Carbapenem-resistant Acinetobacter Baumannii Clinical Isolates Research Articles

Carbapenem-resistant Acinetobacter baumannii (CRAB): metabolic adaptation and transcriptional response to human urine (HU).

Carbapenem-resistant Acinetobacter baumannii (CRAB) is a major human pathogen and a research priority for developing new antimicrobial agents. CRAB is a causative agent of a variety of infections in different body sites. One of the manifestations is catheter-associated urinary tract infection, which exposes the bacteria to the host's urine, creating a particular environment. Exposure of two CRAB clinical isolates, AB5075 and AMA40, to human urine (HU) resulted in the differential expression levels of 264 and 455 genes, respectively, of which 112 were common to both strains. Genes within this group play roles in metabolic pathways such as phenylacetic acid (PAA) catabolism, the Hut system, the tricarboxylic acid (TCA) cycle, and other processes like quorum sensing and biofilm formation. These results indicate that the presence of HU induces numerous adaptive changes in gene expression of the infecting bacteria. These modifications presumably help bacteria establish and thrive in the hostile conditions in the urinary tract. These analyses advance our understanding of CRAB's metabolic adaptations to human fluids, as well as expanding knowledge on bacterial responses to distinct human fluids containing different concentrations of human serum albumin (HSA).

Emergence of eravacycline heteroresistance in carbapenem-resistant Acinetobacter baumannii isolates in China.

Carbapenem-resistant Acinetobacter baumannii (CRAB) is resistant to almost all antibiotics. Eravacycline, a newer treatment option, has the potential to treat CRAB infections, however, the mechanism by which CRAB isolates develop resistance to eravacycline has yet to be clarified. This study sought to investigate the features and mechanisms of eravacycline heteroresistance among CRAB clinical isolates. A total of 287 isolates were collected in China from 2020 to 2022. The minimum inhibitory concentration (MIC) of eravacycline and other clinically available agents against A. baumannii were determined using broth microdilution. The frequency of eravacycline heteroresistance was determined by population analysis profiling (PAP). Mutations and expression levels of resistance genes in heteroresistant isolates were determined by polymerase chain reaction (PCR) and quantitative real-time PCR (qRT-PCR), respectively. Antisense RNA silencing was used to validate the function of eravacycline heteroresistant candidate genes. Twenty-five eravacycline heteroresistant isolates (17.36%) were detected among 144 CRAB isolates with eravacycline MIC values ≤4 mg/L while no eravacycline heteroresistant strains were detected in carbapenem-susceptible A. baumannii (CSAB) isolates. All eravacycline heteroresistant strains contained OXA-23 carbapenemase and the predominant multilocus sequence typing (MLST) was ST208 (72%). Cross-resistance was observed between eravacycline, tigecycline, and levofloxacin in the resistant subpopulations. The addition of efflux pump inhibitors significantly reduced the eravacycline MIC in resistant subpopulations and weakened the formation of eravacycline heteroresistance in CRAB isolates. The expression levels of adeABC and adeRS were significantly higher in resistant subpopulations than in eravacycline heteroresistant parental strains (P < 0.05). An ISAba1 insertion in the adeS gene was identified in 40% (10/25) of the resistant subpopulations. Decreasing the expression of adeABC or adeRS by antisense RNA silencing significantly inhibited eravacycline heteroresistance. In conclusion, this study identified the emergence of eravacycline heteroresistance in CRAB isolates in China, which is associated with high expression of AdeABC and AdeRS.

In vitro activity of sulbactam-durlobactam against colistin-resistant and/or cefiderocol-non-susceptible, carbapenem-resistant Acinetobacter baumannii collected in U.S. hospitals.

The activity of a novel β-lactamase inhibitor combination, sulbactam-durlobactam (SUL-DUR), was tested against 87 colistin-resistant and/or cefiderocol-non-susceptible carbapenem-resistant Acinetobacter baumannii clinical isolates collected from U.S. hospitals between 2017 and 2019. Among them, 89% and 97% were susceptible to SUL-DUR and imipenem plus SUL-DUR, with MIC50/MIC90 values of 2 µg/mL/8 µg/mL and 1 µg/mL/4 µg/mL, respectively. The presence of amino acid substitutions in penicillin-binding protein 3, including previously reported A515V or T526S, was associated with SUL-DUR non-susceptibility.

Comparison of loop-mediated isothermal amplification, multiplex PCR, and REP- PCR techniques for identification of carbapenem-resistant Acinetobacter baumannii clinical isolates

Background and Objectives: Acinetobacter baumannii, an opportunistic pathogen, is related to hospital-acquired infections and increased mortality. This study aimed to develop the loop-mediated isothermal amplification (LAMP) test for the fast-de- tecting of A. baumannii isolates as well as determining genetic relatedness for these isolates via the REP-PCR technique.&#x0D; Materials and Methods: LAMP primers and multiplex PCR primers were designed for recognizing A. baumannii isolates harboring the bla SHV-1 , bla PER-1 , bla , AMPC, qnr, and aac (6)-1 genes, were collected (October 2020 to February 2021) from Shahid Motahari Hospital, Tehran, Iran. Combination disc test (CDT) results were used to assess the phenotypic iden- tification of isolates from ESBL producers. The sensitivity of the LAMP method was evaluated using a range of serial dilu- tions of genomic DNA. Results were compared between the LAMP technique, and multiplex PCR. The genetic diversity of clinical isolates was determined by REP-PCR.&#x0D; Results: Among one hundred A. baumannii samples and based on the combined disc test, 56% of isolates were ESBL pro- ducers. The sensitivity of the LAMP technique for the identification of A. baumannii was 4.06 ng/μl whilst the multiplex PCR was (16.2 ng/μl). Regarding multiplex PCR, (68%) of the isolates were bla SHV-1 positive, (40%) bla , (85%) aac (6́)-1, AMPC (67%), bla TEM-1 (63%), and (15%) qnr respectively. While in LAMP, (69%) of isolates were bla positive, (86%) aac (6')-1, and (20%) qnr. The results of AMPC, bla TEM-1 , and bla PER-1 genes showed 100% compatibility between multiplex PCR and LAMP assays. The results of REP-PCR indicated there were 17 clones, clone A at 14% was the most prevalent of the isolates.&#x0D; Conclusion: Wherever equipment and financial constraints are crucial, the LAMP test offers a better and more potent detec- tion rate for the identification of A. baumannii isolates than multiplex PCR. Furthermore, the genetic diversity of A. bauman- nii in these clinical isolates showed frequent commonality of genotypes.

In vitro activity of cefiderocol against carbapenem-resistant Acinetobacter baumannii clinical isolates: a single center experience.

Introduction: Cefiderocol (CFDC) is a novel siderophore cephalosporin with broad-spectrum activity against carbapenem-resistant Gram-negative bacteria. Gram-negative bacterial isolates' resistance to cefiderocol (CFDC) is emerging in clinical practice.

Functional characterization and clinical implication of a novel epidemic carbapenem-resistant Acinetobacter baumannii genetic marker

ObjectivesThe aim of the study was to evaluate the distribution and function of contact-dependent growth inhibition (CDI) systems associated with carbapenem-resistant Acinetobacter baumannii (CRAB) isolates. MethodsIsolates were examined by multilocus sequence typing (MLST) and polymerase chain reaction (PCR) for the presence of CDI genes in CRAB and carbapenem-susceptible A. baumannii (CSAB) from patients with invasive disease in a medical center in Taiwan. Inter-bacterial competition assays were performed to characterize the in vitro function of the CDI system. ResultsA total of 89 (61.0%) CSAB and 57 (39.0%) CRAB isolates were collected and examined. ST787 (20/57; 35.1%) was the predominant sequence type among CRAB, followed by ST455 (10/57; 17.5%). More than half the CRAB (56.1%, 32/57) belonged to CC455 and more than one third (38.6%, 22/57) to CC92. A novel CDI system, cdiTYTH1, was found in 87.7% (50/57) of the CRAB but in only 1.1% (1/89) of the CSAB isolates (P<0.00001). The cdiTYTH1 was also identified in 94.4% (17/18) of previously genome-sequenced CRAB isolates and only one CSAB isolate from Taiwan. Two other previously reported CDI (cdi19606-1 and cdi19606-2) were not found in these isolates, except both were found in one CSAB. All six CRAB without cdiTYTH1 showed growth inhibition by a CSAB carrying cdiTYTH1 in vitro. All clinical CRAB isolates belonging to the predominant CC455 carried the newly identified cdiTYTH1. ConclusionsThis CDI system was widespread in CRAB clinical isolates and appeared to be an epidemic genetic marker for CRAB in Taiwan. The cdiTYTH1 was functional in vitro in bacterial competition assay.

Detection of the blaVIM-2 Gene in Carbapenem-Resistant Acinetobacter baumannii Clinical Isolates in Sudan

Background: Acinetobacter baumannii is a pleomorphic aerobic Gram-negative bacillus that is notorious for having multidrug resistance traits. Carbapenem-resistant Acinetobacter baumannii (CRAB) is a global concern due to its ability to retain and disseminate resistance genes, which poses a threat to the spread of resistance among bacterial communities in hospital settings. The aim of our study was to evaluate the existence of the blaVIM-2 gene in carbapenem-resistant Acinetobacter baumannii clinical isolates from Sudanese hospitals. Methods and Results: Forty clinical isolates of Acinetobacter baumannii were collected from June 2021 to April 2022. All isolates of Acinetobacter baumannii were identified via BioMérieux's Vitek-2 automated system (Marcy l'Étoile, France) and evaluated for phenotypic resistance to carbapenem, using imipenem and meropenem. The enzymatic mode of resistance was assessed by the Modified Hodge test (MHT). A real-time PCR was used to detect the presence of the blaVIM-2 gene. Of 40 isolates, 32(80%) were resistant to imipenem, 4(10%) were moderately resistant, and 4(10%) were susceptible to imipenem; 24(60%) were resistant to meropenem, 10(25%) were moderately resistant, and 6(15%) were susceptible to meropenem. MHT was 70% positive with imipenem use and 55% positive with meropenem use. Real-time PCR revealed that only 30% of the samples were positive for the blaVIM-2 gene. All blaVIM-2-positive isolates were resistant to both imipenem and meropenem. Conclusion: Resistance to carbapenem poses a serious threat, denying patients treatment options. It is essential to make continuous surveillance of these strains to prevent the development of resistant strains.

Antimicrobial Activity of a Repurposed Harmine-Derived Compound on Carbapenem-Resistant Acinetobacter baumannii Clinical Isolates.

ObjectivesThe spread of antibiotic resistant bacteria is an important threat for human health. Acinetobacter baumannii bacteria impose such a major issue, as multidrug- to pandrug-resistant strains have been isolated, rendering some infections untreatable. In this context, carbapenem-resistant A. baumannii bacteria were ranked as top priority by both WHO and CDC. In addition, A. baumannii bacteria survive in harsh environments, being capable of resisting to disinfectants and to persist prolonged periods of desiccation. Due to the high degree of variability found in A. baumannii isolates, the search for new antibacterials is very challenging because of the requirement of drug target conservation amongst the different strains. Here, we screened a chemical library to identify compounds active against several reference strains and carbapenem-resistant A. baumannii bacteria.MethodsA repurposing drug screen was undertaken to identify A. baumannii growth inhibitors. One hit was further characterized by determining the IC50 and testing the activity on 43 modern clinical A. baumannii isolates, amongst which 40 are carbapenem-resistant.ResultsThe repurposing screen led to the identification of a harmine-derived compound, called HDC1, which proves to have bactericidal activity on the multidrug-resistant AB5075-VUB reference strain with an IC50 of 48.23 µM. In addition, HDC1 impairs growth of 43 clinical A. baumannii isolates.ConclusionsWe identified a compound with inhibitory activity on all tested strains, including carbapenem-resistant clinical A. baumannii isolates.

Whole-genome analysis of carbapenem-resistant Acinetobacter baumannii from clinical isolates in Southern Thailand

The worldwide spread of carbapenem-resistant Acinetobacter baumannii (CRAB) has become a healthcare challenge for some decades. To understand its molecular epidemiology in Southern Thailand, we conducted whole-genome sequencing (WGS) of 221 CRAB clinical isolates. A comprehensive bioinformatics analysis was performed using several tools to assemble, annotate, and identify sequence types (STs), antimicrobial resistance (AMR) genes, mobile genetic elements (MGEs), and virulence genes. ST2 was the most prevalent ST in the CRAB isolates. For the detection of AMR genes, almost all CRAB isolates carried the blaOXA-23 gene, while certain isolates harbored the blaNDM-1 or blaIMP-14 genes. Also, various AMR genes were observed in these CRAB isolates, particularly aminoglycoside resistance genes (e.g., armA, aph(6)-Id, and aph(3″)-Ib), fosfomycin resistance gene (abaF), and tetracycline resistance genes (tet(B) and tet(39)). For plasmid replicon typing, RepAci1 and RepAci7 were the predominant replicons found in the CRAB isolates. Many genes encoding for virulence factors such as the ompA, adeF, pgaA, lpxA, and bfmR genes were also identified in all CRAB isolates. In conclusion, most CRAB isolates contained a mixture of AMR genes, MGEs, and virulence genes. This study provides significant information about the genetic determinants of CRAB clinical isolates that could assist the development of strategies for improved control and treatment of these infections.

In Vitro and In Vivo Activity of AS101 against Carbapenem-Resistant Acinetobacter baumannii.

The increasing trend of carbapenem-resistant Acinetobacter baumannii (CRAB) worldwide has become a concern, limiting therapeutic alternatives and increasing morbidity and mortality rates. The immunomodulation agent ammonium trichloro (dioxoethylene-O,O′-) tellurate (AS101) was repurposed as an antimicrobial agent against CRAB. Between 2016 and 2018, 27 CRAB clinical isolates were collected in Taiwan. The in vitro antibacterial activities of AS101 were evaluated using broth microdilution, time-kill assay, reactive oxygen species (ROS) detection and electron microscopy. In vivo effectiveness was assessed using a sepsis mouse infection model. The MIC range of AS101 for 27 CRAB isolates was from 0.5 to 32 µg/mL, which is below its 50% cytotoxicity (approximately 150 µg/mL). Bactericidal activity was confirmed using a time-kill assay. The antibacterial mechanism of AS101 was the accumulation of the ROS and the disruption of the cell membrane, which, in turn, results in cell death. The carbapenemase-producing A. baumannii mouse sepsis model showed that AS101 was a better therapeutic effect than colistin. The mice survival rate after 120 h was 33% (4/12) in the colistin-treated group and 58% (7/12) in the high-dose AS101 (3.33 mg/kg/day) group. Furthermore, high-dose AS101 significantly decreased bacterial population in the liver, kidney and spleen (all p < 0.001). These findings support the concept that AS101 is an ideal candidate for further testing in future studies.

Efficacy of EBL-1003 (apramycin) against Acinetobacter baumannii lung infections in mice

ObjectivesNovel therapeutics are urgently required for the treatment of carbapenem-resistant Acinetobacter baumannii (CRAB) causing critical infections with high mortality. Here we assessed the therapeutic potential of the clinical-stage drug candidate EBL-1003 (crystalline free base of apramycin) in the treatment of CRAB lung infections. MethodsThe genotypic and phenotypic susceptibility of CRAB clinical isolates to aminoglycosides and colistin was assessed by database mining and broth microdilution. The therapeutic potential was assessed by target attainment simulations on the basis of time–kill kinetics, a murine lung infection model, comparative pharmacokinetic analysis in plasma, epithelial lining fluid (ELF) and lung tissue, and pharmacokinetic/pharmacodynamic (PKPD) modelling. ResultsResistance gene annotations of 5451 CRAB genomes deposited in the National Database of Antibiotic Resistant Organisms (NDARO) suggested >99.9% of genotypic susceptibility to apramycin. Low susceptibility to standard-of-care aminoglycosides and high susceptibility to EBL-1003 were confirmed by antimicrobial susceptibility testing of 100 A. baumannii isolates. Time–kill experiments and a mouse lung infection model with the extremely drug-resistant CRAB strain AR Bank #0282 resulted in rapid 4-log CFU reduction both in vitro and in vivo. A single dose of 125 mg/kg EBL-1003 in CRAB-infected mice resulted in an AUC of 339 h × μg/mL in plasma and 299 h × μg/mL in ELF, suggesting a lung penetration of 88%. PKPD simulations suggested a previously predicted dose of 30 mg/kg in patients (creatinine clearance (CLCr) = 80 mL/min) to result in >99% probability of –2 log target attainment for MICs up to 16 μg/mL. ConclusionsThis study provides proof of concept for the efficacy of EBL-1003 in the treatment of CRAB lung infections. Broad in vitro coverage, rapid killing, potent in vivo efficacy, and a high probability of target attainment render EBL-1003 a strong therapeutic candidate for a priority pathogen for which treatment options are very limited.

Virulence role of the outer membrane protein CarO in carbapenem-resistant Acinetobacter baumannii

ABSTRACT Novel approaches to treat carbapenem-resistant Acinetobacter baumannii (CRAB) infections are urgently needed and anti-virulence drugs represent promising alternatives, but our knowledge on potential targets is scarce. We searched for potential A. baumannii virulence factors by whole-genome sequencing-based comparisons of CRAB clinical isolates causing bloodstream infections secondary to ventilator-associated pneumonia from demographics and clinically homogeneous patients, who received optimal treatment but with different clinical outcomes. Thus, the carO gene was interrupted in CRAB isolates from surviving patients, while it was intact in isolates from non-surviving patients, and proteomic/immunoblot techniques corroborated it. When the virulence role of A. baumannii CarO was analyzed in model systems, isogenic ΔcarO mutants and a CRAB clinical isolate with truncated CarO, showed lower ability to adhere and invade A549 cells and in vivo virulence. This unnoticed virulence role for CarO postulate this A. baumannii outer membrane protein as a potential target for new therapies against CRAB infections.

Rescued chlorhexidine activity by resveratrol against carbapenem-resistant Acinetobacter baumannii via down-regulation of AdeB efflux pump.

The aim of this study was to determine the activity and synergistic mechanisms of resveratrol in combination with chlorhexidine against carbapenem-resistant Acinetobacter baumannii clinical isolates. The activity of resveratrol plus antimicrobial agents was determined by checkerboard and time-kill assay against carbapenem-resistant A. baumannii isolated from patients at the King Chulalongkorn Memorial Hospital, Bangkok, Thailand. Overexpression of efflux pumps that mediates chlorhexidine susceptibility was characterized by the ethidium bromide accumulation assay. The effect of resveratrol on the expression of efflux pump genes (adeB, adeJ, adeG abeS, and aceI) and the two-component regulators, adeR and adeS was determined by RT-qPCR. The combination of resveratrol and chlorhexidine resulted in strong synergistic and bactericidal activity against carbapenem-resistant A. baumannii. Up-regulation of adeB and aceI was induced by chlorhexidine. However, the addition of resveratrol increased chlorhexidine susceptibility with increased intracellular accumulation of ethidium bromide in A. baumannii indicating that resveratrol acts as an efflux pump inhibitor. Expression of adeB was significantly reduced in the combination of resveratrol with chlorhexidine indicating that resveratrol inhibits the AdeB efflux pump and restores chlorhexidine effect on A. baumannii. In conclusion, reduced adeB expression in A. baumannii was mediated by resveratrol suggesting that AdeB efflux pump inhibition contributes to the synergistic mechanism of resveratrol with chlorhexidine. Our finding highlights the potential importance of resveratrol in clinical applications.

Reliability of phenotypic methods for detection of colistin resistance among carbapenem-resistant Acinetobacter baumannii clinical isolates from Egypt.

Acinetobacter baumannii is a challenging pathogen responsible for serious nosocomial infections. Colistin resistance in carbapenem-resistant A. baumannii strains is a critical health problem as it limits the available therapeutic options. The current work aimed to study the reliability of several phenotypic methods for the detection of colistin resistance among carbapenem-resistant A. baumannii isolates in Egypt. A total of 22 carbapenem-resistant A. baumannii isolates were recovered. Colistin minimum inhibitory concentrations (MICs) were determined using broth microdilution (BMD) and compared to agar dilution (AD), automated system (VITEK-2) and gradient test (E-test) and were analyzed by statistical methods. Phenotypic testing showed that nine of 22 isolates (40.9%) were colistin-resistant by BMD and seven of them were also resistant by AD, with the categorical agreement (CA) of 72.7% and essential agreement (EA) of 90.9%. Colistin MIC results ranged from 1-8 µg/mL and 1-32 µg/mL by both AD and BMD respectively. Detection of colistin resistance by gradient test and automated system showed high very major error (VME) rates (40.9%) compared to BMD with a lack of CA between them. AD gave moderate agreement with BMD by 90.9% EA, 72.7% CA and only 9.1% VME. In delineating colistin breakpoints BMD followed by AD method are defined as the only reliable phenotypic methods for colistin resistance evaluation. More rapid and reliable tests, other than BMD and AD, are required for the convenient detection of colistin resistance in the routine clinical microbiology laboratory daily workflow.

Genetic diversity and molecular characterization of carbapenem-resistant Acinetobacter baumannii clinical isolates from the Punjab, Pakistan

Genetic diversity and molecular characterization of carbapenem-resistant Acinetobacter baumannii clinical isolates from the Punjab, Pakistan

PmrB mutations including a novel 10-amino acid repeat sequence insertion associated with low-level colistin resistance in carbapenem-resistant Acinetobacter baumannii.

The global emergence of colistin resistance in carbapenem-resistant Acinetobacter baumannii (CRAB) clinical isolates is a serious public health concern. We therefore aimed to investigate colistin resistance mechanisms in 5 colistin-resistant (COL-R) CRAB isolates collected from Thai patients in 2016 by whole genome sequencing (WGS) compared with those of 5 colistin-intermediate (COL-I) CRAB isolates from the same period. All isolates were subjected to antimicrobial susceptibility testing, efflux pump inhibitor-based test and WGS. Mutations in known genes associated with colistin resistance were analyzed and deleterious mutations were then predicted by PROVEAN tool. The 10 CRAB isolates carried blaOXA-23 with the addition of blaOXA-58 in 1 isolate. All COL-R isolates exhibited colistin MICs of 4μg/mL except for 1 isolate with that of 16μg/mL. They belonged to ST2, ST16, ST23, ST164 and ST215, whereas the COL-I isolates with colistin MICs of ≤0.25-1μg/mL were ST2, ST164 and ST215. Neither increased efflux pump activity nor mcr gene was found in any COL-R isolate. Three COL-R isolates contained different PmrB variants: a novel 10-amino acid (aa) repeat sequence insertion, VILGCILIFS between positions 27 and 28 (S27_A28insVILGCILIFS) in transmembrane domain (TM); a 1-aa insertion, alanine between positions 162 and 163 (A162_I163insA) in TM; and a 1-aa substitution, A226T in histidine kinase domain. One COL-R isolate possessed PmrA variant with A80V substitution. These alterations were predicted as deleterious. Mechanisms of colistin resistance in the remaining COL-R isolate were still unknown. In conclusion, the alterations in both PmrB and PmrA were predicted and suggested as initial mutations responsible for low-level colistin resistance in our CRAB isolates. Under selective pressure, these isolates may exhibit higher level colistin resistance by the additional mutations, leading to more therapeutic difficulties.

Comparative in vitro activity of sitafloxacin against multidrug-resistant and carbapenem-resistant Acinetobacter baumannii clinical isolates in Thailand

Comparative in vitro activity of sitafloxacin against multidrug-resistant and carbapenem-resistant Acinetobacter baumannii clinical isolates in Thailand

In vitro interactions of ambroxol hydrochloride or amlodipine in combination with antibacterial agents against carbapenem-resistant Acinetobacter baumannii.

The aim of this study was to investigate the in vitro interactions of ambroxol hydrochloride (ABH) or amlodipine (AML) with commonly used antibacterial agents, including meropenem, imipenem-cilastatin sodium, biapenem, cefoperazone-sulbactam, polymyxin B, and tigecycline, against six carbapenem-resistant Acinetobacter baumannii (CRAB) clinical isolates. Drug interactions were interpreted using two models, that is, the fractional inhibitory concentration index (FICI) model and the percentage of growth difference (ΔE) model. The results show that a majority of the combination groups exhibited partial synergy and additive interactions, such as the combinations of carbapenems and cefoperazone-sulbactam (SCF) with ABH or AML. While the combination of PB/AML exhibited synergistic interactions against all tested isolates, and PB/ABH exhibited synergistic interactions against two isolates. The FICI and ΔE model correlated very well for the combinations of PBABH and PB/AML against AB2. The combinations of TGC with ABH or AML mainly exhibited additive and indifferent interactions. There were no antagonistic interactions observed in any of the combinations. In conclusion, this study revealed that the non-antibacterial agents ABH or AML can work synergistically or partial synergistically with antibacterial agents against CRAB. This finding is crucial for overcoming the carbapenem resistance of A. baumannii. SIGNIFICANCE AND IMPACT OF THE STUDY: Drug combination is an effective approach for the treatment of resistant bacterial infection. The significance of using drug combination is that it can reduce drug dosage requirements, reduce the toxic effects of agents and prevent or delay the emergence of drug resistance. This study measured the in vitro interactions between non-antimicrobial agents and antibacterial agents against carbapenem-resistant Acinetobacter baumannii and the results of this study provide new insight to find strategies to overcome the carbapenem resistance in A. baumannii.

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 β-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.

Activity of TP-6076 against carbapenem-resistant Acinetobacter baumannii isolates collected from inpatients in Greek hospitals

TP-6076 is a synthetic fluorocycline antibiotic that inhibits bacterial protein synthesis. In this study, carbapenem-resistant Acinetobacter baumannii clinical isolates from 13 Greek hospitals were tested for susceptibility to TP-6076 and comparator antibiotics. Broth microdilution plates were used to determine minimum inhibitory concentrations (MICs). A total of 121 non-duplicate A. baumannii isolates were tested. The MIC50 and MIC90 values of TP-6076 were 0.03 mg/L and 0.06 mg/L, respectively. Tigecycline was the second most active antibiotic (MIC90, 2 mg/L), followed by minocycline (MIC90, 8 mg/L). TP-6076 exhibited MIC90 values that were one dilution lower against tigecycline- and minocycline-susceptible isolates than against resistant isolates. There was no difference in the MIC90 value for colistin-susceptible or -resistant isolates. In conclusion, TP-6076 exhibited greater antimicrobial activity in vitro against carbapenem-resistant A. baumannii than comparator antibiotics.