Problematic clinical isolates of Pseudomonas aeruginosa from the university hospitals in Sofia, Bulgaria: current status of antimicrobial resistance and prevailing resistance mechanisms

Phenotypic and molecular characterization of extended spectrum- and metallo- beta lactamase producing Pseudomonas aeruginosa clinical isolates from Egypt

BACKGROUND

Antimicrobial resistance among Pseudomonas aeruginosa (P. aeruginosa), a leading cause of nosocomial infections worldwide, is escalating. This study investigated the prevalence of extended-spectrum β-lactamases (ESBLs) and metallo-β-lactamases (MBLs) among 104 P. aeruginosa clinical isolates from Alexandria Main University Hospital, Alexandria, Egypt.

METHODS

Antimicrobial susceptibility testing was performed using agar dilution technique, or broth microdilution method in case of colistin. ESBL and MBL prevalence was assessed phenotypically and genotypically using polymerase chain reaction (PCR). The role of plasmids in mediating resistance to extended-spectrum β-lactams was studied via transformation technique using plasmids isolated from ceftazidime-resistant isolates.

RESULTS

Antimicrobial susceptibility testing revealed alarming resistance rates to carbapenems, cephalosporins, and fluoroquinolones. Using PCR as the gold standard, phenotypic methods underestimated ESBL production while overestimating MBL production. Eighty-five isolates (81.7%) possessed only ESBL encoding genes, among which 69 isolates harbored a single ESBL gene [blaOXA-10 (n = 67) and blaPER (n = 2)]. Four ESBL-genotype combinations were detected: blaPER + blaOXA-10 (n = 8), blaVEB-1 + blaOXA-10 (n = 6), blaPSE + blaOXA-10 (n = 1), and blaPER + blaVEB-1 + blaOXA-10 (n = 1). Three isolates (2.9%) possessed only the MBL encoding gene blaVIM. Three ESBL + MBL- genotype combinations: blaOXA-10 + blaAIM, blaOXA-10 + blaVIM, and blaPER + blaOXA-10 + blaAIM were detected in 2, 1 and 1 isolate(s), respectively. Five plasmid preparations harboring blaVEB-1 and blaOXA-10 were successfully transformed into chemically competent Escherichia coli DH5α with transformation efficiencies ranging between 6.8 × 10 3 and 3.7 × 10 4    CFU/μg DNA plasmid. Selected tested transformants were ceftazidime-resistant and harbored plasmids carrying blaOXA-10.

CONCLUSIONS

The study highlights the importance of the expeditious characterization of ESBLs and MBLs using genotypic methods among P. aeruginosa clinical isolates to hinder the development and dissemination of multidrug resistant strains.

Genomic Insights into Vietnamese Extended-Spectrum β-Lactamase-9-Producing Extensively Drug-Resistant Pseudomonas aeruginosa Isolates Belonging to the High-Risk Clone ST357 Obtained from Bulgarian Intensive Care Unit Patients

Extensively drug-resistant P. aeruginosa (XDR-PA) has been highlighted as a serious public health threat. The present study aimed to explore the genomic characteristics of two Vietnamese extended-spectrum β-lactamase-9 (VEB-9)-producing XDR-PA isolates from Bulgaria in comparison to all blaVEB-9-positive strains with available genomes. The isolates designated Pae51 and Pae52 were obtained from tracheobronchial aspirates of intensive care unit (ICU) patients. Antimicrobial susceptibility testing, whole-genome sequencing, RT-qPCR, and phylogenomic analysis were performed. Pae51 and Pae52 were resistant to most antipseudomonal β-lactams including carbapenems, aminoglycosides, and fluoroquinolones but remained susceptible to colistin and cefiderocol. Numerous resistance determinants were detected: blaVEB-9, blaPDC-3, blaOXA-10, blaOXA-50, aac(6')-II, ant(2″)-Ia, ant(3″)-IIa, aph(3')-IIb, cprP, catB7, dfrB2, sul1, fosA, and tet(A). Both isolates carried complex integrons with blaVEB-9 and tet(A) embedded next to the conservative 3' end sequences. A variety of virulence factors were also identified, including the type III secretion system exotoxin U. Pae51 and Pae52 differed by only four SNPs and belonged to the high-risk clone ST357. To our knowledge, this is the first report of blaVEB-9-positive XDR-PA isolates in Bulgaria presenting a detailed genomic analysis. The development of novel antimicrobial strategies for such pathogens should be an essential part of infection control stewardship practices in ICU wards.

In vitro activity of cefiderocol against carbapenem-resistant Acinetobacter baumannii carrying various β-lactamase encoding genes

OBJECTIVES

This study aimed to determine the in vitro efficacy of cefiderocol in carbapenem-resistant Acinetobacter baumannii (CRAB) isolates and evaluate the disk-diffusion (DD) method as an alternative method to broth-microdilution (BMD).

METHODS

Totally 89 CRAB isolates were included. Cluster analysis was determined by Pulsed-Field Gel Electrophoresis (PFGE). Resistance genes; blaOXA-51, blaOXA-23, blaOXA-24, blaOXA-58,blaPER-1, blaNDM, blaIMP and mcr-1 were screened. Cefiderocol susceptibility testing was performed by both DD and BMD. Interpretation was made according to EUCAST and CLSI. Categorical agreement (CA), minor errors (mEs), major errors (MEs), and very major errors (VMEs) were determined.

RESULTS

PFGE revealed 5 distinct pulsotypes; 86 of the isolates were extensively drug-resistant (XDR). All the isolates were negative for blaNDM, blaIMP, mcr-1, while positive for blaOXA-58 and blaOXA51. blaPER-1 was positive for 33.7%; blaOXA-23 for 74.2%; blaOXA-24 for 12.3%. According to CLSI, the MEs rate was 1.85%, mEs was 7.86% and there were no VMEs. According to EUCAST, MEs rate was 3.70%, there were no mEs and VMEs. CA was 91% for CLSI and 97.8% for EUCAST. MICs of cefiderocol against A. baumannii isolates ranged from 0.06 to > 128 mg/L, with MIC50 and MIC90 values of 0.5 and > 128 mg/L, respectively.

CONCLUSIONS

Cefiderocol susceptibility was 60.7% in CRAB isolates. MIC50, MIC90 of blaPER-1 positive and blaPER-1 negative groups were > 128/>128 and 0.25/>128 mg/L. A correlation between the presence of blaPER-1 and cefiderocol resistance was observed (p < 0.0001). Among colistin-resistant isolates, the presence of blaPER-1 was 47.1% and 75% of them were resistant to cefiderocol respectively.

Molecular Detection of Extended Spectrum Beta-Lactamases in Clinical Isolates of Pseudomonas aeruginosa

Pseudomonas aeruginosa producing extended spectrum beta lactamases (ESBL) is a major concern in the hospital settings. It is usually reported in Enterobacteriaceae and is less frequently observed in P. aeruginosa. There is no recommended test for ESBL detection in P.aeruginosa. Therefore, we determined the occurrence of ESBL in clinical isolates of P.aeruginosa by both phenotypic and genotypic methods. Antimicrobial susceptibility tests were done on two hundred and thirteen isolates of P. aeruginosa. Phenotypic detection of ESBL was performed using combined disk method and ESBL encoding genes such as blaVEB, blaPER, blaPSE, blaGES, blaTEM, blaSHV, blaCTX-M, blaBEL, blaOXA1, blaOXA10, blaOXA2 were studied by simplex PCR. Of the 213 isolates, 85 were identified as resistant to ceftazidime and 27/85 isolates were confirmed to be ESBL producers by phenotypic method. The presence of genes encoding ESBLs comprising of blaTEM (n=44), blaOXA-10 (n=19) isolates, blaOXA-1 (n=5), blaOXA-2 (n=3) were found. All OXA gene positive isolates exhibited the ESBL phenotype. The blaGES gene were identified in 4/85 (5%) isolates. This study shows the prevalence of ESBL among clinical isolates of P.aeruginosa and in particular, the presence of GES β lactamases.

Role of nanomaterials in deactivating multiple drug resistance efflux pumps - A review

The changes in lifestyle and living conditions have affected not only humans but also microorganisms. As man invents new drugs and therapies, pathogens alter themselves to survive and thrive. Multiple drug resistance (MDR) is the talk of the town for decades now. Many generations of medications have been termed useless as MDR rises among the infectious population. The surge in nanotechnology has brought a new hope in reducing this aspect of resistance in pathogens. It has been observed in several laboratory-based studies that the use of nanoparticles had a synergistic effect on the antibiotic being administered to the pathogen; several resistant strains scummed to the stress created by the nanoparticles and became susceptible to the drug. The major cause of resistance to date is the efflux system, which makes the latest generation of antibiotics ineffective without reaching the target site. If species-specific nanomaterials are used to control the activity of efflux pumps, it could revolutionize the field of medicine and make the previous generation resistant medications active once again. Therefore, the current study was devised to assess and review nanoparticles' role on efflux systems and discuss how specialized particles can be designed towards an infectious host's particular drug ejection systems.

Effect of naturally isolated hydroquinone in disturbing the cell membrane integrity of Pseudomonas aeruginosa MTCC 741 and Staphylococcus aureus MTCC 740

Nosocomial pathogens cause various health problems in human and many novel drugs are under investigation to combat the pathogens. The present study explains the naturally derived hydroquinone possible mode of action against Pseudomonas aeruginosa MTCC 741 and Staphylococcus aureus MTCC 740. Time kill studies, cell viability assays, membrane potential assays, and potassium release assays were carried out to study the mode of action. Time kill studies revealed the rapid death of bacterial pathogens exposed to 4X MIC (Minimum inhibitory concentration) of the hydroquinone. Cell viability assay results showed that nearly half of the cell destruction of test pathogens occurred within one hour. Transmission electron microscopic (TEM) observations revealed the disruption of the cell membrane, which caused severe ultrastructural changes in both test pathogens. Hydroquinone dissipated the membrane potential of test pathogens, as confirmed by the depolarization of membrane potential, increases in permeability and leakage of intracellular potassium ions. At the concentration of 2X MIC hydroquinone in 5 min, about 91.41% and 84.85% potassium ions were released from P. aeruginosa MTCC 741 and S. aureus MTCC 740, respectively. This is the first report on the mode of action of naturally derived hydroquinone against clinical pathogens.

Acinetobacter baumannii as a community foodborne pathogen: Peptide mass fingerprinting analysis, genotypic of biofilm formation and phenotypic pattern of antimicrobial resistance

Acinetobacter baumannii (A. baumannii) is one of the most common Gram-negative pathogens that represent a major threat to human life. Because the prevalence of Multidrug-resistant biofilm-forming A. baumannii is increasing all over the world, this may lead to outbreaks of hospital infections. Nonetheless, the role of raw meat as a reservoir for A. baumannii remains unclear. Here our research was aimed to exhibit the frequency, precise identification, and genotyping of biofilm-related genes as well as antimicrobial resistance of A. baumannii isolates of raw meat specimens. Fifty-five A. baumannii strains were recovered from 220 specimens of different animal meat and then identified by Peptide Mass Fingerprinting Technique (PMFT). All identified isolates were genotyped by the qPCR method for the existence of biofilm-related genes (ompA, bap, blaPER-1, csuE, csgA, and fimH). In addition, the antimicrobial resistance against A. baumannii was detected by the Kirby-Bauer method. Based on our findings, the frequency rate of 55 A. baumannii isolates was 46.55%, 32.50%, 15.00%, and 9.68% of sheep, chicken, cow, and camel raw meat samples, respectively. The PMFT was able to identify all strains by 100%. the percentages of csuE, ompA, bla_PER-1, bap, and csgA genes in biofilm and non-biofilm producer A. baumannii were 72.73%, 60%, 58.2%, 52.74%, and 25.45%, respectively. In contrast, the fimH was not detected in all non-biofilm and biofilm producer strains. The ompA, bap, blaPER-1, csgA were detected only in biofilm-producing A. baumannii isolates. The maximum degree of resistance was observed against amoxicillin/clavulanic acid (89.10%), gentamicin (74.55%), tetracycline (72.73%), ampicillin (65.45%), and tobramycin (52.73%). In conclusion, our investigation demonstrated the high incidence of multi-drug resistant A. baumannii in raw meat samples, with a high existence of biofilm-related virulence genes of ompA, bap, blaPER-1, csgA. Therefore, it has become necessary to take the control measures to limit the development of A. baumannii.

Phenotypic and genetic properties of susceptible and multidrug-resistant Pseudomonas aeruginosa isolates in Southern Serbia

Drug resistance of Pseudomonas aeruginosa is a leading problem in hospital infections. The aim of this study was to determine the best molecular genetic discrimination method for Pseudomonas spp. isolates among 94 outpatients and inpatients and see their grouping by phenotype characteristics (biofilm formation, frequency of serotypes, pigmentation, production of different class of beta-lactamases, and susceptibility to different antibiotic classes) and genotype. The most common serotypes were P1, P6, and P11, while co-productions of pyoverdine and pyocyanin were observed in 70 % of isolates. A total of 77.66 % isolates were mostly weak and moderate biofilm producers. Isolates were susceptible to colistin (100 %), aztreonam (97.87 %), imipenem (91.49 %), doripenem (90.43 %), and meropenem (84.04 %). MICs values confirmed susceptibility to ceftazidime and cefepime and singled out meripenem as the most effective inhibitor. Most isolates were resistant to aminoglycosides and fluoroquinolones. Only two isolates produced ESBL, eight were carbapenemase producers, and five isolates produced MBLs. Twenty-nine isolates were multidrug-resistant; 82.8 % of which produced both pigments, 58.3 % were non-typeable, while the P6 and P11 serotypes were equally distributed (16.7 %). Thirteen MDR isolates were strong enzyme producers. RAPD PCR analysis using primer 272 proved the best at discriminatory fingerprinting for Pseudomonas isolates, as it allocated 12 clusters. A correlation between DNA patterns and antibiotic resistance, production of pigments, serotypes distribution, and biofilm formation was not observed, and only confirmed higher genetic heterogeneity among P. aeruginosa isolates, which suggests that other molecular methods are needed to reveal potential relations between genotypic patterns and phenotypic characteristics.

A hospital based surveillance of metallo-beta-lactamase producing gram negative bacteria in Nepal by imipenem-EDTA disk method

BACKGROUND

A rising threat of the rapid spread of acquired metallo-beta-lactamases (MBLs) among major Gram-negative pathogens is a matter of public health concern worldwide. Hence, for a low income nation like Nepal, surveillance data on MBL producing clinical isolates via a cost effective technique is necessary to prevent their dissemination as well as formulation and regulation of antimicrobial stewardship policy.

METHODS

The prospective study was conducted at Nepal Medical College, Kathmandu from May to October, 2014 to assess the prevalence of MBL production among ceftazidime-resistant Gram-negative rods (GNRs) isolates. The samples were processed according to standard microbiological procedure following the Manual of clinical Microbiology. Isolated GNRs were subjected to susceptibility testing against the selected panel of antibiotics by Kirby- Bauer disc diffusion method and interpretation made in conformity with the Clinical and Laboratory Standards Institute (CLSI) guidelines. Ceftazidime-resistant isolates were subjected to the detection of MBL production by imipenem-EDTA combined disc (CD) method.

RESULTS

Among the Gram-negative isolates, 5.80% (21/362) were found to be MBL positive with Acinetobacter spp. showing the highest prevalence i.e. 85.71% (18/21), followed by P. aeruginosa i.e. 14.29% (3/21). None of the other cefazidime resistant gram negative bacteria tested were found to be positive for MBL production with all the positive isolates determined to be Multidrug resistant (MDR) strains.

CONCLUSION

This study demonstrated a higher rate of resistance among P. aeruginosa and Acinetobacter spp. to a wide variety of antibiotic categories with an additional burden of MBL production within them, warranting a need for strict surveillance and rapid detection of MBL production among the GNRs.

Distribution of the Strains of Multidrug-resistant, Extensively Drug-resistant, and Pandrug-resistant Pseudomonas aeruginosa Isolates from Burn Patients

Background:

Pseudomonas aeruginosa is an opportunistic and Gram-negative pathogen that is used as the most important factor in burn wound infections, and due to the rapid acquisition of multidrug resistance (MDR), it causes high mortality rates in these sectors. Thus, diagnosis and assessment of antibiotic resistance patterns are very important in these patients. The aim of this study was to evaluate antibiotic resistance pattern and determining P. aeruginosa MDR.

Materials and Methods:

In this study, phenotypic, biochemical, and polymerase chain reaction tests were used to identify P. aeruginosa from 120 wound burn samples that 96 samples were detected to P. aeruginosa species. In the next step, according to the Clinical and Laboratory Standard Institute standard guidelines, antibiogram test was performed by disk diffusion method for amikacin, ciprofloxacin, norfloxacin, gentamicin, cefepime, aztreonam, meropenem, colistin, ceftazidime, and piperacillin-tazobactam antibiotics. Antibiotic data were analyzed by WHONET software; finally, the rate of antibiotic resistance and MDR strains was determined.

Results:

The highest antibiotic resistance belonged to amikacin (94.8%) and norfloxacin (90.6%); in contrast, colistin (8.3%) had the lowest and the MDR strains were MDR (95.8%) and extensively drug resistance (XDR) (87.5%).

Conclusion:

In this study, there was MDR with an alarming rate including MDR (95.8%), XDR (87.5%), and pan-drug resistance (0%). As a result, given antibiotics to patients should be controlled by the antibiogram results to avoid increasing MDR strains.

Molecular Analysis and Expression of bap Gene in Biofilm-Forming Multi-Drug-Resistant Acinetobacter baumannii

BACKGROUND

Acinetobacter baumannii is commonly resistant to nearly all antibiotics due to presence of antibiotic resistance genes and biofilm formation. In this study we determined the presence of certain antibiotic-resistance genes associated with biofilm production and the influence of low iron concentration on expression of the biofilm-associated protein gene (bap) in development of biofilm among multi-drug-resistant A. baumannii (MDRAB).

METHODS

Sixty-five MDRAB isolates from clinical samples were collected. Molecular typing was carried out by random amplified polymorphism DNA polymerase chain reaction (RAPD-PCR). Biofilm formation was assayed by the microtiter method.

RESULTS

The sequence of bap was determined and deposited in the GenBank database (accession no. KR080550.1). Expression of bap in the presence of low iron was analyzed by relative quantitative real time PCR (rqRT-PCR). Nearly half of the isolates belonged to RAPD-types A and B remaining were either small clusters or singleton. The results of biofilm formation revealed that 23 (35.4%), 18 (27.7%), 13 (20%), and 11 (16.9%) of the isolates had strong, moderate, weak, and no biofilm activities, respectively. ompA and csuE genes were detected in all, while bap and bla_PER-1 were detected in 43 (66%) and 42 (64%) of the isolates that showed strong and moderate biofilm activities (p ≤ 0.05), respectively. Analysis of bap expression by rqRT-PCR revealed five isolates with four-fold bap overexpression in the presence of low iron concentration (20 µM).

CONCLUSION

The results suggest that bap overexpression may influence biofilm formation in presence of low iron concentration.

Pseudomonas aeruginosa: arsenal of resistance mechanisms, decades of changing resistance profiles, and future antimicrobial therapies

Antimicrobial resistance is one of the most serious public health issues facing humans since the discovery of antimicrobial agents. The frequent, prolonged, and uncontrolled use of antimicrobial agents are major factors in the emergence of antimicrobial-resistant bacterial strains, including multidrug-resistant variants. Pseudomonas aeruginosa is a leading cause of nosocomial infections. The abundant data on the increased resistance to antipseudomonal agents support the need for global action. There is a paucity of new classes of antibiotics active against P. aeruginosa. Here, we discuss recent antibacterial resistance profiles and mechanisms of resistance by P. aeruginosa. We also review future potential methods for controlling antibiotic-resistant bacteria, such as phage therapy, nanotechnology and antipseudomonal vaccines.

Molecular characterization and in vitro susceptibilities of β-lactamase producing Escherichia coli, Klebsiella species, Acinetobacter baumannii, Pseudomonas aeruginosa and Staphylococcus aureus to CSE1034 and other β-lactams

OBJECTIVE

To study the prevalence of extended-spectrum β-lactamases (ESBLs) among 663 clinical isolates obtained from various parts of India and to study the occurrence of different variants of ESBLs among these isolates.

METHODS

Phenotypic characterization and susceptibility studies were performed according to the methods described in Clinical and Laboratory Standards Institute guidelines. The occurrence of ESBL variants was analyzed with PCR using the previously reported primers.

RESULTS

Among the six hundred sixty three isolates, the identified isolates were Acinetobacter baumannii (72), Escherichia coli (218), Klebsiella pneumoniae (30), Klebsiella oxytoca (63), Pseudomonas aeruginosa (264) and Staphylococcus aureus (16). PCR results revealed that approximately 89.0% of Pseudomonas aeruginosa isolates were positive for ESBL followed by Escherichia coli (85.3%), Klebsiella pneumoniae (76.6%), Klebsiella oxytoca (73.0%), Acinetobacter baumannii (72.2%) and Staphylococcus aureus (31.2%). The overall prevalence of ESBL was 82.5%. The presence of TEM type ESBLs were the predominant (in 186 isolates), followed by SHV (138), OXA (92), CTX-M (65), AmpC (33), KPC (28) and blaZ (5). Of the drugs involved in the study, CSE1034 was found to be the most efficacious against all of ESBL positive clinical isolates showing susceptibility approximately 95.7% with minimal inhibitory concentration values between 0.125 and 8.000 μg/mL for all strains tested. The susceptibilities of penems (meropenem and imipenem and cilastatin) ranged between 83% and 93% for all the isolates. The susceptibilities of other drugs like piperacillin and tazobactam, amoxicillin and clavulanic acid, cefoperazone and sulbactam were <45% for all the isolates.

CONCLUSIONS

Results of the present study indicated that majority of the isolates was susceptible to CSE1034 and it could be a potent antibacterial agent for the treatment of severe bacterial infections caused by such organisms.

Antibacterial activity of extracellular compounds produced by a Pseudomonas strain against methicillin-resistant Staphylococcus aureus (MRSA) strains

BACKGROUND

The emergence of multidrug-resistant bacteria is a world health problem. Staphylococcus aureus, including methicillin-resistant S. aureus (MRSA) strains, is one of the most important human pathogens associated with hospital and community-acquired infections. The aim of this work was to evaluate the antibacterial activity of a Pseudomonas aeruginosa-derived compound against MRSA strains.

METHODS

Thirty clinical MRSA strains were isolated, and three standard MRSA strains were evaluated. The extracellular compounds were purified by vacuum liquid chromatography. Evaluation of antibacterial activity was performed by agar diffusion technique, determination of the minimal inhibitory concentration, curve of growth and viability and scanning electron microscopy. Interaction of an extracellular compound with silver nanoparticle was studied to evaluate antibacterial effect.

RESULTS

The F3 (ethyl acetate) and F3d (dichloromethane- ethyl acetate) fractions demonstrated antibacterial activity against the MRSA strains. Phenazine-1-carboxamide was identified and purified from the F3d fraction and demonstrated slight antibacterial activity against MRSA, and synergic effect when combined with silver nanoparticles produced by Fusarium oxysporum. Organohalogen compound was purified from this fraction showing high antibacterial effect. Using scanning electron microscopy, we show that the F3d fraction caused morphological changes to the cell wall of the MRSA strains.

CONCLUSIONS

These results suggest that P. aeruginosa-produced compounds such as phenazines have inhibitory effects against MRSA and may be a good alternative treatment to control infections caused by MRSA.

Molecular epidemiology and multidrug resistance mechanisms of Pseudomonas aeruginosa isolates from Bulgarian hospitals

A panel of 29 multidrug-resistant (MDR) Pseudomonas aeruginosa isolates recovered from seven hospitals as part of a country-wide surveillance of antimicrobial resistance in Bulgarian hospitals was studied. Molecular typing through multiple-locus variable number tandem-repeat analysis (MLVA6) yielded 23 different profiles. Phenotypic and genotypic tests for the detection of acquired carbapenemases yielded negative results in all cases. In contrast, 76% of the isolates produced other acquired β-lactamases, including extended-spectrum β-lactamases (ESBLs). Namely, 6 of the isolates (21%) produced a VEB-1 ESBL; 14 (48%) produced an OXA-10-type enzyme (7 OXA-10 and 7 OXA-10 ESBL variants, including 2 OXA-17 [A218G], 2 OXA-74 [C197T, A218G], and 3 OXA-142 [A218G, G470A]); 8 (28%) an OXA-2-type enzyme (all OXA-2); and 1 (3%) a PSE-1 carbenicillinase. Further analysis through multilocus sequence typing (MLST) revealed that the six VEB-1-producing strains, recovered from four hospitals, belonged to ST111 or ST244 international high-risk clones. Additionally, nearly all of the isolates (97%) lacked OprD production, explaining carbapenem resistance. Overexpression of AmpC was documented in 5 (17%) of the isolates, including most of the MDR isolates not producing any acquired β-lactamase. Particularly noteworthy was the very high prevalence of MexXY-OprM overexpression, documented in 72% of the isolates, whereas the prevalence of MexAB-OprM overexpression was lower (21%). In summary, while the production of metallo-β-lactamases is uncommon among P. aeruginosa isolates from Bulgarian hospitals, MDR profiles frequently result from the production of ESBLs combined with the lack of production of the carbapenem porin OprD and the overexpression of the MexXY-OprM efflux pump.

Analysis of integrons and associated gene cassettes of metallo-β-lactamase-positive Pseudomonas aeruginosa in Malaysia

In this study, 90 non-replicate imipenem-resistant Pseudomonas aeruginosa (IRPA) Malaysian isolates collected between October 2005 and March 2008 were subjected to a screening test for detection of the integron and the gene cassette. Class 1 integrons were detected in 54 IRPA clinical isolates, whilst three isolates contained class 2 integrons. Analysis of the gene cassettes associated with the class 1 integrons showed the detection of accC1 in isolates carrying bla(IMP-7) and aacA7 in isolates carrying bla(VIM-2). aadA6 was detected in two isolates carrying bla(IMP-4). Using random amplification of polymorphic DNA analysis, 14 PCR fingerprint patterns were generated from the 32 isolates carrying metallo-β-lactamase (MBL) genes (35.5 %), whilst 20 patterns were generated from the 58 non-MBL gene isolates (64.4 %). Based on the differences in the fingerprinting patterns, two clusters (A and B) were identified among the MBL-producing isolates. Cluster A comprised 18 isolates (56 %) carrying the bla(VIM) gene, whereas cluster B comprised 14 (44 %) isolates carrying the bla(IMP) gene. The non-MBL isolates were divided into clusters C and D. Cluster C comprised 22 non-MBL isolates harbouring class 1 integrons, whilst cluster D consisted of three isolates carrying class 2 integrons. These findings suggest that the class 1 integron is widespread among P. aeruginosa isolated in Malaysia and that characterization of cassette arrays of integrons will be a useful epidemiological tool to study the evolution of multidrug resistance and the dissemination of antibiotic resistance genes.

Carbapenem resistance mechanism and risk factors of Pseudomonas aeruginosa clinical isolates from a University Hospital in Xi'an, China

PURPOSE

Carbapenems are important agents for the therapy of Gram-negative bacillus infections, and the development of their resistance hampers effective therapeutic options. The purpose of this study was to assess the major mechanisms and risk factors leading to carbapenem resistance in clinical Pseudomonas aeruginosa isolates.

METHODS

Thirty-four clinical isolates with differing degrees of carbapenem susceptibility were analyzed for carbapenemase, porin, and efflux systems. Risk factor analysis was performed using a case-control study.

RESULTS

Eighteen of 24 carbapenem-resistant isolates were producers of carbapenemase. Diminished expression of oprD and overexpression of effluxes were present in five and seven carbapenem-resistant isolates, respectively. The number of days from admission to the day of positive culture and days of antibiotic apply were identified as the independent predictors of infection with carbapenem-resistant P. aeruginosa.

CONCLUSIONS

Carbapenemase production is a major mechanism of P. aeruginosa isolates involved in this study. Increased length of hospital stay and days of antibiotic application were the most important risk factors identified for carbapenem resistance.

Antibacterial nitric oxide-releasing polyester for the coating of blood-contacting artificial materials

The emergence of multidrug-resistant bacteria associated with blood-contacting artificial materials is a growing health problem, which demands new approaches in the field of biomaterials research. In this study, a poly(sulfhydrylated polyester) (PSPE) was synthesized by the polyesterification reaction of mercaptosuccinic acid with 3-mercapto-1,2-propanediol and blended with poly(methyl methacrylate) (PMMA) from solution, leading to solid PSPE/PMMA films, with three different PSPE : PMMMA mass ratios. These films were subsequently S-nitrosated through the immersion in acidified nitrite solution, yielding poly(nitrosated)polyester/PMMA (PNPE/PMMA) films. A polyurethane intravascular catheter coated with PNPE/PMMA was shown to release nitric oxide (NO) in phosphate buffered saline solution (pH 7.4) at 37 degrees C at rates of 4.6 nmol/cm(2)/h in the first 6 h and 0.8 nmol/cm(2)/h in the next 12 h. When used to coat the bottom of culture plates, NO released from these films exerted a potent dose- and time-dependent antimicrobial activity against Staphylococcus aureus and a multidrug-resistant Pseudomonas aeruginosa strains. This antibacterial effect of PSPE/PMMA films opens a new perspective for the coating of blood-contacting artificial materials, for avoiding their colonization with highly resistant bacteria.

Efflux-mediated drug resistance in bacteria: an update

Drug efflux pumps play a key role in drug resistance and also serve other functions in bacteria. There has been a growing list of multidrug and drug-specific efflux pumps characterized from bacteria of human, animal, plant and environmental origins. These pumps are mostly encoded on the chromosome, although they can also be plasmid-encoded. A previous article in this journal provided a comprehensive review regarding efflux-mediated drug resistance in bacteria. In the past 5 years, significant progress has been achieved in further understanding of drug resistance-related efflux transporters and this review focuses on the latest studies in this field since 2003. This has been demonstrated in multiple aspects that include but are not limited to: further molecular and biochemical characterization of the known drug efflux pumps and identification of novel drug efflux pumps; structural elucidation of the transport mechanisms of drug transporters; regulatory mechanisms of drug efflux pumps; determining the role of the drug efflux pumps in other functions such as stress responses, virulence and cell communication; and development of efflux pump inhibitors. Overall, the multifaceted implications of drug efflux transporters warrant novel strategies to combat multidrug resistance in bacteria.

Antimicrobial susceptibility and ESBL prevalence in Pseudomonas aeruginosa isolated from burn patients in the North West of Pakistan

Pseudomonas aeruginosa is one of the most prevalent pathogen in burn infections. Infections with P. aeruginosa are associated with higher mortality rate and antibiotic costs in hospitalized patients. These bacteria also produce enzymes called Expanded Spectrum Beta-Lactamases (ESBL) which render penicillins and cephalosporins inactive. The aim of this study was to assess the antimicrobial susceptibility pattern and prevalence of ESBL in P. aeruginosa in Peshawar, North West of Pakistan. During 2005-2006, one hundred and six P. aeruginosa isolates were collected from burn patients at a tertiary care hospital. Antibiotic susceptibility testing and ESBL detection were carried out according to Clinical Laboratory and Standards Institute (CLSI) criteria. Eighteen antibiotics were tested in this study. A total of 38 (35.85%) isolates were found to be ESBL producers. Thirty one (29.24%) isolates were resistant to 3 or more antibiotics (multidrug resistance). Meropenem and imipenem showed high potency with 99% and 96% isolates being susceptible respectively. Susceptibility to amikacin was 70%; gentamicin 25%; ciprofloxacin 49%; enoxacin 47%; gatifloxacin 42%; doxycycline 21% and to co-trimoxazole only 16%. This study reveals that P. aeruginosa isolated from burns in this region are multidrug resistant and produce ESBL in large proportions.

A blaVEB-1 variant, blaVEB-6, associated with repeated elements in a complex genetic structure

bla(VEB-6) was found on the Proteus mirabilis chromosome in a context similar to those of bla(VEB-1a) and bla(VEB-1b), in a truncated gene cassette flanked by 135-bp elements and duplications of the 3'-conserved segment of class 1 integrons. A linked aacA4-aadB-dfrA1-orfC cassette array includes components of Tn1331, illustrating the complex mosaicism of multiresistance regions.

The safety of cefepime in the treatment of infection

BACKGROUND

Cefepime is a fourth-generation cephalosporin usually reserved for treating severe nosocomial pneumonia, as well as empirical treatment of febrile neutropenia, uncomplicated and complicated urinary tract infections, uncomplicated skin and skin structure infections, and complicated intra-abdominal infections.

OBJECTIVE

Since reports of neurotoxic effects and of an all-cause mortality higher with cefepime than with comparators have created some concerns regarding its safety, this paper reviews data available in the PubMed database up to December 2007 on cefepime safety.

METHODS

Literature data from PubMed obtained by combining cefepime and safety, or cefepime and clinical trials, were examined.

RESULTS/CONCLUSIONS

Caution in the use of cefepime should be adopted until new evidence on cefepime safety is available.