Contribution of mexAB-oprM and mexXY (-oprA) efflux operons in antibiotic resistance of clinical Pseudomonas aeruginosa isolates in Tabriz, Iran

The frequency of AmpC overproduction, OprD downregulation and OprM efflux pump expression in Pseudomonas aeruginosa: A comprehensive meta-analysis

OBJECTIVES

Pseudomonas aeruginosa is a major opportunistic pathogen responsible for a wide range of infections. The emergence of antibiotic resistance in this pathogen poses a significant public health challenge. This study aims to conduct a comprehensive meta-analysis of studies conducted in Iran to determine the frequency of key antibiotic resistance mechanisms in Pseudomonas aeruginosa and their association with multidrug-resistant and extensively drug-resistant strains or pandrug-resistant strains.

METHODS

Systematic database searches encompassing literature up to June 2023 were undertaken. The selected studies centered on OprD downregulation, efflux pump (mexAB-OprM, mexXY-OprM) expression, and AmpC overproduction. Extracted data were synthesised in a meta-analysis for pooled frequency determination of each resistance mechanism.

RESULTS

In total, 24 studies were included. OprD downregulation exhibited a pooled frequency of 61%. Efflux pump component frequency ranged from 48% to 77.5%. AmpC overproduction was identified in 29.1% of isolates. Polymyxin B and colistin demonstrated lower antibiotic resistance rates, with pooled frequency of 1% and 1.6%, respectively. Conversely, resistance to other antibiotics ranged widely, with pooled frequency spanning 38.4% to 98.2%.

CONCLUSIONS

This study underscores the concerning frequency of diverse antibiotic resistance mechanisms in Pseudomonas aeruginosa strains from Iran. Concurrent OprD downregulation, mexAB, mexXY, OprM expression, and AmpC overproduction highlight the urgent need for stringent infection control and prudent antibiotic usage to curb the dissemination of these resistant strains.

PROSPERO

CRD42022379311.

Bile effects on the Pseudomonas aeruginosa pathogenesis in cystic fibrosis patients with gastroesophageal reflux

Gastroesophageal reflux (GER) occurs in most cystic fibrosis (CF) patients and is the primary source of bile aspiration in the airway tract of CF individuals. Aspirated bile is associated with the severity of lung diseases and chronic inflammation caused by Pseudomonas aeruginosa as the most common pathogen of CF respiratory tract infections. P. aeruginosa is equipped with several mechanisms to facilitate the infection process, including but not limited to the expression of virulence factors, biofilm formation, and antimicrobial resistance, all of which are under the strong regulation of quorum sensing (QS) mechanism. By increasing the expression of lasI, rhlI, and pqsA-E, bile exposure directly impacts the QS network. An increase in psl expression and pyocyanin production can promote biofilm formation. Along with the loss of flagella and reduced swarming motility, GER-derived bile can repress the expression of genes involved in creating an acute infection, such as expression of Type Three Secretion (T3SS), hydrogen cyanide (hcnABC), amidase (amiR), and phenazine (phzA-E). Inversely, to cause persistent infection, bile exposure can increase the Type Six Secretion System (T6SS) and efflux pump expression, which can trigger resistance to antibiotics such as colistin, polymyxin B, and erythromycin. This review will discuss the influence of aspirated bile on the pathogenesis, resistance, and persistence of P. aeruginosa in CF patients.

Biogenic synthesized copper oxide nanoparticles by Bacillus subtilis: Investigating antibacterial activity on the mexAB-oprM efflux pump genes and cytotoxic effect on MCF-7 cells

One of the main characteristics of Pseudomonas aeruginosa is remarkable intrinsic antibiotic resistance which is associated with production of β-lactamases and the expression of inducible efflux pumps. Nanoparticles (NPs) are a novel option for coping with this resistant bacteria. Hence, the aim of present study was production of CuO NPs via Bacillus subtilis and applied them to deal with resistant bacteria. For this purpose, first NPs were synthesized and were analyzed with different standard techniques containing scanning electron microscope, Fourier-transform infrared spectroscopy, and X-ray powder diffraction. Microdilution Broth Method and real-time polymerase chain reaction were used to antibacterial properties of the CuO NPs and expression of mexAB-oprM in clinical samples of P. aeruginosa, respectively. The cytotoxic effect of CuO NPs was also evaluated on MCF7 as a breast cancer cell line. Finally, the data were analyzed by one-way analysis of variance and Tukey's tests. The size of CuO NPs was in the range of 17-26 nm and showed antibacterial effect at <1000 μg/mL concentrations. Our evidence noted that the antibacterial effects of the CuO NPs occurred through the downregulation of mexAB-oprM and upregulation of mexR. The interesting point was that CuO NPs had an inhibitory effect on MCF7 cell lines with the optimal inhibition concentration at IC50 = 25.73 µg/mL. Therefore, CuO NPs can be considered as a promising medical candidate in the pharmaceutical industry.

Clinical characteristics and homology analysis of Staphylococcus aureus from would infection at a tertiary hospital in southern Zhejiang, China

OBJECTIVE

Staphylococcus aureus (S. aureus), especially Methicillin resistant S. aureus (MRSA), has been disseminated across communities and hospitals, associated with severe infections and organ failure. In order to understand the clinical epidemiological characteristics of S. aureus stains in the First Affiliated Hospital of Wenzhou Medical University in 2018, the prevalence and the drug resistance of S. aureus stains were investigated, for improving the clinical effective prevention and control of S. aureus infection.

METHODS

A total of 105 S. aureus isolates were separated from wound infection of inpatients in the First Affiliated Hospital of Wenzhou Medical University in 2018, and the department distributions and drug resistance of the isolates were analyzed. The genotyping homology analysis was conducted through the random amplified polymorphic DNA typing (RAPD-PCR) coupled with NTSYS cluster analysis.

RESULTS

Among the 105 strains of S. aureus, 31 isolates were MRSA. The prevalence of MRSA among inpatients in the Departments of Burn, Trauma, Orthopedics, Nephrology and Neurosurgery were 35.48%, 19.35%, 9.68%, 6.45%, and 29.03%, respectively. Among the 105 strains, 35.24% strains were the hospital-acquired infections (HAI) and 64.76% strains were community-acquired infections (CAI). DNA genotyping of the 105 S. aureus strains showed seventeen different groups, most of which were type I, type VII, type IX, and type VII, the others were scattered.

CONCLUSION

This study highlights the prevalence of S. aureus strains in the First Affiliated Hospital of Wenzhou Medical University in 2018. The emergence and mutation of the strains should be closely monitored for the prevention and control of the S. aureus infection and transmission in the nosocomial settings.

The Art of War with Pseudomonas aeruginosa: Targeting Mex Efflux Pumps Directly to Strategically Enhance Antipseudomonal Drug Efficacy

Pseudomonas aeruginosa (P. aeruginosa) poses a grave clinical challenge due to its multidrug resistance (MDR) phenotype, leading to severe and life-threatening infections. This bacterium exhibits both intrinsic resistance to various antipseudomonal agents and acquired resistance against nearly all available antibiotics, contributing to its MDR phenotype. Multiple mechanisms, including enzyme production, loss of outer membrane proteins, target mutations, and multidrug efflux systems, contribute to its antimicrobial resistance. The clinical importance of addressing MDR in P. aeruginosa is paramount, and one pivotal determinant is the resistance-nodulation-division (RND) family of drug/proton antiporters, notably the Mex efflux pumps. These pumps function as crucial defenders, reinforcing the emergence of extensively drug-resistant (XDR) and pandrug-resistant (PDR) strains, which underscores the urgency of the situation. Overcoming this challenge necessitates the exploration and development of potent efflux pump inhibitors (EPIs) to restore the efficacy of existing antipseudomonal drugs. By effectively countering or bypassing efflux activities, EPIs hold tremendous potential for restoring the antibacterial activity against P. aeruginosa and other Gram-negative pathogens. This review focuses on concurrent MDR, highlighting the clinical significance of efflux pumps, particularly the Mex efflux pumps, in driving MDR. It explores promising EPIs and delves into the structural characteristics of the MexB subunit and its substrate binding sites.

Role of MexAB-OprM efflux pump in the emergence of multidrug-resistant clinical isolates of Pseudomonas aeruginosa in Mazandaran province of Iran

BACKGROUND

Multidrug-resistant clinical isolates can cause many therapeutic problems. The MexAB-OprM efflux pump plays a significant role in expelling toxins and drugs from the bacterial cells resulting in multidrug-resistant Pseudomonas aeruginosa isolates.

PURPOSE

This study aimed to investigate the effect of the MexAB-OprM efflux pump in the emergence of multidrug-resistant clinical isolates of P. aeruginosa.

METHODS AND RESULTS

For the present study, 100 clinical isolates of P. aeruginosa were collected from different wards of teaching hospitals (2018-2019). After confirmation and detection of bacteria by standard methods, the antibiotic resistance pattern of the isolates was determined by the disk agar diffusion method. Also, the minimum inhibitory concentration (MIC) of ciprofloxacin was measured in the presence and absence of phenylalanine arginine beta-naphthylamide by the broth microdilution method. Then, the real-time PCR was used to investigate the expression level of the mexB gene compared to the standard PAO1 strain. Forty-one/100 isolates exhibited multidrug-resistant phenotype (MDR), while piperacillin-tazobactam and levofloxacin were the most and least effective antibiotics tested, respectively. Also, 54/100 isolates showed no increased expression of mexB gene compared to the standard PAO1 strain. However, among the 41 MDR isolates, 12 (29.26%) showed a more than three-fold increase in the expression level of the mexB gene. In this study, a significant relationship was observed between the resistance to tested antibiotics in MDR strains and the increased expression of the mexB gene.

CONCLUSION

We found that increasing the expression of the mexB gene can cause the emergence of multidrug-resistant strains by increasing the minimum inhibitory concentration of the antibiotics. Then, we need to evaluate the resistance mechanisms separately in different area of a country to improve the antibiotic stewardship.

The resistance mechanisms of bacteria against ciprofloxacin and new approaches for enhancing the efficacy of this antibiotic

For around three decades, the fluoroquinolone (FQ) antibiotic ciprofloxacin has been used to treat a range of diseases, including chronic otorrhea, endocarditis, lower respiratory tract, gastrointestinal, skin and soft tissue, and urinary tract infections. Ciprofloxacin's main mode of action is to stop DNA replication by blocking the A subunit of DNA gyrase and having an extra impact on the substances in cell walls. Available in intravenous and oral formulations, ciprofloxacin reaches therapeutic concentrations in the majority of tissues and bodily fluids with a low possibility for side effects. Despite the outstanding qualities of this antibiotic, Salmonella typhi, Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa have all shown an increase in ciprofloxacin resistance over time. The rise of infections that are resistant to ciprofloxacin shows that new pharmacological synergisms and derivatives are required. To this end, ciprofloxacin may be more effective against the biofilm community of microorganisms and multi-drug resistant isolates when combined with a variety of antibacterial agents, such as antibiotics from various classes, nanoparticles, natural products, bacteriophages, and photodynamic therapy. This review focuses on the resistance mechanisms of bacteria against ciprofloxacin and new approaches for enhancing its efficacy.

Metabolomics and proteomics analyses revealed mechanistic insights on the antimicrobial activity of epigallocatechin gallate against Streptococcus suis

Streptococcus suis (S. suis) is a highly virulent zoonotic pathogen and causes severe economic losses to the swine industry worldwide. Public health security is also threatened by the rapidly growing antimicrobial resistance in S. suis. Therefore, there is an urgent need to develop new and safe antibacterial alternatives against S. suis. The green tea polyphenol epigallocatechin gallate (EGCG) with a number of potential health benefits is known for its antibacterial effect; however, the mechanism of its bactericidal action remains unclear. In the present, EGCG at minimal inhibitory concentration (MIC) showed significant inhibitory effects on S. suis growth, hemolytic activity, and biofilm formation, and caused damage to S. suis cells in vitro. EGCG also reduced S. suis pathogenicity in Galleria mellonella larvae in vivo. Metabolomics and proteomics analyses were performed to investigate the underlying mechanism of antibacterial activity of EGCG at MIC. Many differentially expressed proteins involved in DNA replication, synthesis of cell wall, and cell membrane, and virulence were down-regulated after the treatment of S. suis with EGCG. EGCG not only significantly reduced the hemolytic activity of S. suis but also down-regulated the expression of suilysin (Sly). The top three shared KEGG pathways between metabolomics and proteomics analysis were ABC transporters, glycolysis/gluconeogenesis, and aminoacyl-tRNA biosynthesis. Taken together, these data suggest that EGCG could be a potential phytochemical compound for treating S. suis infection.

Bacterial Multidrug Efflux Pumps at the Frontline of Antimicrobial Resistance: An Overview

Multidrug efflux pumps function at the frontline to protect bacteria against antimicrobials by decreasing the intracellular concentration of drugs. This protective barrier consists of a series of transporter proteins, which are located in the bacterial cell membrane and periplasm and remove diverse extraneous substrates, including antimicrobials, organic solvents, toxic heavy metals, etc., from bacterial cells. This review systematically and comprehensively summarizes the functions of multiple efflux pumps families and discusses their potential applications. The biological functions of efflux pumps including their promotion of multidrug resistance, biofilm formation, quorum sensing, and survival and pathogenicity of bacteria are elucidated. The potential applications of efflux pump-related genes/proteins for the detection of antibiotic residues and antimicrobial resistance are also analyzed. Last but not least, efflux pump inhibitors, especially those of plant origin, are discussed.

Therapeutic Strategies for Emerging Multidrug-Resistant Pseudomonas aeruginosa

Multidrug-resistant (MDR) and extensively drug-resistant (XDR) Pseudomonas aeruginosa isolates are frequent causes of serious nosocomial infections that may compromise the selection of antimicrobial therapy. The goal of this review is to summarize recent epidemiologic, microbiologic, and clinical data pertinent to the therapeutic management of patients with infections caused by MDR/XDR-P. aeruginosa. Historically, conventional antipseudomonal β-lactam antibiotics have been used for the empiric treatment of MDR/XDR-P. aeruginosa. Owing to the remarkable capacity of P. aeruginosa to confer resistance via multiple mechanisms, these traditional therapies are often rendered ineffective. To increase the likelihood of administering empiric antipseudomonal therapy with in vitro activity, a second agent from a different antibiotic class is often administered concomitantly with a traditional antipseudomonal β-lactam. However, combination therapy may pose an increased risk of antibiotic toxicity and secondary infection, notably, Clostridioides difficile. Multiple novel agents that demonstrate in vitro activity against MDR-P. aeruginosa (e.g., β-lactam/β-lactamase inhibitor combinations and cefiderocol) have been recently granted US Food and Drug Administration (FDA) approval and are promising additions to the antipseudomonal armamentarium. Even so, comparative clinical data pertaining to these novel agents is sparse, and concerns surrounding the scarcity of antibiotics active against refractory MDR/XDR-P. aeruginosa necessitates continued assessment of alternative therapies. This is particularly important in patients with cystic fibrosis (CF) who may be chronically colonized and suffer from recurrent infections and disease exacerbations due in part to limited efficacious antipseudomonal agents. Bacteriophages represent a promising candidate for combatting recurrent and refractory infections with their ability to target specific host bacteria and circumvent traditional mechanisms of antibiotic resistance seen in MDR/XDR-P. aeruginosa. Future goals for the management of these infections include increased comparator clinical data of novel agents to determine in what scenario certain agents may be preferred over others. Until then, appropriate treatment of these infections requires a thorough evaluation of patient- and infection-specific factors to guide empiric and definitive therapeutic decisions.

In-vitro Effect of Imipenem, Fosfomycin, Colistin, and Gentamicin Combination against Carbapenem-resistant and Biofilm-forming Pseudomonas aeruginosa Isolated from Burn Patients

The aim of this study was to investigate in-vitro antibacterial and antibiofilm effect of colistin, imipenem, gentamicin, and fosfomycin alone and the various combinations against carbapenem-resistant Pseudomonas aeruginosa (P. aeruginosa). Eight carbapenem-resistant and biofilm-forming P. aeruginosa isolates from burn patients were collected. The mechanisms of resistance to carbapenem were determined by the phenotypic, PCR, and Real-Time PCR assays. The minimum inhibitory concentration (MIC) of antimicrobial agents was determined by the broth micro dilution. To detect any inhibitory effect of antibiotics against the biofilm, the biofilm inhibitory concentration was determined. To detect synergetic effects of the combinations of antibiotics, the checkerboard assay and the fractional inhibitory concentration (FIC) were used. The highest synergic effect was observed in colistin/fosfomycin and gentamicin/fosfomycin (5 of 8 isolates), and the lowest synergic effect was found in gentamicin/imipenem and colistin/gentamicin (1 of 8 isolates). Colistin/fosfomycin, imipenem/fosfomycin, colistin/imipenem, gentamicin/fosfomycin, and gentamicin/imipenem were shown synergic effect for 3, 2, 2, 2 and 1 isolates, respectively. The combination of antibiotics had different effects on biofilm and planktonic forms of P. aeruginosa. Therefore, a separate determination of inhibitory effects of the antibiotic in the combination is necessary. Fosfomycin/colistin and fosfomycin/gentamicin were more effective against planktonic form and fosfomycin/colistin against biofilm forms.

Molecular Detection of Carbapenemases and Extended-Spectrum β-Lactamases-Encoding Genes in Clinical Isolates of Pseudomonas aeruginosa in Iran

Background: Pseudomonas aeruginosa is a unique Gram-negative opportunistic pathogen that is the leading cause of nosocomial infections. Objectives: This study aimed to investigate the prevalence of the main carbapenemase and extended-spectrum β-lactamases encoding genes in P. aeruginosa clinical isolates. Methods: In the present study, we collected 85 P. aeruginosa clinical isolates from different wards of three military hospitals in Tehran, Iran. We used disk diffusion and agar dilution methods to determine resistance to 12 different antibiotics in these isolates. Also, we assessed the blaIMP, blaVIM, blaSHV, blaTEM, and blaCTX genes by polymerase chain reaction methods among all isolates. Results: Our results revealed that all isolates were resistant to two antibiotics, and 76 (89.4%) of isolates were multidrug-resistant. We observed maximum and minimum resistance rates against ticarcillin (n = 77; 90.5%) and colistin (n = 7; 8.2%), respectively. The blaVIM, blaIPM, blaTEM, blaSHV, and blaCTX genes were harbored by 44 (51.8%), 20 (23.5%), 41 (48.2%), 24 (28.2%), and 16 (18.8%) isolates, respectively. Conclusions: The resistance rate among P. aeruginosa strains is significantly increasing that causes nosocomial infections due to different mechanisms, including the high frequency of metallo-β-lactamases and extended-spectrum β-lactamases genes.

Role of RND Efflux Pumps in Drug Resistance of Cystic Fibrosis Pathogens

Drug resistance represents a great concern among people with cystic fibrosis (CF), due to the recurrent and prolonged antibiotic therapy they should often undergo. Among Multi Drug Resistance (MDR) determinants, Resistance-Nodulation-cell Division (RND) efflux pumps have been reported as the main contributors, due to their ability to extrude a wide variety of molecules out of the bacterial cell. In this review, we summarize the principal RND efflux pump families described in CF pathogens, focusing on the main Gram-negative bacterial species (Pseudomonas aeruginosa, Burkholderia cenocepacia, Achromobacter xylosoxidans, Stenotrophomonas maltophilia) for which a predominant role of RND pumps has been associated to MDR phenotypes.

Molecular epidemiology and carbapenem resistance of Pseudomonas aeruginosa isolated from patients with burns

OBJECTIVE

The aim of this study was to investigate the molecular epidemiology and carbapenem resistance mechanisms of Pseudomonas aeruginosa isolated from patients with burns in Azerbaijan, Iran.

METHOD

Pseudomonas aeruginosa was isolated from 38 patients with burns. Disk diffusion and agar dilution methods were used to determine antibiotic susceptibility patterns. The overproduction of AmpC β-lactamase and efflux pumps were detected by phenotypic methods. The presence of carbapenemase-encoding genes was detected by multiplex polymerase chain reaction (PCR). Expression of the OprD gene and MexAB efflux pumps were also evaluated with real-time PCR. Random amplified polymorphic DNA typing (RAPD-PCR) was used for genotyping of carbapenem-resistant Pseudomonas aeruginosa (CRPA).

RESULTS

Minimum inhibitory concentration (MIC) assays demonstrated high levels of resistance to all classes of antibiotics except colistin and polymyxin B. The initial screening by carbapenem disks indicated 24 isolates (63.15%) as CRPA. Different mechanisms of carbapenem resistance were observed, including carbapenemase production (8.4%), overexpression of AmpC (25%) and decreased expression of OprD (75%). The overexpression of MexAB efflux pumps was detected in 19 (79.1%) isolates by phenotypic assay or real-time PCR. The resistance to carbapenem was multifactorial in most cases (58.3%). The RAPD genotyping revealed different patterns with nine clusters.

CONCLUSION

According to our results, the prevalence of CRPA is at an alarming level. Our results did not demonstrate an epidemic clone. The most common mechanism of carbapenem resistance was decreased expression of OprD. Therefore, we suggest a reconsideration in the management of CRPA infections of patients in our burn care hospital in Azerbaijan, Iran.

Gene-Gene Interactions Dictate Ciprofloxacin Resistance in Pseudomonas aeruginosa and Facilitate Prediction of Resistance Phenotype from Genome Sequence Data

Ciprofloxacin is one of the most widely used antibiotics for treating Pseudomonas aeruginosa infections. However, P. aeruginosa acquires mutations that confer ciprofloxacin resistance, making treatment more difficult. Resistance is multifactorial, with mutations in multiple genes influencing the resistance phenotype. However, the contributions of individual mutations and mutation combinations to the amounts of ciprofloxacin that P. aeruginosa can tolerate are not well understood. Engineering P. aeruginosa strain PAO1 to contain mutations in any one of the resistance-associated genes gyrA, nfxB, rnfC, parC, and parE showed that only gyrA mutations increased the MIC for ciprofloxacin. Mutations in parC and parE increased the MIC of a gyrA mutant, making the bacteria ciprofloxacin resistant. Mutations in nfxB and rnfC increased the MIC, conferring resistance, only if both were mutated in a gyrA background. Mutations in all of gyrA, nfxB, rnfC, and parC/E further increased the MIC. These findings reveal an epistatic network of gene-gene interactions in ciprofloxacin resistance. We used this information to predict ciprofloxacin resistance/susceptibility for 274 isolates of P. aeruginosa from their genome sequences. Antibiotic susceptibility profiles were predicted correctly for 84% of the isolates. The majority of isolates for which prediction was unsuccessful were ciprofloxacin resistant, demonstrating the involvement of additional as yet unidentified genes and mutations in resistance. Our data show that gene-gene interactions can play an important role in antibiotic resistance and can be successfully incorporated into models predicting resistance phenotype.

The Building Blocks of Antimicrobial Resistance in Pseudomonas aeruginosa: Implications for Current Resistance-Breaking Therapies

P. aeruginosa is classified as a priority one pathogen by the World Health Organisation, and new drugs are urgently needed, due to the emergence of multidrug-resistant (MDR) strains. Antimicrobial-resistant nosocomial pathogens such as P. aeruginosa pose unwavering and increasing threats. Antimicrobial stewardship has been a challenge during the COVID-19 pandemic, with a majority of those hospitalized with SARS-CoV2 infection given antibiotics as a safeguard against secondary bacterial infection. This increased usage, along with increased handling of sanitizers and disinfectants globally, may further accelerate the development and spread of cross-resistance to antibiotics. In addition, P. aeruginosa is the primary causative agent of morbidity and mortality in people with the life-shortening genetic disease cystic fibrosis (CF). Prolonged periods of selective pressure, associated with extended antibiotic treatment and the actions of host immune effectors, results in widespread adaptive and acquired resistance in P. aeruginosa found colonizing the lungs of people with CF. This review discusses the arsenal of resistance mechanisms utilized by P. aeruginosa, how these operate under high-stress environments such as the CF lung and how their interconnectedness can result in resistance to multiple antibiotic classes. Intrinsic, adaptive and acquired resistance mechanisms will be described, with a focus on how each layer of resistance can serve as a building block, contributing to multi-tiered resistance to antimicrobial activity. Recent progress in the development of anti-resistance adjuvant therapies, targeting one or more of these building blocks, should lead to novel strategies for combatting multidrug resistant P. aeruginosa. Anti-resistance adjuvant therapy holds great promise, not least because resistance against such therapeutics is predicted to be rare. The non-bactericidal nature of anti-resistance adjuvants reduce the selective pressures that drive resistance. Anti-resistance adjuvant therapy may also be advantageous in facilitating efficacious use of traditional antimicrobials, through enhanced penetration of the antibiotic into the bacterial cell. Promising anti-resistance adjuvant therapeutics and targets will be described, and key remaining challenges highlighted. As antimicrobial stewardship becomes more challenging in an era of emerging and re-emerging infectious diseases and global conflict, innovation in antibiotic adjuvant therapy can play an important role in extending the shelf-life of our existing antimicrobial therapeutic agents.

Antimicrobial and antibiofilm activities of meropenem loaded-mesoporous silica nanoparticles against carbapenem-resistant Pseudomonas aeruginosa

The aims of the present study were the determination of antimicrobial and antibiofilm effects of meropenem-loaded mesoporous silica nanoparticles (MSNs) on carbapenem resistant Pseudomonas aeruginosa (P. aeruginosa) and cytotoxicity properties in vitro. The meropenem-loaded MSNs had shown antibacterial and biofilm inhibitory activities on all isolates at different levels lower than MICs and BICs of meropenem. The viability of HC-04 cells treated with serial concentrations as MICs and BICs of meropenem-loaded MSNs was 92-100%. According to the obtained results, meropenem-loaded MSNs display the significant antibacterial and antibiofilm effects against carbapenem resistant and biofilm forming P. aeruginosa and low cell toxicity in vitro. Then, the prepared system can be an appropriate option for the delivery of carbapenem for further evaluation in vivo assays.

Expression of RND efflux pumps mediated antibiotic resistance in Pseudomonas aeruginosa clinical strains

Resistance-Nodulation-Division (RND) efflux pumps are responsible for multidrug resistance in Pseudomonas aeruginosa. The present study aimed to evaluate the overexpression of RND efflux pumps and its role in the antibiotic resistance of P. aeruginosa clinical isolates. A number of 122 isolates were obtained from three military hospitals in Tehran, Iran. In order to determine the antibiotic resistance, the isolates were identified and assessed by the disk diffusion and agar dilution methods. This study investigated the gene expression of four multi-drug efflux pump systems (MexAB-OprM, MexCD-OprJ, MexEF-OprN and MexXY (-OprA)) and its correlation with antibiotic resistance. The isolates indicated that the highest resistance rate was against ticarcillin (80%), followed by ciprofloxacin (74%) and meropenem (71%). Most of them expressed mexB (69%), mexC (28.7%), mexE (43.4%), and mexY (74.6%), suggesting that mexB and mexY were highly expressed in the studied strains. The overexpression of mexB and mexY was significantly more prevalent in the ICU wards (p = 0.033). Furthermore, there was a significant correlation between the expression of RND-type efflux pumps and the resistance to most anti-pseudomonal antibiotics.

Evaluation of MexAB-OprM efflux pump and determination of antimicrobial susceptibility in Pseudomonas aeruginosa human and veterinary isolates

Pseudomonas aeruginosa could cause serious infections in hospitals and is highlighted as a source of financial problems in farms. The revelation of drug resistant, particularly multi-drug resistant (MDR) P. aeruginosa is important around the world. The efflux pump activity is identified as one of the most important intrinsic resistant mechanisms in P. aeruginosa. A total of 96 P. aeruginosa isolates from inpatient and animal sources were tested for antimicrobial susceptibility and subjected to multiplex PCR (mPCR) assay to detect MexAB-OprM efflux pump system. The human isolates have shown the highest resistance against cefazolin, ampicillin, nalidixic acid, trimethoprim/sulfamethoxazole, cephalothin, oxacillin (100%). All farm animal isolates were resistant to cefazolin, kanamycin, amoxicillin clavulanic acid, and cephalothin (100%). In both isolate groups, the presence of MexA was more common than that of MexB. MexAB-OprM was demonstrated as a valuable mechanism in P. aeruginosa antimicrobial resistant strains.

Bacterial ecology and antibiotic resistance mechanisms of isolated resistant strains from diabetic foot infections in the north west of Algeria

BACKGROUND

In front of the polymorphic bacterial ecology and antibiotic resistance in diabetic patients with foot infections and good patient care, collaboration between clinicians and microbiologists is needed to improve assessment and management of patients with this pathology.

OBJECTIVE

This study was designed to characterize the bacterial ecology of diabetic foot infection (DFIs) and to determine the different mechanisms of resistance involved.

METHODS

In this study bacterial strains and antibiotic resistance profiles were determined from diabetic foot infections patients (n = 117). The identification of resistance mechanisms, such as penicillinase and/or extended-spectrum β-lactamase production (ESBL), methicillin-resistant Staphylococcus aureus (MRSA) and efflux pump over-expression were performed.

RESULTS

A high prevalence of Gram-negative bacteria (61%) with Escherichia coli, and other Enterobacteriaceae and Pseudomonas aeruginosa being the predominant isolates. Gram positive bacteria mainly represented by Staphylococcus aureus accounted for 39% of the isolates. 93.5% of the Enterobacteriaceae were resistant to, at least, one molecule in the β-lactam family, while the majority of the Staphylococci were resistant to penicillin G and tetracycline (93.3% and 71.7%). The majority of non-fermenting Gram negative bacteria were also resistant to fluoroquinolones. β-lactamase detection tests revealed the presence of extended-spectrum β-lactamase in 43.5% of the Enterobacteriaceae, while methicillin-resistant Staphylococcus aureus represented 18.2% of the isolates. Additionally, 50.9% of non-fermenting Gram negative bacteria were overproducing efflux pumps.

CONCLUSION

All Acinetobacter Baumannii were Multidrug-Resistant (MDR), as the majority of Staphylococci, and Enterobacteriaceae. These results should be taken into account by the clinician in the prescription of probabilistic antibiotic therapy in this context.

Efficacy of a ciprofloxacin/amikacin combination against planktonic and biofilm cultures of susceptible and low-level resistant Pseudomonas aeruginosa

BACKGROUND

Eradicating bacterial biofilm without mechanical dispersion remains a challenge. Combination therapy has been suggested as a suitable strategy to eradicate biofilm.

OBJECTIVES

To evaluate the efficacy of a ciprofloxacin/amikacin combination in a model of in vitro Pseudomonas aeruginosa biofilm.

METHODS

The antibacterial activity of ciprofloxacin and amikacin (alone, in combination and successively) was evaluated by planktonic and biofilm time-kill assays against five P. aeruginosa strains: PAO1, a WT clinical strain and three clinical strains overexpressing the efflux pumps MexAB-OprM (AB), MexXY-OprM (XY) and MexCD-OprJ (CD), respectively. Amikacin MIC was 16 mg/L for XY and ciprofloxacin MIC was 0.5 mg/L for CD. The other strains were fully susceptible to ciprofloxacin and amikacin. The numbers of total and resistant cells were determined.

RESULTS

In planktonic cultures, regrowth of high-level resistant mutants was observed when CD was exposed to ciprofloxacin alone and XY to amikacin alone. Eradication was obtained with ciprofloxacin or amikacin in the other strains, or with the combination in XY and CD strains. In biofilm, bactericidal reduction after 8 h followed by a mean 4 log10 cfu/mL plateau in all strains and for all regimens was noticed. No regrowth of resistant mutants was observed whatever the antibiotic regimen. The bacterial reduction obtained with a second antibiotic used simultaneously or consecutively was not significant.

CONCLUSIONS

The ciprofloxacin/amikacin combination prevented the emergence of resistant mutants in low-level resistant strains in planktonic cultures. Biofilm persister cells were not eradicated, either with monotherapy or with the combination.

Characterization of carbapenem-resistant but cephalosporin-susceptible Pseudomonas aeruginosa

In this study, mechanisms of carbapenem resistance in carbapenem-resistant but cephalosporin-susceptible (Car-R/Ceph-S) Pseudomonas aeruginosa were investigated. A total of 243 P. aeruginosa isolates were studied. The disk diffusion and agar dilution methods were used for determination of antibiotic susceptibility patterns. AmpC and efflux pump overproductions were detected by phenotypic methods. The presence of carbapenemase-encoding genes was detected by polymerase chain reaction (PCR). The expression of OprD, MexAB-OprM, and MexXY-OprM efflux pumps was assessed by real-time PCR. According to disk diffusion method, altogether 116 P. aeruginosa isolates (47.7%) were carbapenem-resistant and among them, 23 isolates (19.8%) were cephalosporin-susceptible. Carbapenemase producer was not detected. Overexpression of AmpC was detected in one (4.3%) isolate that was ceftazidime-susceptible but cefepime-resistant. Overexpression of MexAB-OprM and MexXY-OprM efflux pumps was detected in 12 (60.9%) and 16 (68.8%) of isolates, respectively. A total of 16 (68.8%) isolates showed decreased expression of OprD. The Car-R/Ceph-S P. aeruginosa did not develop by carbapenemase production. The resistance to carbapenem was mediated in our clinical isolates by decreased expression of OprD and overexpression of MexAB-OprM and MexXY-OprM efflux systems or the combination of these mechanisms.

Changes in the resistance and epidemiological characteristics of Pseudomonas aeruginosa during a ten-year period

PURPOSE

The aim of this study was to investigate the changes over a ten-year period in the resistance and epidemiological characteristics of Pseudomonas aeruginosa strains isolated from the Department of Respiratory in Southwest Hospital.

METHODS

Antimicrobial resistance was detected using the plate double dilution method. PCR amplification and sequencing were performed to evaluate the carbapenemase genes and the oprD gene. Bacterial genotypes were analyzed by multilocus sequence typing (MLST). Quantitative real-time PCR experiments were performed to assess the expression of efflux pump (mexA and mexX) and ampC gene.

RESULTS

We collected 233 P. aeruginosa isolates in 2006-2007 and 128 isolates in 2016-2017. The resistance rate of P. aeruginosa strains to the tested antibiotics was significantly lower in 2016-2017 than in 2006-2007. The MLST results showed 27 genotypes in 2006-2007 and 18 genotypes in 2016-2017. ST235 was the most prevalent sequence type, and there was no significant change in the genotypes over the ten-year period. Both VIM-2 and IMP-4 genes were found in 2006-2007, whereas only IMP-4 was found in 2016-2017. The oprD mutational inactivation was the main factor responsible for carbapenem resistance, and the overexpression of mexX had a good correlation with aminoglycoside resistance.

CONCLUSION

These results indicated that the antibiotic resistance of P. aeruginosa in our respiratory department decreased. The loss of oprD gene was the main mechanism of carbapenem resistance, and mexX overexpression was the major contributing factor to aminoglycoside resistance.

Proteomic Analysis of Alterations in Aeromonas hydrophila Outer Membrane Proteins in Response to Oxytetracycline Stress

In Gram-negative bacteria, the outer membrane proteins (OMPs) perform a crucial role in antibiotic resistance, but it is largely unknown how they behave in response to antibiotic stress. In this study, we treated Aeromonas hydrophila with two different doses of oxytetracycline (OXY) to induce antibiotic stress. Proteins were isolated from sarcosine-insoluble fractions and quantitatively examined by using tandem mass tag labeling-based mass spectrometry to identify differentially expressed proteins. As a result, we identified 125 differential proteins in the 5 μg/ml OXY treatment group, including 20 OMPs, and 150 proteins from the 10 μg/ml OXY group, including 22 OMPs. Gene ontology analysis showed that translation-related proteins, including 30S and 50S ribosome proteins, were significantly enriched in increasing abundance under OXY stress; whereas the downregulated proteins were associated with the transport process, such as maltodextrin, maltose, and oligosaccharide transport. We then validated a subset of the identified differential proteins by using Western blot and quantitative polymerase chain reaction analyses. Finally, the quantitative real-time PCR (qPCR) results showed that at the transcription level, the expression of five OMP genes, including AHA_1280 (protein name A0KHS0), AHA_1281 (A0KHS1), AHA_1447 (A0KI84, BamE), AHA_1861 (A0KJE1), and AHA_2766 (A0KLX3), and one lipoprotein gene AHA_1740 (A0KJ25) was consistent with proteomic results under 5 and 10 μg/ml OXY treatment, respectively. In addition, the Western blotting also demonstrated that two altered OMP proteins A0KHS1 and A0KHH2 were upregulated for both OXY treatment groups. This study indicates that bacteria regulate the expression levels of OMPs in response to antibiotic stress and further contribute to our understanding of the functions of OMPs in antibiotic resistance. Moreover, our results suggest that the upregulation of translation and downregulation of the transport process may affect bacterial fitness during OXY stress. These findings may provide new clues to the antibiotic resistance mechanism in A. hydrophila.

An efflux pump (MexAB-OprM) of Pseudomonas aeruginosa is associated with antibacterial activity of Epigallocatechin-3-gallate (EGCG)

BACKGROUND

Pseudomonas aeruginosa is a notorious multidrug resistant nosocomial pathogen. An efflux pump (MexAB-OprM) is the main contributor to the multidrug resistance in clinical isolates of P. aeruginosa. Epigallocatechin-3-gallate (EGCG), a polyphenolic compound extracted from green tea, exhibits antibacterial activity. It is unclear that molecular details of the antibacterial activity of EGCG, EGCG-effect on antibiotic susceptibility, and clinical relevance of EGCG in bacteria.

PURPOSE

This study aimed to determine the roles of the efflux pump and an efflux pump inhibitor (phenylalanine-arginine β-naphthylamide; PAβN) in the antibacterial activity of EGCG and the EGCG-effect on antibiotic susceptibility.

METHODS

Twenty-two multidrug resistant clinical isolates of P. aeruginosa and a wild type P. aeruginosa PAO1 were used to determine antibacterial activity of EGCG and EGCG-effect on antibiotic susceptibility. An efflux pump (MexAB-OPrM) mutant strain, its complemented strain carrying an intact mexAB-oprM, and their parental strain were used to determine roles of MexAB-OprM in the antibacterial activity of EGCG and EGCG-mediated antibiotic susceptibility. PAβN was also used to evaluate EGCG as a possible efflux pump inhibitor.

RESULTS

EGCG inhibited cellular growth and killed 100% of cells at 64-512 µg/ml and at 256-1024 µg/ml, respectively, in all tested 22 clinical isolates including the wild type strain. A subinhibitory concentration of EGCG significantly enhanced susceptibility to antibiotics, unexceptionally to chloramphenicol and tetracyclines (≥4-fold) of the clinical isolates. Both the antibacterial activity of EGCG and the EGCG-mediated antibiotic susceptibility were enhanced more in the efflux pump mutant strain (mexB::Gm) than the parental strain, suggesting additionally accumulated-EGCG produced the more antibacterial activity in the mutant strain. EGCG was synergistically interacted with PAβN with enhancing susceptibility to all tested antibiotics (up to >500-fold) at higher levels than either EGCG alone or PAβN alone, suggesting EGCG may also inhibit the efflux pump with additional accumulation of the antibiotics.

CONCLUSION

The results demonstrate that EGCG exhibits antibacterial activity and enhances antibiotic effects against clinical isolates of P. aeruginosa. EGCG may inhibit the efflux pump (MexAB-OprM) through which are associated with the antibacterial activity of EGCG and the EGCG-mediated antibiotic susceptibility in P. aeruginosa.

Role of MexAB-OprM and MexXY-OprM efflux pumps and class 1 integrons in resistance to antibiotics in burn and Intensive Care Unit isolates of Pseudomonas aeruginosa

BACKGROUND

The overexpression of efflux pumps and existence of class 1 integrons are the most important mechanisms that contribute to antimicrobial resistance in Pseudomonas aeruginosa especially in burn and Intensive Care Units (ICUs). The present study evaluated the role of MexAB-OprM and MexXY-OprM efflux pumps and class 1 integrons in resistance to antibiotics in burn and ICU isolates of P. aeruginosa.

METHODS

Fifteen burn and forty-two ICU isolates were obtained from four hospitals in Northwest Iran. The isolates were identified and evaluated by the disk diffusion and agar dilution methods for determining antibiotic resistances. The presence of class 1 integrons and associated resistance gene cassettes were detected by PCR and sequencing of the products. The expression levels of efflux pumps were evaluated by phenotypic and genotypic (Quantitative Real-time PCR) methods. The isolates were genotyped by Random Amplified Polymorphic DNA Typing (RAPD-PCR).

RESULTS

All burn isolates were integron positive and Multi-drug resistant (MDR), while 78.5% and 69% of ICU isolates were found as MDR and integron positive, respectively. The aadB gene was the most prevalent gene cassette (63.6%) followed by aacA4 (47.7%). Thirty-nine (68.4%) and 43 (75.4%) isolates exhibited an overexpression of MexAB-OprM and MexXY-OprM. Among burn isolates, 80% and 86.6% of them were mexB and mexY overexpressed, while 64.2% and 71.4% of ICU isolates exhibited mexB and mexY overexpression, correspondingly. The isolates were genotyped as 24 different RAPD profiles and were grouped into 15 clusters.

CONCLUSIONS

The data suggested that class 1 integron had a more significant role than efflux pumps in resistance to beta-lactams and aminoglycosides in burn and ICUs except for gentamicin in burn isolates. Based on our data, it is possible that efflux pumps were not the main cause of high-level resistance to antibiotics.

Evaluation of Carbapenem Resistance Mechanisms and Its Association with Pseudomonas aeruginosa Infections in the Northwest of Iran

The aims of this study were to determine carbapenem resistance mechanisms, molecular epidemiological relationship, clinical impact, and patient outcome of carbapenem-resistant Pseudomonas aeruginosa (CRPA) infections. A total of 42 nonduplicated CRPA were recovered from Urmia, Iran. Antimicrobial susceptibility tests were carried out using phenotypic methods. The carbapenem resistance mechanisms such as carbapenemase genes, efflux pump hyperexpression, AmpC overproduction, and OprD gene downregulation were determined by phenotypic and molecular methods. Eighteen metallo-β-lactamase (MBL) producer isolates were found to be sensitive to amikacin. Among the CRPA, 52.3%, 26.1%, 26.1%, and 59.5% were identified as carbapenemase, efflux pump hyperexpression, AmpC overproduction, and reduced expression OprD gene, respectively. Random Amplified Polymorphic DNA analysis yielded 25 distinct profiles. Most MBL-positive isolates were recovered from patients hospitalized in urology and internal wards with urinary tract infections. Most of the strains showed downregulation of porin. The clonal distribution of the strains was related to carbapenem resistance mechanisms (most of MBL producers belong to the same clones) and the same hospital wards where the isolates were collected. The study demonstrates that the main risk factor of MBL-related infections was hospitalization in non-intensive wards. Amikacin was considered a very efficient antibiotic to treatment of MBL-producing CRPA isolates. Our results showed that OprD downregulation and IMP-type MBL are the main carbapenem resistance mechanisms in CRPA isolates from northwest of Iran.

Systematic review and meta-analysis of imipenem-resistant Pseudomonas aeruginosa prevalence in Iran

INTRODUCTION

Imipenem-resistant Pseudomonas aeruginosa (IRPA), due to resistance to different classes of antibiotics and its remarkable capacity to survive in harsh and adverse conditions such as those in the hospital environment, is considered a serious threat to the healthcare system. Given the great impact of IRPA on patients' outcome and in order to possibly improve antibiotic prescription, this study was conducted to determine the prevalence of clinical isolates of IRPA in different parts of Iran.

METHODS

A systematic literature search was performed in PubMed, Web of Science, Google Scholar and Scopus, as well as in two Iranian domestic search engines, i.e., Iranian Scientific Information Database and Magiran. Finally, after applying exclusion and inclusion criteria 37 articles with full-texts describing the prevalence of imipenem-resistant P. aeruginosa were selected for meta-analysis and systematic review.

RESULTS

The pooled estimation of 5227 P. aeruginosa isolates in this analysis showed that the percentage of imipenem-resistant P. aeruginosa is about 54% in the Iranian population (95%CI: 0.47-0.62, logit event rate=0.19, 95%CI: -0.12,0.49).

CONCLUSION

The findings of this analysis show that in the majority of Iranian hospitals the relative frequency of IRPA is high, therefore, in order to prevent further dissemination of IRPA, more appropriate antibiotic prescription and infection control policies must be implemented by decision-makers.