In vitro activity, pharmacodynamic profile and dose optimization of biapenem against NDM and OXA-48-like carbapenemase-producing Klebsiella pneumoniae: A multicentre study in Thailand.

BACKGROUND: Biapenem (BIPM) exhibited a less efficient substrate for various metallo-ß-lactamase (MBL) than other carbapenems. OBJECTIVE: We aimed to evaluate in vitro susceptibility data of BIPM and optimal dose based on Monte Carlo simulation to extend treatment options. METHODS: We collected 192 carbapenem-resistant Klebsiella pneumoniae (CRKP) clinical isolates from unique patients among multicentres in Thailand, from June 2019 to March 2023. BIPM disk diffusion and broth-microdilution testing were performed to obtain minimum inhibitory concentration (MIC). Each BIPM regimen was simulated using the Monte Carlo technique to calculate the probability of target attainment (PTA) and the cumulative fraction of response (CFR). RESULTS: The most common genotypes among 192 CRKP isolates were blaOXA-48 (62.3%), blaOXA-48+blaNDM (22.6%) and blaNDM (15.1%). BIPM showed 22.4 and 28.6% susceptible rate when interpreted at clinical breakpoints of 1 and 2 mg/L. The MIC50 and MIC90 of BIPM against CRKP were 8 and 32 mg/L. The BIPM dosing regimens of 300 mg q 6 h infused 6 h and 600 mg q 8 h infused 8 h met the PTA target of %fTime >MIC at 50%, 75% and 100% against isolates MICs of ≤2 mg/L. Based on CFR ≥90%, no BIPM regimens were effective against all the studied CRKP isolates. CONCLUSION: BIPM exhibited a partially susceptible rate among the CRKP isolates in Thailand. The current suggested dose of BIPM with prolonged infusion appears appropriate regimen against CRKP MICs of ≤2 mg/L. However, the empirical use of BIPM for severe CRE infection is not recommended unless the susceptibility has been confirmed.

Analysis of carbapenem-resistant Acinetobacter baumannii carbapenemase gene distribution and biofilm formation.

OBJECTIVE: In recent years, Acinetobacter baumannii has been appearing in hospitals with high drug resistance and strong vitality, which brings many difficulties to clinical treatment. In this study, 255 strains of A. baumannii were isolated from Youjiang Medical University for Nationalities Affiliated Hospital clinical samples and found to be highly resistant to carbapenems. The drug resistance, biofilm-forming ability, and carbapenase gene distribution of 145 carbapenem-resistant A. baumannii (CRAB) strains were analyzed statistically. METHODS: The clinically isolated strains were detected using Vitek mass spectrometry and Vitek2-compact for bacterial identification and susceptibility testing, respectively. The biofilms of clinical isolates were quantitatively detected by microplate crystal violet staining, and qualitatively observed by confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM). And the common carbapenemase genes were detected by polymerase chain reaction (PCR). RESULTS: The 255 clinical isolates from the Youjiang District of western Guangxi Province had a high resistance rate to carbapenems antibiotics. The main specimens were from the intensive care unit (49%), and the most important specimens were sputum specimens (80%). All 145 strains of CRAB produced different degrees of biofilm, and six carbapenenase genes were detected. We found that there were significant differences in biofilm formation between resistant and sensitive strains of tobramycin, levofloxacin, ciprofloxacin, tigecycline, and doxycycline (P<0.05). The distribution of blaOXA-23 and blaOXA51 genes was significantly different from CRAB biofilm formation (P<0.05). In addition, AmpC, blaOXA-23, blaOXA-51, and TEM genes were more distributed in antibiotic-resistant strains. CONCLUSION: The clinical strains have a high resistance rate to carbapenems, and the CRAB with blaOXA-51 and blaOXA-23 genes has a high resistance to antibiotics and a strong biofilm.

Acinetobacter baumannii Carbapenemase Producers in Morocco: Genetic Diversity.

INTRODUCTION:  Carbapenem resistance in Acinetobacter baumannii (A. baumannii) is a public health problem worldwide. Although carbapenem resistance is emerging in Morocco, few studies have shown the epidemiological profile of carbapenemase genes in Moroccan healthcare facilities. The aim of this study was to characterize the molecular profile of the carbapenemase enzyme in Acinetobacter baumannii from clinical isolates. METHODS: Clinical strains isolated in the laboratory from various samples were subjected to several phenotypic tests. Antibiotic susceptibility and identification were tested using Phoenix 100 (Becton Dickinson Co., Sparks, MD, USA) and Api 20 (bioMérieux, Marcy-l'Etoile, France). Simple phenotypic assays were used to detect carbapenemase oxacillinase (OXA) and metallo-ß-lactamase (MBL) production, including the modified Hodge test (MHT) and ethylenediaminetetraacetic acid (EDTA) test. The detection of carbapenemase genes was performed by multiplex and simple polymerase chain reaction (PCR). RESULTS: A total of 140 strains or 100% of isolates contained OXA-51 and ISbA1 sequences, 89% contained OXA-23 and OXA-58 sequences, and 1% contained OXA-24 sequence. The MBL genes were predominated by Verona integron-encoded metallo-ß-lactamase (VIM) (56%), followed by Seoul imipenemase (SIM) (39%), German imipenemase (GIM) (37%), São Paulo metallo-ß-lactamase (SPM) (13%), imipenemase (IMP) (11%), and New Delhi metallo-ß-lactamase (NDM) (4%). Guyana extended-spectrum ß-lactamase (GES) was not found in any isolation. CONCLUSION: Our study shows a high frequency of carbapenem resistance in Acinetobacter baumannii, as it reports a high molecular diversity of carbapenemase-encoding genes, mainly dominated by the carbapenemase ISaba1/OXA-23, which represents an emerging threat in our hospital.

Cefiderocol activity is compromised by acquired extended-spectrum oxacillinases in Pseudomonas aeruginosa.

OBJECTIVES: Cefiderocol has an excellent in vitro activity on clinical strains of Pseudomonas aeruginosa (P. aeruginosa). However, the resistance of some isolates has been associated with the production of some ß-lactamases. Whether some acquired extended-spectrum oxacillinases (ES-OXA) common in this species may compromise the susceptibility of P. aeruginosa to cefiderocol has not been evaluated so far. METHODS: Eighteen genes encoding OXA belonging to the major subgroups identified in P. aeruginosa OXA-1 (n = 3); - 2 (n = 5); - 10 (n = 8), and - 46 (n = 2) were cloned into pUCP24 shuttle vector and transferred into reference strain PAO1. RESULTS: Although production of the OXA-1 subgroup enzymes did not alter cefiderocol MICs, the ß-lactamases of OXA-2, OXA-46, and four variants of the OXA-10 subgroup resulted in an 8-fold to 32-fold decrease in susceptibility in the PAO1 background. Interestingly, point mutations Ala149Pro and Asp150Gly in OXA-2 subgroup, Trp154Cys and Gly157Asp in OXA-10 subgroup (all located in the Ω loop), and the duplication of a Thr206 and a Gly207 in the ß5-ß6 loop of OXA-10 subgroup were related to decreased susceptibility to cefiderocol. We also showed that some ES-OXA, including the most frequent ES-OXA in P. aeruginosa strains, OXA-19 (derived from OXA-10 subgroup), significantly compromised activity of cefiderocol in addition to ceftazidime, ceftolozane/tazobactam, and ceftazidime/avibactam in clinical strains. CONCLUSION: This work shows that several ES-OXA have a significant effect on cefiderocol susceptibility. Of concern are the Trp154Cys and Gly157Asp mutations that occur in some of these ß-lactamases, as they are associated with a decreased activity of the most recent cephalosporins introduced to combat P. aeruginosa infections.

Unveiling the Emergence and Genetic Diversity of OXA-48-like Carbapenemase Variants in Shewanella xiamenensis.

An increase in the carbapenem-hydrolyzing capacity of class D ß-lactamase has been observed in strains of multiple species, posing a significant challenge to the control of antibiotic resistance. In this study, we aimed to investigate the genetic diversity and phylogenetic characteristics of new blaOXA-48-like variants derived from Shewanella xiamenensis. Three ertapenem-non-susceptible S. xiamenensis strains were identified, one isolated from the blood sample of an inpatient, the other two isolated from the aquatic environment. Phenotypic characterization confirmed that the strains were carbapenemase producers and exhibited antimicrobial resistance patterns to ertapenem, with some showing lower susceptibility to imipenem, chloramphenicol, ciprofloxacin, and tetracycline. No significant resistance to cephalosporins was observed. Sequence analysis revealed that one strain harbored blaOXA-181 and the other two strains harbored blaOXA-48-like genes, with open reading frame (ORF) similarities with blaOXA-48 ranging from 98.49% to 99.62%. The two novel blaOXA-48-like genes, named blaOXA-1038 and blaOXA-1039, respectively, were cloned and expressed in E. coli. The three OXA-48-like enzymes demonstrated significant hydrolysis activity against meropenem, and the classical ß-lactamase inhibitor had no significant inhibitory effect. In conclusion, this study demonstrated the diversity of the blaOXA gene and highlighted the emergence of novel OXA carbapenemases in S. xiamenensis. Further attention to S. xiamenensis and OXA carbapenemases is recommended for the effective prevention and control of antibiotic-resistant bacteria.

Molecular Characterization of Carbapenem-Resistant Acinetobacter baumannii with Special Reference to Carbapenemases: A Systematic Review.

Carbapenemases are ß-lactamase enzymes that hydrolyze a variety of ß-lactams including carbapenem and belong to different Ambler classes (A, B, D). These enzymes can be encoded by plasmid or chromosomal-mediated genes. The major issues associated with carbapenemases-producing organisms are compromising the activity and increasing the resistance to carbapenems which are the last resort antibiotics used in treating serious infections. The global increase of pathogen, carbapenem-resistant A. baumannii has significantly threatened public health. Thus, there is a pressing need for a better understanding of this pathogen, to know the various carbapenem resistance encoding genes and dissemination of resistance genes from A. baumannii which help in developing strategies to overcome this problem. The horizontal transfer of resistant determinants through mobile genetic elements increases the incidence of multidrug, extensive drug, and Pan-drug resistant A. baumannii. Therefore, the current review aims to know the various mechanisms of carbapenem resistance, categorize and discuss carbapenemases encoding genes and various mobile genetic elements, and the prevalence of carbapenemase genes in recent years in A. baumannii from various geographical regions.

Kinetics Analysis of ß-Lactams Hydrolysis by OXA-50 Variants of Pseudomonas aeruginosa.

Pseudomonas aeruginosa is an opportunist pathogen usually associated with life threatening infections and exhibits a set of intrinsic and acquired antimicrobial mechanisms. Although resistance to penicillins-like compounds is commonly associated with the chromosomal Pseudomonas-derived cephalosporinases ß-lactamase, the real contribution of OXA-50, a second chromosomally encoded ß-lactamase, remains unclear. In this study, we characterized the biochemical properties of OXA-50, OXA-488, and OXA-494. Both oxacilinases differ from OXA-50 in two amino acids each. The blaOXA-50, blaOXA-488, and blaOXA-494 were cloned into pET26b+ that was transformed into Escherichia coli DH5α strain, expressed in E. coli BL21 strain, and then purified for obtaining the hydrolytic parameters. Benzylpenicillin was the preferential substrate instead of oxacillin. Besides, OXA-488 showed a threefold increase in catalytic efficiency for benzylpenicillin, and it was twofold more efficient in hydrolyzing imipenem, compared with OXA-50, although such carbapenemase activity was considered weak. In addition, OXA-488 and OXA-494 showed an increased affinity for penicillins, which contributed to the increased catalytic efficiency against ampicillin, especially OXA-488. Chromosomally encoded resistance mechanisms are usually overshadowed by acquired mechanisms. However, understanding their real contribution is essential to comprehend the versatile profiles verified in P. aeruginosa isolates. Such information can help to choose the best therapy in a scenario of limited options.

High Prevalence of ST502 Carrying an OXA-24 Carbapenemase gene in Carbapenem-Nonsusceptible Acinetobacter baumannii-calcoaceticus Isolates in Romania.

Background: Acinetobacter baumannii can cause difficult-to-treat infections because it can acquire extensive antimicrobial resistance mechanisms. We aim to describe the antimicrobial resistance pattern and the genetic basis of carbapenem-nonsusceptible A. baumannii isolates in a University Hospital in Romania, a country where multidrug-resistant A. baumannii is widespread. Methods: We collected 104 consecutive meropenem-nonsusceptible A. baumannii isolates from 104 patients (36% female, mean age [SD] of 63 [16] years) between May 2015 and August 2017 from a large tertiary center in Romania. Whole-genome sequencing of representative isolates from amplified fragment length polymorphism clusters was used to determine clonality and resistance patterns. Results: All isolates were resistant to piperacillin/tazobactam, ceftazidime, and ciprofloxacin; 88.5% to gentamicin; and 90.4% to trimethoprim/sulfamethoxazole. In contrast, 79.8% and 99.0% were susceptible to tobramycin and colistin, respectively. The only isolate resistant to colistin had an minimum inhibitory concentration (MIC) of ≥16 mg/L. The blaOXA-24 gene was detected in 79.1% and blaOXA-23 in 20.9% of the isolates. In one isolate, blaOXA-23 was copresent with blaOXA-24. ST502 (Oxford scheme) was the most prevalent sequence type and was exclusively associated with blaOXA-24. Conclusions: ST502 associated with blaOXA-24 was frequently observed in the region where carbapenem-nonsusceptible A. baumannii was found to be endemic. In these isolates, tobramycin and colistin might be the remaining therapeutic options. Due to differences in gentamicin and tobramycin resistance in these isolates, surveillance data should not group gentamicin, tobramycin, and amikacin together as aminoglycosides.

Detection of metallo-beta lactamases and oxacillinase genes in carbapenem-resistant Acinetobacter baumannii strains isolated in Morocco.

INTRODUCTION: resistance to carbapenem is widespread among Acinetobacter baumannii (A. baumannii) strains. Metallo-beta lactamases enzymes (MBL) are responsible for carbapenem resistance, as are oxacillinases (OXA). In recent years, MBL producing carbapenem-resistant strains have been reported in the world and Morocco at increasing rates. Our study aimed to investigate the presence of carbapenemases in acinetobacter strains isolated from hospitalized patients in CHU Fez. METHODS: a total of 58 imipenem-resistant A. baumannii strains isolated from clinical samples were investigated. The presence of MBL was described phenotypically by the double-disk synergy test (DDST), MBL E-test, and modified Hodge test. The blaIMP, blaVIM, genes, and blaOXA-23, blaOXA-51 genes were investigated by multiplex polymerase chain reaction (PCR). The blaNDM-1 gene was determined by simplex PCR. RESULTS: fifty-eight strains were resistant to imipenem (98%), the modified Hodge test (MHT) was positive for 58 strains (100%), 47 strains (82%) were found to be positive for MBL by the test of double-disk synergy (DDST), 58 strains (100%) were positive by E-test MBL. The OXA 51 gene was detected in all strains, and the OXA 23 gene was detected in 53 strains (91%). In addition, the MBL genes were not detected by genotypic methods. CONCLUSION: the OXA-23 and OXA-51 carbapenemases type are responsible for the resistance to carbapenems in A. baumannii resistant to carbapenems in our establishment. Resistance to carbapenems by MBL enzymes has been found by phenotypic tests, which must be confirmed by genotypic methods; and solicit other MBL genes.

Oxacillinase Gene Distribution, Antibiotic Resistance, and Their Correlation with Biofilm Formation in Acinetobacter baumannii Bloodstream Isolates.

Objectives: The limitations of treatment options in bloodstream infections caused by multidrug-resistant Acinetobacter baumannii (MDRAB) have been related to high morbidity and mortality. The aim of our present study was to determine antimicrobial susceptibility profiles, molecular resistance patterns, and biofilm properties of A. baumannii isolated from bloodstream infections. Materials and Methods: In the present study, a total of 44 A. baumannii bloodstream isolates were included. Antimicrobial susceptibility profiles and biofilm formation ability were assessed. The distribution of class D carbapenemases, ISAba1, ISAba1/blaOXA-23, blaNDM-1, mcr-1, and ompA was investigated by polymerase chain reaction (PCR). Arbitrarily primed-PCR (AP-PCR) was performed to evaluate clonal relationships. Results: A total of 32 isolates were MDRAB, whereas 6 isolates were also resistant to colistin without mcr-1 positivity. All isolates were harboring blaOXA-51 gene, whereas blaOXA-23 positivity was 63.6%. Fifty percent of the isolates had ISAba1. ISAba1 upstream of blaOXA-23 was determined in 18 isolates. None of the isolates were positive for blaNDM-1 gene. Majority of the strains were strong biofilm producers (86.8%). A total of 56.8% of the isolates were positive for ompA gene with no direct association with strong biofilm formation. However, blaOXA-51 + 23 genotype and trimethoprim-sulfamethoxazole resistance showed a significant relationship with biofilm formation. AP-PCR analysis revealed six distinct clusters of A. baumannii. Conclusions: Herein, majority of the A. baumannii blood isolates were characterized as blaOXA-51+OXA-23 carbapenemase genotype and were strong biofilm formers. None of the isolates were positive for blaNDM-1, which was promising. Resistant isolates were tended to form strong biofilms. Our results highlight the emergence of oxacillinase-producing MDRAB isolated from bloodstream with high biofilm formation ability.

The Current Burden of Carbapenemases: Review of Significant Properties and Dissemination among Gram-Negative Bacteria.

Carbapenemases are ß-lactamases belonging to different Ambler classes (A, B, D) and can be encoded by both chromosomal and plasmid-mediated genes. These enzymes represent the most potent ß-lactamases, which hydrolyze a broad variety of ß-lactams, including carbapenems, cephalosporins, penicillin, and aztreonam. The major issues associated with carbapenemase production are clinical due to compromising the activity of the last resort antibiotics used for treating serious infections, and epidemiological due to their dissemination into various bacteria across almost all geographic regions. Carbapenemase-producing Enterobacteriaceae have received more attention upon their first report in the early 1990s. Currently, there is increased awareness of the impact of nonfermenting bacteria, such as Acinetobacter baumannii and Pseudomonas aeruginosa, as well as other Gram-negative bacteria that are carbapenemase-producers. Outside the scope of clinical importance, carbapenemases are also detected in bacteria from environmental and zoonotic niches, which raises greater concerns over their prevalence, and the need for public health measures to control consequences of their propagation. The aims of the current review are to define and categorize the different families of carbapenemases, and to overview the main lines of their spread across different bacterial groups.

PCR Detection of Oxacillinases in Bacteria.

Oxacillinases (OXA) have been mostly described in Enterobacteriaceae, Acinetobacter, and Pseudomonas species. Recent years have witnessed an increased prevalence of intrinsic and/or acquired ß-lactamase-producing Acinetobacter in food-producing animals. This study was conducted to assess the prevalence of OXA among selected bacterial species and to characterize these enzymes by in silico analysis. Screening of OXA was performed by PCR amplification using specific pairs of oligonucleotides. Overall, 40 pairs of primers were designed, of which 6 were experimentally tested in vitro. Among 49 bacterial isolates examined, the presence of blaOXA-1-like genes was confirmed in 20 cases (41%; 19 times in Klebsiella pneumoniae and once in Enterobacter cloacae). No OXA were found in animal isolates. The study results confirmed the specificity of the designed oligonucleotide pairs. Furthermore, the designed primers were found to possess the ability to specifically detect 90.2% of all OXA. These facts suggest that the in silico and in vitro tested primers could be used for single or multiplex PCR to screen for the presence of OXA in various bacteria, as well as to monitor their spread. At the same time, the presence of conserved characteristic amino acids and motifs was confirmed by in silico analysis of sequences of representative members of OXA.

Substrate Specificity of OXA-48 after ß5-ß6 Loop Replacement.

OXA-48 carbapenemase has rapidly spread in many countries worldwide with several OXA-48-variants being described, differing by a few amino acid (AA) substitutions or deletions, mostly in the ß5-ß6 loop. While single AA substitutions have only a minor impact on OXA-48 hydrolytic profiles, others with 4 AA deletions result in loss of carbapenem hydrolysis and gain of expanded-spectrum cephalosporin (ESC) hydrolysis. We have replaced the ß5-ß6 loop of OXA-48 with that of OXA-18, a clavulanic-acid inhibited oxacillinase capable of hydrolyzing ESCs but not carbapenems. The hybrid enzyme OXA-48Loop18 was able to hydrolyze ESCs and carbapenems (although with a lower kcat), even though the ß5-ß6 loop was longer and its sequence quite different from that of OXA-48. The kinetic parameters of OXA-48Loop18 were in agreement with the MIC values. X-ray crystallography and molecular modeling suggest that the conformation of the grafted loop allows the binding of bulkier substrates, unlike that of the native loop, expanding the hydrolytic profile. This seems to be due not only to differences in AA sequence, but also to the backbone conformation the loop can adopt. Finally, our results provide further experimental evidence for the role of the ß5-ß6 loop in substrate selectivity of OXA-48-like enzymes and additional details on the structure-function relationship of ß-lactamases, demonstrating how localized changes in these proteins can alter or expand their function, highlighting their plasticity.

Evaluation of a Loop-Mediated Isothermal Amplification Assay to Detect Carbapenemases Directly From Bronchoalveolar Lavage Fluid Spiked With Acinetobacter spp.

Carbapenem-resistant Acinetobacter spp. mainly Acinetobacter baumannii are frequently causing nosocomial infections with high mortality. In this study, the efficacy of the Eazyplex® SuperBug Complete A system, based on loop-mediated isothermal amplification (LAMP), to detect the presence of carbapenemases in Acinetobacter spp. directly from bronchoalveolar lavage (BAL) samples was assessed. A total of 22 Acinetobacter spp. strains producing OXA-23, OXA-40, OXA-58, NDM, and IMP were selected. Eazyplex SuperBug Complete A kit, used with the Genie II device, is a molecular diagnostics kit that detects a selection of genes that express carbapenemases (bla KPC , bla NDM , bla VIM , bla OXA-48 , bla OXA-23 , bla OXA-40 , and bla OXA-58 ). Negative BAL samples were identified, McFarland solutions were prepared from each of the 22 Acinetobacter strains and serial dilutions in saline solution were made to finally spike BAL samples to a concentration of 102 and 103 CFU/ml. Fifteen concentrations out of the 44 tested out did not provide detection of the carbapenemase-producing gene, all but one being at the lowest concentration tested at 102 CFU/ml; therefore, the limit of sensitivity is 103 CFU/ml. This assay represents the kind of advantages that investing in molecular diagnostics brings to the clinical practice, allowing the identification of carbapenemases in less than 30 min with a sensitivity of 103 CFU/ml.

In vitro and in vivo Virulence Potential of the Emergent Species of the Acinetobacter baumannii (Ab) Group.

The increased use of molecular identification methods and mass spectrometry has revealed that Acinetobacter spp. of the A. baumannii (Ab) group other than A. baumannii are increasingly being recovered from human samples and may pose a health challenge if neglected. In this study 76 isolates of 5 species within the Ab group (A. baumannii n = 16, A. lactucae n = 12, A. nosocomialis n = 16, A. pittii n = 20, and A. seifertii n = 12), were compared in terms of antimicrobial susceptibility, carriage of intrinsic resistance genes, biofilm formation, and the ability to kill Caenorhabditis elegans in an infection assay. In agreement with previous studies, antimicrobial resistance was common among A. baumannii while all other species were generally more susceptible. Carriage of genes encoding different efflux pumps was frequent in all species and the presence of intrinsic class D ß-lactamases was reported in A. baumannii, A. lactucae (heterotypic synonym of A. dijkshoorniae) and A. pittii but not in A. nosocomialis and A. seifertii. A. baumannii and A. nosocomialis presented weaker pathogenicity in our in vitro and in vivo models than A. seifertii, A. pittii and, especially, A. lactucae. Isolates from the former species showed decreased biofilm formation and required a longer time to kill C. elegans nematodes. These results suggest relevant differences in terms of antibiotic susceptibility patterns among the members of the Ab group as well as highlight a higher pathogenicity potential for the emerging species of the group in this particular model. Nevertheless, the impact of such potential in the human host still remains to be determined.

Prevalence and Mechanisms of Carbapenem Resistance Among Acinetobacter baumannii Clinical Isolates in Egypt.

The increasing number of carbapenem-resistant Acinetobacter baumannii clinical isolates is a major concern, which restricts therapeutic options for treatment of serious infections caused by this emerging pathogen. The aim of this work is to assess the antimicrobial resistance profile and identify the molecular mechanisms involved in carbapenem resistance in A. baumannii isolated from different clinical sources in Mansoura University Hospitals, Egypt. Antimicrobial susceptibility testing has shown that resistance to carbapenem has dramatically increased (98%) with concomitant elevated levels of resistance to quinolones, trimethoprim/sulfamethoxazole, and aminoglycosides. Polymyxin B and colistin are considered the last resort. Random amplified polymorphic DNA (RAPD) typing method revealed great diversity among A. baumannii isolates. Coexistence of diverse intrinsic and acquired carbapenem-hydrolyzing ß-lactamases has been detected in the tested isolates: Ambler class A: blaKPC (56%) and blaGES (48%), and Ambler class B: blaNDM (30%), blaSIM (28%), blaVIM (20%), and blaIMP (10%). Most isolates (94%) carried blaOXA-23-like and blaOXA-51-like simultaneously. blaOXA-23-like was preceded by ISAba1 providing a potent promoter activity for its expression. Sequencing analysis revealed that ISAba1 has been also inserted in carbapenem resistance-associated outer membrane protein (OMP) (carO) gene in three isolates, two of which were clonal based on RAPD typing, leading to interruption of its expression as confirmed by SDS-PAGE analysis of OMP fractions. Carbapenem resistance genes are widely distributed among A. baumannii clinical isolates from different clinical sources. Therefore, enhanced infection control measures, effective barriers, and rational use of antimicrobials should be enforced in hospitals for minimizing the widespread resistance to carbapenems and all other antibiotics.

Acinetobacter spp in a Third World Country with Socio-economic and Immigrants Challenges.

INTRODUCTION: In the last decade, Acinetobacter species have taken a major public health concern. This is mainly due the increased resistance to a wide range of antibiotics causing treatment challenges. In view of the constant population mobilization and the economic crisis that Lebanon is currently facing, it becomes a necessity to re-evaluate the real threat of Acinetobacter spp and its implication in the one health. METHODOLOGY: This review was conducted through the analysis of 45 research papers and reports pertaining to Acinetobacter spp performed in Lebanon. More than 82% of the papers consulted were published in international journals and more than 70 percent of them had received impact factor. RESULTS: An in depth description of the involvement of this organism in human infection and its role as potential pathogen or simple colonizer was performed. In addition, the different aspects of resistance, mostly to carbapenems and colistin was studied and summarized. While in animals and environment, susceptible strains were mostly isolated, OXA-23/OXA-24 were predominant in humans. Recently, NDM-1 producing Acinetobacter spp was detected in a Syrian refugee which then was reported in Lebanese patients. The bacterial identification procedures are non-systematic and not always reliable in the Lebanese studies presenting sometimes discrepancies an inconsistency. CONCLUSION: Acinetobacter is commonly isolated Lebanon. In view of the spread of resistance among these isolated and their dissemination, Infection control measures attempting to control the spread of this genus in and outside hospitals are lacking and thus require more attention and stewardship activities.

Bacteremia and meningitis caused by OXA-23-producing Acinetobacter baumannii - molecular characterization and susceptibility testing for alternative antibiotics.

BACKGROUND: Carbapenem-resistant Acinetobacter baumannii infection is a concern in developing countries due to high incidence, few therapeutic options, and increasing costs. OBJECTIVE: Characterize and analyze the antibiotic susceptibility patterns of carbapenem-resistant A. baumannii isolates and evaluate clinical data of meningitis and bacteremia caused by this microorganism. METHODS: Twenty-six A. baumannii isolates from 23 patients were identified by MALDI-TOF and automated methods and genotyped using pulsed field genotyping electrophoresis. Clinical data and outcomes were evaluated. Susceptibility of isolates to colistin, tigecycline, meropenem, imipenem, and doxycycline was determined. RESULTS: Mortality due to A. baumannii infections was 73.91%; all patients with meningitis and 7/8 patients with ventilator-associated pneumonia died. All isolates were susceptibility to polymyxin (100%; MIC50, MIC90: 1µg/mL, 1µg/mL) and colistin (100%; MIC50, MIC90: 2µg/mL, 2µg/mL), and 92% were susceptible to tigecycline (MIC50, MIC90: 1µg/mL, 1µg/mL) and doxycycline (MIC50, MIC90: 2µg/mL, 2µg/mL). blaOXA-23 was identified in 24 isolates. Molecular typing showed 8 different patterns: 13 isolates belonged to pattern A (50%). CONCLUSION: Carbapenem-resistant A. baumannii infections mortality is high. Alternative antimicrobial therapy (doxycycline) for selected patients with carbapenem-resistant A. baumannii infection should be considered.

Emergence and Persistence of High-Risk Clones Among MDR and XDR A. baumannii at a Brazilian Teaching Hospital.

Dissemination of carbapenem-resistant Acinetobacter baumannii is currently one of the priority themes discussed around the world, including in Brazil, where this pathogen is considered endemic. A total of 107 carbapenem-resistant A. baumannii (CRAB) isolates were collected from patients with bacteraemia attended at a teaching hospital in Brazil from 2008 to 2014. From these samples, 104 (97.2%) carried bla OXA-23-like, all of them associated with ISAba1 The bla OXA-231 (1.9%) and bla OXA-72 (0.9%) genes were also detected in low frequencies. All isolates were susceptible to minocycline, and 38.3% of isolates presented intermediate susceptibility to tigecycline (MIC = 4 µg/ml). Molecular typing assessed by multi-locus sequence typing demonstrated that the strains were mainly associated with clonal complexes CC79 (47.4%), followed by CC1 (16.9%), and CC317 (18.6%), belonging to different pulsotypes and in different prevalences over the years. Changes in the clones' prevalence reinforce the need of identifying and controlling CRAB in hospital settings to preserve the already scarce therapeutic options available.