Antibiotic resistance patterns of efflux pumps MexAB-Opr M in pathogenic Pseudomonas aeruginosa isolates

Abstract Objectives Pseudomonas aeruginosa is one of the most important causes of Hospital infection especially in burn victims. The current study aimed to determine antibiotic resistance of the efflux Pumps MexAB-Opr M. In the present study, 115 samples of urine, blood, sputum, and ICU were collected from the reconstructive section of the patients. The drug susceptibility patterns were determined by disk diffusion method. Phenotypic activity of the efflux pump from the E-test was evaluated, in the presence and without the presence of efflux pump inhibitor. The MexAB gene was analyzed by PCR reaction. Results The resistant isolated was shown to be Ciprofloxacin 33.91%, Nurfloxacin 38.26%, Gentamicin 71.7%, Nalidixic acid 95.95%, Ceftazidim 38.46%, Emipenem 24.34%, Meropenem 26.36%, and Cefotaxim 40.86%. The highest and lowest resistance rates were Co-trimoxazole and Piperacilin, respectively. The findings of PCR reaction among 115 P. aeruginosa isolates indicated that 62.62% was MexAB gene. The results of MIC with E-test revealed that the role of efflux pumps in antibiotic resistance was 19 isolated. Due to the importance of antibiotic resistance to investigate other efflux pumps, comparison of efflux pump involvement in antibiotic resistance, and relationship between efflux pumps MexAB-Opr M are highly required and suggested.

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MexAB-OprM and MexXY-OprM efflux pumps overexpression; additional mechanism for carbapenems resistance among nosocomial Pseudomonas aeruginosa isolates

10.51429/ejmm29403 ◽

2020 ◽

Vol EJMM29 (4) ◽

pp. 17-25

Author(s):

Asmaa M. Elbrolosy ◽

Amira H. Elkhayat ◽

Dina M. Hassan ◽

Eman H. Salem

Keyword(s):

Pseudomonas Aeruginosa ◽

Target Genes ◽

Efflux Pump ◽

Early Recognition ◽

Efflux Pumps ◽

Diffusion Method ◽

University Hospitals ◽

Pcr Assay ◽

Efflux Pump Inhibitor ◽

Disk Diffusion Method

Background: Multidrug-resistant pathogens have been on the rise during the last few years. Pseudomonas aeruginosa is commonly encountered in nosocomial infections with remarkable ability to develop antimicrobial resistance of which carbapenems are of great concern. Objectives: To explore the role of MexAB-OprM and MexXY-OprM efflux pumps overexpression as carbapenems resistance mechanisms among nosocomial P. aeruginosa isolates at both Menoufia and Kasr Al Ainy University Hospitals by phenotypic and molecular characterization methods. Methodology: A total of 120 P. aeruginosa isolates were collected from patients with hospital-acquired infections and subjected to antibiotic susceptibility testing by the Kirby-Bauer disk diffusion method. Carbapenems-resistant isolates were selected and investigated phenotypically for the contribution of MexAB-OprM and MexXY-OprM efflux pumps by both disk synergy and MIC reduction assays with cyanide-m-chlorophenyl hydrazone (CCCP) as an efflux pump inhibitor. Real time PCR assay verified the existence of mexA and mexX genes as regulators of MexAB-OprM and MexXY-OprM overexpression. Laboratory results were correlated with data regarding patients' clinical findings as well as risk factors. Results: Out of 120 P. aeruginosa isolates, 88 (73.3%) isolates were carbapenems-resistant of which 100% were MDR isolates. The highest resistance rate was for piperacillin and piperacillin/tazobactam (100% for each) and the lowest rate was seen against colistin (7.5%).The RT-PCR assay revealed that, 54/88 (61.3%) P. aeruginosa isolates harbored the target genes: 21 isolates (38.9%) were positive for mexA alone, 12 isolates (22.2%) were positive for mexX alone and 21 isolates (38.9%) showed co-existence of the two genes. In relation to PCR results, the sensitivity, specificity and accuracy of CCCP disk synergy test respectively were 46%, 94% and 64.8% while, those for MIC method were 88.9%, 55.9% and 76.1% respectively. Conclusion: Carbapenems resistance mediated by the overexpression of efflux pumps has also now emerged. Early recognition of this resistance mechanism to allow the use of alternative b-lactams is imperative.

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Role of efflux pump inhibitor in decreasing antibiotic cross-resistance of Pseudomonas aeruginosa in a burn hospital in Iran

The Journal of Infection in Developing Countries ◽

10.3855/jidc.7619 ◽

2016 ◽

Vol 10 (06) ◽

pp. 600-604 ◽

Cited By ~ 2

Author(s):

Mahshid Talebi-Taher ◽

َAli Majidpour ◽

Abbas Gholami ◽

Samira Rasouli-Kouhi ◽

Maryam Adabi

Keyword(s):

Pseudomonas Aeruginosa ◽

Efflux Pump ◽

Efflux Pumps ◽

Disk Diffusion ◽

Diffusion Method ◽

Cross Resistance ◽

Beta Lactams ◽

Efflux Pump Inhibitor ◽

Efflux Pump Inhibitors

Introduction: Multidrug resistance in Pseudomonas aeruginosa may be due to efflux pump overexpression. This study phenotypically examined the role of efflux pump inhibitors in decreasing antibiotic cross-resistance between beta-lactams, fluoroquinolones, and aminoglycosides in P. aeruginosa isolates from burn patients in Iran. Methodology: A total of 91 phenotypically and genotypically confirmed P. aeruginosa samples were studied. Multidrug cross-resistance was determined using the disk diffusion method and minimum inhibitory concentration (MIC) test. The contribution of efflux pumps was determined by investigating MIC reduction assay to markers of beta-lactams, fluoroquinolones, and aminoglycosides in the absence and presence of an efflux pump inhibitor. All the isolates were also tested by polymerase chain reaction for the presence of mexA, mexC, and mexE efflux genes. Results: Of the isolates, 81 (89%) and 83 (91.2%) were multidrug resistant according to the disk diffusion and MIC method, respectively. Cross-resistance was observed in 67 (73.6%) and 68 (74.7%) of isolates according to the disk diffusion and MIC method, respectively. In the presence of the efflux pump inhibitor, twofold or higher MIC reduction to imipenem, cefepime, ciprofloxacin, and gentamicin was observed in 59, 65, 55, and 60 isolates, respectively. Except for two isolates that were negative for mexC, all isolates were positive for mexA, mexC, and mexE genes simultaneously. Conclusion: Efflux pumps could cause different levels of resistance based on their expression in clinical isolates. Early detection of different efflux pumps in P. aeruginosa could allow the use of other antibiotics and efflux pump inhibitors in combination with antibiotic therapy.

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Resistance to Azithromycin and β-Lactam Antibiotics by Clinical Isolates of E. coli Isolated from Dhaka, Bangladesh

Bangladesh Journal of Microbiology ◽

10.3329/bjm.v34i2.39613 ◽

2019 ◽

Vol 34 (2) ◽

pp. 61-66

Author(s):

Sunjukta Ahsan ◽

Mayen Uddin ◽

Juthika Mandal ◽

Marufa Zerin Akhter

Keyword(s):

Antibiotic Resistance ◽

Efflux Pump ◽

Clinical Isolates ◽

Diffusion Method ◽

Disk Diffusion Method ◽

Antibiotic Resistant ◽

E Coli ◽

Resistance Patterns ◽

Ready Availability ◽

Antibiotic Resistance Patterns

Antibiotic resistant E. coli are prevalent in Bangladesh. The indiscriminate use of antimicrobials and ready availability of over the counter drugs are responsible for this. This study was conducted to investigate the susceptibility of clinical Escherichia coli to the antibiotics Imipenem, Ceftriaxone, Ceftazidime and Azithromycin. Kirby-Bauer disk diffusion method was used to determine sensitivity to antimicrobials. Agar based assay was employed for the detection of efflux pumps. PCR was used amplify antibiotic resistance genes.All isolates were resistant to Ceftriaxone whereas most were sensitive to Imipenem. The MICs of Ceftazidime and Azithromycin ranged between 128 μg/ml and 256 μg/ml. The prevalence of ²-lactamase producers was 57.89 % with 36.84 % of the isolates exhibiting ESBL activity. No specific correlation could be found between plasmid sizes and antibiotic resistance patterns. Efflux pump was found to be involved in Azithromycin resistance in 63.15% of the isolates. The gene for phosphotransferase, mph(A) was the most common among the macrolide modifying genes, being present in 73.68% (14/19) of the isolates followed by both erm(A) anderm(C) esterases each present in 10.53% (2/19) isolates. This study concluded that clinical isolates of E. coli in Bangladesh could be resistant to multiple classes of antibiotics through different mechanisms of resistance. Bangladesh J Microbiol, Volume 34 Number 2 December 2017, pp 61-66

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Detection of OqxAB and QepA Efflux Pumps and Their Association with Antibiotic Resistance in Klebsiella pneumoniae Isolated From Urinary Tract Infection

International Journal of Infection ◽

10.5812/iji.107397 ◽

2020 ◽

Vol 7 (4) ◽

Author(s):

Manijeh Dehnamaki ◽

Maryam Ghane ◽

Laleh Babaeekhou

Keyword(s):

Urinary Tract Infection ◽

Antibiotic Resistance ◽

Urinary Tract ◽

Tract Infection ◽

Klebsiella Pneumoniae ◽

Efflux Pump ◽

Efflux Pumps ◽

Diffusion Method ◽

Beta Lactam ◽

Disk Diffusion Method

Background: The emergence and spread of drug resistance among Klebsiella pneumoniae clinical isolates have limited the treatment options for these bacteria. Efflux pumps are considered as one of the key mechanisms of antibiotic resistance in K. pneumoniae isolates. Objectives: The present study aimed to detect oqxA, oqxB, and qepA efflux genes in K. pneumoniae isolated from urinary tract infection (UTI) and survey their association with antibiotic resistance. Methods: In total, 100 K. pneumoniae isolates were obtained from urine samples, and an antimicrobial susceptibility test was conducted using the disk diffusion method according to the Clinical and Laboratory Standards Institute (CLSI) instructions. Polymerase chain reaction (PCR) was done for the detection of efflux pump genes including, oqxA, oqxB, and qepA, and their association was statistically analyzed with resistance to antibiotics. Results: The highest rate of resistance was obtained against trimethoprim-sulfamethoxazole (72%), amikacin (70%), levofloxacin (68%), gentamicin (56%), ceftazidime (56%), and ceftriaxone (51%), and the lowest resistance was against imipenem (10%). Thirty one percent of isolates were multidrug resistant (MDR). Molecular distribution test showed that 57% and 56% of isolates carried the oqxA and oqxB genes, respectively. Also, the frequency of qepA genes was 21%. The presence of oqxA/oqxB and qepA efflux genes were significantly associated with fluoroquinolone and beta-lactam resistance phenotypes (P < 0.05). Conclusions: The high frequency of efflux genes showed that this resistance mechanism is the main way, along with other resistance mechanisms in K. pneumoniae isolates. It is necessary to adopt appropriate treatment to reduce the incidence of resistance.

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MULTIDRUG-RESISTANCE PATTERNS AND DETECTION OF PstS GENE IN CLINICAL ISOLATES OF PSEUDOMONAS AERUGINOSA FROM NSUKKA, SOUTHEAST NIGERIA

Asian Journal of Pharmaceutical and Clinical Research ◽

10.22159/ajpcr.2020.v13i4.36669 ◽

2020 ◽

pp. 115-119

Author(s):

MARTINA C AGBO ◽

IFEOMA M EZEONU ◽

ANTHONY C IKE ◽

CELESTINA C UGWU

Keyword(s):

Pseudomonas Aeruginosa ◽

Antibiotic Resistance ◽

Multidrug Resistance ◽

Test Strip ◽

Clinical Isolates ◽

Diffusion Method ◽

Disk Diffusion Method ◽

Rdna Sequencing ◽

Resistance Patterns ◽

Antibiotic Resistance Patterns

Objective: This study was aimed to determine the antibiotic resistance patterns of clinical Pseudomonas aeruginosa isolates and to detect the presence of PstS gene. Methods: One hundred and ninety-two clinical isolates of P. aeruginosa were characterized using polymerase chain reaction (PCR) and 16S rDNA sequencing. Antibiotic resistance patterns were determined using the disk diffusion method, while the minimum inhibitory concentrations (MICs) of selected antibiotics against resistant isolates were determined by macro broth dilution and E-test strip methods. The resistant isolates were screened for the presence of PstS gene using PCR. Results: Of 192 clinical isolates of P. aeruginosa, 136 (70.83%) were resistant to at least two antibiotics. Of these, 135 (99%) could be classified as multidrug-resistant P. aeruginosa (MDR-PA), 63 (46%) were extensively drug-resistant (XDR-PA), while 38 (28%) were pandrug-resistant (PDR-PA). The isolates exhibited high level of resistance to cefotaxime and ticarcillin, and low levels of resistance to meropenem and imipenem. The MIC values for meropenem against the resistant isolates were generally <32 mg/L, while the values for other antibiotics ranged from 32 to >128 mg/L. Multiple antibiotic resistance indexes of the MDR-PA ranged from 0.27 to 0.91 and the most prevalent pattern of resistance was PiperacillinR – TicarcillinR – Piperacillin/TazobactamR – CefotaximeR – CeftazidimeR – GentamicnR – TobramycinR– CiprofloxacinR. About 50% of the resistant isolates possessed the PstS gene. Conclusions: The results confirmed the presence of XDR, PDRPA, and PstS gene in P. aeruginosa strains. There is an urgent need for healthcare practitioners to address the problem of multidrug resistance, by implementing a more rational and appropriate use of antibiotics.

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Antibiotic Resistance of Uropathogens Isolated from Patients Hospitalized in District Hospital in Central Poland in 2020

Antibiotics ◽

10.3390/antibiotics10040447 ◽

2021 ◽

Vol 10 (4) ◽

pp. 447

Author(s):

Barbara Kot ◽

Agata Grużewska ◽

Piotr Szweda ◽

Jolanta Wicha ◽

Urszula Parulska

Keyword(s):

Antibiotic Resistance ◽

Multidrug Resistant ◽

Diffusion Method ◽

Disk Diffusion Method ◽

Beta Lactamases ◽

E Coli ◽

Central Poland ◽

Resistance Patterns ◽

Extended Spectrum Beta Lactamases ◽

Tract Infections

The aim of this study was to determine antibiotic resistance patterns and the prevalence of uropathogenes causing urinary tract infections (UTIs) in patients hospitalized in January–June 2020 in central Poland. Antimicrobial susceptibility testing was performed using the disk-diffusion method. Escherichia coli (52.2%), Klebsiella pneumoniae (13.7%), Enterococcus faecalis (9.3%), E. faecium (6.2%), and Proteus mirabilis (4,3%) were most commonly isolated from urine samples. E. coli was significantly more frequent in women (58.6%) (p = 0.0089) and in the age group 0–18, while K. pneumoniae was more frequent in men (24.4%) (p = 0.0119) and in individuals aged 40–60 and >60. Gram-negative species showed resistance to ampicillin. K. pneumoniae were resistant to amoxicillin plus clavulanic acid (75.0%), piperacillin plus tazobactam (76.2%), cefotaxime (76.2%), cefuroxime (81.0%), ciprofloxacin (81.0%), and trimethoprim plus sulphamethoxazole (81.0%). Carbapenems were effective against all E. coli and P. mirabilis. Some K. pneumoniae (13.6%) produced metallo-β-lactamases (MBLs). E. coli (22.6%), K. pneumoniae (81.8%), and all E. faecium were multidrug-resistant (MDR). Some E. coli (26.2%), K. pneumoniae (63.6%), and P. mirabilis (14.3%) isolates produced extended-spectrum beta-lactamases (ESBL). Vancomycin-resistant E. faecium was also found. This study showed that the possibilities of UTIs therapy using available antibiotics become limited due to the increasing number of antibiotic-resistant uropathogens.

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Curcumin as Efflux Pump Inhibitor Agent for Enhancement Treatment Against Multidrug Resistant Pseudomonas aeruginosa Isolates

Iraqi Journal of Science ◽

10.24996/ijs.2020.61.1.6 ◽

2020 ◽

pp. 59-67

Author(s):

Sulaiman D. Sulaiman ◽

Ghusoon A. Abdulhasan

Keyword(s):

Pseudomonas Aeruginosa ◽

Inhibitory Concentration ◽

Efflux Pump ◽

Multidrug Resistant ◽

Diffusion Method ◽

Disc Diffusion Method ◽

Efflux Pump Inhibitor ◽

Before And After ◽

Chromogenic Agar ◽

Susceptibility Patterns

Pseudomonas aeruginosa is considered as a developing opportunistic nosocomial pathogen and is well-known for its multidrug resistance that can be efficiently treated by a combination of antibiotics andefflux pump inhibitors (EPI). Therefore, the purpose of this study was to investigate the effect of curcumin as an EPI for the enhancement of the effectiveness of antibiotics against multidrug resistant (MDR) isolates ofP. aeruginosa. Susceptibility patterns of suspected bacteria was determined using the disc diffusion method andresistant bacteria were identified using chromogenic agar and 16S rDNA. The effectsof curcuminon the enhancement of antibiotics’s activity was evaluated usingthe broth microdilution method.The susceptibility patterns for 50 (67.6%) suspectedP. aeruginosaisolates showed that 36 (72%) of these isolateswere resistant to one of the used antibiotics,whereasonly 21 (42%) were MDR. The highest percentage of resistance was observedtoceftazidime (66%) followed by ciprofloxacin and levofloxacin (40%). Only 35 isolates were specified by chromogenic agar and 16S rDNAas P. aeruginosa.The minimal inhibitory concentration (MIC) of 35 isolates for ciprofloxacin resistant was between 4 and128 µg/ml while for ceftazidime was between 64and 512 µg/ml. After the addition of 50 μg/ml curcumin with ciprofloxacin, there wasa significant increase in the sensitivity (p≤ 0.01) of 13 MDR P.aeroginosa isolates whereas no differences in the sensitivity to ceftazidime were recorded before and after addition ofcurcumin. In conclusion, the results of this study show that curcumin can decrease the MIC value of ciprofloxacin in MDR isolates of P. aeruginosaand can be used as a native compound to enhance the treatment of resistant isolates with ciprofloxacin.

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Prevalence of Virulence Genes and Drug Resistance Profiles of Pseudomonas aeruginosa Isolated From Clinical Specimens

Jundishapur Journal of Microbiology ◽

10.5812/jjm.118452 ◽

2021 ◽

Vol 14 (8) ◽

Author(s):

Seyed Ali Bazghandi ◽

Mohsen Arzanlou ◽

Hadi Peeridogaheh ◽

Hamid Vaez ◽

Amirhossein Sahebkar ◽

...

Keyword(s):

Pseudomonas Aeruginosa ◽

Drug Resistance ◽

Antibiotic Resistance ◽

Virulence Genes ◽

Virulence Gene ◽

Clinical Isolates ◽

Diffusion Method ◽

Disk Diffusion Method ◽

Clinical Specimens ◽

Resistance Rates

Background: Drug resistance and virulence genes are two key factors for the colonization of Pseudomonas aeruginosa in settings with high antibiotic pressure, such as hospitals, and the development of hospital-acquired infections. Objectives: The objective of this study was to investigate the prevalence of drug resistance and virulence gene profiles in clinical isolates of P. aeruginosa in Ardabil, Iran. Methods: A total of 84 P. aeruginosa isolates were collected from clinical specimens of Ardabil hospitals and confirmed using laboratory standard tests. The disk diffusion method was used for antibiotic susceptibility testing and polymerase chain reaction (PCR) for the identification of P. aeruginosa virulence genes. Results: The highest and the lowest antibiotic resistance rates of P. aeruginosa strains were against ticarcillin-clavulanate (94%) and doripenem (33.3%), respectively. In addition, the frequency of multidrug-resistant (MDR) P. aeruginosa was 55.9%. The prevalence of virulence factor genes was as follows: algD 84.5%, lasB 86.9%, plcH 86.9%, plcN 86.9%, exoU 56%, exoS 51.2%, toxA 81%, nan1 13.1%, and pilB 33.3%. A significant association was observed between resistance to some antibiotics and the prevalence of virulence genes in P. aeruginosa. Conclusions: Our results revealed a high prevalence of antibiotic resistance, especially MDR, and virulence-associated genes in clinical isolates of P. aeruginosa in Ardabil hospitals. Owing to the low resistance rates against doripenem, gentamicin, and tobramycin, these antibiotics are recommended for the treatment of infections caused by highly resistant and virulent P. aeruginosa strains.

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A Preliminary Study: Antibiotic Resistance Patterns of Escherichia coli and Enterococcus Species from Wildlife Species Subjected to Supplementary Feeding on Various South African Farms

Animals ◽

10.3390/ani10030396 ◽

2020 ◽

Vol 10 (3) ◽

pp. 396 ◽

Cited By ~ 1

Author(s):

Michaela Sannettha van den Honert ◽

Pieter Andries Gouws ◽

Louwrens Christiaan Hoffman

Keyword(s):

Escherichia Coli ◽

Antibiotic Resistance ◽

Supplementary Feeding ◽

Health Concern ◽

Diffusion Method ◽

Disk Diffusion Method ◽

E Coli ◽

Wildlife Species ◽

Human Contact ◽

Resistance Patterns

Studies have shown that antibiotic resistance among wild animals is becoming a public health concern, owing to increased contact and co-habitation with domestic animals that, in turn, results in increased human contact, indirectly and directly. This type of farming practice intensifies the likelihood of antibiotic resistant traits in microorganisms transferring between ecosystems which are linked via various transfer vectors, such as rivers and birds. This study aimed to determine whether the practice of wildlife supplementary feeding could have an influence on the antibiotic resistance of the bacteria harboured by the supplementary fed wildlife, and thus play a potential role in the dissemination of antibiotic resistance throughout nature. Escherichia coli and Enterococcus were isolated from the faeces of various wildlife species from seven different farms across South Africa. The Kirby-Bauer disk diffusion method was used according to the Clinical and Laboratory Standards Institute 2018 guidelines. The E. coli (F: 57%; N = 75% susceptible) and Enterococcus (F: 67%; N = 78% susceptible) isolates from the supplementary fed (F) wildlife were in general, found to be more frequently resistant to the selection of antibiotics than from those which were not supplementary fed (N), particularly towards tetracycline (E. coli F: 56%; N: 71%/Enterococcus F: 53%; N: 89% susceptible), ampicillin (F: 82%; N = 95% susceptible) and sulphafurazole (F: 68%; N = 98% susceptible). Interestingly, high resistance towards streptomycin was observed in the bacteria from both the supplementary fed (7% susceptible) and non-supplementary fed (6% susceptible) wildlife isolates. No resistance was found towards chloramphenicol and ceftazidime.

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Expression of Pseudomonas aeruginosa Multidrug Efflux Pumps MexA-MexB-OprM and MexC-MexD-OprJ in a Multidrug-Sensitive Escherichia coli Strain

Antimicrobial Agents and Chemotherapy ◽

10.1128/aac.42.1.65 ◽

1998 ◽

Vol 42 (1) ◽

pp. 65-71 ◽

Cited By ~ 119

Author(s):

Ramakrishnan Srikumar ◽

Tatiana Kon ◽

Naomasa Gotoh ◽

Keith Poole

Keyword(s):

Escherichia Coli ◽

Pseudomonas Aeruginosa ◽

Antibiotic Resistance ◽

Crystal Violet ◽

Efflux Pump ◽

Efflux Pumps ◽

Multidrug Efflux ◽

Efflux System ◽

E Coli ◽

Multidrug Efflux Pumps

ABSTRACT The mexCD-oprJ and mexAB-oprM operons encode components of two distinct multidrug efflux pumps inPseudomonas aeruginosa. To assess the contribution of individual components to antibiotic resistance and substrate specificity, these operons and their component genes were cloned and expressed in Escherichia coli. Western immunoblotting confirmed expression of the P. aeruginosa efflux pump components in E. coli strains expressing and deficient in the endogenous multidrug efflux system (AcrAB), although only the ΔacrAB strain, KZM120, demonstrated increased resistance to antibiotics in the presence of the P. aeruginosa efflux genes. E. coli KZM120 expressing MexAB-OprM showed increased resistance to quinolones, chloramphenicol, erythromycin, azithromycin, sodium dodecyl sulfate (SDS), crystal violet, novobiocin, and, significantly, several β-lactams, which is reminiscent of the operation of this pump in P. aeruginosa. This confirmed previous suggestions that MexAB-OprM provides a direct contribution to β-lactam resistance via the efflux of this group of antibiotics. An increase in antibiotic resistance, however, was not observed when MexAB or OprM alone was expressed in KZM120. Thus, despite the fact that β-lactams act within the periplasm, OprM alone is insufficient to provide resistance to these agents. E. coli KZM120 expressing MexCD-OprJ also showed increased resistance to quinolones, chloramphenicol, macrolides, SDS, and crystal violet, though not to most β-lactams or novobiocin, again somewhat reminiscent of the antibiotic resistance profile of MexCD-OprJ-expressing strains ofP. aeruginosa. Surprisingly, E. coli KZM120 expressing MexCD alone also showed an increase in resistance to these agents, while an OprJ-expressing KZM120 failed to demonstrate any increase in antibiotic resistance. MexCD-mediated resistance, however, was absent in a tolC mutant of KZM120, indicating that MexCD functions in KZM120 in conjunction with TolC, the previously identified outer membrane component of the AcrAB-TolC efflux system. These data confirm that a tripartite efflux pump is necessary for the efflux of all substrate antibiotics and that the P. aeruginosa multidrug efflux pumps are functional and retain their substrate specificity in E. coli.

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