Insertional inactivation ofoprD in clinical isolates ofPseudomonas aeruginosaleading to carbapenem resistance

Antibiotic influx and efflux in Pseudomonas aeruginosa: Regulation and therapeutic implications

Pseudomonas aeruginosa is a notorious multidrug-resistant pathogen that poses a serious and growing threat to the worldwide public health. The expression of resistance determinants is exquisitely modulated by the abundant regulatory proteins and the intricate signal sensing and transduction systems in this pathogen. Downregulation of antibiotic influx porin proteins and upregulation of antibiotic efflux pump systems owing to mutational changes in their regulators or the presence of distinct inducing molecular signals represent two of the most efficient mechanisms that restrict intracellular antibiotic accumulation and enable P. aeruginosa to resist multiple antibiotics. Treatment of P. aeruginosa infections is extremely challenging due to the highly inducible mechanism of antibiotic resistance. This review comprehensively summarizes the regulatory networks of the major porin proteins (OprD and OprH) and efflux pumps (MexAB-OprM, MexCD-OprJ, MexEF-OprN, and MexXY) that play critical roles in antibiotic influx and efflux in P. aeruginosa. It also discusses promising therapeutic approaches using safe and efficient adjuvants to enhance the efficacy of conventional antibiotics to combat multidrug-resistant P. aeruginosa by controlling the expression levels of porins and efflux pumps. This review not only highlights the complexity of the regulatory network that induces antibiotic resistance in P. aeruginosa but also provides important therapeutic implications in targeting the inducible mechanism of resistance.

Advances in Development of Novel Therapeutic Strategies against Multi-Drug Resistant Pseudomonas aeruginosa

Pseudomonas aeruginosa (P. aeruginosa) with multi-drug resistance (MDR) is a major cause of serious healthcare-associated infections, leading to high morbidity and mortality. This opportunistic pathogen is responsible for various infectious diseases, such as those seen in cystic fibrosis, ventilator-associated pneumonia, urinary tract infection, otitis externa, and burn and wound injuries. Due to its relatively large genome, P. aeruginosa has great diversity and can use various molecular mechanisms for antimicrobial resistance. For example, outer membrane permeability can contribute to antimicrobial resistance and is determined by lipopolysaccharide (LPS) and porin proteins. Recent findings on the regulatory interaction between peptidoglycan and LPS synthesis provide additional clues against pathogenic P. aeruginosa. This review focuses on recent advances in antimicrobial agents and inhibitors targeting LPS and porin proteins. In addition, we explore current and emerging treatment strategies for MDR P. aeruginosa, including phages, vaccines, nanoparticles, and their combinatorial therapies. Novel strategies and their corresponding therapeutic agents are urgently needed for combating MDR pathogens.

Prioritization of Critical Factors for Surveillance of the Dissemination of Antibiotic Resistance in Pseudomonas aeruginosa: A Systematic Review

Pseudomonas aeruginosa is the primary opportunistic human pathogen responsible for a range of acute and chronic infections; it poses a significant threat to immunocompromised patients and is the leading cause of morbidity and mortality for nosocomial infections. Its high resistance to a diverse array of antimicrobial agents presents an urgent health concern. Among the mechanisms contributing to resistance in P. aeruginosa, the horizontal acquisition of antibiotic resistance genes (ARGs) via mobile genetic elements (MGEs) has gained recognition as a substantial concern in clinical settings, thus indicating that a comprehensive understanding of ARG dissemination within the species is strongly required for surveillance. Here, two approaches, including a systematic literature analysis and a genome database survey, were employed to gain insights into ARG dissemination. The genome database enabled scrutinizing of all the available sequence information and various attributes of P. aeruginosa isolates, thus providing an extensive understanding of ARG dissemination within the species. By integrating both approaches, with a primary focus on the genome database survey, mobile ARGs that were linked or correlated with MGEs, important sequence types (STs) carrying diverse ARGs, and MGEs responsible for ARG dissemination were identified as critical factors requiring strict surveillance. Although human isolates play a primary role in dissemination, the importance of animal and environmental isolates has also been suggested. In this study, 25 critical mobile ARGs, 45 critical STs, and associated MGEs involved in ARG dissemination within the species, are suggested as critical factors. Surveillance and management of these prioritized factors across the One Health sectors are essential to mitigate the emergence of multidrug-resistant (MDR) and extensively resistant (XDR) P. aeruginosa in clinical settings.

High Prevalence of GES-5 Variant and Co-Expression of VIM-2 and GES-45 among Clinical Pseudomonas aeruginosa Strains in Tunisia

Carbapenem-resistant Pseudomonas aeruginosa (CRPA) are a global health concern. The antimicrobial resistance, virulence, and molecular typing of 57 CRPA isolated from 43 patients who attended a specific Tunisian hospital from September 2018 to July 2019 were analyzed. All but one were multidrug-resistant CRPA, and 77% were difficult-to-treat-resistant (DTR) isolates. The blaVIM-2 gene was detected in four strains (6.9%), and among the 36 blaGES-positive CRPA (62%), the blaGES-5 gene was the predominant variant (86%). Three strains co-harbored the blaVIM-2 and blaGES-45 genes, and seven CRPA carried the blaSHV-2a gene (14%). OprD alterations, including truncations by insertion sequences, were observed in 18 strains. Regarding the 46 class 1 integron-positive CRPA (81%), the blaGES-5 gene was located in integron In717, while the blaGES-29 and blaGES-45 genes were found in two new integrons (In2122 and In4879), and the blaVIM-2 gene was found in In1183 and the new integron In2142. Twenty-four PFGE patterns and thirteen sequence types (three new ones) were identified. The predominant serotype O:11 and exoU (81%) were mostly associated with ST235 and the new ST3385 clones. The seven blaSHV-2a-CRPA from different patients belonged to ST3385 and the same PFGE pattern. The blaGES-5- and blaVIM-2 + blaGES-45-positive CRPA recovered mostly from ICU patients belonged to the high-risk clone ST235. Our results highlight the alarming prevalence of blaGES-5- and ST235-CRPA, the co-existence of blaGES-45 and blaVIM-2, and their location within integrons favoring their dissemination.

Antimicrobial Resistance in Romania: Updates on Gram-Negative ESCAPE Pathogens in the Clinical, Veterinary, and Aquatic Sectors

Multidrug-resistant Gram-negative bacteria such as Acinetobacter baumannii, Pseudomonas aeruginosa, and members of the Enterobacterales order are a challenging multi-sectorial and global threat, being listed by the WHO in the priority list of pathogens requiring the urgent discovery and development of therapeutic strategies. We present here an overview of the antibiotic resistance profiles and epidemiology of Gram-negative pathogens listed in the ESCAPE group circulating in Romania. The review starts with a discussion of the mechanisms and clinical significance of Gram-negative bacteria, the most frequent genetic determinants of resistance, and then summarizes and discusses the epidemiological studies reported for A. baumannii, P. aeruginosa, and Enterobacterales-resistant strains circulating in Romania, both in hospital and veterinary settings and mirrored in the aquatic environment. The Romanian landscape of Gram-negative pathogens included in the ESCAPE list reveals that all significant, clinically relevant, globally spread antibiotic resistance genes and carrying platforms are well established in different geographical areas of Romania and have already been disseminated beyond clinical settings.

Antibacterial Nanomaterials: Mechanisms, Impacts on Antimicrobial Resistance and Design Principles

Antimicrobial resistance (AMR) is one of the biggest threats to the environment and health. AMR rapidly invalidates conventional antibiotics, and antimicrobial nanomaterials have been increasingly explored as alternatives. Interestingly, several antimicrobial nanomaterials show AMR-independent antimicrobial effects without detectable new resistance and have therefore been suggested to prevent AMR evolution. In contrast, some are found to trigger the evolution of AMR. Given these seemingly conflicting findings, a timely discussion of the two faces of antimicrobial nanomaterials is urgently needed. This review systematically compares the killing mechanisms and structure-activity relationships of antibiotics and antimicrobial nanomaterials. We then focus on nano-microbe interactions to elucidate the impacts of molecular initiating events on AMR evolution. Finally, we provide an outlook on future antimicrobial nanomaterials and propose design principles for the prevention of AMR evolution.

Adaptation and Evolution of Pathogens in the Cystic Fibrosis Lung

As opposed to acute respiratory infections, the persistent bacterial infections of the lung that characterize cystic fibrosis (CF) provide ample time for bacteria to evolve and adapt. The process of adaptation is recorded in mutations that accumulate over time in the genomes of the infecting bacteria. Some of these mutations lead to obvious phenotypic differences such as antibiotic resistance or the well-known mucoid phenotype of Pseudomonas aeruginosa. Other mutations may be just as important but harder to detect such as increased mutation rates, cell surface changes, and shifts in metabolism and nutrient acquisition. Remarkably, many of the adaptations occur again and again in different patients, signaling that bacteria are adapting to solve specific challenges in the CF respiratory tract. This parallel evolution even extends across distinct bacterial species. This review addresses the bacterial systems that are known to change in long-term CF infections with a special emphasis on cross-species comparisons. Consideration is given to how adaptation may impact health in CF, and the possible evolutionary mechanisms that lead to the repeated parallel adaptations.

'To be, or not to be' - the dilemma of 'silent' antimicrobial resistance genes in bacteria

Antimicrobial resistance is a serious threat to public health that dramatically undermines our ability to treat bacterial infections. Microorganisms exhibit resistance to different drug classes by acquiring resistance determinants through multiple mechanisms including horizontal gene transfer. The presence of drug resistance genotypes is mostly associated with corresponding phenotypic resistance against the particular antibiotic. However, bacterial communities harboring silent antimicrobial resistance genes - genes whose presence is not associated with a corresponding resistant phenotype, do exist. Under suitable conditions, the expression pattern of such genes often revert and regain resistance, and could potentially lead to therapeutic failure. We often miss the presence of silent genes, since the current experimental paradigms are focused on resistant strains. Therefore, the knowledge on the prevalence, importance, and mechanism of silent antibiotic resistance genes in bacterial pathogens is very limited. Silent genes, therefore, provide an additional level of complexity in the war against drug-resistant bacteria, reminding us that not only phenotypically resistant strains but also susceptible strains should be carefully investigated. In this review, we discuss the presence of silent antimicrobial resistance genes in bacteria, their relevance, and their importance in public health.

Adaptation and genomic erosion in fragmented Pseudomonas aeruginosa populations in the sinuses of people with cystic fibrosis

Pseudomonas aeruginosa notoriously adapts to the airways of people with cystic fibrosis (CF), yet how infection-site biogeography and associated evolutionary processes vary as lifelong infections progress remains unclear. Here we test the hypothesis that early adaptations promoting aggregation influence evolutionary-genetic trajectories by examining longitudinal P. aeruginosa from the sinuses of six adults with CF. Highly host-adapted lineages harbored mutator genotypes displaying signatures of early genome degradation associated with recent host restriction. Using an advanced imaging technique (MiPACT-HCR [microbial identification after passive clarity technique]), we find population structure tracks with genome degradation, with the most host-adapted, genome-degraded P. aeruginosa (the mutators) residing in small, sparse aggregates. We propose that following initial adaptive evolution in larger populations under strong selection for aggregation, P. aeruginosa persists in small, fragmented populations that experience stronger effects of genetic drift. These conditions enrich for mutators and promote degenerative genome evolution. Our findings underscore the importance of infection-site biogeography to pathogen evolution.

Metallo-β-lactamases in the Age of Multidrug Resistance: From Structure and Mechanism to Evolution, Dissemination, and Inhibitor Design

Antimicrobial resistance is one of the major problems in current practical medicine. The spread of genes coding for resistance determinants among bacteria challenges the use of approved antibiotics, narrowing the options for treatment. Resistance to carbapenems, last resort antibiotics, is a major concern. Metallo-β-lactamases (MBLs) hydrolyze carbapenems, penicillins, and cephalosporins, becoming central to this problem. These enzymes diverge with respect to serine-β-lactamases by exhibiting a different fold, active site, and catalytic features. Elucidating their catalytic mechanism has been a big challenge in the field that has limited the development of useful inhibitors. This review covers exhaustively the details of the active-site chemistries, the diversity of MBL alleles, the catalytic mechanism against different substrates, and how this information has helped developing inhibitors. We also discuss here different aspects critical to understand the success of MBLs in conferring resistance: the molecular determinants of their dissemination, their cell physiology, from the biogenesis to the processing involved in the transit to the periplasm, and the uptake of the Zn(II) ions upon metal starvation conditions, such as those encountered during an infection. In this regard, the chemical, biochemical and microbiological aspects provide an integrative view of the current knowledge of MBLs.

Upstream region of OprD mutations in imipenem-resistant and imipenem-sensitive Pseudomonas isolates

The current study was aimed at investigating the prevalence of the mutations upstream of the oprD coding region and its promoters among imipenem-resistant and sensitive Pseudomonas aeruginosa isolated from educational hospitals in Yazd City, Iran. All isolates were identified by the conventional biochemical tests. Then, the antibiotic resistance of these isolates was determined using the disk diffusion method according to the CLSI guidelines. Also, the E.test was performed to determine the minimum inhibitory concentrations (MIC) of imipenem. The mutations of this gene were recognized by the amplification of this region and subsequently sequenced. Sequencing of the genomic region upstream of oprD these regions were done in the 29 clinical strains. Statistical analysis was done by the statistical software SPSS-18. Seventy (77.7%) of isolates had MIC ≥ 16 and were resistant to imipenem. Mutations of the upstream of the oprD gene and its promoters were seen in 25 (86.2%) isolates and 4 isolates had no mutation. One isolate had a base substitution A→Cat nt 25 in the coding region and this isolate had a point mutation leading to an amino acid change at positions 9 (I→L). Our study results indicated that none of the strains had mutation in Shine-Dalgarno and the point mutations were the most common mutations upstream of the oprD coding region among P. aeruginosa isolates. Mutations were observed in imipenem-resistant isolates and it seems this mechanism is effective in resistance of isolates to imipenem and this confirmed that the indiscriminate use of antibiotic should be controlled.

How to Enter a Bacterium: Bacterial Porins and the Permeation of Antibiotics

Despite tremendous successes in the field of antibiotic discovery seen in the previous century, infectious diseases have remained a leading cause of death. More specifically, pathogenic Gram-negative bacteria have become a global threat due to their extraordinary ability to acquire resistance against any clinically available antibiotic, thus urging for the discovery of novel antibacterial agents. One major challenge is to design new antibiotics molecules able to rapidly penetrate Gram-negative bacteria in order to achieve a lethal intracellular drug accumulation. Protein channels in the outer membrane are known to form an entry route for many antibiotics into bacterial cells. Up until today, there has been a lack of simple experimental techniques to measure the antibiotic uptake and the local concentration in subcellular compartments. Hence, rules for translocation directly into the various Gram-negative bacteria via the outer membrane or via channels have remained elusive, hindering the design of new or the improvement of existing antibiotics. In this review, we will discuss the recent progress, both experimentally as well as computationally, in understanding the structure-function relationship of outer-membrane channels of Gram-negative pathogens, mainly focusing on the transport of antibiotics.

Location of OprD porin in Pseudomonas aeruginosa clinical isolates

Multidrug-resistant Pseudomonas aeruginosa is one of the main opportunistic pathogens causing severe infection. One of the mechanisms involved in the resistance to imipenem in clinical isolates is the loss of the OprD porin. Changes like substitutions, deletions, insertions, or mutations in the oprD gene can modify the conformation of OprD porin or inhibit its presence and generate resistance to carbapenems. The aim of this work was to obtain anti-OprD polyclonal antibodies and to determine by both immunofluorescence microscopy (IFI) and Western blot assays, the presence of the OprD porin in resistant-carbapenem P. aeruginosa strains with different changes in the oprD gene. Changes in the gene oprD were identified in clinical isolates of P. aeruginosa. When proteins were translated, several polymorphisms were found; however, these did not affect the presence of OprD porin (PCM25, PCM36, and PCM78). Also it was detected an insertion sequence ISPa1328 (PCM52) and a premature stop codon (PCM91), which inhibited the presence of the OprD porin. This study shows how changes in the oprD gene of P. aeruginosa clinical isolates affect the presence of the OprD porin detected by Western blot and indirect immunofluorescence assays using specific polyclonal anti-OprD antibodies generated in this work.

Mutational Variation Analysis of oprD Porin Gene in Multidrug-Resistant Clinical Isolates of Pseudomonas aeruginosa

The present study deals with the outer membrane OprD porin protein in 29 clinical bacterial isolates of multidrug-resistant Pseudomonas aeruginosa. oprD porin gene expression was investigated using real-time reverse transcription-PCR. Amplicons from oprD and its transcriptional regulator mexT gene were sequenced and analyzed for mutations. Hypothetical models of selected mutant OprD-porin proteins were predicted and refined by homology modeling approach. oprD ampliconic sequences were also screened for restriction fragment length polymorphism (RFLP). The oprD gene was found to be downregulated in 89.7% (n = 26) of the isolates in comparison to the transcript levels in the reference strain P. aeruginosa-PAO (MTCC-3541). Interestingly, all these isolates displayed the presence of a conspicuous 8-bp deletion (GGCCAGCC) at nucleotide position 235 of mexT regulatory gene. Based on the mutational patterns observed in oprD gene, the isolates were classified into categories designated as A, B1-2, C1-4, D1-6, E1-2, and F. Our hypothetical models revealed that mutations were predominantly confined to the extracellular loops emanating from the β-barrel porin protein. These protein models also enabled clear visualization of loss of substantial portions of the truncated polypeptide. Incidentally, since most of the oprD amplicons of the clinical isolates were found to display distinct RFLP banding patterns, our results also provide a useful diagnostic tool for detection of P. aeruginosa porin mutants.

Analysis of a long term starved Pseudomonas aeruginosa ATCC27853 in seawater microcosms

The persistence of pathogenic bacteria in the marine environment has been thoroughly investigated. The potential threat that these microorganisms pose to public health in recreational waters has always been a concern. In this study, the persistence and the response of Pseudomonas aeruginosa ATCC27853 to starvation and osmotic stress were studied after its incubation in sterilized seawater during 12 months. Three different colonial variants were isolated: A7 after one month, and A81 and A82 after 8 months of incubation period. The incubation effect on the bacterial phenotype and genotype were studied by analyzing modifications in morphology, antibiotic and metal resistance, molecular typing (PFGE and MLST), pigment production and virulence factors. The starved variants showed three different colony forms, but an indistinguishable PFGE pattern and belonged to ST155, as P. aeruginosa ATCC27853. The starved variants maintained the susceptibility to the 13 tested antibiotics, with the exception of the imipenem-resistant A82 strain, which also showed a small colony variant phenotype and the highest values of tolerance to the CuSO₄ + NaCl combination. Significant differences were detected in the pigment production, the elastase activity and cytotoxic potential of the starved isolates in comparison to P. aeruginosa ATCC27853. Long-term exposure to stress, such as the incubation in seawater, was shown to induce different responses in P. aeruginosa, including virulent and resistant phenotypes.

Distribution and molecular characterization of beta-lactamases in Gram-negative bacteria in Colombia, 2001-2016

Beta-lactamases are enzymes with hydrolytic activity over beta-lactam antibiotics and they are the main resistance mechanism in Gram-negative bacteria. Extended-spectrum beta-lactamases (ESBL), AmpC, and carbapenemases have the greatest clinical and epidemiological impact in hospital settings. The increasing frequency and worldwide spread of these enzymes have limited the therapeutic options in hospital-acquired infections and those originating in the community. In Colombia, surveillance networks and research groups began studying them in the late 90s. Different variants of these enzymes have been molecularly characterized and their high prevalence and dissemination in medium and high complexity hospitals, along with a high clinical impact, have been reported. Furthermore, many studies in Colombia have evidenced high endemicity for some of these beta-lactamases, which requires an urgent implementation of antimicrobial stewardship programs in order to preserve the few therapeutic options and infection control strategies to prevent and limit their dissemination. In this publication, we carried out a review of the different enzyme variants, geographic distribution, and molecular characterization of these beta-lactamases in Colombia. Additionally, we describe the available information in the literature regarding studies conducted between the late 1990s and 2016, which provide an overview of the beta-lactamases circulating in different regions of Colombia, their increase over time, and their clinical implications.

lptG contributes to changes in membrane permeability and the emergence of multidrug hypersusceptibility in a cystic fibrosis isolate of Pseudomonas aeruginosa

PURPOSE

In the lungs of cystic fibrosis patients, Pseudomonas aeruginosa is exposed to a myriad of antibiotics leading to alterations in antibiotic susceptibility. This study identifies mutations resulting in hypersusceptibility in isogenic mutants of a P. aeruginosa clinical isolate, PA34.

METHODS

PA34 was exposed to subinhibitory concentrations of doripenem or meropenem during growth to mid-log phase. Antibiotic susceptibility of surviving colonies was determined by agar dilution. Two carbapenem-resistant colonies hypersusceptible to non-carbapenem antibiotics were selected for further analysis. Antibiotic resistance gene expression was evaluated by RT-rtPCR and OprD production by SDS-PAGE. PA34 and isogenic mutants were evaluated with whole genome sequencing. Sequence variants were confirmed by Sanger sequencing, and cognate genes in eight carbapenem-resistant clinical isolates hypersusceptible to non-carbapenem antibiotics were sequenced. Lipopolysaccharide preparations of PA34 and hypersusceptible mutants were evaluated with ProQ-Emerald stain.

RESULTS

Isogenic mutants showed 4- to 8-fold MIC increase for imipenem, meropenem, and doripenem. However, they were hypersusceptible (≥4-fold MIC decrease) to aminoglycosides, fluoroquinolones, and non-carbapenem β-lactams. Expression of ampC or mex-opr efflux pumps was unchanged, but OprD production was decreased. Mutations causing Q86H AlgU and G77C LptG amino acid substitutions and nonsense mutations within OprD were observed in both mutants. Lipopolysaccharide modifications were observed between isogenic mutants and PA34. Non-synonymous mutations in LptF or LptG were observed in 6/8 hypersusceptible clinical isolates resistant to carbapenem antibiotics.

CONCLUSION

Evaluation of hypersusceptible mutants identified the association between lptG and a hypersusceptible phenotype. Modifications in lipopolysaccharide profiles suggests LptG modification interferes with lipopolysaccharide transport and contributes to hypersusceptibility.

High prevalence of imipenem-resistant and metallo-beta-lactamase-producing Pseudomonas aeruginosa in the Burns Hospital in Tunisia: detection of a novel class 1 integron

Pseudomonas aeruginosa is one of the most important causes of nosocomial infections, and its eradication is very difficult due to its multidrug resistance. The objective of the present study was to characterize the metallo-beta-lactamases (MBLs), integrons, OprD modifications and virulence factors of P. aeruginosa strains isolated from burn patients and to analyze their genetic relatedness by pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST). Sixty-seven P. aeruginosa isolates were recovered from different clinical samples of burn patients hospitalized in the Intensive Care Burn Unit of the Centre de Traumatologie et des Grands Brulés (Ben Arous, Tunisia), and MBLs and alterations in porin OprD were analyzed among imipenem-resistant isolates. Class 1 and 2 integrons were studied by PCR and sequencing of corresponding variable regions. The presence of eight genes involved in the virulence of P. aeruginosa was investigated by PCR. Fourteen of the 36 imipenem-resistant P. aeruginosa (IRPA) isolates (38.8%) were MBLs producers and harbored the bla_VIM-2 gene, in all cases included into class 1 integrons. A new class 1 integron was identified (intI1-bla_OXA-10-aadB-bla_VIM-2-aadB-bla_OXA-10). Five sequence types were detected among IRPA isolates: ST1, ST112, ST238, ST308 and ST395. P. aeruginosa is a major nosocomial pathogen in patients suffering burns, and the spreading of multidrugs resistant and MBL-producing isolates should be controlled in burn units. Moreover, the implantation of infection control guidelines is crucial to decrease the morbidity and mortality of nosocomial infections due to multidrug resistant P. aeruginosa.

Inactivation of the oprD porin gene by a novel insertion sequence ISPa195 associated with large deletion in a carbapenem-resistant Pseudomonas aeruginosa clinical isolate

OBJECTIVES

Alteration of the porin-encoding gene oprD by insertion sequences (ISs) is one mechanism conferring carbapenem resistance in Pseudomonas aeruginosa. Here we describe a carbapenem-resistant clinical P. aeruginosa isolate 36-989 harbouring a novel IS (ISPa195) in oprD.

METHODS

Minimum inhibitory concentrations (MICs) of antimicrobial agents were determined by the broth microdilution method. Carbapenemase activity was assessed using a MALDI-TOF/MS-based assay of meropenem hydrolysis. Efflux-dependent carbapenem resistance was evaluated using an assay with carbonyl cyanide 3-chlorophenylhydrazone (CCCP). The oprD gene and IS sequence were analysed by the Sanger method. Whole-genome sequencing was performed on an Illumina HiSeq 2500 platform.

RESULTS

Antimicrobial susceptibility testing demonstrated that P. aeruginosa 36-989 was resistant to imipenem (MIC=32mg/L) and meropenem (MIC=16mg/L). No carbapenemase activity was detected, however an efflux-mediated component of carbapenem resistance was revealed. A new IS element (ISPa195) was found in the oprD gene of P. aeruginosa 36-989. ISPa195 was 1190bp in length, belonging to the IS3 family, and contained two open reading frames that overlapped through a ribosomal slippage to translate the full-size transposase enzyme. There was an IS-associated 284-bp deletion in the oprD gene; no direct repeats at flanking regions of the IS were detected.

CONCLUSION

The absence of direct repeats at flanking regions in combination with the IS-associated deletion distinguished ISPa195 from other ISs previously detected in oprD. Carbapenem resistance in P. aeruginosa 36-989 was conferred by a combination of oprD alteration and carbapenem efflux.

Mechanisms of Bacterial Resistance to Antimicrobial Agents

During the past decades resistance to virtually all antimicrobial agents has been observed in bacteria of animal origin. This chapter describes in detail the mechanisms so far encountered for the various classes of antimicrobial agents. The main mechanisms include enzymatic inactivation by either disintegration or chemical modification of antimicrobial agents, reduced intracellular accumulation by either decreased influx or increased efflux of antimicrobial agents, and modifications at the cellular target sites (i.e., mutational changes, chemical modification, protection, or even replacement of the target sites). Often several mechanisms interact to enhance bacterial resistance to antimicrobial agents. This is a completely revised version of the corresponding chapter in the book Antimicrobial Resistance in Bacteria of Animal Origin published in 2006. New sections have been added for oxazolidinones, polypeptides, mupirocin, ansamycins, fosfomycin, fusidic acid, and streptomycins, and the chapters for the remaining classes of antimicrobial agents have been completely updated to cover the advances in knowledge gained since 2006.

Antibiotic resistance in Pseudomonas aeruginosa: mechanisms and alternative therapeutic strategies

Pseudomonas aeruginosa is an opportunistic pathogen that is a leading cause of morbidity and mortality in cystic fibrosis patients and immunocompromised individuals. Eradication of P. aeruginosa has become increasingly difficult due to its remarkable capacity to resist antibiotics. Strains of Pseudomonas aeruginosa are known to utilize their high levels of intrinsic and acquired resistance mechanisms to counter most antibiotics. In addition, adaptive antibiotic resistance of P. aeruginosa is a recently characterized mechanism, which includes biofilm-mediated resistance and formation of multidrug-tolerant persister cells, and is responsible for recalcitrance and relapse of infections. The discovery and development of alternative therapeutic strategies that present novel avenues against P. aeruginosa infections are increasingly demanded and gaining more and more attention. Although mostly at the preclinical stages, many recent studies have reported several innovative therapeutic technologies that have demonstrated pronounced effectiveness in fighting against drug-resistant P. aeruginosa strains. This review highlights the mechanisms of antibiotic resistance in P. aeruginosa and discusses the current state of some novel therapeutic approaches for treatment of P. aeruginosa infections that can be further explored in clinical practice.

Prevalence and antibiotic resistance of Pseudomonas aeruginosa in water samples in central Italy and molecular characterization of oprD in imipenem resistant isolates

Scope

This study aimed to analyse the prevalence, antibiotic resistance and genetic relatedness of P. aeruginosa isolates obtained from potable and recreational water samples (n. 8,351) collected from different settings (swimming pools, n. 207; healthcare facilities, n 1,684; accommodation facilities, n. 1,518; municipal waterworks, n. 4,500; residential buildings, n. 235). Possible mechanisms underlying resistance to imipenem, with particular focus on those involving oprD-based uptake, were also explored.

Methods and results

Isolation and identification of Pseudomonas aeruginosa was performed according to the standardized procedure UNI EN ISO 16266:2008 followed by PCR confirmation. Antibiotic Susceptibility testing was conducted according to EUCAST standardized disk diffusion method. Genetic relatedness of strains was carried out by RAPD. The sequence of the oprD gene was analyzed by standard method. Fifty-three samples (0.63%) were positive for P. aeruginosa, of which 10/207 (4.83%) were from swimming pools. Five isolates (9.43%) were resistant to imipenem, one to Ticarcillin + Clavulanate, one to both Piperacillin and Ticarcillin + Clavulanate. The highest isolation rate of imipenem resistant P. aeruginosa was observed in swimming pool water. Identical RAPD profiles were found in isolates from the same location in the same year or even in different years.

Conclusions

Imipenem resistant strains were identified as carbapenemase-negative and resistance has been associated with inactivating mutations within the oprD gene, with a concomitant loss of porin. RAPD results proved that a water system can remain colonized by one strain for long periods and the contamination may be difficult to eradicate.

This study has revealed the presence of P. aeruginosa in different water samples, including resistant strains, especially in swimming pools, and confirmed the role of porins as a contributing factor in carbapenem resistance in Gram-negative bacteria.

Probing the sRNA regulatory landscape of P. aeruginosa: post-transcriptional control of determinants of pathogenicity and antibiotic susceptibility

During environmental adaptation bacteria use small regulatory RNAs (sRNAs) to repress or activate expression of a large fraction of their proteome. We extended the use of the in vivo RNA proximity ligation method toward probing global sRNA interactions with their targets in Pseudomonas aeruginosa and verified the method with a known regulon controlled by the PrrF1 sRNA. We also identified two sRNAs (Sr0161 and ErsA) that interact with the mRNA encoding the major porin OprD responsible for the uptake of carbapenem antibiotics. These two sRNAs base pair with the 5' UTR of oprD leading to increase in resistance of the bacteria to meropenem. Additional proximity ligation experiments and enrichment for Sr0161 targets identified the mRNA for the regulator of type III secretion system. Interaction between the exsA mRNA and Sr0161 leads to a block in the synthesis of a component of the T3SS apparatus and an effector. Another sRNA, Sr006, positively regulates, without Hfq, the expression of PagL, an enzyme responsible for deacylation of lipid A, reducing its pro-inflammatory property and resulting in polymyxin resistance. Therefore, an analysis of global sRNA-mRNA interactions can lead to discoveries of novel pathways controlling gene expression that are likely integrated into larger regulatory networks.

Structure, function and regulation of Pseudomonas aeruginosa porins

Pseudomonas aeruginosa is a Gram-negative bacterium belonging to the γ-proteobacteria. Like other members of the Pseudomonas genus, it is known for its metabolic versatility and its ability to colonize a wide range of ecological niches, such as rhizosphere, water environments and animal hosts, including humans where it can cause severe infections. Another particularity of P. aeruginosa is its high intrinsic resistance to antiseptics and antibiotics, which is partly due to its low outer membrane permeability. In contrast to Enterobacteria, pseudomonads do not possess general diffusion porins in their outer membrane, but rather express specific channel proteins for the uptake of different nutrients. The major outer membrane 'porin', OprF, has been extensively investigated, and displays structural, adhesion and signaling functions while its role in the diffusion of nutrients is still under discussion. Other porins include OprB and OprB2 for the diffusion of glucose, the two small outer membrane proteins OprG and OprH, and the two porins involved in phosphate/pyrophosphate uptake, OprP and OprO. The remaining nineteen porins belong to the so-called OprD (Occ) family, which is further split into two subfamilies termed OccD (8 members) and OccK (11 members). In the past years, a large amount of information concerning the structure, function and regulation of these porins has been published, justifying why an updated review is timely.

Resistance of Animal Strains of Pseudomonas aeruginosa to Carbapenems

Carbapenems are major antibiotics reserved to human medicine. This study aimed to investigate the mechanisms of carbapenem resistance of a selection of Pseudomonas aeruginosa veterinary strains from the French network Resapath. Thirty (5.7%) imipenem and/or meropenem non-susceptible P. aeruginosa of canine (n = 24), feline (n = 5), or bovine (n = 1) origin were identified in a large collection of 527 veterinary strains gathered by the Resapath. These resistant isolates belonged to 25 MultiLocus Sequence Types (MLST), of which 17 (68%) are shared with clinical (human) strains, such as high risk clones ST233 and ST395. Interestingly, none of the veterinary strains produced a carbapenemase, and only six of them (20%) harbored deletions or insertion sequence (IS) disrupting the porin OprD gene. The remaining 24 strains contained mutations or IS in various loci resulting in down-regulation of gene oprD coupled with upregulation of efflux system CzcCBA (n = 3; activation of sensor kinase CzcS ± CopS), MexEF-OprN (n = 4; alteration of oxido reductase MexS), MexXY (n = 8; activation of two-component system ParRS), or MexAB-OprM (n = 12; alteration of regulator MexR, NalC ± NalD). Two efflux pumps were co-produced simultaneously in three mutants. Finally, in 11 out of 12 strains displaying an intact porin OprD, derepression of MexAB-OprM accounted for a decreased susceptibility to meropenem relative to imipenem. Though not treated by carbapenems, animals thus represent a reservoir of multidrug resistant P. aeruginosa strains potentially able to contaminate fragile outpatients.

The impact of insertion sequences on bacterial genome plasticity and adaptability

Transposable elements (TE), small mobile genetic elements unable to exist independently of the host genome, were initially believed to be exclusively deleterious genomic parasites. However, it is now clear that they play an important role as bacterial mutagenic agents, enabling the host to adapt to new environmental challenges and to colonize new niches. This review focuses on the impact of insertion sequences (IS), arguably the smallest TE, on bacterial genome plasticity and concomitant adaptability of phenotypic traits, including resistance to antibacterial agents, virulence, pathogenicity and catabolism. The direct consequence of IS transposition is the insertion of one DNA sequence into another. This event can result in gene inactivation as well as in modulation of neighbouring gene expression. The latter is usually mediated by de-repression or by the introduction of a complete or partial promoter located within the element. Furthermore, transcription and transposition of IS are affected by host factors and in some cases by environmental signals offering the host an adaptive strategy and promoting genetic variability to withstand the environmental challenges.

Carbapenem nonsusceptibility with modified OprD in clinical isolates of Pseudomonas aeruginosa from India

This study was undertaken to investigate OprD porin-mediated carbapenem nonsusceptibility in clinical isolates of Pseudomonas aeruginosa from a tertiary referral hospital of Northeast India. A total of 267 nonduplicate, consecutive clinical isolates of P. aeruginosa were obtained. Mutation and expression levels of OprD gene were determined in carbapenem-nonsusceptible carbapenemase-nonproducing isolates. Among 19 carbapenem-nonsusceptible carbapenemase-nonproducing isolates, 11 of them demonstrated variable band pattern while performing denaturing gradient gel electrophoresis with amplified products of OprD gene. Sequencing of variable band products revealed three mutation patterns in three isolates. Relevant decrease in expression of OprD gene could also be observed in them. All the three isolates exhibited a higher minimum inhibitory concentration for imipenem (64-128 μg/mL) compared to meropenem (16-64 μg/mL). Inactivating mutation and decreased expression of OprD contribute mainly to imipenem resistance as well as to meropenem.

Multidrug Resistant Pseudomonas aeruginosa Causing Prosthetic Valve Endocarditis: A Genetic-Based Chronicle of Evolving Antibiotic Resistance

A rare case of MDR P. aeruginosa causing PVE is analyzed at the genetic level with the goal of understanding acquired resistance mechanisms. The molecular basis of evolving antibiotic resistance gives clinicians insight into the nature of persistent P. aeruginosa infections.

Background. Successful treatment of infections caused by multidrug-resistant (MDR) Pseudomonas aeruginosa is thwarted by the emergence of antibiotic resistance and biofilm formation on prosthetic devices. Our aims were to decipher the molecular basis of resistance in a unique case of prosthetic valve endocarditis (PVE) caused by MDR P. aeruginosa.

Methods. Five sequential MDR P. aeruginosa blood isolates collected during a 7-month period were recovered from a patient suffering from PVE previously exposed to β-lactam antibiotics. Minimum inhibitory concentrations (MICs) of several classes of antibiotics were used to indicate clinical resistance characteristics; relatedness of the isolates was determined using multilocus sequence typing and repetitive sequence-based polymerase chain reaction. Amplification and sequencing of regulatory and resistance genes was performed.

Results. All isolates belonged to ST 298, possessed bla_PDC-16, and were resistant to fluoroquinolones and carbapenems. In the course of therapy, we observed a >2-fold increase in cephalosporin resistance (4 µg/mL to >16 µg/mL). Sequencing of the AmpC regulator, ampR, revealed a D135N point mutation in cephalosporin-resistant isolates. Common carbapenemase genes were not identified. All isolates demonstrated a premature stop codon at amino acid 79 of the outer membrane protein OprD and mutations in the quinolone resistance-determining regions of gyrA and parC. Point mutations in nalC, an efflux pump regulator, were also observed.

Conclusions. In this analysis, we chart the molecular evolution of β-lactam resistance in a case of PVE. We show that mutations in regulatory genes controlling efflux and cephalosporinase production contributed to the MDR phenotype.

Insertion sequence ISRP10 inactivation of the oprD gene in imipenem-resistant Pseudomonas aeruginosa clinical isolates

Carbapenem resistance mechanisms were investigated in 32 imipenem-resistant Pseudomonas aeruginosa clinical isolates recovered from hospitalised children. Sequence analysis revealed that 31 of the isolates had an insertion sequence element ISRP10 disrupting the porin gene oprD, demonstrating that ISRP10 inactivation of oprD conferred imipenem resistance in the majority of the isolates. Multilocus sequence typing (MLST) was used to discriminate the isolates. In total, 11 sequence types (STs) were identified including 3 novel STs, and 68.3% (28/41) of the tested strains were characterised as clone ST253. In combination with random amplified polymorphic DNA (RAPD) analysis, the imipenem-resistant isolates displayed a relatively high degree of genetic variability and were unlikely associated with nosocomial infections.

One ring to rule them all: Current trends in combating bacterial resistance to the β-lactams

From humble beginnings of a contaminated petri dish, β-lactam antibiotics have distinguished themselves among some of the most powerful drugs in human history. The devastating effects of antibiotic resistance have nevertheless led to an "arms race" with disquieting prospects. The emergence of multidrug resistant bacteria threatens an ever-dwindling antibiotic arsenal, calling for new discovery, rediscovery, and innovation in β-lactam research. Here the current state of β-lactam antibiotics from a structural perspective was reviewed.

Characterization of a Carbapenem-Hydrolyzing Enzyme, PoxB, in Pseudomonas aeruginosa PAO1

Pseudomonas aeruginosa is an opportunistic pathogen often associated with severe and life-threatening infections that are highly impervious to treatment. This microbe readily exhibits intrinsic and acquired resistance to varied antimicrobial drugs. Resistance to penicillin-like compounds is commonplace and provided by the chromosomal AmpC β-lactamase. A second, chromosomally encoded β-lactamase, PoxB, has previously been reported in P. aeruginosa. In the present work, the contribution of this class D enzyme was investigated using a series of clean in-frame ampC, poxB, and oprD deletions, as well as complementation by expression under the control of an inducible promoter. While poxB deletions failed to alter β-lactam sensitivities, expression of poxB in ampC-deficient backgrounds decreased susceptibility to both meropenem and doripenem but had no effect on imipenem, penicillin, and cephalosporin MICs. However, when expressed in an ampCpoxB-deficient background, that additionally lacked the outer membrane porin-encoding gene oprD, PoxB significantly increased the imipenem as well as the meropenem and doripenem MICs. Like other class D carbapenem-hydrolyzing β-lactamases, PoxB was only poorly inhibited by class A enzyme inhibitors, but a novel non-β-lactam compound, avibactam, was a slightly better inhibitor of PoxB activity. In vitro susceptibility testing with a clinical concentration of avibactam, however, failed to reduce PoxB activity against the carbapenems. In addition, poxB was found to be cotranscribed with an upstream open reading frame, poxA, which itself was shown to encode a 32-kDa protein of yet unknown function.

Faecal carriage of Pseudomonas aeruginosa in healthy humans: antimicrobial susceptibility and global genetic lineages

The aim of this study was to analyse the Pseudomonas aeruginosa faecal carriage rate in 98 healthy humans and to perform the phenotypic and genotypic characterization of recovered isolates. The genetic relatedness among the isolates was analysed by pulsed-field gel electrophoresis and multilocus sequence typing that was compared with worldwide epidemic clones. Pseudomonas aeruginosa was isolated from eight healthy individuals (8.2%), and two of them remained colonized after 5 months (in one case by the same clone). All 10 isolates (one/sample) were susceptible to 14 tested antipseudomonal agents and lacked integron structures. Six pulsed-field gel electrophoresis patterns and six sequence types (ST245, ST253, ST254, ST274, ST663 and the new one, ST1059) were identified among them. Four groups of OprD alterations were detected based on mutations and deletions related to PAO1 reference strain in our carbapenem-susceptible strains. This is the first study focused on P. aeruginosa from faecal samples of healthy humans that provides additional insights into the antimicrobial resistance and genetic diversity of P. aeruginosa. Although the isolates were antimicrobial susceptible, most of the sequence types detected were genetically related to Spanish epidemic clones or globally spread sequence types, such as ST274 and ST253.

Carbapenem-resistant-only Pseudomonas aeruginosa infection in patients formerly infected by carbapenem-susceptible strains

Pseudomonas aeruginosa isolates that were initially carbapenem-susceptible and later became selective carbapenem-resistant following antimicrobial therapy were identified from individual cases during the same hospitalisation. Cross-resistance to other β-lactams was not found and their susceptibilities remained identical in consecutive isolates. Real-time quantitative reverse transcription PCR was performed to investigate the role of OprD, an outer membrane protein regulating the entry of carbapenems, in the appearance of carbapenem-resistant-only P. aeruginosa (CROPA). Fifteen paired isolates of carbapenem-susceptible P. aeruginosa (CS-PA) and CROPA were identified. All of the cases had carbapenem exposure history within 1 month before the appearance of CROPA (mean 10 days). Reduced OprD expression was found in 93% (14/15) of the isolates, suggesting that oprD inactivation was the major contributor to selective carbapenem resistance. Of the 14 cases with CROPA due to oprD mutation, 71% (10/14) were persistent infection, as genotype analysis revealed that their paired strains were isogenic; 29% (4/14) represented re-infections as they were heterogenic, suggesting that oprD-deficient CROPA existed in the hospital and that carbapenem selective pressure promoted its spread to patients. We conclude that CROPA may occur soon after the use of carbapenems to treat CS-PA infections and that oprD mutation is the major mechanism of resistance in CROPA. Restriction of empirical use of carbapenems by antibiotic stewardship is important to halt the occurrence of CROPA.

Antibiotic resistance and extended spectrum beta-lactamases: Types, epidemiology and treatment

Antibiotic resistance is a problem of deep scientific concern both in hospital and community settings. Rapid detection in clinical laboratories is essential for the judicious recognition of antimicrobial resistant organisms. Production of extended-spectrum β-lactamases (ESBLs) is a significant resistance-mechanism that impedes the antimicrobial treatment of infections caused by Enterobacteriaceae and is a serious threat to the currently available antibiotic armory. ESBLs are classified into several groups according to their amino acid sequence homology. Proper infection control practices and barriers are essential to prevent spread and outbreaks of ESBL producing bacteria. As bacteria have developed different strategies to counter the effects of antibiotics, the identification of the resistance mechanism may help in the discovery and design of new antimicrobial agents. The carbapenems are widely regarded as the drugs of choice for the treatment of severe infections caused by ESBL-producing Enterobacteriaceae, although comparative clinical trials are scarce. Hence, more expeditious diagnostic testing of ESBL-producing bacteria and the feasible modification of guidelines for community-onset bacteremia associated with different infections are prescribed.

Investigating the link between imipenem resistance and biofilm formation by Pseudomonas aeruginosa

Pseudomonas aeruginosa, a ubiquitous environmental organism, is a difficult-to-treat opportunistic pathogen due to its broad-spectrum antibiotic resistance and its ability to form biofilms. In this study, we investigate the link between resistance to a clinically important antibiotic, imipenem, and biofilm formation. First, we observed that the laboratory strain P. aeruginosa PAO1 carrying a mutation in the oprD gene, which confers resistance to imipenem, showed a modest reduction in biofilm formation. We also observed an inverse relationship between imipenem resistance and biofilm formation for imipenem-resistant strains selected in vitro, as well as for clinical isolates. We identified two clinical isolates of P. aeruginosa from the sputum of cystic fibrosis patients that formed robust biofilms, but were sensitive to imipenem (MIC ≤ 2 μg/ml). To test the hypothesis that there is a general link between imipenem resistance and biofilm formation, we performed transposon mutagenesis of these two clinical strains to identify mutants defective in biofilm formation, and then tested these mutants for imipenem resistance. Analysis of the transposon mutants revealed a role for previously described biofilm factors in these clinical isolates of P. aeruginosa, including mutations in the pilY1, pilX, pilW, algC, and pslI genes, but none of the biofilm-deficient mutants became imipenem resistant (MIC ≥ 8 μg/ml), arguing against a general link between biofilm formation and resistance to imipenem. Thus, assessing biofilm formation capabilities of environmental isolates is unlikely to serve as a good predictor of imipenem resistance. We also discuss our findings in light of the limited literature addressing planktonic antibiotic resistance factors that impact biofilm formation.

Emergence of carbapenem resistance due to the novel insertion sequence ISPa8 in Pseudomonas aeruginosa

Chronic lung infections due to the persistence of Pseudomonas aeruginosa in cystic fibrosis patients are typically associated with the emergence of antibiotic resistance. The purpose of this study was to investigate the mechanisms responsible for the emergence of carbapenem resistance when a clinical isolate of P. aeruginosa collected from a patient with cystic fibrosis was challenged with meropenem. Nine carbapenem-resistant mutants were selected with subinhibitory concentrations of meropenem from a clinical isolate of P. aeruginosa and characterized for carbapenem resistance. Increased carbapenem MICs were associated with the identification of the novel insertion sequence ISPa8 within oprD or its promoter region in all the mutants. The position of ISPa8 was different for each of the mutants evaluated. In addition, Southern blot analyses identified multiple copies of ISPa8 within the genomes of the mutants and their parent isolate. These data demonstrate that transposition of IS elements within the Pseudomonas genome can influence antibiotic susceptibility. Understanding the selective pressures associated with the emergence of antibiotic resistance is critical for the judicious use of antimicrobial chemotherapy and the successful treatment of bacterial infections.

Carbapenem-resistant Pseudomonas aeruginosa strains from a Spanish hospital: characterization of metallo-beta-lactamases, porin OprD and integrons

Molecular typing and mechanisms of carbapenem resistance such as alterations in porin OprD and presence of metallo-beta-lactamases (MBLs), as well as integrons have been studied in a collection of carbapenem-resistant Pseudomonas aeruginosa (CRPA) isolates from a Spanish hospital. One hundred and twenty-three CRPA isolates were recovered from different samples of 80 patients. Clonal relationship among CRPA was analyzed by SpeI-PFGE. Susceptibility testing to 11 antibiotics and MBL phenotype was determined by microdilution, IP/IPI E-test and double disc method. The oprD gene was studied by PCR and sequencing, and mutations were determined comparing with P. aeruginosa PAO1 sequence. Characterization of MBLs, and class 1 and 2 integrons were studied by PCR and sequencing. SDS-PAGE analysis of outer membrane proteins of selected strains was performed. Seventy-four-per-cent of patients with CRPA were hospitalised in the ICU setting and 50% had long hospitalization stays. Sixty-four different PFGE patterns were detected, and 87 CRPA strains were further analyzed. MBL phenotype was detected in 43 of 87 strains (49.4%), which contained blaVIM-2 gene inside class 1 integrons. VIM-2-producing strains belonged to lineages ST175, ST235, and ST973. A great diversity of nucleotide insertions, deletions, and mutations in oprD gene, and the presence of a new insertion sequence (ISPa45) truncating oprD were identified among CRPA strains. Class 1 integrons were detected in 75% of CRPA strains, blaVIM-2 and the new arrangement aac(3)-Ia+ISPa34+aadA1 (named as In661) being the most frequent gene-cassette arrays detected. Other gene cassettes detected in integrons were: aadB, aadA6, aadA7, aac(6')-Ib', and blaOXA-46.

Carbapenems in the USA: focus on doripenem

The threat of antibacterial resistance continues to increase globally, and therapeutic options for the treatment of some serious infectious diseases are diminishing. The carbapenems are a potent class of broad-spectrum drugs, and their stability against hydrolysis by many important beta-lactamases make them an important weapon in the treatment of beta-lactamase-producing bacterial pathogens. This review focuses on four carbapenems of clinical importance in the USA: imipenem, meropenem, ertapenem and doripenem. After a historical review of carbapenem development, these four carbapenems are evaluated based on their mechanism of action, spectrum of activity, potency, pharmacodynamics, clinical pharmacokinetics, clinical profiles and toxicity issues.

Treatment ofPseudomonas aeruginosainfection in critically ill patients

Critically ill patients are on the increase in the present clinical setting. Aging of our population and increasingly aggressive medical and therapeutic interventions, including implanted foreign bodies, organ transplantation and advances in the chemotherapy of malignant diseases, have created a cohort of particularly vulnerable patients. Pseudomonas aeruginosa is one of the leading gram-negative organisms associated with nosocomial infections. This organism is frequently feared because it causes severe hospital-acquired infections, especially in immunocompromised hosts, and is often antibiotic resistant, complicating the choice of therapy. The epidemiology, microbiology, mechanisms of resistance and currently available and future treatment options for the most relevant infections caused by P. aeruginosa are reviewed.

Mechanisms of carbapenem resistance in cephalosporin-susceptible Pseudomonas aeruginosa in China

Twenty-nine Pseudomonas aeruginosa isolates, which are resistant to carbapenems but susceptible to ceftazidime or/and cefepime, were recovered from our hospital from July 2011 to October 2011. The results of Western blotting showed that the OprD was reduced or lost. None of the 29 clinical isolates produced carbapenemases, extended-spectrum β-lactamases, or Ambler class C β-lactamases enzymes by the modified 3-dimensional test. The sequencing of oprD for these isolates showed that there are multiple point mutations, large fragment substitutions, deletions, and insertions. It showed that the expression of oprD decreased while mexA and mexX increased by real-time reverse transcriptase-PCR. These results suggested that the loss of OprD and overexpression of mexXY-OprM and mexAB-OprM are associated with carbapenem resistance in cephalosporin-susceptible Pseudomonas aeruginosa.

Molecular investigation of carbapenem resistance among multidrug-resistant Pseudomonas aeruginosa isolated clinically in Thailand

Carbapenem resistant Pseudomonas aeruginosa were isolated among multidrug-resistant (CR-MDR) organisms from tertiary hospitals in Thailand. Decreased expression of oprD mRNA (93.65%) was predominant followed by increased expression of mexAB-oprM mRNA (92.06%) and mexXY mRNA (63.49%). Interestingly, 23 of 126 (18.25%) isolates were susceptible to imipenem with down-regulated oprD expression and non-up-regulated mexCD-oprJ mRNA expression. Metallo-β-lactamases production was clearly positive in 24 isolates (18.46%) and weakly positive in 12 isolates (9.23%). Among both of these sets of isolates, imp-1, imp-14 and vim-2 were identified. Hyperproduction of AmpC β-lactamase had the lowest prevalence rate (3.97%). It was concluded that CR-MDR P. aeruginosa clinical isolates in Thailand possess multifactorial resistance mechanisms.

Investigation of antibiotic resistance in the genomic era of multidrug-resistant Gram-negative bacilli, especially Enterobacteriaceae, Pseudomonas and Acinetobacter

The increase and spread of multidrug-resistant (MDR) Gram-negative bacteria, including Enterobacteriaceae, Pseudomonas and Acinetobacter species, have become major concerns worldwide. Although the frequent misuse of antibiotic drugs has greatly contributed to worldwide antibiotic resistance by causing a large dispersal of resistance determinants, recent studies demonstrate that these resistance determinants could have emerged from ancient or environmental sources. Moreover, during the last 10 years, we have been witnessing the emergence and development of technologies for high-throughput sequencing, coinciding with an exponential increase in the number of bacterial genomes sequenced. These sequencing technologies allow a complete study of MDR bacterial genomes and are the best way to investigate the genetic determinants of antimicrobial resistance. Accordingly, studies using genome sequencing to decipher resistance determinants in Enterobacteriaceae, Pseudomonas and Acinetobacter species have demonstrated several advantages including, among others: an exhaustive identification of resistance determinants from any clinical, epidemiological or environmental MDR bacterium; identification of the acquisition mechanisms for resistance determinants exchanged between bacterial species through mobile genetic elements and elucidation and understanding, in record time (less than 1 week), of some critical or epidemic events caused by particular pathogenic bacteria. Therefore, it is clear today that the bacterial genome sequencing approach has revolutionized all fields of scientific research and represents a powerful tool to explore the world of microorganisms.