis and functions. Genes belonging to the regulon involved in synthesis of Cys are upregulated. In addition, rpoS and RpoS-regulated genes responding to various stresses and a number of genes responding to oxidative stress are upregulated.

Escherichia coli gene expression responsive to levels of the response regulator EvgA

To investigate the function of the EvgA response regulator, we compared the genome-wide transcription profile of EvgA-overexpressing and EvgA-lacking Escherichia coli strains by oligonucleotide microarrays. The microarray measurements allowed the identification of at least 37 EvgA-activated genes, including acid resistance-related genes gadABC and hdeAB, efflux pump genes yhiUV and emrK, and 21 genes with unknown function. EvgA overexpression conferred acid resistance to exponentially growing cells. This acid resistance was abolished by deletion of ydeP, ydeO, or yhiE, which was induced by EvgA overexpression. These results suggest that ydeP, ydeO, and yhiE are novel genes related to acid resistance and that EvgA regulates several acid resistance genes. Furthermore, the deletion of yhiE completely abolished acid resistance in stationary-phase cells, suggesting that YhiE plays a critical role in stationary-phase acid resistance. The multidrug resistance in an acrB deletion mutant caused by EvgA overexpression was completely abolished by deletion of yhiUV, while the emrKY deletion had no effect on the increase in resistance by EvgA overexpression. In addition, EvgA overexpression did not confer resistance in a tolC-deficient strain. These results suggest that YhiUV induced by EvgA overexpression is functionally associated with TolC and contributes to multidrug resistance.

Antibiotic susceptibility profiles of Escherichia coli strains lacking multidrug efflux pump genes

The contribution of seven known and nine predicted genes or operons associated with multidrug resistance to the susceptibility of Escherichia coli W3110 was assessed for 20 different classes of antimicrobial compounds that include antibiotics, antiseptics, detergents, and dyes. Strains were constructed with deletions for genes in the major facilitator superfamily, the resistance nodulation-cell division family, the small multidrug resistance family, the ATP-binding cassette family, and outer membrane factors. The agar dilution MICs of 35 compounds were determined for strains with deletions for multidrug resistance (MDR) pumps. Deletions in acrAB or tolC resulted in increased susceptibilities to the majority of compounds tested. The remaining MDR pump gene deletions resulted in increased susceptibilities to far fewer compounds. The results identify which MDR pumps contribute to intrinsic resistance under the conditions tested and supply practical information useful for designing sensitive assay strains for cell-based screening of antibacterial compounds.

Glutathione is a target in tellurite toxicity and is protected by tellurite resistance determinants inEscherichia coli

Tellurite (TeO32-) is highly toxic to most microorganisms. The mechanisms of toxicity or resistance are poorly understood. It has been shown that tellurite rapidly depletes the reduced thiol content within wild-type Escherichia coli. We have shown that the presence of plasmid-borne tellurite-resistance determinants protects against general thiol oxidation by tellurite. In the present study we observe that the tellurite-dependent depletion of cellular thiols in mutants of the glutathione and thioredoxin thiol:redox system was less than in wild-type cells. To identify the type of low-molecular-weight thiol compounds affected by tellurite exposure, the thiol-containing molecules were analyzed by reverse phase HPLC as their monobromobimane derivatives. Results indicated that reduced glutathione is a major initial target of tellurite reactivity within the cell. Other thiol species are also targeted by tellurite, including reduced coenzyme A. The presence of the tellurite resistance determinants kilA and ter protect against the loss of reduced glutathione by as much as 60% over a 2 h exposure. This protection of glutathione oxidation is likely key to the resistance mechanism of these determinants. Additionally, the thiol oxidation response curves were compared between selenite and tellurite. The loss of thiol compounds within the cell recovered from selenite but not to tellurite.Key words: tellurite, resistance, thiol oxidation, heavy metal toxicity, selenite, glutathione.

Molecular properties of bacterial multidrug transporters

One of the mechanisms that bacteria utilize to evade the toxic effects of antibiotics is the active extrusion of structurally unrelated drugs from the cell. Both intrinsic and acquired multidrug transporters play an important role in antibiotic resistance of several pathogens, including Neisseria gonorrhoeae, Mycobacterium tuberculosis, Staphylococcus aureus, Streptococcus pneumoniae, Pseudomonas aeruginosa, and Vibrio cholerae. Detailed knowledge of the molecular basis of drug recognition and transport by multidrug transport systems is required for the development of new antibiotics that are not extruded or of inhibitors which block the multidrug transporter and allow traditional antibiotics to be effective. This review gives an extensive overview of the currently known multidrug transporters in bacteria. Based on energetics and structural characteristics, the bacterial multidrug transporters can be classified into five distinct families. Functional reconstitution in liposomes of purified multidrug transport proteins from four families revealed that these proteins are capable of mediating the export of structurally unrelated drugs independent of accessory proteins or cytoplasmic components. On the basis of (i) mutations that affect the activity or the substrate specificity of multidrug transporters and (ii) the three-dimensional structure of the drug-binding domain of the regulatory protein BmrR, the substrate-binding site for cationic drugs is predicted to consist of a hydrophobic pocket with a buried negatively charged residue that interacts electrostatically with the positively charged substrate. The aromatic and hydrophobic amino acid residues which form the drug-binding pocket impose restrictions on the shape and size of the substrates. Kinetic analysis of drug transport by multidrug transporters provided evidence that these proteins may contain multiple substrate-binding sites.

Escherichia coli TehB requires S-adenosylmethionine as a cofactor to mediate tellurite resistance

The Escherichia coli chromosomal determinant for tellurite resistance consists of two genes (tehA and tehB) which, when expressed on a multicopy plasmid, confer resistance to K(2)TeO(3) at 128 microg/ml, compared to the MIC of 2 microg/ml for the wild type. TehB is a cytoplasmic protein which possesses three conserved motifs (I, II, and III) found in S-adenosyl-L-methionine (SAM)-dependent non-nucleic acid methyltransferases. Replacement of the conserved aspartate residue in motif I by asparagine or alanine, or of the conserved phenylalanine in motif II by tyrosine or alanine, decreased resistance to background levels. Our results are consistent with motifs I and II in TehB being involved in SAM binding. Additionally, conformational changes in TehB are observed upon binding of both tellurite and SAM. The hydrodynamic radius of TehB measured by dynamic light scattering showed a approximately 20% decrease upon binding of both tellurite and SAM. These data suggest that TehB utilizes a methyltransferase activity in the detoxification of tellurite.

The role of cysteine residues in tellurite resistance mediated by the TehAB determinant

TehATehB is a tellurite (TeO(2-)(3)) resistance determinant found on the Escherichia coli chromosome. Normally silent, it specifies a minimal inhibitory concentration (MIC) of 2 microg K(2)TeO(3)/ml unless upregulated or present on a multicopy plasmid which results in an MIC of 128 microg/ml. Both TehA and TehB have three cysteine residues. Oligonucleotide site-directed mutagenesis was carried out to systematically replace all six cysteine residues by alaninies. The results showed that cysteine residues in both TehA and TehB play a role in tellurite resistance: A single cysteine change had no effect, however increasing combinations of two or three cysteine substitutions demonstrated strong phenotypic effects with minimal inhibitory concentrations ranging from 16-64 microg K(2)TeO(3)/ml. A cysteine-free mutant in which all six cysteine residues were replaced by alanines maintained a MIC of 16 microg/ml. Further investigations on the role of cysteines in resistance were studied using thiol reactive reagents on the soluble subunit TehB. These studies confirmed that TehB is a dimer and undergoes a conformational change with tellurite and S-adenosyl-l-methionine binding. Studies using native and SDS denaturing PAGE under reducing and oxidizing conditions suggested that a cysteine in TehB is involved in binding tellurite.

Tellurite-mediated thiol oxidation in Escherichia coli

The oxyanion of tellurium, tellurite (TeO3(2-)), is toxic to most micro-organisms, particularly gram-negative bacteria. The mechanism of tellurite toxicity is presently unknown. Many heavy metals and oxyanions, including tellurite, interact with reduced thiols (RSH). To determine if tellurite interaction with RSH groups is involved in the toxicity mechanism, the RSH content of Escherichia coli cultures was assayed. After exposure to tellurite, cells were harvested and lysed in the presence of the RSH-specific reagent 5,5'-dithiobis(2-nitrobenzoic acid). Upon exposure of tellurite-susceptible cells to TeO3(2-), the RSH content decreased markedly. Resistance to potassium tellurite (Te(r)) in gram-negative bacteria is encoded by plasmids of incompatibility groups IncFI, IncP alpha, IncHI2, IncHI3 and IncHII, as well as the tehAtehB operon from the E. coli chromosome. When cells harbouring a Te(r) determinant were exposed to TeO3(2-), only a small fraction of the RSH content became oxidized. In addition to tellurite-dependent thiol oxidation, the resistance of E. coli mutants affected in proteins involved in disulfide-bond formation (dsb) was investigated. Mutant strains of dsbA and dsbB were found to be hypersensitive to tellurite (MIC 0.008-0.015 microg K2TeO3 ml(-1) compared to wild-type E. coli with MICs of 1-2 microg K2TeO3 ml(-1)). In contrast, dsbC and dsbD mutants showed no hypersensitivity. The results suggest that hypersensitivity to tellurite is reliant on the presence of an isomerase activity and not the thiol oxidase activity of the Dsb proteins. The results establish that the Te(r) determinants play an important role in maintaining homeostasis of the intracellular reducing environment within gram-negative cells through specific reactions with either TeO3(2-) or thiol:tellurium products.

Bacterial resistance and topical antimicrobial wash products

Current scientific evidence has not shown that a link exists between the use of topical antimicrobial formulations and antiseptic or antibiotic resistance. As a result of the extensive history and varied use of antiseptic products and ingredients, any selective pressure for antibiotic resistance that may be occurring or may be uncovered in the future because of antiseptic use would be expected to be insignificant compared with the selective pressure because of antibiotic use. This review illustrates the effectiveness of topical antimicrobial wash products against antibiotic-resistant and antiseptic-resistant bacteria in use settings as well as the studies performed (antiseptic, deodorant, and oral care) demonstrating the lack of development of resistance in long-term clinical studies. Although these studies illustrate that the use of topical antimicrobial products have not been shown to play a role in the fluctuations of the specific composition or resistance of the skin flora, changes in skin flora have been shown to occur. Based on current knowledge, the benefit from use of topical antimicrobial wash products in combination with standard infection control and personal hygiene practices far outweighs the risk of increased antibiotic resistance.

Characterization of gram-positive tellurite resistance encoded by the Streptococcus pneumoniae tehB gene

Streptococcus pneumoniae is a Gram-positive bacterium which is naturally resistant to tellurite. In this study, we cloned and sequenced a homologue of the Escherichia coli tellurite resistance gene tehB from S. pneumoniae. It encoded a protein of 284 amino acids which is 86 residues longer than E. coli TehB, but similar in size to Haemophilus influenzae TehB and Eikenella corrodens hemagglutinin (Hag1) as well as homologues from Actinobacillus actinomycetemcomitans, Neisseria gonorrhoeae and Neisseria meningitidis. The S. pneumoniae TehB displayed 46-58% identity (52-68% similarity) to these proteins. The results in this study showed that the S. pneumoniae tehB alone not only conferred on E. coli high level resistance to tellurite, but also caused filamentous morphology in E. coli.

Bacterial tellurite resistance

Tellurium compounds are used in several industrial processes, although they are relatively rare in the environment. Genes associated with tellurite resistance (TeR) are found in many pathogenic bacteria. Tellurite can be detoxified through interactions with cellular thiols, such as glutathione, or a methyltransferase-catalyzed reaction, although neither process appears involved in plasmid-mediated TeR.

Linkage map of Escherichia coli K-12, edition 10: the traditional map

This map is an update of the edition 9 map by Berlyn et al. (M. K. B. Berlyn, K. B. Low, and K. E. Rudd, p. 1715-1902, in F. C. Neidhardt et al., ed., Escherichia coli and Salmonella: cellular and molecular biology, 2nd ed., vol. 2, 1996). It uses coordinates established by the completed sequence, expressed as 100 minutes for the entire circular map, and adds new genes discovered and established since 1996 and eliminates those shown to correspond to other known genes. The latter are included as synonyms. An alphabetical list of genes showing map location, synonyms, the protein or RNA product of the gene, phenotypes of mutants, and reference citations is provided. In addition to genes known to correspond to gene sequences, other genes, often older, that are described by phenotype and older mapping techniques and that have not been correlated with sequences are included.

Mechanisms of multidrug transporters

Drug resistance, mediated by various mechanisms, plays a crucial role in the failure of the drug-based treatment of various infectious diseases. As a result, these infectious diseases re-emerge rapidly and cause many victims every year. Another serious threat is imposed by the development of multidrug resistance (MDR) in eukaryotic (tumor) cells, where many different drugs fail to perform their therapeutic function. One of the causes of the occurrence of MDR in these cells is the action of transmembrane transport proteins that catalyze the active extrusion of a large number of structurally and functionally unrelated compounds out of the cell. The mode of action of these MDR transporters and their apparent lack of substrate specificity is poorly understood and has been subject to many speculations. In this review we will summarize our current knowledge about the occurrence, mechanism and molecular basis of (multi-)drug resistance especially as found in bacteria.