Antagonistic Interactions of Pseudomonas aeruginosa Antibiotic Resistance Mechanisms in Planktonic but Not Biofilm Growth

ABSTRACTPseudomonas aeruginosahas an extraordinary capacity to evade the activity of antibiotics through a complex interplay of intrinsic and mutation-driven resistance pathways, which are, unfortunately, often additive or synergistic, leading to multidrug (or even pandrug) resistance. However, we show that one of these mechanisms, overexpression of the MexCD-OprJ efflux pump (driven by inactivation of its negative regulator NfxB), causes major changes in the cell envelope physiology, impairing the backbone ofP. aeruginosaintrinsic resistance, including the major constitutive (MexAB-OprM) and inducible (MexXY-OprM) efflux pumps and the inducible AmpC β-lactamase. Moreover, it also impaired the most relevant mutation-driven β-lactam resistance mechanism (constitutive AmpC overexpression), through a dramatic decrease in periplasmic β-lactamase activity, apparently produced by an abnormal permeation of AmpC out of the cell. While these results could delineate future strategies for combating antibiotic resistance in cases of acute nosocomial infections, a major drawback for the potential exploitation of the described antagonistic interaction between resistance mechanisms came from the differential bacterial physiology characteristics of biofilm growth, a hallmark of chronic infections. Although the failure to concentrate AmpC activity in the periplasm dramatically limits the protection of the targets (penicillin-binding proteins [PBPs]) of β-lactams at the individual cell level, the expected outcome for cells growing as biofilm communities, which are surrounded by a thick extracellular matrix, was less obvious. Indeed, our results showed that AmpC produced bynfxBmutants is protective in biofilm growth, suggesting that the permeation of AmpC into the matrix protects biofilm communities against β-lactams.

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The analysis of the role of MexAB-OprM on quorum sensing homeostasis shows that the apparent redundancy of Pseudomonas aeruginosa multidrug efflux pumps allows keeping the robustness and the plasticity of this intercellular signaling network

10.1101/2020.03.10.986737 ◽

2020 ◽

Author(s):

Manuel Alcalde-Rico ◽

Jorge Olivares-Pacheco ◽

Nigel Halliday ◽

Miguel Cámara ◽

José Luis Martínez

Keyword(s):

Pseudomonas Aeruginosa ◽

Antibiotic Resistance ◽

Quorum Sensing ◽

Efflux Pump ◽

Efflux Pumps ◽

Multidrug Efflux ◽

Intrinsic Resistance ◽

Bacterial Physiology ◽

Multidrug Efflux Pumps ◽

Depth Analysis

AbstractMultidrug efflux pumps are key determinants for antibiotic resistance. Besides contributing to intrinsic resistance, their overexpression is frequently a cause of the increased resistance acquired during therapy. In addition to their role in resistance to antimicrobials, efflux pumps are ancient and conserved elements with relevant roles in different aspects of the bacterial physiology. It is then conceivable that their overexpression might cause a burden that will be translated into a fitness cost associated with the acquisition of resistance. In the case of Pseudomonas aeruginosa, it has been stated that overexpression of different efflux pumps is linked to the impairment of the quorum sensing (QS) response. Nevertheless, the causes of such impairment are different for each analyzed efflux pump. In this study, we performed an in-depth analysis of the QS-mediated response of a P. aeruginosa antibiotic resistant mutant that overexpresses MexAB-OprM. Although previous work claimed that this efflux pump extrudes the QS signal 3-oxo-C12-HSL, we show otherwise. Our results suggest that the observed attenuation in the QS response when overexpressing this pump is related to a reduced availability of intracellular octanoate, one of the precursors of the biosynthesis of alkyl quinolone QS signals. The overexpression of other P. aeruginosa efflux pumps has been shown to also cause a reduction in intracellular levels of QS signals or their precursors impacting on these signaling mechanisms. However, the molecules involved are distinct for each efflux pump, indicating that they can differentially contribute to the P. aeruginosa quorum sensing homeostasis.ImportanceThe success of bacterial pathogens to cause disease relies on their virulence capabilities as well as in their resistance to antibiotic interventions. In the case of the important nosocomial pathogen Pseudomonas aeruginosa, multidrug efflux pumps participate in the resistance/virulence crosstalk since, besides contributing to antibiotic resistance, they can also modulate the quorum sensing (QS) response. We show that mutants overexpressing the MexAB-OprM efflux pump, present an impaired QS response due to the reduced availability of the QS signal precursor octanoate, not because they extrude, as previously stated, the QS signal 3-oxo-C12-HSL. Together with previous studies, this indicates that, although the consequences of overexpressing efflux pumps are similar (impaired QS response), the mechanisms are different. This ‘apparent redundancy’ of RND efflux systems can be understood as a P. aeruginosa strategy to keep the robustness of the QS regulatory network and modulate its output in response to different signals.

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PA3225 Is a Transcriptional Repressor of Antibiotic Resistance Mechanisms in Pseudomonas aeruginosa

Antimicrobial Agents and Chemotherapy ◽

10.1128/aac.02114-16 ◽

2017 ◽

Vol 61 (8) ◽

Cited By ~ 5

Author(s):

Clayton W. Hall ◽

Li Zhang ◽

Thien-Fah Mah

Keyword(s):

Pseudomonas Aeruginosa ◽

Antibiotic Resistance ◽

Efflux Pump ◽

Regulatory Region ◽

Resistance Mechanisms ◽

Wild Type ◽

Type Vi Secretion System ◽

Planktonic Cells ◽

Content Type ◽

Dependent Protein

ABSTRACT The tssABC1 locus is part of the Hcp secretion island I (HSI-I) type VI secretion system (T6SS) in Pseudomonas aeruginosa. Previous work implicated the tssC1 gene in P. aeruginosa biofilm-specific antibiotic resistance, and tssC1 is preferentially expressed in biofilms compared to planktonic cells. Using a DNA-dependent protein pulldown approach, we discovered that PA3225, an uncharacterized LysR-type transcriptional regulator, specifically bound to the tssABC1 upstream regulatory region. The deletion of PA3225 led to a 2-fold decrease in tssA1 expression levels in planktonic cells compared to the wild type, and tssA1 expression was slightly reduced in ΔPA3225 biofilms compared to wild-type biofilms. Intriguingly, further investigations revealed that the ΔPA3225 mutant was less susceptible to multiple, structurally unrelated antibiotics with various mechanisms of action when grown planktonically. The ΔPA3225 mutant was additionally more resistant to ciprofloxacin when grown in a biofilm. The decreased antibiotic susceptibility of the ΔPA3225 strain was linked to the transcriptional upregulation of the MexAB-OprM efflux pump. By using transcriptome sequencing (RNA-seq), other PA3225-regulated genes were identified, and the products of these genes, such as the putative ABC transporter PA3228, may also contribute to antibiotic resistance.

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Lack of the Major Multifunctional Catalase KatA in Pseudomonas aeruginosa Accelerates Evolution of Antibiotic Resistance in Ciprofloxacin-Treated Biofilms

Antimicrobial Agents and Chemotherapy ◽

10.1128/aac.00766-19 ◽

2019 ◽

Vol 63 (10) ◽

Cited By ~ 1

Author(s):

Marwa N. Ahmed ◽

Andreas Porse ◽

Ahmed Abdelsamad ◽

Morten Sommer ◽

Niels Høiby ◽

...

Keyword(s):

Oxidative Stress ◽

Pseudomonas Aeruginosa ◽

Antibiotic Resistance ◽

Defense Mechanism ◽

Efflux Pump ◽

Negative Regulator ◽

Content Type ◽

Iron Assimilation ◽

In The Wild

ABSTRACT During chronic biofilm infections, Pseudomonas aeruginosa bacteria are exposed to increased oxidative stress as a result of the inflammatory response. As reactive oxygen species (ROS) are mutagenic, the evolution of resistance to ciprofloxacin (CIP) in biofilms under oxidative stress conditions was investigated. We experimentally evolved six replicate populations of P. aeruginosa lacking the major catalase KatA in colony biofilms and stationary-phase cultures for seven passages in the presence of subinhibitory levels (0.1 mg/liter) of CIP or without CIP (eight replicate lineages for controls) under aerobic conditions. In CIP-evolved biofilms, a larger CIP-resistant subpopulation was isolated in the ΔkatA strain than in the wild-type (WT) PAO1 population, suggesting oxidative stress as a promoter of the development of antibiotic resistance. A higher number of mutations identified by population sequencing were observed in evolved ΔkatA biofilm populations (CIP and control) than in WT PAO1 populations evolved under the same conditions. Genes involved in iron assimilation were found to be exclusively mutated in CIP-evolved ΔkatA biofilm populations, probably as a defense mechanism against ROS formation resulting from Fenton reactions. Furthermore, a hypermutable lineage due to mutL inactivation developed in one CIP-evolved ΔkatA biofilm lineage. In CIP-evolved biofilms of both the ΔkatA strain and WT PAO1, mutations in nfxB, the negative regulator of the MexCD-OprJ efflux pump, were observed while in CIP-evolved planktonic cultures of both the ΔkatA strain and WT PAO1, mutations in mexR and nalD, regulators of the MexAB-OprM efflux pump, were repeatedly found. In conclusion, these results emphasize the role of oxidative stress as an environmental factor that might increase the development of antibiotic resistance in in vivo biofilms.

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Multidrug Adaptive Resistance of Pseudomonas aeruginosa Swarming Cells

Antimicrobial Agents and Chemotherapy ◽

10.1128/aac.01999-19 ◽

2019 ◽

Vol 64 (3) ◽

Cited By ~ 2

Author(s):

Shannon R. Coleman ◽

Travis Blimkie ◽

Reza Falsafi ◽

Robert E. W. Hancock

Keyword(s):

Pseudomonas Aeruginosa ◽

Antibiotic Resistance ◽

Efflux Pump ◽

Iron Acquisition ◽

Polymyxin B ◽

Rna Seq ◽

Multidrug Efflux ◽

Multidrug Efflux Pump ◽

Content Type ◽

Adaptive Resistance

ABSTRACT Swarming surface motility is a complex adaptation leading to multidrug antibiotic resistance and virulence factor production in Pseudomonas aeruginosa. Here, we expanded previous studies to demonstrate that under swarming conditions, P. aeruginosa PA14 is more resistant to multiple antibiotics, including aminoglycosides, β-lactams, chloramphenicol, ciprofloxacin, tetracycline, trimethoprim, and macrolides, than swimming cells, but is not more resistant to polymyxin B. We investigated the mechanism(s) of swarming-mediated antibiotic resistance by examining the transcriptomes of swarming cells and swarming cells treated with tobramycin by transcriptomics (RNA-Seq) and reverse transcriptase quantitative PCR (qRT-PCR). RNA-Seq of swarming cells (versus swimming) revealed 1,581 dysregulated genes, including 104 transcriptional regulators, two-component systems, and sigma factors, numerous upregulated virulence and iron acquisition factors, and downregulated ribosomal genes. Strain PA14 mutants in resistome genes that were dysregulated under swarming conditions were tested for their ability to swarm in the presence of tobramycin. In total, 41 mutants in genes dysregulated under swarming conditions were shown to be more resistant to tobramycin under swarming conditions, indicating that swarming-mediated tobramycin resistance was multideterminant. Focusing on two genes downregulated under swarming conditions, both prtN and wbpW mutants were more resistant to tobramycin, while the prtN mutant was additionally resistant to trimethoprim under swarming conditions; complementation of these mutants restored susceptibility. RNA-Seq of swarming cells treated with subinhibitory concentrations of tobramycin revealed the upregulation of the multidrug efflux pump MexXY and downregulation of virulence factors.

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The Efflux Pump MexXY/OprM Contributes to the Tolerance and Acquired Resistance of Pseudomonas aeruginosa to Colistin

Antimicrobial Agents and Chemotherapy ◽

10.1128/aac.02033-19 ◽

2020 ◽

Vol 64 (4) ◽

Author(s):

Hélène Puja ◽

Arnaud Bolard ◽

Aurélie Noguès ◽

Patrick Plésiat ◽

Katy Jeannot

Keyword(s):

Pseudomonas Aeruginosa ◽

Lipid A ◽

Efflux Pump ◽

Acquired Resistance ◽

Intrinsic Resistance ◽

Drug Induced ◽

Functional Link ◽

Content Type ◽

Regulatory Systems ◽

Early Drug

ABSTRACT The intrinsic resistance of Pseudomonas aeruginosa to polymyxins in part relies on the addition of 4-amino-4-deoxy-l-arabinose (Ara4N) molecules to the lipid A of lipopolysaccharide (LPS), through induction of operon arnBCADTEF-ugd (arn) expression. As demonstrated previously, at least three two-component regulatory systems (PmrAB, ParRS, and CprRS) are able to upregulate this operon when bacteria are exposed to colistin. In the present study, gene deletion experiments with the bioluminescent strain PAO1::lux showed that ParRS is a key element in the tolerance of P. aeruginosa to this last-resort antibiotic (i.e., resistance to early drug killing). Other loci of the ParR regulon, such as those encoding the efflux proteins MexXY (mexXY), the polyamine biosynthetic pathway PA4773-PA4774-PA4775, and Ara4N LPS modification process (arnBCADTEF-ugd), also contribute to the bacterial tolerance in an intricate way with ParRS. Furthermore, we found that both stable upregulation of the arn operon and drug-induced ParRS-dependent overexpression of the mexXY genes accounted for the elevated resistance of pmrB mutants to colistin. Deletion of the mexXY genes in a constitutively activated ParR mutant of PAO1 was associated with significantly increased expression of the genes arnA, PA4773, and pmrA in the absence of colistin exposure, thereby highlighting a functional link between the MexXY/OprM pump, the PA4773-PA4774-PA4775 pathway, and Ara4N-based modification of LPS. The role played by MexXY/OprM in the adaptation of P. aeruginosa to polymyxins opens new perspectives for restoring the susceptibility of resistant mutants through the use of efflux inhibitors.

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Role of the MexEF-OprN Efflux System in Low-Level Resistance of Pseudomonas aeruginosa to Ciprofloxacin

Antimicrobial Agents and Chemotherapy ◽

10.1128/aac.00101-11 ◽

2011 ◽

Vol 55 (12) ◽

pp. 5676-5684 ◽

Cited By ~ 48

Author(s):

Catherine Llanes ◽

Thilo Köhler ◽

Isabelle Patry ◽

Barbara Dehecq ◽

Christian van Delden ◽

...

Keyword(s):

Pseudomonas Aeruginosa ◽

Reference Strain ◽

Efflux Pump ◽

Resistance Mechanisms ◽

Efflux System ◽

Content Type ◽

Clinical Strains ◽

Major Mechanism ◽

Level Resistance

ABSTRACTIn this study, we investigated the resistance mechanisms to fluoroquinolones of 85 non-cystic fibrosis strains ofPseudomonas aeruginosaexhibiting a reduced susceptibility to ciprofloxacin (MICs from 0.25 to 2 μg/ml). In addition to MexAB-OprM (31 of 85 isolates) and MexXY/OprM (39 of 85), the MexEF-OprN efflux pump (10 of 85) was found to be commonly upregulated in this population that is considered susceptible or of intermediate susceptibility to ciprofloxacin, according to current breakpoints. Analysis of the 10 MexEF-OprN overproducers (nfxCmutants) revealed the presence of various mutations in themexT(2 isolates),mexS(5 isolates), and/ormvaT(2 isolates) genes, the inactivation of which is known to increase the expression of themexEF-oprNoperon in reference strain PAO1-UW. However, these genes were intact in 3 of 10 of the clinical strains. Interestingly, ciprofloxacin at 2 μg/ml or 4 μg/ml preferentially selectednfxCmutants from wild-type clinical strains (n= 10 isolates) and from first-step mutants (n= 10) overexpressing Mex pumps, thus indicating that MexEF-OprN represents a major mechanism by whichP. aeruginosamay acquire higher resistance levels to fluoroquinolones. These data support the notion that thenfxCmutants may be more prevalent in the clinical setting than anticipated and strongly suggest the involvement of still unknown genes in the regulation of this efflux system.

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Expression ofPseudomonas aeruginosaAntibiotic Resistance Genes Varies Greatly during Infections in Cystic Fibrosis Patients

Antimicrobial Agents and Chemotherapy ◽

10.1128/aac.01789-18 ◽

2018 ◽

Vol 62 (11) ◽

Cited By ~ 8

Author(s):

Lois W. Martin ◽

Cynthia L. Robson ◽

Annabelle M. Watts ◽

Andrew R. Gray ◽

Claire E. Wainwright ◽

...

Keyword(s):

Gene Expression ◽

Cystic Fibrosis ◽

Antibiotic Resistance ◽

Efflux Pump ◽

Antibiotic Resistance Gene ◽

Resistance Mechanisms ◽

Laboratory Culture ◽

Bacterial Cells ◽

Content Type ◽

Key Factor

ABSTRACTThe lungs of individuals with cystic fibrosis (CF) become chronically infected withPseudomonas aeruginosathat is difficult to eradicate by antibiotic treatment. Two keyP. aeruginosaantibiotic resistance mechanisms are the AmpC β-lactamase that degrades β-lactam antibiotics and MexXYOprM, a three-protein efflux pump that expels aminoglycoside antibiotics from the bacterial cells. Levels of antibiotic resistance gene expression are likely to be a key factor in antibiotic resistance but have not been determined during infection. The aims of this research were to investigate the expression of theampCandmexXgenes during infection in patients with CF and in bacteria isolated from the same patients and grown under laboratory conditions.P. aeruginosaisolates from 36 CF patients were grown in laboratory culture and gene expression measured by reverse transcription-quantitative PCR (RT-qPCR). The expression ofampCvaried over 20,000-fold and that ofmexXover 2,000-fold between isolates. The median expression levels of both genes were increased by the presence of subinhibitory concentrations of antibiotics. To measureP. aeruginosagene expression during infection, we carried out RT-qPCR using RNA extracted from fresh sputum samples obtained from 31 patients. The expression ofampCvaried over 4,000-fold, whilemexXexpression varied over 100-fold, between patients. Despite these wide variations, median levels of expression ofampCin bacteria in sputum were similar to those in laboratory-grown bacteria. The expression ofmexXwas higher in sputum than in laboratory-grown bacteria. Overall, our data demonstrate that genes that contribute to antibiotic resistance can be highly expressed in patients, but there is extensive isolate-to-isolate and patient-to-patient variation.

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Comparative Genomics Reveals a Well-Conserved Intrinsic Resistome in the Emerging Multidrug-Resistant Pathogen Cupriavidus gilardii

mSphere ◽

10.1128/msphere.00631-19 ◽

2019 ◽

Vol 4 (5) ◽

Cited By ~ 2

Author(s):

Cristian Ruiz ◽

Ashley McCarley ◽

Manuel Luis Espejo ◽

Kerry K. Cooper ◽

Dana E. Harmon

Keyword(s):

Antibiotic Resistance ◽

Comparative Genomics ◽

Resistance Genes ◽

Antibiotic Resistance Genes ◽

Multidrug Resistant ◽

Resistance Mechanisms ◽

Antibiotics Resistance ◽

Whole Genome ◽

Intrinsic Resistance ◽

Content Type

ABSTRACT The Gram-negative bacterium Cupriavidus gilardii is an emerging multidrug-resistant pathogen found in many environments. However, little is known about this species or its antibiotic resistance mechanisms. We used biochemical tests, antibiotic susceptibility experiments, and whole-genome sequencing to characterize an environmental C. gilardii isolate. Like clinical isolates, this isolate was resistant to meropenem, gentamicin, and other antibiotics. Resistance to these antibiotics appeared to be related to the large number of intrinsic antibiotic resistance genes found in this isolate. As determined by comparative genomics, this resistome was also well conserved in the only two other C. gilardii strains sequenced to date. The intrinsic resistome of C. gilardii did not include the colistin resistance gene mcr-5, which was in a transposon present only in one strain. The intrinsic resistome of C. gilardii was comprised of (i) many multidrug efflux pumps, such as a homolog of the Pseudomonas aeruginosa MexAB-OprM pump that may be involved in resistance to meropenem, other β-lactams, and aminoglycosides; (ii) a novel β-lactamase (OXA-837) that decreases susceptibility to ampicillin but not to other β-lactams tested; (iii) a new aminoglycoside 3-N-acetyltransferase [AAC(3)-IVb, AacC10] that decreases susceptibility to gentamicin and tobramycin; and (iv) a novel partially conserved aminoglycoside 3ʺ-adenylyltransferase [ANT(3ʺ)-Ib, AadA32] that decreases susceptibility to spectinomycin and streptomycin. These findings provide the first mechanistic insight into the intrinsic resistance of C. gilardii to multiple antibiotics and its ability to become resistant to an increasing number of drugs during therapy. IMPORTANCE Cupriavidus gilardii is a bacterium that is gaining increasing attention both as an infectious agent and because of its potential use in the detoxification of toxic compounds and other biotechnological applications. In recent years, however, there has been an increasing number of reported infections, some of them fatal, caused by C. gilardii. These infections are hard to treat because this bacterium is naturally resistant to many antibiotics, including last-resort antibiotics, such as carbapenems. Moreover, this bacterium often becomes resistant to additional antibiotics during therapy. However, little is known about C. gilardii and its antibiotic resistance mechanisms. The significance of our research is in providing, for the first time, whole-genome information about the natural antibiotic resistance genes found in this bacterium and their conservation among different C. gilardii strains. This information may provide new insights into the appropriate use of antibiotics in combating infections caused by this emerging pathogen.

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Activity of Ceftolozane-Tazobactam against Carbapenem-Resistant, Non-Carbapenemase-Producing Pseudomonas aeruginosa and Associated Resistance Mechanisms

Antimicrobial Agents and Chemotherapy ◽

10.1128/aac.01970-17 ◽

2017 ◽

Vol 62 (1) ◽

Cited By ~ 12

Author(s):

Yu Mi Wi ◽

Kerryl E. Greenwood-Quaintance ◽

Audrey N. Schuetz ◽

Kwan Soo Ko ◽

Kyong Ran Peck ◽

...

Keyword(s):

Pseudomonas Aeruginosa ◽

Efflux Pump ◽

Multidrug Resistant ◽

Resistance Mechanisms ◽

Resistance Rate ◽

Content Type ◽

Reverse Transcription Pcr ◽

Carbapenem Resistant ◽

Kill Curve ◽

Time Kill

ABSTRACT Although carbapenems are effective for treating serious multidrug-resistant Pseudomonas aeruginosa infections, carbapenem-resistant P. aeruginosa (CRPA) is now being reported worldwide. Ceftolozane-tazobactam (C/T) demonstrates activity against many multidrug-resistant isolates. We evaluated the activity of C/T and compared its activity to that of ceftazidime-avibactam (C/A) using a well-characterized collection of non-carbapenemase-producing CRPA isolates. Forty-two non-carbapenemase-producing CRPA isolates from a previous study (J. Y. Lee and K. S. Ko, Int J Antimicrob Agents 40:168–172, 2012, https://doi.org/10.1016/j.ijantimicag.2012.04.004) were included. All had been previously shown to be negative for bla IMP, bla VIM, bla SPM, bla GIM, bla SIM, and bla KPC by PCR. In the prior study, expression of oprD, ampC, and several efflux pump genes had been defined by quantitative reverse transcription-PCR. Here, antimicrobial susceptibility was determined by broth microdilution according to Clinical and Laboratory Standards Institute (CLSI) guidelines. Time-kill curve assays were performed using three C/T- and C/A-susceptible CRPA isolates. Among 42 non-carbapenemase-producing CRPA isolates, overall susceptibility to C/T was 95.2%, compared to 71.4%, 42.9%, 23.8%, 21.4%, and 2.4% for C/A, ceftazidime, piperacillin-tazobactam, cefepime, and meropenem, respectively. The C/T resistance rate was significantly lower than that of C/A among isolates showing decreased oprD and increased mexB expression (5.1% versus 25.6%, P = 0.025, and 4.3% versus 34.8%, P = 0.022, respectively). In time-kill curve studies, C/T was less bactericidal than C/A against an isolate with decreased oprD and increased ampC expression. C/T was active against 95.2% of non-carbapenemase-producing CRPA clinical isolates. No apparent correlation of C/T MIC values with specific mutation-driven resistance mechanisms was noted.

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Mutations in nalc gene of Mex AB-OprM efflux pump in carbapenem resistant Pseudomonas aeruginosa isolated from burn wounds in Yazd, Iran

Iranian Journal of Microbiology ◽

10.18502/ijm.v12i1.2514 ◽

2020 ◽

Author(s):

Fatemeh Akhavan Tafti ◽

Gilda Eslami ◽

Hengameh Zandi ◽

Kazem Barzegar

Keyword(s):

Pseudomonas Aeruginosa ◽

Efflux Pump ◽

Resistance Mechanisms ◽

Resistant Isolate ◽

Wound Infections ◽

Intrinsic Resistance ◽

Burn Wound ◽

Cross Sectional ◽

Burn Wounds ◽

Carbapenem Resistant

Background and Objectives: Burn wound infections have emerged as an important cause of morbidity and mortality in patients due to prolonged hospital stay. Pseudomonas aeruginosa, is the second cause of bacterial burn wound infections. Resistance mechanisms among P. aeruginosa are intrinsic or acquired. Intrinsic resistance mechanisms among P. aeruginosa isolates are inducible AmpC cephalosporinase, decrease of specific porin OprD, and overexpression of RND efflux pump. The aim of this study was detection of mutations in nalC gene in carbapenem resistant P. aeruginosa isolated from burn wounds. Materials and Methods: In this cross-sectional study, 180 burn-wound specimens were collected. Suspected lactose-nega- tive colonies were identified by conventional biochemical methods. Kirby-Bauer and Etest methods were used for suscepti- bility testing. PCR and sequencing techniques were used for the detection of nalC mutation. Results: Out of 180 specimens received in the laboratory, 54 of isolates were isolated and identified as P. aeroginosa (30%). Of these isolates 20 (37%) were resistant to at least two carbapenems simultaneously. From these carbapenem resistant iso- lates, 19 (95%), 14 (70%), 14 (70%), 19 (95%) and 16 (80%) were resistant to imipenem, cefepime, piperacillin, ceftizoxime and gentamicin, respectively. Only 1 (2%) isolate was sensitive to all carbapenems and did not has mutation in nalC gene, 20 (37%) isolates were resistant to at least two carbapenems, and had mutations in nalC gene (Gly71►Glu and Ser209►Arg). Conclusion: As the results showed, mutation in efflux pump was observed in carbapenem resistant isolate and this confirmed that the indiscriminate use of antibiotics for treatment or prophylaxis can increase mutation in efflux pump.

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