Awareness, treatment, and control of hypertension among women at risk or living with HIV in the US South: a prospective study.

OBJECTIVES: Timely control of hypertension is vital to prevent comorbidities. We evaluated the association of race/ethnicity and HIV infection with incident hypertension outcomes, including awareness, treatment, and control. DESIGN: We evaluated cisgender women living with HIV and sociodemographically matched women living without HIV recruited into four Southern sites of the Women's Interagency HIV Study (2013-2019). METHODS: We calculated measurements of the time to four events or censoring: incident hypertension, hypertension awareness, hypertension treatment, and hypertension control. Hazard ratios for race/ethnicity and HIV status were calculated for each outcome using Cox proportional-hazards models adjusted for sociodemographic, behavioral, and clinical risk factors. RESULTS: Among 712 women, 56% were hypertensive at baseline. Forty-five percent of the remaining women who were normotensive at baseline developed incident hypertension during follow-up. Non-Hispanic White and Hispanic women had faster time to hypertension control compared to non-Hispanic Black women (p = 0.01). In fully adjusted models, women living with HIV who were normotensive at baseline had faster time to treatment compared to normotensive women living without HIV (p = 0.04). CONCLUSIONS: In our study of women in the US South, non-Hispanic Black women became aware of their hypertension diagnosis more quickly than non-Hispanic White and Hispanic women but were slower to control their hypertension. Additionally, women living with HIV more quickly treated and controlled their hypertension compared to women living without HIV.

Functional outcomes of diets in multiple sclerosis (FOOD for MS): Protocol for a parallel arm randomized feeding trial for low glycemic load and calorie restriction.

BACKGROUND: Pilot trials indicate that both a low glycemic load (GL) diet and calorie restriction (CR) can be implemented successfully in people with multiple sclerosis (pMS) and may improve MS symptoms and physical function, but large randomized clinical trials (RCTs) have not yet been conducted. The purpose of this study is to test these interventions alone and in combination to determine their efficacy for improving clinical and patient reported outcomes (PROs) in pMS. METHODS: This 32-week, two-arm, RCT at two centers will randomly assign 100 adults with relapsing-remitting or secondary progressive MS to a low GL diet (n = 50) or a standard GL diet (n = 50). Both diet groups will complete two study phases: a eucaloric phase (16 weeks) and a CR phase (16 weeks). Groceries for the study meal plans will be delivered to participants' homes weekly. The primary outcome is physical function, measured by timed 25-ft walk test. Secondary outcomes are pain, fatigue, mood, and anxiety. DISCUSSION: This will be the most rigorous intervention trial to date of a low GL diet and CR in adults with MS, and among the first to assess the impact of intentional weight loss on MS symptoms. Results will provide valuable insight for recommending dietary change, weight loss, or both to adults with MS. These non-drug interventions pose few risks and have potential to yield significant improvements in MS symptoms. TRIAL REGISTRATION ID: NCT05327322.

Differential development of antibiotic resistance and virulence between Acinetobacter species.

The two species that account for most cases of Acinetobacter-associated bacteremia in the United Kingdom are Acinetobacter lwoffii, often a commensal but also an emerging pathogen, and Acinetobacter baumannii, a well-known antibiotic-resistant species. While these species both cause similar types of human infection and occupy the same niche, A. lwoffii (unlike A. baumannii) has thus far remained susceptible to antibiotics. Comparatively little is known about the biology of A. lwoffii, and this is the largest study on it conducted to date, providing valuable insights into its behaviour and potential threat to human health. This study aimed to explain the antibiotic susceptibility, virulence, and fundamental biological differences between these two species. The relative susceptibility of A. lwoffii was explained as it encoded fewer antibiotic resistance and efflux pump genes than A. baumannii (9 and 30, respectively). While both species had markers of horizontal gene transfer, A. lwoffii encoded more DNA defense systems and harbored a far more restricted range of plasmids. Furthermore, A. lwoffii displayed a reduced ability to select for antibiotic resistance mutations, form biofilm, and infect both in vivo and in in vitro models of infection. This study suggests that the emerging pathogen A. lwoffii has remained susceptible to antibiotics because mechanisms exist to make it highly selective about the DNA it acquires, and we hypothesize that the fact that it only harbors a single RND system restricts the ability to select for resistance mutations. This provides valuable insights into how development of resistance can be constrained in Gram-negative bacteria. IMPORTANCE: Acinetobacter lwoffii is often a harmless commensal but is also an emerging pathogen and is the most common cause of Acinetobacter-derived bloodstream infections in England and Wales. In contrast to the well-studied and often highly drug-resistant A. baumannii, A. lwoffii has remained susceptible to antibiotics. This study explains why this organism has not evolved resistance to antibiotics. These new insights are important to understand why and how some species develop antibiotic resistance, while others do not, and could inform future novel treatment strategies.

Disparities in Hypertension Prevalence, Awareness, Treatment, and Control Among Women Living With and Without HIV in the US South.

Background: Hypertension-related diseases are major causes of morbidity among women living with HIV. We evaluated cross-sectional associations of race/ethnicity and HIV infection with hypertension prevalence, awareness, treatment, and control. Methods: Among women recruited into Southern sites of the Women's Interagency HIV Study (2013-2015), hypertension was defined as (1) systolic blood pressure ≥140 mm Hg or diastolic blood pressure ≥90 mm Hg according to clinical guidelines when data were collected, (2) self-report of hypertension, or (3) use of antihypertensive medication. Awareness was defined as self-report of hypertension, and treatment was self-report of any antihypertensive medication use. Blood pressure control was defined as <140/90 mm Hg at baseline. Prevalence ratios for each hypertension outcome were estimated through Poisson regression models with robust variance estimators adjusted for sociodemographic, behavioral, and clinical risk factors. Results: Among 712 women, 56% had hypertension and 83% were aware of their diagnosis. Of those aware, 83% were using antihypertensive medication, and 63% of those treated had controlled hypertension. In adjusted analyses, non-Hispanic White and Hispanic women had 31% and 48% lower prevalence of hypertension than non-Hispanic Black women, respectively. Women living with HIV who had hypertension were 19% (P = .04) more likely to be taking antihypertension medication when compared with women living without HIV. Conclusions: In this study population of women living with and without HIV in the US South, the prevalence of hypertension was lowest among Hispanic women and highest among non-Hispanic Black women. Despite similar hypertension prevalence, women living with HIV were more likely to be taking antihypertensive medication when compared with women living without HIV.

Comparative Discrimination of Life's Simple 7 and Life's Essential 8 to Stratify Cardiovascular Risk: Is the Added Complexity Worth It?

BACKGROUND: Life's Simple 7 (LS7) is an easily calculated and interpreted metric of cardiovascular health based on 7 domains: smoking, diet, physical activity, body mass index, blood pressure, cholesterol, and fasting glucose. The Life's Essential 8 (LE8) metric was subsequently introduced, adding sleep metrics and revisions of the previous 7 domains. Although calculating LE8 requires additional information, we hypothesized that it would be a more reliable index of cardiovascular health. METHODS: Both the LS7 and LE8 metrics yield scores with higher values indicating lower risk. These were calculated among 11 609 Black and White participants free of baseline cardiovascular disease (CVD) in the Reasons for Geographic and Racial Differences in Stroke study, enrolled in 2003 to 2007, and followed for a median of 13 years. Differences in 10-year risk of incident CVD (coronary heart disease or stroke) were calculated as a function LS7, and LE8 scores were calculated using Kaplan-Meier and proportional hazards analyses. Differences in incident CVD discrimination were quantified by difference in the c-statistic. RESULTS: For both LS7 and LE8, the 10-year risk was approximately 5% for participants around the 99th percentile of scores, and a 4× higher 20% risk for participants around the first percentile. Comparing LS7 to LE8, 10-year risk was nearly identical for individuals at the same relative position in score distribution. For example, the "cluster" of 2013 participants with an LS7 score of 7 was at the 35.8th percentile in distribution of LS7 scores, and had an estimated 10-year CVD risk of 8.4% (95% CI, 7.2%-9.8%). In a similar location in the LE8 distribution, the 1457 participants with an LE8 score of 60±2.5 at the 39.4th percentile of LE8 scores had a 10-year risk of CVD of 8.5% (95% CI, 7.1%-10.1%), similar to the cluster defined by LS7. The age-race-sex adjusted c-statistic of the LS7 model was 0.691 (95% CI, 0.667-0.705), and 0.695 for LE8 (95% CI, 0.681-0.709) (P for difference, 0.12). CONCLUSIONS: Both LS7 and LE8 were associated with incident CVD, with discrimination of the 2 indices practically indistinguishable. As a simpler metric, LS7 may be favored for use by the general population and clinicians.

Microbial Primer: Multidrug efflux pumps.

Multidrug efflux pumps are molecular machines that sit in the bacterial cell membrane and pump molecules out from either the periplasm or cytoplasm to outside the cell. While involved in a variety of biological roles, they are primarily known for their contribution to antibiotic resistance by limiting the intracellular accumulation of antimicrobial compounds within bacteria. These transporters are often overexpressed in clinical isolates, leading to multidrug-resistant phenotypes. Efflux pumps are classified into several families based on their structure and understanding the characteristics of each family is important for the development of novel therapies to restore antibiotic potency.

History of obstructive sleep apnea associated with incident cognitive impairment in white but not black individuals in a US national cohort study.

BACKGROUND: We sought to determine if risk for obstructive sleep apnea (OSA), a history of OSA, and/or treatment of OSA has a different association with incident cognitive impairment or cognitive decline in Black individuals and White individuals. METHODS: To determine whether the risk for OSA, a history of OSA, and/or treatment of OSA has a different association with incident cognitive impairment or cognitive decline in Black individuals and White individuals; data from the REasons for Geographic and Racial Differences in Stroke (REGARDS) was used. Participants that completed the sleep questionnaire module, had baseline cognitive assessment, and at least one cognitive assessment during follow-up were included. Risk of OSA was determined based on Berlin Sleep Questionnaire. History of sleep apnea was determined based on structured interview questions. Optimally treated OSA was defined as treated sleep apnea as at least 4 h of continuous positive airway pressure use per night for ≥5 nights per week. RESULTS: In 19,017 participants stratified by race, White participants with history of OSA were 1.62 times more likely to have incident cognitive impairment compared to White participants without history of OSA after adjusting for demographic characteristics, history, and lifestyle factors (OR = 1.62, 95% CI = 1.05-2.50, p-value = 0.03). This relationship was not seen in Black participants (OR = 0.92, 95% CI = 0.60-1.43, p-value = 0.72). DISCUSSION: A previous diagnosis of OSA is associated with incident cognitive impairment in White Americans but not Black Americans. Further investigations are required to determine the mechanism for this difference.

Neighborhood Factors, Individual Stressors, and Cardiovascular Health Among Black and White Adults in the US: The Reasons for Geographic and Racial Differences in Stroke (REGARDS) Study.

Importance: Chronic stress has been posited to contribute to racial disparities in cardiovascular health. Investigation of whether neighborhood- and individual-level stressors mediate this disparity is needed. Objective: To examine whether racial differences in ideal cardiovascular health (ICH) are attenuated by experiences with neighborhood- and individual-level stressors within a racially and geographically diverse population sample. Design, Setting, and Participants: This cross-sectional study examined data from 7720 participants in the Reasons for Geographic and Racial Differences in Stroke (REGARDS) Study who completed the second in-home visit (2013-2016). The REGARDS study is a population-based, longitudinal study of 30 239 non-Hispanic Black and non-Hispanic White adults aged 45 years or older at baseline (2003-2007). Data for the present study were analyzed from June to July 2021 and in March 2022. Exposures: Neighborhood physical environment (eg, excessive noise, violence; scored from 7-28, with higher scores indicating more problems), neighborhood safety (scored as very safe, safe, or not safe), neighborhood social cohesion (eg, shared values; scored from 5-25, with higher scores indicating higher cohesion), perceived stress (eg, coping; scored from 0-16, with higher scores indicating greater perceived stress), and the experience of discrimination (yes or no). Main Outcomes and Measures: Ideal cardiovascular health (ICH), measured as a composite of 4 health behaviors (cigarette smoking, diet, physical activity, body mass index) and 3 health factors (blood pressure, cholesterol, and glucose levels). Results: The sample included 7720 participants (mean [SD] age, 71.9 [8.3] years; 4390 women [56.9%]; 2074 Black participants [26.9%]; and 5646 White participants [73.1%]). Black participants compared with White participants reported higher perceived stress (mean [SD] score, 3.2 [2.8] vs 2.8 [2.7]) and more often reported discrimination (77.0% vs 24.0%). Black participants also reported poorer neighborhood physical environment (mean [SD] score, 11.2 [3.8] vs 9.8 [2.9]) and social cohesion (mean [SD] score, 15.5 [2.0] vs 15.7 [1.9]) and more often reported their neighborhoods were unsafe (54.7% vs 24.3%). The odds of having a high total ICH score (ie, closer to ideal) were lower for Black adults compared with White adults, both overall (adjusted odds ratio [AOR], 0.53; 95% CI, 0.45-0.61) and by gender (men: AOR, 0.73 [95% CI, 0.57-0.93]; women: AOR, 0.45 [95% CI, 0.37-0.54]). In mediation analyses, the racial disparity in total ICH score was attenuated by neighborhood physical environment (5.14%), neighborhood safety (6.27%), neighborhood social cohesion (1.41%), and discrimination (11.01%). In stratified analyses, the factors that most attenuated the racial disparity in total ICH scores were neighborhood safety among men (12.32%) and discrimination among women (14.37%). Perceived stress did not attenuate the racial disparity in total ICH scores. Conclusions and Relevance: In this cross-sectional study of Black and White US adults aged 45 years and older, neighborhood-level factors, including safety and physical and social environments, and individual-level factors, including discrimination, attenuated racial disparities in cardiovascular health. Interventional approaches to improve ICH that separately target neighborhood context and discrimination by gender and race are warranted.

Pseudomonas aeruginosa increases the susceptibility of Candida albicans to amphotericin B in dual-species biofilms.

BACKGROUND: Biofilms are the leading cause of nosocomial infections and are hard to eradicate due to their inherent antimicrobial resistance. Candida albicans is the leading cause of nosocomial fungal infections and is frequently co-isolated with the bacterium Pseudomonas aeruginosa from biofilms in the cystic fibrosis lung and severe burn wounds. The presence of C. albicans in multispecies biofilms is associated with enhanced antibacterial resistance, which is largely mediated through fungal extracellular carbohydrates sequestering the antibiotics. However, significantly less is known regarding the impact of polymicrobial biofilms on antifungal resistance. RESULTS: Here we show that, in dual-species biofilms, P. aeruginosa enhances the susceptibility of C. albicans to amphotericin B, an effect that was biofilm specific. Transcriptional analysis combined with gene ontology enrichment analysis identified several C. albicans processes associated with oxidative stress to be differentially regulated in dual-species biofilms, suggesting that P. aeruginosa exerts oxidative stress on C. albicans, likely through the secretion of phenazines. However, the mitochondrial superoxide dismutase SOD2 was significantly down-regulated in the presence of P. aeruginosa. Monospecies biofilms of the sod2Δ mutant were more susceptible to amphotericin B, and the susceptibility of these biofilms was further enhanced by exogenous phenazines. CONCLUSIONS: We propose that in dual-species biofilms, P. aeruginosa simultaneously induces mitochondrial oxidative stress, while down-regulating key detoxification enzymes, which prevents C. albicans mounting an appropriate oxidative stress response to amphotericin B, leading to fungal cell death. This work highlights the importance of understanding the impact of polymicrobial interactions on antimicrobial susceptibility.

Chelating silica nanoparticles for efficient antibiotic delivery and particle imaging in Gram-negative bacteria.

The inefficacy of antibiotics against Gram-negative bacteria is a major challenge for treatment of many clinically important bacterial infections. The complex structure of the double cell membrane of Gram-negative bacteria makes it inaccessible to many key antibiotics such as vancomycin and also presents a major challenge for drug development. In this study we design of a novel hybrid silica nanoparticle system bearing membrane targeting groups with the antibiotic encapsulated together with a ruthenium luminescent tracking agent, for optical detection of the nanoparticle delivery in the bacterial cell. The hybrid system shows delivery of vancomycin and efficacy against a library of Gram negative bacterial species. Evidence of penetration of nanoparticles in bacteria cells is achieved via luminescence of the ruthenium signal. Our studies show that nanoparticles modified with aminopolycarboxylate chelating groups are an effective delivery system in bacterial growth inhibition in species whereas the molecular antibiotic is ineffective. This design provides a new platform for delivery of antibiotics that cannot alone penetrate the bacterial membrane.

E. coli ST11 (O157:H7) does not encode a functional AcrF efflux pump.

Escherichia coli is a facultative anaerobe found in a wide range of environments. Commonly described as the laboratory workhorse, E. coli is one of the best characterized bacterial species to date, however much of our understanding comes from studies involving the laboratory strain E. coli K-12. Resistance-nodulation-division efflux pumps are found in Gram-negative bacteria and can export a diverse range of substrates, including antibiotics. E. coli K-12 has six RND pumps; AcrB, AcrD, AcrF, CusA, MdtBC and MdtF, and it is frequently reported that all E. coli strains possess these six pumps. However, this is not true of E. coli ST11, a lineage of E. coli, which is primarily composed of the highly virulent important human pathogen, E. coli O157:H7. Here we show that acrF is absent from the pangenome of ST11 and that this lineage of E. coli has a highly conserved insertion within the acrF gene, which when translated encodes 13 amino acids and two stop codons. This insertion was found to be present in 97.59 % of 1787 ST11 genome assemblies. Non-function of AcrF in ST11 was confirmed in the laboratory as complementation with acrF from ST11 was unable to restore AcrF function in E. coli K-12 substr. MG1655 ΔacrB ΔacrF. This shows that the complement of RND efflux pumps present in laboratory bacterial strains may not reflect the situation in virulent strains of bacterial pathogens.

Characteristics of antimicrobial peptide OaBac5mini and its bactericidal mechanism against Escherichia coli.

Introduction: Antimicrobial peptides (AMPs) play an important role in defending against the attack of pathogenic microorganisms. Among them, the proline-rich antibacterial peptides (PrAMPs) have been attracting close attention due to their simple structure, strong antibacterial activity, and low cell toxicity. OaBac5mini is an active fragment of the sheep-derived OaBac5 belonging to the PrAMPs family. Methods: In this study, the antibacterial activity of OaBac5mini was investigated by testing the MICs against different stains of E. coli and S. aureus as well as the time-kill curve. The bactericidal mechanism was explored by determining the effect of OaBac5mini on the cell membrane. The stability and biosafety were also evaluated. Results: The susceptibility test demonstrated that OaBac5mini showed potent antibacterial activity against the multidrug-resistant (MDR) E. coli isolates. It is noticeable that the absence of inner membrane protein SbmA in E. coli ATCC 25922 caused the MIC of OaBac5mini to increase 4-fold, implying OaBac5mini can enter into the cytoplasm via SbmA and plays its antibacterial activity. Moreover, the antibacterial activity of OaBac5mini against E. coli ATCC 25922 was not remarkably affected by the serum salts except for CaCl2 at a physiological concentration, pH, temperature, repeated freeze-thawing and proteases (trypsin < 20 µg/mL, pepsin or proteinase K). Time-kill curve analysis showed OaBac5mini at the concentration of 200 µg/mL (8 × MICs) could effectively kill E. coli ATCC 25922 after co-incubation for 12 h. In addition, OaBac5mini was not hemolytic against rabbit red blood cells and also was not cytotoxic to porcine small intestinal epithelial cells (IPEC-J2). Bioinformatic analysis indicated that OaBac5mini is a linear peptide with 8 net positive charges. Furthermore, OaBac5mini significantly increased the outer membrane permeability and impaired the inner membrane integrity and ultrastructure of E. coli ATCC25922. Conclusion: OaBac5mini is a stable and potent PrAMP that kills E. coli by two different modes of action - inhibiting intracellular target(s) and damaging cell membrane.

RND pumps across the genus Acinetobacter: AdeIJK is the universal efflux pump.

Acinetobacter are generally soil-dwelling organisms that can also cause serious human infections. A. baumannii is one of the most common causative agents of Acinetobacter infections and is often multidrug resistant. However, an additional 25 species within the genus have also been associated with infection. A. baumannii encodes six resistance nodulation division (RND) efflux pumps, the most clinically relevant class of efflux pumps for antibiotic export, but the distribution and types of RND efflux pumps across the genus is currently unknown. Sixty-four species making up the genus Acinetobacter were searched for RND systems within their genomes. We also developed a novel method using conserved RND residues to predict the total number of RND proteins including currently undescribed RND pump proteins. The total number of RND proteins differed both within a species and across the genus. Species associated with infection tended to encode more pumps. AdeIJK/AdeXYZ was found in all searched species of Acinetobacter, and through genomic, structural and phenotypic work we show that these genes are actually homologues of the same system. This interpretation is further supported by structural analysis of the potential drug-binding determinants of the associated RND-transporters, which reveal their close similarity to each other, and distinctiveness from other RND-pumps in Acinetobacter, such as AdeB. Therefore, we conclude that AdeIJK is the fundamental RND system for species in the genus Acinetobacter. AdeIJK can export a broad range of antibiotics and provides crucial functions within the cell, for example lipid modulation of the cell membrane, and therefore it is likely that all Acinetobacter require AdeIJK for survival and homeostasis. In contrast, additional RND systems, such as AdeABC and AdeFGH, were only found in a subset of Acinetobacter that are associated with infection. By understanding the roles and mechanisms of RND efflux systems in Acinetobacter, treatments for infections can avoid efflux-mediated resistance and improve patient outcomes.

Transcriptional profiling of Pseudomonas aeruginosa mature single- and dual-species biofilms in response to meropenem.

Pseudomonas aeruginosa is a Gram-negative opportunistic pathogen frequently isolated from chronic infections of the cystic fibrosis lung and burn wounds, and is a major cause of antimicrobial-resistant nosocomial infections. P. aeruginosa is frequently co-isolated with the opportunistic fungal pathogen Candida albicans, with the presence of C. albicans in dual-species biofilms promoting tolerance to meropenem. Here, transcription profiling of mature P. aeruginosa single- or dual-species biofilms was carried out to understand the molecular mechanism(s) by which C. albicans enhances meropenem tolerance. C. albicans appeared to have a mild impact on the transcriptome of P. aeruginosa mature biofilms, with most differentially regulated genes being involved in interkingdom interactions (i.e. quorum sensing and phenazine biosynthesis). The addition of meropenem to mature single- or dual-species biofilms resulted in a significant bacterial transcriptional response, including the induction of the beta-lactamase, ampC, genes involved in biofilm formation. P. aeruginosa elicited a similar transcriptional response to meropenem in the presence of C. albicans, but C. albicans promoted the expression of additional efflux pumps, which could play roles in increasing the tolerance of P. aeruginosa to meropenem.

Hypertension and Cardiovascular Disease Risk Among Individuals With Versus Without HIV.

BACKGROUND: A high proportion of individuals with HIV have hypertension, and the incidence of cardiovascular disease (CVD) is high in individuals with HIV. METHODS: We determined if the association between hypertension and CVD, including acute myocardial infarction (AMI), stroke, and heart failure, differs between individuals with and without HIV. We analyzed data for 108 980 adults with HIV matched (1:4) to 435 920 adults without HIV in 2011 to 2019 from the Marketscan database, which includes US adults with health insurance. The primary outcome, incident CVD, defined by an AMI, stroke or heart failure, was identified using validated claims-based algorithms. RESULTS: Over a median follow-up of 2.3 years, there were 4027 CVD events, including 2345 AMI, 1153 stroke, and 684 heart failure events. After multivariable adjustment, the hazard ratio for CVD associated with hypertension was 1.56 (95% CI, 1.44-1.69) among individuals without HIV and 1.73 (95% CI, 1.52-1.96) among individuals with HIV (P value for interaction=0.159). The multivariable-adjusted hazard ratio for AMI associated with hypertension was 1.35 (95% CI, 1.22-1.51) among individuals without HIV and 1.70 (95% CI, 1.44-2.01) among individuals with HIV (P value for interaction=0.017). Hypertension was associated with stroke and heart failure among individuals without and with HIV with no evidence of effect modification (P value for interaction >0.40). CONCLUSIONS: Hypertension was associated with increased CVD, AMI, stroke, and heart failure risk among individuals with and without HIV, with a stronger association for AMI among individuals with versus without HIV. This study emphasizes the high CVD risk associated with hypertension among individuals with HIV.

Molecular mechanisms of antibiotic resistance revisited.

Antibiotic resistance is a global health emergency, with resistance detected to all antibiotics currently in clinical use and only a few novel drugs in the pipeline. Understanding the molecular mechanisms that bacteria use to resist the action of antimicrobials is critical to recognize global patterns of resistance and to improve the use of current drugs, as well as for the design of new drugs less susceptible to resistance development and novel strategies to combat resistance. In this Review, we explore recent advances in understanding how resistance genes contribute to the biology of the host, new structural details of relevant molecular events underpinning resistance, the identification of new resistance gene families and the interactions between different resistance mechanisms. Finally, we discuss how we can use this information to develop the next generation of antimicrobial therapies.

EnvR is a potent repressor of acrAB transcription in Salmonella.

BACKGROUND: Resistance nodulation division (RND) family efflux pumps, including the major pump AcrAB-TolC, are important mediators of intrinsic and evolved antibiotic resistance. Expression of these pumps is carefully controlled by a network of regulators that respond to different environmental cues. EnvR is a TetR family transcriptional regulator encoded upstream of the RND efflux pump acrEF. METHODS: Binding of EnvR protein upstream of acrAB was determined by electrophoretic mobility shift assays and the phenotypic consequence of envR overexpression on antimicrobial susceptibility, biofilm motility and invasion of eukaryotic cells in vitro was measured. Additionally, the global transcriptome of clinical Salmonella isolates overexpressing envR was determined by RNA-Seq. RESULTS: EnvR bound to the promoter region upstream of the genes coding for the major efflux pump AcrAB in Salmonella, inhibiting transcription and preventing production of AcrAB protein. The phenotype conferred by overexpression of envR mimicked deletion of acrB as it conferred multidrug susceptibility, decreased motility and decreased invasion into intestinal cells in vitro. Importantly, we demonstrate the clinical relevance of this regulatory mechanism because RNA-Seq revealed that a drug-susceptible clinical isolate of Salmonella had low acrB expression even though expression of its major regulator RamA was very high; this was caused by very high EnvR expression. CONCLUSIONS: In summary, we show that EnvR is a potent repressor of acrAB transcription in Salmonella, and can override binding by RamA so preventing MDR to clinically useful drugs. Finding novel tools to increase EnvR expression may form the basis of a new way to prevent or treat MDR infections.

The role of bacterial transport systems in the removal of host antimicrobial peptides in Gram-negative bacteria.

Antibiotic resistance is a global issue that threatens our progress in healthcare and life expectancy. In recent years, antimicrobial peptides (AMPs) have been considered as promising alternatives to the classic antibiotics. AMPs are potentially superior due to their lower rate of resistance development, since they primarily target the bacterial membrane ('Achilles' heel' of the bacteria). However, bacteria have developed mechanisms of AMP resistance, including the removal of AMPs to the extracellular space by efflux pumps such as the MtrCDE or AcrAB-TolC systems, and the internalization of AMPs to the cytoplasm by the Sap transporter, followed by proteolytic digestion. In this review, we focus on AMP transport as a resistance mechanism compiling all the experimental evidence for the involvement of efflux in AMP resistance in Gram-negative bacteria and combine this information with the analysis of the structures of the efflux systems involved. Finally, we expose some open questions with the aim of arousing the interest of the scientific community towards the AMPs-efflux pumps interactions. All the collected information broadens our understanding of AMP removal by efflux pumps and gives some clues to assist the rational design of AMP-derivatives as inhibitors of the efflux pumps.