Mechanisms of multidrug resistance in Acinetobacter species and Pseudomonas aeruginosa

Biofilm-Related Genes: Analyses in Multi-Antibiotic Resistant Acinetobacter Baumannii Isolates From Mainland China

BACKGROUND Acinetobacter baumannii is an important nosocomial pathogen which shows a high level of mortality risk. Several papers have reported biofilm formation as a well-known pathogenic mechanism in A. baumannii infections and exceptional antibiotic resistance. The study aims to explore the potential relationships between biofilm-related genes and antimicrobial resistance. MATERIAL AND METHODS Samples from 122 patients with lower respiratory tract infections of A. baumannii were collected at Fujian Longyan First Hospital from January 2013 to September 2014. A. baumannii was isolated from sputum specimens. Biofilm-related genes including abaI, csuE, ompA, and bla-PER1 were analyzed by PCR. The minimum inhibitory concentration method was used to determine the sensitivity of each strain to antibiotics. RESULTS The clinical manifestations of A. baumannii-induced lower respiratory tract infections lacked specificity. Infected patients were most commonly admitted to intensive care units (54.9%) and frequently had chronic obstructive pulmonary disease (27.0%). The detection rates of abaI and csuE were both 59.8%, and those of ompA and bla-PER1 were 100% and 0%, respectively. After genetic testing, antimicrobial resistance to amikacin, ampicillin/sulbactam, and 14 other types of antimicrobials was higher in abaI- and csuE-positive strains than in abaI- and csuE-negative strains (P<0.05). CONCLUSIONS The findings of our study suggest that abaI- and csuE-positive Acinetobacter baumannii strains are associated with a higher incidence of antibiotic resistance in 14 types of antimicrobials.

Clinical and Epidemiological Significance of Carbapenem Resistance in Acinetobacter baumannii Infections

Carbapenems are considered the treatment of choice for Acinetobacter baumannii infections. Many facilities implement preventive measures toward only carbapenem-resistant A. baumannii (CRAB). However, the independent role of the carbapenem resistance determinant on patient outcomes remains controversial. In a 6-year analysis of adults with A. baumannii bloodstream infection (BSI), the outcomes of 149 CRAB isolates were compared to those of 91 patients with carbapenem-susceptible A. baumannii In bivariable analyses, CRAB BSIs were significantly associated with worse outcomes and with a delay in the initiation of appropriate antimicrobial therapy (DAAT). However, in multivariable analyses, carbapenem resistance status was no longer associated with poor outcomes, while DAAT remained an independent predictor. The epidemiological significance of A. baumannii should not be determined by its resistance to carbapenems.

The Distribution and Resistance of Pathogens Among Solid Organ Transplant Recipients with Pseudomonas aeruginosa Infections

Background

Pseudomonas aeruginosa infection remains a life-threatening complication after solid organ transplantation (SOT). We aimed to investigate the distribution and drug susceptibility of pathogens, and clinical characteristics of SOT recipients with Pseudomonas aeruginosa infections.

Material/Methods

A total of 55 SOT recipients who developed 61 episodes of Pseudomonas aeruginosa infections between January 1, 2003 and July 31, 2015 were retrospectively analyzed. The distribution and the drug susceptibility of Pseudomonas aeruginosa were reviewed.

Results

The most common site from which 61 Pseudomonas aeruginosa rods were isolated were the lungs (57.4%, n=37), followed by the blood (27.9%, n=17). There were 35, 18, and 9 recipients accompanied with a serum creatinine level of >1.5 mg/dL, lymphocyte count of <300/mm³, and a serum albumin level of <30 g/L, respectively. Seven patients each presented with white blood cell count of >15 000/mm³ and platelet count of <50 000/mm³. There were 6 (10.9%) cases of septic shocks and 18 (32.7%) deaths. Antibiotic resistance rate of all Pseudomonas aeruginosa to 4 of 10 antibiotics investigated was more than 50%. Of these 61 Pseudomonas aeruginosa isolates, 47.5% were carbapenem-resistant. The rods were relatively sensitive to piperacillin-tazobactam, levofloxacin, amikacin, and cefoperazone-sulbactam (resistance rate <40%).

Conclusions

The clinical presentation of Pseudomonas aeruginosa infections included high body temperature, decreased platelet count, elevated white blood cell count, a high nosocomial origin and mortality, and onset in the late period after transplantation. According to our findings, piperacillin-tazobactam, levofloxacin, amikacin, and cefoperazone-sulbactam, alone or combination, are recommended to treat SOT recipients with Pseudomonas aeruginosa infections.

Presence of blaPER-1 and blaVEB-1 beta-lactamase genes among isolates of Pseudomonas aeruginosa from South West of Iran

Pseudomonas aeruginosa isolates have acquired resistance to antibiotics such as novel beta-lactams. The aim of this study was to investigate the bla_PER-1, bla_VEB-1, and bla_PSE-1 genes among isolates of P. aeruginosa among intensive care unit (ICU) patients. Sixty-five isolates were collected. The antibiotic susceptibility testing and combined disk tests were performed to detect the isolates producing extended spectrum beta-lactamases (ESBLs) among ceftazidime-resistant isolates. Polymerase chain reaction (PCR) amplification of bla_PER-1, bla_VEB-1, and bla_PSE-1 genes was conducted. Ten (15.3%) isolates were ESBL-positive, of which 40% (n = 4) belonged to males and 60% (n = 6) were collected from females. Moreover, two and one isolates harbored bla_PER-1 and bla_VEB-1 genes, respectively.

Intranasal treatment with bacteriophage rescues mice from Acinetobacter baumannii-mediated pneumonia

AIM

With the emergence of drug-resistant bacteria, finding alternative agents to treat antibiotic-resistant bacterial infections is imperative.

MATERIALS & METHODS

A mouse pneumonia model was developed by combining cyclophosphamide pretreatment and Acinetobacter baumannii challenge, and a lytic bacteriophage was evaluated for its therapeutic efficacy in this model by examining the survival rate, bacterial load in the lung and lung pathology.

RESULTS

Intranasal instillation with bacteriophage rescued 100% of mice following lethal challenge with A. baumannii. Phage treatment reduced bacterial load in the lung. Microcomputed tomography indicated a reduction in lung inflammation in mice given phage.

CONCLUSION

This research demonstrates that intranasal application of bacteriophage is viable, and could provide complete protection from pneumonia caused by A. baumannii.

Structural and Enzymatic Characterization of ABgp46, a Novel Phage Endolysin with Broad Anti-Gram-Negative Bacterial Activity

The present study demonstrates the antibacterial potential of a phage endolysin against Gram-negative pathogens, particularly against multidrug resistant strains of Acinetobacter baumannii. We have cloned, heterologously expressed and characterized a novel endolysin (ABgp46) from Acinetobacter phage vb_AbaP_CEB1 and tested its antibacterial activity against several multidrug-resistant A. baumannii strains. LC-MS revealed that ABgp46 is an N-acetylmuramidase, that is also active over a broad pH range (4.0-10.0) and temperatures up to 50°C. Interestingly, ABgp46 has intrinsic and specific anti-A. baumannii activity, reducing multidrug resistant strains by up to 2 logs within 2 h. By combining ABgp46 with several organic acids that act as outer membrane permeabilizing agents, it is possible to increase and broaden antibacterial activity to include other Gram-negative bacterial pathogens. In the presence of citric and malic acid, ABgp46 reduces A. baumannii below the detection limit (>5 log) and more than 4 logs Pseudomonas aeruginosa and Salmonella typhimurium strains. Overall, this globular endolysin exhibits a broad and high activity against Gram-negative pathogens, that can be enhanced in presence of citric and malic acid, and be used in human and veterinary medicine.

Carbapenem resistance: overview of the problem and future perspectives

Carbapenem resistance, mainly among Gram-negative pathogens, is an ongoing public-health problem of global dimensions. This type of antimicrobial resistance, especially when mediated by transferable carbapenemase-encoding genes, is spreading rapidly causing serious outbreaks and dramatically limiting treatment options. In this article, important key points related to carbapenem resistance are reviewed and future perspectives are discussed.

SOS response and its regulation on the fluoroquinolone resistance

Bacteria can survive fluoroquinolone antibiotics (FQs) treatment by becoming resistant through a genetic change-mutation or gene acquisition. The SOS response is widespread among bacteria and exhibits considerable variation in its composition and regulation, which is repressed by LexA protein and derepressed by RecA protein. Here, we take a comprehensive review of the SOS gene network and its regulation on the fluoroquinolone resistance. As a unique survival mechanism, SOS may be an important factor influencing the outcome of antibiotic therapy in vivo.

Comparative Genomics of Two ST 195 Carbapenem-Resistant Acinetobacter baumannii with Different Susceptibility to Polymyxin Revealed Underlying Resistance Mechanism

Acinetobacter baumannii is a Gram-negative nosocomial pathogen of importance due to its uncanny ability to acquire resistance to most antimicrobials. These include carbapenems, which are the drugs of choice for treating A. baumannii infections, and polymyxins, the drugs of last resort. Whole genome sequencing was performed on two clinical carbapenem-resistant A. baumannii AC29 and AC30 strains which had an indistinguishable ApaI pulsotype but different susceptibilities to polymyxin. Both genomes consisted of an approximately 3.8 Mbp circular chromosome each and several plasmids. AC29 (susceptible to polymyxin) and AC30 (resistant to polymyxin) belonged to the ST195 lineage and are phylogenetically clustered under the International Clone II (IC-II) group. An AbaR4-type resistance island (RI) interrupted the comM gene in the chromosomes of both strains and contained the bla OXA-23 carbapenemase gene and determinants for tetracycline and streptomycin resistance. AC29 harbored another copy of bla OXA-23 in a large (~74 kb) conjugative plasmid, pAC29b, but this gene was absent in a similar plasmid (pAC30c) found in AC30. A 7 kb Tn1548::armA RI which encodes determinants for aminoglycoside and macrolide resistance, is chromosomally-located in AC29 but found in a 16 kb plasmid in AC30, pAC30b. Analysis of known determinants for polymyxin resistance in AC30 showed mutations in the pmrA gene encoding the response regulator of the two-component pmrAB signal transduction system as well as in the lpxD, lpxC, and lpsB genes that encode enzymes involved in the biosynthesis of lipopolysaccharide (LPS). Experimental evidence indicated that impairment of LPS along with overexpression of pmrAB may have contributed to the development of polymyxin resistance in AC30. Cloning of a novel variant of the bla AmpC gene from AC29 and AC30, and its subsequent expression in E. coli also indicated its likely function as an extended-spectrum cephalosporinase.

Research on the treatment of Pseudomonas aeruginosa pneumonia in children by macrolide antibiotics

To observe a therapeutic effect of macrolide antibiotics in children with Pseudomonas aeruginosa pneumonia. Fifty-four cases of children with Pseudomonas aeruginosa pneumonia were randomly divided into an observation group (n=30) and a control group (n=24). The observation group was treated with macrolide antibiotics and cefoperazone/sulbactam. The control group was treated with cefoperazone/sulbactam during a course of 10-14 days. The total effective rate was 93.3% in the observation group, and 58.3% in the control group, and results in the observation group were superior to the control group notably (P>0.05). There were no significant differences in bacterial clearance rate, adverse reaction rate between two groups (P>0.05). The combined application of cefoperazone/sulbactam with macrolide antibiotics to treat Pseudomonas aeruginosa pneumonia in children would be a more effective clinical method.

Genetic Mechanisms of Antimicrobial Resistance of Acinetobacter baumannii

OBJECTIVE

To summarize published data identifying known genetic mechanisms of antibiotic resistance in Acinetobacter baumannii and the correlating phenotypic expression of antibiotic resistance.

DATA SOURCES

MEDLINE databases (1966-July 15, 2010) were searched to identify original reports of genetic mechanisms of antibiotic resistance in A. baumannii.

DATA SYNTHESIS

Numerous genetic mechanisms of resistance to multiple classes of antibiotics are known to exist in A. baumannii, a gram-negative bacterium increasingly implicated in nosocomial infections. Mechanisms may be constitutive or acquired via plasmids, integrons, and transposons. Methods of resistance include enzymatic modification of antibiotic molecules, modification of antibiotic target sites, expression of efflux pumps, and downregulation of cell membrane porin channel expression. Resistance to β-lactams appears to be primarily caused by β-lactamase production, including extended spectrum β-lactamases (b/aTEM, blaSHV, b/aTX-M,b/aKPC), metallo-β-lactamases (blaMP, blaVIM, bla, SIM), and most commonly, oxacillinases (blaOXA). Antibiotic target site alterations confer resistance to fluoroquinolones (gyrA, parC) and aminoglycosides (arm, rmt), and to a much lesser extent, β-lactams. Efflux pumps (tet, ade, abe) contribute to resistance against β-lactams, tetracyclines, fluoroquinolones, and aminoglycosides. Finally, porin channel deletion (carO, oprD) appears to contribute to β-lactam resistance and may contribute to rarely seen polymyxin resistance. Of note, efflux pumps and porin deletions as solitary mechanisms may not render clinical resistance to A. baumannii.

CONCLUSIONS

A. baumannii possesses copious genetic resistance mechanisms. Knowledge of local genotypes and expressed phenotypes for A. baumannii may aid clinicians more than phenotypic susceptibilities reported in large epidemiologic studies.

Pharmacodynamic Profiling of a Siderophore-Conjugated Monocarbam in Pseudomonas aeruginosa: Assessing the Risk for Resistance and Attenuated Efficacy

The objective of this study was to investigate the risk of attenuated efficacy due to adaptive resistance for the siderophore-conjugated monocarbam SMC-3176 in Pseudomonas aeruginosa by using a pharmacokinetic/pharmacodynamic (PK/PD) approach. MICs were determined in cation-adjusted Mueller-Hinton broth (MHB) and in Chelex-treated, dialyzed MHB (CDMHB). Spontaneous resistance was assessed at 2× to 16× the MIC and the resulting mutants sequenced. Efficacy was evaluated in a neutropenic mouse thigh model at 3.13 to 400 mg/kg of body weight every 3 h for 24 h and analyzed for association with free time above the MIC (fT>MIC). To closer emulate the conditions of the in vivo model, we developed a novel assay testing activity mouse whole blood (WB). All mutations were found in genes related to iron uptake: piuA, piuC, pirR, fecI, and pvdS. Against four P. aeruginosa isolates, SMC-3176 displayed predictable efficacy corresponding to the fT>MIC using the MIC in CDMHB (R(2) = 0.968 to 0.985), with stasis to 2-log kill achieved at 59.4 to 81.1%. Efficacy did not translate for P. aeruginosa isolate JJ 4-36, as the in vivo responses were inconsistent with fT>MIC exposures and implied a threshold concentration that was greater than the MIC. The results of the mouse WB assay indicated that efficacy was not predictable using the MIC for JJ 4-36 and four additional isolates, against which in vivo failures of another siderophore-conjugated β-lactam were previously reported. SMC-3176 carries a risk of attenuated efficacy in P. aeruginosa due to rapid adaptive resistance preventing entry via the siderophore-mediated iron uptake systems. Substantial in vivo testing is warranted for compounds using the siderophore approach to thoroughly screen for this in vitro-in vivo disconnect in P. aeruginosa.

First Detection of OXA-10 Extended-Spectrum Beta-Lactamases and the Occurrence of mexR and nfxB in Clinical Isolates of Pseudomonas aeruginosa from Nigeria

BACKGROUND

The characterization of β-lactamase production in Pseudomonasaeruginosa is rarely reported in Nigeria. The objective of this study was to investigate the occurrence and characterize the different β-lactamases as well as mechanisms of fluoroquinolones resistance among P. aeruginosa isolated from various clinical sources from Nigeria.

MATERIALS AND METHOD

Isolates were investigated using PCR, RFLP and sequencing for the detection of various β-lactamases and efflux pump regulator genes.

RESULT

The prevalence of OXA-10, AmpC, CTX-M and SHV in P. aeruginosa was 80, 70, 5 and 5%, respectively. The coexistence of blaOXA-10 with blaAmpC, blaSHV and blaCTX-M was reported in 40, 5 and 5% of isolates, respectively. The efflux pump regulator genes mexR and nfxB were both amplified in 45% of the OXA-10-positive isolates.

CONCLUSION

This is the first report of the characterization of OXA-10 extended-spectrum β-lactamases and occurrence of mexR and nfxB efflux regulator genes in clinical isolates of P. aeruginosa in Nigeria.

Acinetobacter baumannii Genes Required for Bacterial Survival during Bloodstream Infection

A. baumannii is a significant cause of bacterial bloodstream infection in humans. Since multiple antibiotic resistance is becoming more common among strains of A. baumannii, there is an urgent need to develop novel tools to treat infections caused by this dangerous pathogen. To develop knowledge-guided treatment approaches for A. baumannii, a thorough understanding of the mechanism by which this pathogen causes bloodstream infection is required. Here, using a mouse model of infection, we report the identification of A. baumannii genes that are critical for the ability of this pathogen to cause bloodstream infections. This study lays the foundation for future research on A. baumannii genes that can be targeted to develop novel therapeutics against this emerging human pathogen.

Acinetobacter baumannii is emerging as a leading global multiple-antibiotic-resistant nosocomial pathogen. The identity of genes essential for pathogenesis in a mammalian host remains largely unknown. Using transposon-directed insertion-site sequencing (TraDIS), we identified A. baumannii genes involved in bacterial survival in a leukopenic mouse model of bloodstream infection. Mice were inoculated with a pooled transposon mutant library derived from 109,000 mutants, and TraDIS was used to map transposon insertion sites in the genomes of bacteria in the inoculum and of bacteria recovered from mouse spleens. Unique transposon insertion sites were mapped and used to calculate a fitness factor for every insertion site based on its relative abundance in the inoculum and postinfection libraries. Eighty-nine transposon insertion mutants that were underrepresented after experimental infection in mice compared to their presence in the inocula were delineated as candidates for further evaluation. Genetically defined mutants lacking feoB (ferrous iron import), ddc (d-ala-d-ala-carboxypeptidase), and pntB (pyridine nucleotide transhydrogenase subunit) exhibited a fitness defect during systemic infection resulting from bacteremia. In vitro, these mutants, as well as a fepA (ferric enterobactin receptor) mutant, are defective in survival in human serum and within macrophages and are hypersensitive to killing by antimicrobial peptides compared to the survival of the parental strain under these conditions. Our data demonstrate that FepA is involved in the uptake of exogenous enterobactin in A. baumannii. Genetic complementation rescues the phenotypes of mutants in assays that emulate conditions encountered during infection. In summary, we have determined novel A. baumannii fitness genes involved in the pathogenesis of mammalian infection.

IMPORTANCEA. baumannii is a significant cause of bacterial bloodstream infection in humans. Since multiple antibiotic resistance is becoming more common among strains of A. baumannii, there is an urgent need to develop novel tools to treat infections caused by this dangerous pathogen. To develop knowledge-guided treatment approaches for A. baumannii, a thorough understanding of the mechanism by which this pathogen causes bloodstream infection is required. Here, using a mouse model of infection, we report the identification of A. baumannii genes that are critical for the ability of this pathogen to cause bloodstream infections. This study lays the foundation for future research on A. baumannii genes that can be targeted to develop novel therapeutics against this emerging human pathogen.

Comparative Phosphoproteomics Reveals the Role of AmpC β-lactamase Phosphorylation in the Clinical Imipenem-resistant Strain Acinetobacter baumannii SK17

Nosocomial infectious outbreaks caused by multidrug-resistant Acinetobacter baumannii have emerged as a serious threat to human health. Phosphoproteomics of pathogenic bacteria has been used to identify the mechanisms of bacterial virulence and antimicrobial resistance. In this study, we used a shotgun strategy combined with high-accuracy mass spectrometry to analyze the phosphoproteomics of the imipenem-susceptible strain SK17-S and -resistant strain SK17-R. We identified 410 phosphosites on 248 unique phosphoproteins in SK17-S and 285 phosphosites on 211 unique phosphoproteins in SK17-R. The distributions of the Ser/Thr/Tyr/Asp/His phosphosites in SK17-S and SK17-R were 47.0%/27.6%/12.4%/8.0%/4.9% versus 41.4%/29.5%/17.5%/6.7%/4.9%, respectively. The Ser-90 phosphosite, located on the catalytic motif S(88)VS(90)K of the AmpC β-lactamase, was first identified in SK17-S. Based on site-directed mutagenesis, the nonphosphorylatable mutant S90A was found to be more resistant to imipenem, whereas the phosphorylation-simulated mutant S90D was sensitive to imipenem. Additionally, the S90A mutant protein exhibited higher β-lactamase activity and conferred greater bacterial protection against imipenem in SK17-S compared with the wild-type. In sum, our results revealed that in A. baumannii, Ser-90 phosphorylation of AmpC negatively regulates both β-lactamase activity and the ability to counteract the antibiotic effects of imipenem. These findings highlight the impact of phosphorylation-mediated regulation in antibiotic-resistant bacteria on future drug design and new therapies.

How Porin Heterogeneity and Trade-Offs Affect the Antibiotic Susceptibility of Gram-Negative Bacteria

Variations in porin proteins are common in Gram-negative pathogens. Altered or absent porins reduce access of polar antibiotics across the outer membrane and can thus contribute to antibiotic resistance. Reduced permeability has a cost however, in lowering access to nutrients. This trade-off between permeability and nutritional competence is the source of considerable natural variation in porin gate-keeping. Mutational changes in this trade-off are frequently selected, so susceptibility to detergents and antibiotics is polymorphic in environmental isolates as well as pathogens. Understanding the mechanism, costs and heterogeneity of antibiotic exclusion by porins will be crucial in combating Gram negative infections.

Impact of a Cross-Kingdom Signaling Molecule of Candida albicans on Acinetobacter baumannii Physiology

Multidrug-resistant (MDR) Acinetobacter baumannii is an opportunistic human pathogen that has become highly problematic in the clinical environment. Novel therapies are desperately required. To assist in identifying new therapeutic targets, the antagonistic interactions between A. baumannii and the most common human fungal pathogen, Candida albicans, were studied. We have observed that the C. albicans quorum-sensing molecule, farnesol, has cross-kingdom interactions, affecting the viability of A. baumannii. To gain an understanding of its mechanism, the transcriptional profile of A. baumannii exposed to farnesol was examined. Farnesol caused dysregulation of a large number of genes involved in cell membrane biogenesis, multidrug efflux pumps (AcrAB-like and AdeIJK-like), and A. baumannii virulence traits such as biofilm formation (csuA, csuB, and ompA) and motility (pilZ and pilH). We also observed a strong induction in genes involved in cell division (minD, minE, ftsK, ftsB, and ftsL). These transcriptional data were supported by functional assays showing that farnesol disrupts A. baumannii cell membrane integrity, alters cell morphology, and impairs virulence characteristics such as biofilm formation and twitching motility. Moreover, we showed that A. baumannii uses efflux pumps as a defense mechanism against this eukaryotic signaling molecule. Owing to its effects on membrane integrity, farnesol was tested to see if it potentiated the activity of the membrane-acting polymyxin antibiotic colistin. When coadministered, farnesol increased sensitivity to colistin for otherwise resistant strains. These data provide mechanistic understanding of the antagonistic interactions between diverse pathogens and may provide important insights into novel therapeutic strategies.

Microbicides Alter the Expression and Function of RND-Type Efflux Pump AdeABC in Biofilm-Associated Cells of Acinetobacter baumannii Clinical Isolates

Acinetobacter baumannii is a Gram-negative bacterium that causes nosocomial infections worldwide. This microbe's propensity to form biofilms allows it to persist and to survive on clinical abiotic surfaces for long periods. In fact, A. baumannii biofilm formation and its multidrug-resistant nature severely compromise our capacity to care for patients in hospital environments. In contrast, microbicides such as cetrimide (CT) and chlorhexidine (CHX) play important roles in the prevention and treatment of infections. We assessed the efficacy of CT and CHX, either alone or in combination, in eradicating A. baumannii biofilms formed by clinical isolates, by using stainless steel washers to mimic hard abiotic surfaces found in hospital settings. We demonstrated that increasing amounts of each microbicide, alone or in combination, were able to damage and to reduce the viability of A. baumannii biofilms efficaciously. Interestingly, the adeB gene of the resistance-nodulation-cell division (RND) family is predominantly associated with acquired resistance to antimicrobials in A. baumannii. We showed that CT and CHX adversely modified the expression and function of the RND-type efflux pump AdeABC in biofilm-associated A. baumannii cells. Furthermore, we established that these microbicides decreased the negative charges on A. baumannii cell membranes, causing dysregulation of the efflux pump and leading to cell death. Our findings suggest that CT and CHX, alone or in combination, can be used efficaciously for eradication of A. baumannii from hospital surfaces, in order to reduce infections caused by this nosocomial agent.

Escherichia coli Overexpressing a Baeyer-Villiger Monooxygenase from Acinetobacter radioresistens Becomes Resistant to Imipenem

Antimicrobial resistance is a global issue currently resulting in the deaths of hundreds of thousands of people a year worldwide. Data present in the literature illustrate the emergence of many bacterial species that display resistance to known antibiotics; Acinetobacter spp. are a good example of this. We report here that Acinetobacter radioresistens has a Baeyer-Villiger monooxygenase (Ar-BVMO) with 100% amino acid sequence identity to the ethionamide monooxygenase of multidrug-resistant (MDR) Acinetobacter baumannii. Both enzymes are only distantly phylogenetically related to other canonical bacterial BVMO proteins. Ar-BVMO not only is capable of oxidizing two anticancer drugs metabolized by human FMO3, danusertib and tozasertib, but also can oxidize other synthetic drugs, such as imipenem. The latter is a member of the carbapenems, a clinically important antibiotic family used in the treatment of MDR bacterial infections. Susceptibility tests performed by the Kirby-Bauer disk diffusion method demonstrate that imipenem-sensitive Escherichia coli BL21 cells overexpressing Ar-BVMO become resistant to this antibiotic. An agar disk diffusion assay proved that when imipenem reacts with Ar-BVMO, it loses its antibiotic property. Moreover, an NADPH consumption assay with the purified Ar-BVMO demonstrates that this antibiotic is indeed a substrate, and its product is identified by liquid chromatography-mass spectrometry to be a Baeyer-Villiger (BV) oxidation product of the carbonyl moiety of the β-lactam ring. This is the first report of an antibiotic-inactivating BVMO enzyme that, while mediating its usual BV oxidation, also operates by an unprecedented mechanism of carbapenem resistance.

Multiple Genetic Mutations Associated with Polymyxin Resistance in Acinetobacter baumannii

We studied polymyxin B resistance in 10 pairs of clinical Acinetobacter baumannii isolates, two of which had developed polymyxin B resistance in vivo. All polymyxin B-resistant isolates had lower growth rates than and substitution mutations in the lpx or pmrB gene compared to their parent isolates. There were significant differences in terms of antibiotic susceptibility and genetic determinants of resistance in A. baumannii isolates that had developed polymyxin B resistance in vivo compared to isolates that had developed polymyxin B resistance in vitro.

Structures of Pseudomonas aeruginosa LpxA Reveal the Basis for Its Substrate Selectivity

In Gram-negative bacteria, the first step of lipid A biosynthesis is catalyzed by UDP-N-acetylglucosamine acyltransferase (LpxA) through the transfer of a R-3-hydroxyacyl chain from the acyl carrier protein (ACP) to the 3-hydroxyl group of UDP-GlcNAc. Previous studies suggest that LpxA is a critical determinant of the acyl chain length found in lipid A, which varies among species of bacteria. In Escherichia coli and Leptospira interrogans, LpxA prefers to incorporate longer R-3-hydroxyacyl chains (C14 and C12, respectively), whereas in Pseudomonas aeruginosa, the enzyme is selective for R-3-hydroxydecanoyl, a 10-hydrocarbon long acyl chain. We now report three P. aeruginosa LpxA crystal structures: apo protein, substrate complex with UDP-GlcNAc, and product complex with UDP-3-O-(R-3-hydroxydecanoyl)-GlcNAc. A comparison between the apo form and complexes identifies key residues that position UDP-GlcNAc appropriately for catalysis and supports the role of catalytic His121 in activating the UDP-GlcNAc 3-hydroxyl group for nucleophilic attack during the reaction. The product-complex structure, for the first time, offers structural insights into how Met169 serves to constrain the length of the acyl chain and thus functions as the so-called hydrocarbon ruler. Furthermore, compared with ortholog LpxA structures, the purported oxyanion hole, formed by the backbone amide group of Gly139, displays a different conformation in P. aeruginosa LpxA, which suggests flexibility of this structural feature important for catalysis and the potential need for substrate-induced conformational change in catalysis. Taken together, the three structures provide valuable insights into P. aeruginosa LpxA catalysis and substrate specificity as well as templates for future inhibitor discovery.

Molecular characterization of selected multidrug resistant Pseudomonas from water distribution systems in southwestern Nigeria

Background

Persistence of antibiotic resistant bacteria, including multidrug resistant (MDR) pseudomonads, is an important environmental health problem associated with drinking water distribution systems (DWDS) worldwide. There is paucity of data on the molecular characteristics of antibiotic resistance genes and their mode of transfer among pseudomonads from DWDS located in resource-challenged areas such as southwestern Nigeria.

Methods

MDR pseudomonads (n = 22) were selected from a panel of 296 different strains that were isolated from treated and untreated water in six DWDS located across southwest Nigeria. Primarily, the isolated pseudomonads strains were identified by 16S rDNA sequencing and antibiotic-resistance testing was completed using agar breakpoints assays. The final panel of strains of resistant to more than three classes of antibiotics (i.e. MDR), were further characterized by PCR genotyping, Sanger sequencing, and plasmid profiling.

Results

Pseudomonad resistance to gentamicin and streptomycin ranged from 22.7 to 54.6 % while resistance to tetracycline, ceftiofur and sulphamethoxazole ranged from 40.9 to 77.3 %. The most commonly detected antibiotic resistance genes were tet(A) (31.8 % of isolates), sul1 (31.8 %), bla_TEM (40.9 %) and aph(3″)^c (36.4 %). Class 1 integron sequences were evident in 27.3 % of isolates and they harbored genes encoding resistance to aminoglycosides (aadA2, aadA1), trimethoprim (dfrA15, dfr7) and sulphonamide (sul1) while the plasmid ranged between 22 and 130 kb.

Conclusions

Pseudomonas spp, isolated from these DWDS possess resistance genes and factors that are of public and environmental health significance. Therefore, has the potential of contributing to the global scourge of resistance genes transfer in human, animals and environments, thereby, useful in the epidemiology of antimicrobial resistance.

Bloodstream infections in intensive care unit patients: distribution and antibiotic resistance of bacteria

Bloodstream infections (BSIs) are among the leading infections in critically ill patients. The case-fatality rate associated with BSIs in patients admitted to intensive care units (ICUs) reaches 35%–50%. The emergence and diffusion of bacteria with resistance to antibiotics is a global health problem. Multidrug-resistant bacteria were detected in 50.7% of patients with BSIs in a recently published international observational study, with methicillin resistance detected in 48% of Staphylococcus aureus strains, carbapenem resistance detected in 69% of Acinetobacter spp., in 38% of Klebsiella pneumoniae, and in 37% of Pseudomonas spp. Prior hospitalization and antibiotic exposure have been identified as risk factors for infections caused by resistant bacteria in different studies. Patients with BSIs caused by resistant strains showed an increased risk of mortality, which may be explained by a higher incidence of inappropriate empirical therapy in different studies. The molecular genetic characterization of resistant bacteria allows the understanding of the most common mechanisms underlying their resistance and the adoption of surveillance measures. Knowledge of epidemiology, risk factors, mechanisms of resistance, and outcomes of BSIs caused by resistant bacteria may have a major influence on global management of ICU patients. The aim of this review is to provide the clinician an update on BSIs caused by resistant bacteria in ICU patients.

Resistance in antimicrobial photodynamic inactivation of bacteria

Antibiotics have increasingly lost their impact to kill bacteria efficiently during the last 10 years. The emergence and dissemination of superbugs with resistance to multiple antibiotic classes have occurred among Gram-positive and Gram-negative strains including Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa and Enterobacter strains. These six superbugs can "escape" more or less any single kind of antibiotic treatment. That means bacteria are very good at developing resistance against antibiotics in a short time. One new approach is called photodynamic antimicrobial chemotherapy (PACT) which already has demonstrated an efficient antimicrobial efficacy among multi-resistant bacteria. Until now it has been questionable if bacteria can develop resistance against PACT. This perspective summarises the current knowledge about the susceptibility of bacteria towards oxidative stress and sheds some light on possible strategies of the development of photodynamic inactivation of bacteria (PACT)-induced oxidative stress resistance by bacteria.

Antibiotic susceptibility of Acinetobacter species in intensive care unit in Montenegro

The global increase in multidrug resistance of Acinetobacter has created widespread problems in the treatment of patients in intensive care units (ICUs). The aim of this study was to assess the current level of antimicrobial susceptibility of Acinetobacter species in ICU of Clinical Centre of Montenegro and determine their epidemiology. Antibiotic susceptibility was tested in 70 isolates of Acinetobacter collected from non-repeating samples taken from 40 patients. The first nine isolates were genotyped by repetitive sequence-based PCR (rep-PCR). Tigecycline was found to be the most active antimicrobial agent with 80.6% of susceptibility. All the isolates were multidrug resistant with fully resistance to cefalosporinas, piperacillin and piperacillin/tazobactam. More than half of them (58.5%) were probably extensively resistant. Seven out of nine examined strains were clonally related by rep-PCR. Our results showed extremely high rate of multidrug resistance (MDR) of Acinetobacter isolates and high percentage of its clonally spreading.

Emerging broad-spectrum resistance in Pseudomonas aeruginosa and Acinetobacter baumannii: Mechanisms and epidemiology

Multidrug resistance is quite common among non-fermenting Gram-negative rods, in particular among clinically relevant species including Pseudomonas aeruginosa and Acinetobacter baumannii. These bacterial species, which are mainly nosocomial pathogens, possess a diversity of resistance mechanisms that may lead to multidrug or even pandrug resistance. Extended-spectrum β-lactamases (ESBLs) conferring resistance to broad-spectrum cephalosporins, carbapenemases conferring resistance to carbapenems, and 16S rRNA methylases conferring resistance to all clinically relevant aminoglycosides are the most important causes of concern. Concomitant resistance to fluoroquinolones, polymyxins (colistin) and tigecycline may lead to pandrug resistance. The most important mechanisms of resistance in P. aeruginosa and A. baumannii and their most recent dissemination worldwide are detailed here.

Dual-tubed multiplex-PCR for molecular characterization of carbapenemases isolated among Acinetobacter spp. and Pseudomonas spp

AIM

To molecularly characterize clinical isolates of Acinetobacter spp. and Pseudomonas spp. from various clinical samples so as to identify the carbapenemases mechanisms harboured by them.

MATERIALS AND RESULTS

A total of 95 carbapenem-resistant, nonduplicate, multi-drug resistant Gram-negative clinical isolates (53 Acinetobacter spp. and 42 Pseudomonas spp.), were collected between July and December 2012. Modified Hodge test (MHT) for the detection of carbapenemases was performed. Inhibitor-based test, EDTA for the detection of metallo-β-lactamases (MBL) and phenyl boronic acid (PBA) for the detection of Klebsiella pneumoniae carbapenemase (KPC), were performed to distinguish between different classes of β-lactamases. Two-tubed multiplex-PCR was performed for genotypic characterization of different classes of carbapenemases ((blaNDM-1 , blaOXA-48 like , blaKPC , blaVIM , blaIMP ), (blaOXA-23 like , blaOXA-24 like , blaOXA-51 like , blaOXA-58 like )). Eighty-five per cent (81/95) isolates were carbapenemase producers. Among these, 56.7% (44) were multiple carbapenemase producers. Furthermore, 48.14% (39) were MBLs, 35.8% (29) were carbapenem hydrolyzing class D β-lactamases (CHDLs), 16% (13) had MBLs as well as CHDLs and 14.7% (14/95) had none of the targeted resistance mechanisms. The overall rate of concordance between phenotypic and genotypic test was 97% and 98% for the detection of carbapenemases and MBL, respectively.

CONCLUSION

This is the first study from Western India which highlights the presence of multiple carbapenemases in nonfermenters Gram-negative bacilli (NFGNB). Co-existence of multiple carbapenemases along with other resistance mechanisms might result in treatment failure. Molecular characterization of the resistance mechanisms of suspected pathogens would help provide appropriate antimicrobial treatment for good clinical outcome.

SIGNIFICANCE AND IMPACT OF THE STUDY

Dual-tubed multiplex PCR decreases the time of amplification and thus the turnaround time which is crucial in clinical microbiology; this would be helpful in rapid characterization of CHDLs and MBLs.

Natural History of Colonization with Gram-Negative Multidrug-Resistant Organisms among Hospitalized Patients

Objective.

To determine the anatomic sites and natural history of colonization with gram-negative multidrug-resistant organisms (MDROs).

Design.

Prospective, longitudinal cohort study.

Setting.

Walter Reed Army Medical Center, a 236-bed tertiary care center in Washington, DC.

Patients.

Deployed subjects (ie, inpatients medically evacuated from Iraq or Afghanistan) or nondeployed subjects admitted to the same hospital.

Methods.

Consenting patients had 6 anatomic sites cultured every 3 days for 2 weeks and then weekly. Gram-negative organisms resistant to 3 or more classes of antibiotics were considered MDROs. Isolates were genotyped using pulsed-field gel electrophoresis. Clinical data, data on antibiotic use, and clinical culture results were collected.

Results.

Of 60 deployed subjects, 14 (23%) were colonized with an MDRO at admission, and 13 (22%) had incident colonization during hospitalization. The groin was the most sensitive anatomic site for detecting MDRO colonization, and all but one subject remained colonized for the duration of their hospitalization. Sixty percent of subjects with incident Acinetobacter colonization and 25% of subjects with incident Klebsiella colonization had strains that were related to those isolated from other subjects. Of 60 nondeployed subjects, 5 (8%) were colonized with an MDRO at admission; all had recent healthcare contact, and 1 nondeployed subject had an isolate related to a strain recovered from a deployed subject.

Conclusions.

Colonization with gram-negative MDROs is common among patients with war-related trauma admitted to a military hospital and also occurs among nondeployed patients with recent healthcare contact. The groin is the most sensitive anatomic site for active surveillance, and spontaneous decolonization is rare.

Microbial composition and antibiotic resistance of biofilms recovered from endotracheal tubes of mechanically ventilated patients

In critically ill patients, breathing is impaired and mechanical ventilation, using an endotracheal tube (ET) connected to a ventilator, is necessary. Although mechanical ventilation is a life-saving procedure, it is not without risk. Because of several reasons, a biofilm often forms at the distal end of the ET and this biofilm is a persistent source of bacteria which can infect the lungs, causing ventilator-associated pneumonia (VAP). There is a link between the microbial flora of ET biofilms and the microorganisms involved in the onset of VAP. Culture dependent and independent techniques were already used to identify the microbial flora of ET biofilms and also, the antibiotic resistance of microorganisms obtained from ET biofilms was determined. The ESKAPE pathogens play a dominant role in the onset of VAP and these organisms were frequently identified in ET biofilms. Also, antibiotic resistant microorganisms were frequently present in ET biofilms. Members of the normal oral flora were also identified in ET biofilms but it is thought that these organisms initiate ET biofilm formation and are not directly involved in the development of VAP.

The genetic basis of the fitness costs of antimicrobial resistance: a meta-analysis approach

The evolution of antibiotic resistance carries a fitness cost, expressed in terms of reduced competitive ability in the absence of antibiotics. This cost plays a key role in the dynamics of resistance by generating selection against resistance when bacteria encounter an antibiotic-free environment. Previous work has shown that the cost of resistance is highly variable, but the underlying causes remain poorly understood. Here, we use a meta-analysis of the published resistance literature to determine how the genetic basis of resistance influences its cost. We find that on average chromosomal resistance mutations carry a larger cost than acquiring resistance via a plasmid. This may explain why resistance often evolves by plasmid acquisition. Second, we find that the cost of plasmid acquisition increases with the breadth of its resistance range. This suggests a potentially important limit on the evolution of extensive multidrug resistance via plasmids. We also find that epistasis can significantly alter the cost of mutational resistance. Overall, our study shows that the cost of antimicrobial resistance can be partially explained by its genetic basis. It also highlights both the danger associated with plasmidborne resistance and the need to understand why resistance plasmids carry a relatively low cost.

Frequency of PER, VEB, SHV, TEM and CTX-M Genes in Resistant Strains of Pseudomonas aeruginosa Producing Extended Spectrum β-Lactamases

Background:

Pseudomonas aeruginosa is the most common pathogen causing nosocomial infections. Resistance of P. aeruginosa strains to broad-spectrum cephalosporins may be mediated by extended-spectrum β-lactamases (ESBLs).

Objectives:

We intended to investigate the prevalence of ESBLs and antimicrobial susceptibilities of P. aeruginosa isolated from patients in Zahedan, Iran.

Materials and Methods:

In this cross-sectional study, during 2012–2013, 116 P. aeruginosa isolates were collected from a teaching hospital in Zahedan, Iran. Susceptibility to eight antimicrobial agents was carried out by disk diffusion method. The ESBL producing strains were detected by combination disk test (CDT). ESBL positive isolates as well as other isolates showing minimum inhibitory concentrations (MICs) ≥ 4 μg/mL for ceftazidime, cefotaxime, ceftriaxone and aztreonam, were screened for the presence of the genes encoding blaTEM, blaSHV, blaPER-1 and blaVEB-1, by polymerase chain reaction (PCR).

Results:

Ciprofloxacin and piperacillin were the most efficient antipseudomonal agents. The results disclosed that 19 (16.37%) of the isolates were multidrug resistant and 8 (6.89%) were ESBL-positive. Of the 116 isolates, 30 (25.86%) were resistant to at least one of the antibiotics ceftazidime, ceftriaxone, cefotaxime or aztreonam and among these 30 (100%), 4 (13.3%), 2 (6.6%) and 2 (6.6%), amplified blaTEM, blaVEB-1, blaPER-1 and blaSHV, respectively. From the 30 TEM-positive isolates, 22 were ESBL-negative. Sequencing of the ESBL genes verified the accuracy of the PCR products.

Conclusions:

According to our results, blaTEM-116 was the most frequent isolated ESBL gene among the P. aeruginosa strains isolated from patients.

Biochemical and structural analysis of inhibitors targeting the ADC-7 cephalosporinase of Acinetobacter baumannii

β-Lactam resistance in Acinetobacter baumannii presents one of the greatest challenges to contemporary antimicrobial chemotherapy. Much of this resistance to cephalosporins derives from the expression of the class C β-lactamase enzymes, known as Acinetobacter-derived cephalosporinases (ADCs). Currently, β-lactamase inhibitors are structurally similar to β-lactam substrates and are not effective inactivators of this class C cephalosporinase. Herein, two boronic acid transition state inhibitors (BATSIs S02030 and SM23) that are chemically distinct from β-lactams were designed and tested for inhibition of ADC enzymes. BATSIs SM23 and S02030 bind with high affinity to ADC-7, a chromosomal cephalosporinase from Acinetobacter baumannii (K_i = 21.1 ± 1.9 nM and 44.5 ± 2.2 nM, respectively). The X-ray crystal structures of ADC-7 were determined in both the apo form (1.73 Å resolution) and in complex with S02030 (2.0 Å resolution). In the complex, S02030 makes several canonical interactions: the O1 oxygen of S02030 is bound in the oxyanion hole, and the R1 amide group makes key interactions with conserved residues Asn152 and Gln120. In addition, the carboxylate group of the inhibitor is meant to mimic the C₃/C₄ carboxylate found in β-lactams. The C₃/C₄ carboxylate recognition site in class C enzymes is comprised of Asn346 and Arg349 (AmpC numbering), and these residues are conserved in ADC-7. Interestingly, in the ADC-7/S02030 complex, the inhibitor carboxylate group is observed to interact with Arg340, a residue that distinguishes ADC-7 from the related class C enzyme AmpC. A thermodynamic analysis suggests that ΔH driven compounds may be optimized to generate new lead agents. The ADC-7/BATSI complex provides insight into recognition of non-β-lactam inhibitors by ADC enzymes and offers a starting point for the structure-based optimization of this class of novel β-lactamase inhibitors against a key resistance target.

High-throughput screening of dipeptide utilization mediated by the ABC transporter DppBCDF and its substrate-binding proteins DppA1-A5 in Pseudomonas aeruginosa

In this study, we show that the dppBCDF operon of Pseudomonas aeruginosa PA14 encodes an ABC transporter responsible for the utilization of di/tripeptides. The substrate specificity of ABC transporters is determined by its associated substrate-binding proteins (SBPs). Whereas in E. coli only one protein, DppA, determines the specificity of the transporter, five orthologous SBPs, DppA1-A5 are present in P. aeruginosa. Multiple SBPs might broaden the substrate specificity by increasing the transporter capacity. We utilized the Biolog phenotype MicroArray technology to investigate utilization of di/tripeptides in mutants lacking either the transport machinery or all of the five SBPs. This high-throughput method enabled us to screen hundreds of dipeptides with various side-chains, and subsequently, to determine the substrate profile of the dipeptide permease. The substrate spectrum of the SBPs was elucidated by complementation of a penta mutant, deficient of all five SBPs, with plasmids carrying individual SBPs. It became apparent that some dipeptides were utilized with different affinity for each SBP. We found that DppA2 shows the highest flexibility on substrate recognition and that DppA2 and DppA4 have a higher tendency to utilize tripeptides. DppA5 was not able to complement the penta mutant under our screening conditions. Phaseolotoxin, a toxic tripeptide inhibiting the enzyme ornithine carbamoyltransferase, is also transported into P. aeruginosa via the DppBCDF permease. The SBP DppA1, and with much greater extend DppA3, are responsible for delivering the toxin to the permease. Our results provide a first overview of the substrate pattern of the ABC dipeptide transport machinery in P. aeruginosa.

Acinetobacter baumannii escape from neutrophil extracellular traps (NETs)

Acinetobacter baumannii and Pseudomonas aeruginosa are the same aerobic gram-negative bacillus and are usually harmless but cause infectious diseases in compromised hosts. Neutrophils play a critical role in infective protection against the extracellular growth of bacteria. Recently, a new biological defense mechanism called neutrophil extracellular traps (NETs) has been attracting attention. In present study, we investigated the responsiveness of neutrophils to A. baumannii and P. aeruginosa, focusing on NET formation. Neutrophils were co-cultured with A. baumannii or P. aeruginosa, and then DNA, histone and neutrophil elastase were stained, and the formation of NETs was evaluated. Neutrophils stimulated with A. baumannii had spread, but their shapes was maintained, and the nucleus was observed as clearly as that in non-stimulated neutrophils. However, neutrophils stimulated with P. aeruginosa did not maintain their cellular morphology, and the nucleus was disrupted with DNA, histones, and neutrophil elastase released into the extracellular space. These results suggest that A. baumannii does not induce NET formation, in contrast to P. aeruginosa. In addition, we measured expression of myeloperoxidase (MPO), reactive oxygen species (ROS) and superoxide in neutrophils, and we found that these expression in P. aeruginosa-stimulated neutrophils was stronger than that in A. baumannii-stimulated neutrophils. Furthermore, A. baumannii was not killed by neutrophils, in contrast to P. aeruginosa. In this study, we show that the reactivity of neutrophils and their biological defense mechanism are different between A. baumannii and P. aeruginosa, which is important for understanding the pathogenicity of these bacteria.

Antibiotic resistance is widespread in urban aquatic environments of Rio de Janeiro, Brazil

Bacterial resistance to antibiotics has become a public health issue. Over the years, pathogenic organisms with resistance traits have been studied due to the threat they pose to human well-being. However, several studies raised awareness to the often disregarded importance of environmental bacteria as sources of resistance mechanisms. In this work, we analyze the diversity of antibiotic-resistant bacteria occurring in aquatic environments of the state of Rio de Janeiro, Brazil, that are subjected to distinct degrees of anthropogenic impacts. We access the diversity of aquatic bacteria capable of growing in increasing ampicillin concentrations through 16S rRNA gene libraries. This analysis is complemented by the characterization of antibiotic resistance profiles of isolates obtained from urban aquatic environments. We detect communities capable of tolerating antibiotic concentrations up to 600 times higher than the clinical levels. Among the resistant organisms are included potentially pathogenic species, some of them classified as multiresistant. Our results extend the knowledge of the diversity of antibiotic resistance among environmental microorganisms and provide evidence that the diversity of drug-resistant bacteria in aquatic habitats can be influenced by pollution.

The hierarchy quorum sensing network in Pseudomonas aeruginosa

Pseudomonas aeruginosa causes severe and persistent infections in immune compromised individuals and cystic fibrosis sufferers. The infection is hard to eradicate as P. aeruginosa has developed strong resistance to most conventional antibiotics. The problem is further compounded by the ability of the pathogen to form biofilm matrix, which provides bacterial cells a protected environment withstanding various stresses including antibiotics. Quorum sensing (QS), a cell density-based intercellular communication system, which plays a key role in regulation of the bacterial virulence and biofilm formation, could be a promising target for developing new strategies against P. aeruginosa infection. The QS network of P. aeruginosa is organized in a multi-layered hierarchy consisting of at least four interconnected signaling mechanisms. Evidence is accumulating that the QS regulatory network not only responds to bacterial population changes but also could react to environmental stress cues. This plasticity should be taken into consideration during exploration and development of anti-QS therapeutics.

Properties of AdeABC and AdeIJK efflux systems of Acinetobacter baumannii compared with those of the AcrAB-TolC system of Escherichia coli

Acinetobacter baumannii contains RND-family efflux systems AdeABC and AdeIJK, which pump out a wide range of antimicrobial compounds, as judged from the MIC changes occurring upon deletion of the responsible genes. However, these studies may miss changes because of the high backgrounds generated by the remaining pumps and by β-lactamases, and it is unclear how the activities of these pumps compare quantitatively with those of the well-studied AcrAB-TolC system of Escherichia coli. We expressed adeABC and adeIJK of A. baumannii, as well as E. coli acrAB, in an E. coli host from which acrAB was deleted. The A. baumannii pumps were functional in E. coli, and the MIC changes that were observed largely confirmed the substrate range already reported, with important differences. Thus, the AdeABC system pumped out all β-lactams, an activity that was often missed in deletion studies. When the expression level of the pump genes was adjusted to a similar level for a comparison with AcrAB-TolC, we found that both A. baumannii efflux systems pumped out a wide range of compounds, but AdeABC was less effective than AcrAB-TolC in the extrusion of lipophilic β-lactams, novobiocin, and ethidium bromide, although it was more effective at tetracycline efflux. AdeIJK was remarkably more effective than a similar level of AcrAB-TolC in the efflux of β-lactams, novobiocin, and ethidium bromide, although it was less so in the efflux of erythromycin. These results thus allow us to compare these efflux systems on a quantitative basis, if we can assume that the heterologous systems are fully functional in the E. coli host.

Treatment option for sepsis in children in the era of antibiotic resistance

Sepsis caused by multidrug-resistant microorganisms is one of the most serious infectious diseases of childhood and poses significant challenges for pediatricians involved in management of critically ill children. This review discusses the use of pharmacokinetic/dynamic principles (i.e., prolonged infusion of β-lactams and vancomycin, once-daily administration of aminoglycosides and rationale of therapeutic drug monitoring) when prescribing antibiotics to critically ill patients. The potential of 'old' agents (i.e., colistin, fosfomycin) and newly approved antibiotics is critically reviewed. The pros and cons of combination antibacterial therapy are discussed and finally suggestions for the treatment of sepsis caused by multidrug-resistant organisms are provided.