Laura J. V. Piddock

Multidrug-resistance efflux pumps - not just for resistance.

It is well established that multidrug-resistance efflux pumps encoded by bacteria can confer clinically relevant resistance to antibiotics. It is now understood that these efflux pumps also have a physiological role(s). They can confer resistance to natural substances produced by the host, including bile, hormones and host-defence molecules. In addition, some efflux pumps of the resistance nodulation division (RND) family have been shown to have a role in the colonization and the persistence of bacteria in the host. Here, I present the accumulating evidence that multidrug-resistance efflux pumps have roles in bacterial pathogenicity and propose that these pumps therefore have greater clinical relevance than is usually attributed to them.

Diagnosis, treatment and prophylaxis of spontaneous bacterial peritonitis: a consensus document

bacterial peritonitis (SBP) is a fre- quent and severe complication of cirrhotic patients with ascites. Much information regarding SBP has ap- peared during recent years, particularly on aspects in- volving the management of this complication. There- fore, the International Ascites Club (IAC) com- missioned a panel of experts to prepare a consensus on the diagnosis, therapy and prophylaxis of SBI? A draft consensus document, drawn up by the panel members, was presented and discussed at the regular Meeting of the IAC held during the 33rd Annual Meeting of the European Association for the Study of the Liver, in Lisbon in April 1998, after which a final consensus was reached. This article represents the final consensus document and is divided into three separate sections concerning the diagnosis, treatment and prophylaxis of SBI? Speci- fic recommendations are formulated and each recom- mendation is rated on the basis of strength and quality according to guidelines from the Practice Guidelines Committee of the American Association for the Study of Liver Diseases, with some modifications (1). The rating system is summarized in Table 1.

Clinically Relevant Chromosomally Encoded Multidrug Resistance Efflux Pumps in Bacteria

SUMMARY Efflux pump genes and proteins are present in both antibiotic-susceptible and antibiotic-resistant bacteria. Pumps may be specific for one substrate or may transport a range of structurally dissimilar compounds (including antibiotics of multiple classes); such pumps can be associated with multiple drug (antibiotic) resistance (MDR). However, the clinical relevance of efflux-mediated resistance is species, drug, and infection dependent. This review focuses on chromosomally encoded pumps in bacteria that cause infections in humans. Recent structural data provide valuable insights into the mechanisms of drug transport. MDR efflux pumps contribute to antibiotic resistance in bacteria in several ways: (i) inherent resistance to an entire class of agents, (ii) inherent resistance to specific agents, and (iii) resistance conferred by overexpression of an efflux pump. Enhanced efflux can be mediated by mutations in (i) the local repressor gene, (ii) a global regulatory gene, (iii) the promoter region of the transporter gene, or (iv) insertion elements upstream of the transporter gene. Some data suggest that resistance nodulation division systems are important in pathogenicity and/or survival in a particular ecological niche. Inhibitors of various efflux pump systems have been described; typically these are plant alkaloids, but as yet no product has been marketed.

Molecular mechanisms of antibiotic resistance.

Antibiotic-resistant bacteria that are difficult or impossible to treat are becoming increasingly common and are causing a global health crisis. Antibiotic resistance is encoded by several genes, many of which can transfer between bacteria. New resistance mechanisms are constantly being described, and new genes and vectors of transmission are identified on a regular basis. This article reviews recent advances in our understanding of the mechanisms by which bacteria are either intrinsically resistant or acquire resistance to antibiotics, including the prevention of access to drug targets, changes in the structure and protection of antibiotic targets and the direct modification or inactivation of antibiotics.

The Comprehensive Antibiotic Resistance Database

ABSTRACT The field of antibiotic drug discovery and the monitoring of new antibiotic resistance elements have yet to fully exploit the power of the genome revolution. Despite the fact that the first genomes sequenced of free living organisms were those of bacteria, there have been few specialized bioinformatic tools developed to mine the growing amount of genomic data associated with pathogens. In particular, there are few tools to study the genetics and genomics of antibiotic resistance and how it impacts bacterial populations, ecology, and the clinic. We have initiated development of such tools in the form of the Comprehensive Antibiotic Research Database (CARD; http://arpcard.mcmaster.ca). The CARD integrates disparate molecular and sequence data, provides a unique organizing principle in the form of the Antibiotic Resistance Ontology (ARO), and can quickly identify putative antibiotic resistance genes in new unannotated genome sequences. This unique platform provides an informatic tool that bridges antibiotic resistance concerns in health care, agriculture, and the environment.

Tackling antibiotic resistance

The development and spread of antibiotic resistance in bacteria is a universal threat to both humans and animals that is generally not preventable but can nevertheless be controlled, and it must be tackled in the most effective ways possible. To explore how the problem of antibiotic resistance might best be addressed, a group of 30 scientists from academia and industry gathered at the Banbury Conference Centre in Cold Spring Harbor, New York, USA, from 16 to 18 May 2011. From these discussions there emerged a priority list of steps that need to be taken to resolve this global crisis.

Quinolone-Resistant Salmonella typhi in Viet Nam: Molecular Basis of Resistance and Clinical Response to Treatment

Nalidixic acid-resistant Salmonella typhi (NARST) was first isolated in Viet Nam in 1993. Analysis of the quinolone resistance-determining region of gyrA in 20 NARST isolates by polymerase chain reaction and single-stranded conformational polymorphism yielded two novel patterns: pattern II corresponding to a point mutation at nucleotide 87 Asp-->Gly (n = 17), and pattern III corresponding to a point mutation at nucleotide 83 Ser-->Phe (n = 3). In trials of short-course ofloxacin therapy for uncomplicated typhoid, 117 (78%) of 150 patients were infected with multidrug-resistant S. typhi, 18 (15%) of which were NARST. The median time to fever clearance was 156 hours (range, 30-366 hours) for patients infected with NARST and 84 hours (range, 12-378 hours) for those infected with nalidixic acid-susceptible strains (P < .001). Six (33.3%) of 18 NARST infections required retreatment, whereas 1 (0.8%) of 132 infections due to susceptible strains required retreatment (relative risk = 44; 95% confidence interval = 5.6-345; P < .0001). We recommend that short courses of quinolones not be used in patients infected with NARST.

Understanding the mechanisms and drivers of antimicrobial resistance

To combat the threat to human health and biosecurity from antimicrobial resistance, an understanding of its mechanisms and drivers is needed. Emergence of antimicrobial resistance in microorganisms is a natural phenomenon, yet antimicrobial resistance selection has been driven by antimicrobial exposure in health care, agriculture, and the environment. Onward transmission is affected by standards of infection control, sanitation, access to clean water, access to assured quality antimicrobials and diagnostics, travel, and migration. Strategies to reduce antimicrobial resistance by removing antimicrobial selective pressure alone rely upon resistance imparting a fitness cost, an effect not always apparent. Minimising resistance should therefore be considered comprehensively, by resistance mechanism, microorganism, antimicrobial drug, host, and context; parallel to new drug discovery, broad ranging, multidisciplinary research is needed across these five levels, interlinked across the health-care, agriculture, and environment sectors. Intelligent, integrated approaches, mindful of potential unintended results, are needed to ensure sustained, worldwide access to effective antimicrobials.

Mechanisms of Fluoroquinolone Resistance: An Update 1994–1998

Fluoroquinolone resistance is mediated by target changes (DNA gyrase and/ or topoisomerase IV) and/or decreased intracellular accumulation. The genes (gyrA/gyrB/parC/parE) and proteins of DNA topoisomerase IV show great similarity, both at the nucleotide and amino acid sequence level to those of DNA gyrase. It has been shown that there are hotspots, called the quinolone resistance determining region (QRDR), for mutations within gyrA and parC. Based on the Escherichia coli co-ordinates, the hotspots most favoured for giving rise to decreased susceptibility and/or full resistance to quinolones are at serine 83 and aspartate 87 of gyrA, and at serine 79 and aspartate 83 for parC. Few mutations in gyrB or parE/grlB of any bacteria have been described. Efflux of fluoroquinolones is the major cause of decreased accumulation of these agents; for Staphylococcus aureus, the efflux pump involved in norfloxacin resistance is NorA, and for Streptococcus pneumoniae, PmrA. By analysis of minimum inhibitory concentration (MIC) data derived in the presence and absence of the efflux inhibitor reserpine, it has been shown that up to 50% of ciprofloxacin-resistant clinical isolates of S. pneumoniae may possess enhanced efflux. This suggests that efflux may be an important mechanism of clinical resistance in this species. In Pseudomonas aeruginosa, several efflux operons have been demonstrated genetically and biochemically. These operons are encoded by mex (Multiple EffluX) genes: mexAmexB-oprM, mexCD-OprJ system and mexEF-oprN system. The E. coli efflux pump is the acrAB — tolC system. Both the mar operon and the sox operon can give rise to multiple antibiotic resistance. It has been shown that mutations giving rise to increased expression of the transcriptional activators marA and soxS affect the expression of a variety of different genes, including ompF and acrAB. The net result is that expression of OmpF is reduced and much less drug is able to enter the cell; expression of acrAB is increased, enhancing efflux from the cell.

Fluoroquinolone resistance: mechanisms, impact on bacteria, and role in evolutionary success

Quinolone and fluoroquinolone antibiotics are potent, broad-spectrum agents commonly used to treat a range of infections. Resistance to these agents is multifactorial and can be via one or a combination of target-site gene mutations, increased production of multidrug-resistance (MDR) efflux pumps, modifying enzymes, and/or target-protection proteins. Fluoroquinolone-resistant clinical isolates of bacteria have emerged readily and recent data have shown that resistance to this class of antibiotics can have diverse, species-dependent impacts on host-strain fitness. Here we outline the impacts of quinolone-resistance mutations in relation to the fitness and evolutionary success of mutant strains.