Evaluation of two automated systems for colistin susceptibility testing of carbapenem-resistant Acinetobacter baumannii clinical isolates

Ceftazidime-Avibactam for the Treatment of Central Nervous System Infection Caused by Pan Drug-Resistant Carbapenem-Resistant Klebsiella Pneumoniae: A Case Report

Background

Central Nervous System (CNS) infections caused by Carbapenem-resistant Klebsiella pneumoniae (CRKP) pose a major clinical challenge and are associated with high mortality rates. Polymyxin is used as a salvage treatment for CRKP CNS infection; however, heteroresistance to polymyxin may impact clinical outcomes. In this study, we report a rare case of polymyxin-resistant Klebsiella intracranial infection, which was successfully treated with intravenous and intraventricular antibiotic injections.

Case Presentation

A 46-year-old woman with a 1-day history of post-traumatic disturbance of consciousness and cerebrospinal fluid (CSF) rhinorrhea was referred to our hospital. She underwent external ventricular drainage and decompressive craniectomy, and had a persistent fever. A CSF test confirmed intracranial infection. The minimum inhibitory concentration of polymyxin in this patient was 16 μg/mL. She was diagnosed with polymyxin-resistant pan drug-resistant (PDR) Klebsiella pneumoniae (PDR-Kp) intracranial infection. We successfully treated the infection using intravenous ceftazidime/avibactam (CAZ/AVI) and polymyxin B, combined with an intraventricular injection of polymyxin B according to the CSF microbiological culture results.

Conclusion

CAZ/AVI combined with polymyxin B may be an effective salvage treatment for CNS infections caused by polymyxin-resistant PDR-KP.

High Prevalence of Carbapenem-Resistant Enterobacterales Producing OXA-48 among Carbapenem-Resistant Isolates in a Regional Hospital in Central Taiwan

In response to the increasing number of carbapenem-resistant Enterobacterales (CRE), we investigated carbapenemase-producing Klebsiella pneumoniae and non-K. pneumoniae epidemiology and genetics. We collected 76 clinical Enterobacterales and 4 stool surveillance Escherichia coli isolates resistant to ertapenem or imipenem. Using polymerase chain reaction (PCR) and DNA sequencing, we assessed carbapenemases, extended-spectrum β-lactamases, and AmpC β-lactamases. Molecular typing via pulsed-field gel electrophoresis (PFGE) and conjugation experiments were conducted to examine resistance gene transfer. Among the 80 isolates, 96.2% harbored at least one carbapenemase gene, with blaOXA-48 in 87.5%. KPC-2 and IMP-8 carbapenemases were found in 15.0 and 22.5% of the isolates, respectively, with 27.5% having 2 or more carbapenemase genes. The PFGE analysis revealed the presence of diverse genotypes. PCR-based plasmid replicon typing identified IncA/C as the most prevalent type among K. pneumoniae isolates (26/29), and IncF and IncFIB among E. coli isolates (22/28). Conjugal transfer was successful for plasmids encoding OXA-48, CTX-M-3, CTX-M-14, CMY-2, and other β-lactamases, except the KPC-2 gene. In conclusion, our study highlights high carbapenemase prevalence in CRE, primarily OXA-48. Multiple carbapenemases within strains were common, and PFGE showed diverse patterns in these carbapenem-resistant isolates.

Comparative evaluation of Vitek®2 and broth microdilution method for colistin susceptibility testing of Gram-negative isolates from intensive care unit in a tertiary care hospital

INTRODUCTION

Colistin is the last resort treatment against resistant Gram-negative bacteria, necessitating reliable and rapid means for sensitivity testing of colistin. Automated systems like VITEK®2 are adopted to determine the minimum inhibitory concentration (MIC) due to easy usage. Broth microdilution (BMD) for colistin MIC was suggested by EUCAST and CLSI.

OBJECTIVE

To compare and evaluate colistin MIC by BMD and VITEK®2 against Gram-negative organisms from the ICU in a tertiary care hospital.

METHOD

Clinically significant organisms isolated from ICU patients were included. MIC was determined using BMD and VITEK®2. Very major error (VME), major error (ME), essential agreement (EA), categorical agreement (CA), positive predictive value (PPV), negative predictive value (NPV), sensitivity, and specificity were analysed.

RESULT

533 isolates were obtained from blood (435,81.60%), respiratory samples (57,10.70%), pus and exudates (20,3.80%), urine (18,3.40%), and CSF (3,0.60%). The Enterobacterales were K. pneumoniae (185,34.70%) E. coli (73,13.70%) and E. cloacae (26,4.90%) while non-fermenters were A. baumannii (209,39.20%) and P. aeruginosa (40,7.50%). The VITEK®2 sensitivity was >99%; specificity ranged from 14.28 to 52.94%. PPV was 93.81% while NPV was 93.75%. VME ranged from 47 to 100% between isolates. ME was up to 20%. The highest VME was obtained in E. coli (100%). The total EA and CA observed were 68.5% and 99.79% respectively.

CONCLUSION

Automated system VITEK®2 failed to detect the resistance in 32 (60%) isolates. The obtained VME and ME values were >3%, which is unacceptable as per the standard guidelines. EA of ≥90% wasn't obtained. Sensitivity for VITEK®2 was >99%, but had low specificity (14.28%). Hence, VITEK®2 is not reliable for colistin susceptibility testing.

Evaluation of an adapted method of relative growth to determine the susceptibility of Enterobacterales to polymyxin B by MALDI-TOF MS

Polymyxin B resistance is an emerging problem worldwide. The reference method to determine susceptibility to polymyxins is broth microdilution (BMD). As BMD is time consuming, it is necessary to develop new methodologies to provide faster evaluation of polymyxin susceptibility. This study aimed to evaluate polymyxin B susceptibility of Enterobacterales using an adapted methodology of relative growth (RG) by Matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS). A total of 60 isolates of Enterobacterales (22 resistant and 38 susceptible to polymyxin B by BMD) were evaluated. The adapted RG technique presented categorical agreement of 96.7% with only 2 major errors (3.3%) in comparison to BMD. Our findings demonstrate a high agreement between BMD and adapted RG, indicating that this methodology is promising for differentiating polymyxin B-susceptible isolates from polymyxin B-resistant isolates and could be implemented routinely in microbiology laboratories that already use the MALDI-TOF MS to identify bacteria.

Acinetobacter baumannii Bloodstream Infections: A Nationwide Study in Israel

Acinetobacter baumannii (Ab) bloodstream infections (BSIs) are a major public health concern and associated with high mortality. We describe the nationwide incidence, antimicrobial resistance, and mortality of Ab-BSI in Israel using laboratory-based BSI surveillance data from January 2018 to December 2019. During the study period, there were 971 Ab-BSI events (508 in 2018 and 463 in 2019), with an average annual incidence of 8.08/100,000 population. The median age of patients was 72 (IQR 62-83), and 56.4% were males. Two-thirds of Ab-BSI events were hospital-onset (HO), with median day of onset 16 (IQR 9-30). HO-BSI incidence was 0.62/10,000 patient-days (rate per 10,000 patient-days: 2.78, 1.17, and 0.2 for intensive care, medical, and surgical wards, respectively). Carbapenem susceptibility was 23.4%; 41.4% and 14.9% in community and HO events, respectively. The 14-day, 30-day, and 1-year mortality were 51.2%, 59.3%, and 81.4%, respectively. Carbapenem-resistant Ab-BSI were associated with a significantly higher 14-day, 30-day, and 1-year mortality (p < 0.001 for all). In the multivariable model, age (aHR 1.02) and carbapenem resistance (aHR 3.21) were independent predictors of 30-day mortality. In conclusion, Ab-BSIs pose a significant burden with high mortality, especially associated with antimicrobial resistance. Attention should be focused on prevention and improving treatment.

Polymyxin combination therapy for multidrug-resistant, extensively-drug resistant, and difficult-to-treat drug-resistant gram-negative infections: is it superior to polymyxin monotherapy?

INTRODUCTION

The increasing prevalence of infections with multidrug-resistant (MDR), extensively-drug resistant (XDR) or difficult-to-treat drug resistant (DTR) Gram-negative bacilli (GNB), including Pseudomonas aeruginosa, Acinetobacter baumannii, Klebsiella pneumoniae, Enterobacter species, and Escherichia coli poses a severe challenge.

AREAS COVERED

The rapid growing of multi-resistant GNB as well as the considerable deceleration in development of new anti-infective agents have made polymyxins (e.g. polymyxin B and colistin) a mainstay in clinical practices as either monotherapy or combination therapy. However, whether the polymyxin-based combinations lead to better outcomes remains unknown. This review mainly focuses on the effect of polymyxin combination therapy versus monotherapy on treating GNB-related infections. We also provide several factors in designing studies and their impact on optimizing polymyxin combinations.

EXPERT OPINION

An abundance of recent in vitro and preclinical in vivo data suggest clinical benefit for polymyxin-drug combination therapies, especially colistin plus meropenem and colistin plus rifampicin, with synergistic killing against MDR, XDR, and DTR P. aeruginosa, K. pneumoniae and A. baumannii. The beneficial effects of polymyxin-drug combinations (e.g. colistin or polymyxin B + carbapenem against carbapenem-resistant K. pneumoniae and carbapenem-resistant A. baumannii, polymyxin B + carbapenem + rifampin against carbapenem-resistant K. pneumoniae, and colistin + ceftolozan/tazobactam + rifampin against PDR-P. aeruginosa) have often been shown in clinical setting by retrospective studies. However, high-certainty evidence from large randomized controlled trials is necessary. These clinical trials should incorporate careful attention to patient's sample size, characteristics of patient's groups, PK/PD relationships and dosing, rapid detection of resistance, MIC determinations, and therapeutic drug monitoring.

Evaluation of Commercial Products for Colistin and Polymyxin B Susceptibility Testing for mcr-Positive and Negative Escherichia coli and Klebsiella pneumoniae in China

Purpose

To evaluate the performance of five widespread commercial products for colistin and polymyxin B susceptibility testing in China for mcr-positive and -negative Escherichia coli and Klebsiella pneumoniae.

Methods

A total of 132 E. coli and 83 K. pneumoniae strains (including 68 mcr-1-positive E. coli and 28 mcr-8-positive K. pneumoniae) were collected. We analysed the performance of colistin susceptibility (with Vitek 2 and Phoenix M50) and the performance of polymyxin B susceptibility (with DL-96II, MA120, and a Polymyxin B Susceptibility Test strip; POL E-strip). Broth microdilution was used as the gold standard. Categorical agreement (CA), essential agreement (EA), major error (ME), and very major error (VME) were calculated for comparisons.

Results

For E. coli, the total CA, EA, ME, and VME to colistin were as follows: Vitek 2, 98.5%/98.5%/0%/2.9%; and Phoenix M50, 98.5%/97.7%/0%/2.9%. The total CA, EA, ME, and VME to polymyxin B were as follows: POL E-strip, 99.2%/63.6%/1.6%/0%; MA120, 70.0%/-/0%/58.8%; and DL-96II, 80.2%/-/1.6%/36.8%. Only Vitek 2 and Phoenix M50 presented satisfactory performances for mcr-1-positive E. coli. For K. pneumoniae, the total CA, EA, ME, and VME to colistin were as follows: Vitek 2, 73.2%/72.0%/0%/61.6%; and Phoenix M50, 74.7%/74.7%/0%/58.3%. The total CA, EA, ME, and VME to polymyxin B were as follows: POL E-strip, 91.6%/74.7%/2.1%/16.7%; MA120, 92.8%/-/2.1%/13.9%; and DL-96II, 92.2%/-/2.1%/8.3%. All systems were unsatisfactory for mcr-8-positive K. pneumoniae. When the susceptibility of mcr-negative strains was tested, all systems presented excellent performance.

Conclusion

Vitek 2 and Phoenix M50 with colistin for E. coli showed acceptable performance regardless of mcr-1 expression, while DL-96II, MA120, and the POL E-strip performed worse for mcr-1-positive strains. Furthermore, mcr-8 greatly affected the performance of all systems with both colistin and polymyxin B for K. pneumoniae isolates.

Evaluation of sulbactam and colistin/sulbactam efficacy against multiple resistant Acinetobacter baumannii blood isolates

PURPOSE

We aimed to compare the results of the BD Phoenix (TM) M50 ID/AST system and the gold standard broth microdilution method. We also evaluated the potential of a new therapeutic combination (colistin/sulbactam) for colistin resistance among Acinetobacter baumanni strains.

METHODS

Growth in blood samples was detected with the BACTEC (BD Becton Dickinson, ABD) continuous monitoring blood culture system. Strains were identified by Phoenix (BD Phoenix™ M50, ABD) automated bacterial identification system and antimicrobial susceptibility results were obtained. A total of 92 A. baumannii complex isolates showing resistance to at least three antibiotic classes were included in the study. Colistin susceptibility results (both susceptible and resistant strains) detected by the Phoenix device were confirmed by the reference method, the liquid microdilution method. The concentration index (FIC) was used to determine the efficacy of fractional inhibitor drug combinations, the efficacy of colistin/sulbactam combination against 50 multiresistant A. baumannii complex strains was investigated using the checkerboard method.

RESULTS

10 (10.9%) of 92 isolates were resistant to colistin and 80 (86.9%) to sulbactam. With the automation system, only 2 of 10 isolates were found resistant to colistin, while 8 isolates were susceptible. For this reason, the very major error rate of the Phoenix M50 automatic system among resistant isolates was determined as 8/10. It was determined that 6 (12%) of the colistin/sulbactam combination had a synergistic effect and 44 (88%) had an additive interaction. No antagonistic interaction was detected with the colistin-sulbactam combination in this study.

CONCLUSION

A. baumannii strains should be confirmed by the broth microdilution method, which is the reference method, against the MIC results detected by automated systems. It was concluded that the use of colistin alone should be avoided in the treatment of A. baumannii infections.

Performance Evaluation of the VITEK2 and Sensititre Systems to Determine Colistin Resistance and MIC for Acinetobacter baumannii

Performances of the colistin antimicrobial susceptibility testing (AST) systems of Acinetobacter baumannii vary depending on the manufacturer, and data on colistin-resistant A. baumannii are limited. We evaluated the VITEK2 and Sensititre systems to determine colistin resistance and minimum inhibitory concentration (MIC) for A. baumannii isolated from a clinical microbiology laboratory. A total of 213 clinical A. baumannii isolates were tested, including 81 colistin-resistant A. baumannii. ASTs were performed using the VITEK2 and Sensititre systems according to the manufacturer’s instructions. Reference MICs for colistin were determined using the manual broth microdilution method (BMD). The results of the two AST methods were compared with the BMD results. VITEK2 and Sensititre systems showed category agreements of 95.3% and 99.1%, respectively. VITEK2 had a relatively high very major error (VME) rate (9.9%). Sensititre reported higher MICs than the reference method for the susceptible isolates and showed low essential agreement. In conclusion, the automated systems investigated in this study showed good category agreements for colistin AST of A. baumannii. However, VITEK2 had a high VME rate, and Sensititre had differences in MIC results. Colistin AST remains a challenging task in the clinical laboratory.

Retrospective analysis of Vitek®2 performance compared to manual broth micro-dilution for colistin susceptibility testing of Acinetobacter baumanniicomplex isolates in South Africa

The manual broth micro-dilution (mBMD) is the recommended reference method for colistin minimum inhibitory concentration determination; however, it is not as readily available in South Africa as the Vitek^®2. This retrospective study compared the performance of Vitek^®2 against mBMD in determining the colistin minimum inhibitory concentration of 337 extensively drug-resistant Acinetobacter baumannii complex isolates. Vitek^®2 yielded a categorical agreement of 89%, an essential agreement of 56%, a major error rate of 8% and a very major error rate of 55%. The Vitek^®2 is not an alternative to mBMD for colistin susceptibility testing.

Performance of Rapid Polymyxin™ NP and Rapid Polymyxin™ Acinetobacter for the detection of polymyxin resistance in carbapenem-resistant Acinetobacter baumannii and Enterobacterales

BACKGROUND

The global spread of carbapenem-resistant Enterobacterales (CRE) and Acinetobacter baumannii (CRAB) has prompted the reintroduction of colistin as a last-resort treatment. Although the recommended method for colistin susceptibility testing is broth microdilution (BMD), methods that are more rapid and easy to use are needed.

OBJECTIVES

To evaluate the performance of two commercial kits for colistin susceptibility testing: Rapid Polymyxin™ NP (RP-NP) for CRE and Rapid Polymyxin™ Acinetobacter (RP-AB) for CRAB.

METHODS

A total of 76 CRE and 87 CRAB isolates were collected from hospitalized patients in Europe and Israel. The isolates were subcultured twice on 5% sheep blood in tryptic soy agar. We tested colistin susceptibility using the RP-NP and RP-AB kits and compared the results with those from BMD.

RESULTS

Of the CRE isolates, 25% (19/76) were resistant to colistin using BMD. Categorical agreement between RP-NP and BMD was 93.4% (71/76), major errors 1.8% (1/57) and very major errors 21.1% (4/19). Sensitivity was 78.9% and specificity was 98.2%. Of the CRAB isolates, 58.6% (51/87) were resistant to colistin by BMD. Categorical agreement between RP-AB and BMD was 59.8% (52/87), major errors 13.9% (5/36) and very major errors 58.8% (30/51). Sensitivity of RP-AB was 41.2% and specificity was 86.1%.

CONCLUSIONS

In many of the tested isolates, weak or inconclusive colour changes in the test wells caused difficulty in interpretation, resulting in an unacceptable rate of very major errors.

Rescuing the Last-Line Polymyxins: Achievements and Challenges

Antibiotic resistance is a major global health challenge and, worryingly, several key Gram negative pathogens can become resistant to most currently available antibiotics. Polymyxins have been revived as a last-line therapeutic option for the treatment of infections caused by multidrug-resistant Gram negative bacteria, in particular Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacterales. Polymyxins were first discovered in the late 1940s but were abandoned soon after their approval in the late 1950s as a result of toxicities (e.g., nephrotoxicity) and the availability of "safer" antibiotics approved at that time. Therefore, knowledge on polymyxins had been scarce until recently, when enormous efforts have been made by several research teams around the world to elucidate the chemical, microbiological, pharmacokinetic/pharmacodynamic, and toxicological properties of polymyxins. One of the major achievements is the development of the first scientifically based dosage regimens for colistin that are crucial to ensure its safe and effective use in patients. Although the guideline has not been developed for polymyxin B, a large clinical trial is currently being conducted to optimize its clinical use. Importantly, several novel, safer polymyxin-like lipopeptides are developed to overcome the nephrotoxicity, poor efficacy against pulmonary infections, and narrow therapeutic windows of the currently used polymyxin B and colistin. This review discusses the latest achievements on polymyxins and highlights the major challenges ahead in optimizing their clinical use and discovering new-generation polymyxins. To save lives from the deadly infections caused by Gram negative "superbugs," every effort must be made to improve the clinical utility of the last-line polymyxins. SIGNIFICANCE STATEMENT: Antimicrobial resistance poses a significant threat to global health. The increasing prevalence of multidrug-resistant (MDR) bacterial infections has been highlighted by leading global health organizations and authorities. Polymyxins are a last-line defense against difficult-to-treat MDR Gram negative pathogens. Unfortunately, the pharmacological information on polymyxins was very limited until recently. This review provides a comprehensive overview on the major achievements and challenges in polymyxin pharmacology and clinical use and how the recent findings have been employed to improve clinical practice worldwide.

Comparison of Phenotypical Antimicrobial Resistance between Clinical and Non-Clinical E. coli Isolates from Broilers, Turkeys and Calves in Four European Countries

Livestock data on antimicrobial resistance (AMR) are commonly collected from bacterial populations of clinical and non-clinical isolates. In contrast to data on non-clinical isolates from livestock, data on clinical isolates are not harmonized in Europe. The Normalized Resistance Interpretation (NRI) method was applied to overcome the lack of harmonization of laboratory methods and interpretation rules between monitoring systems. Statistical analyses were performed to identify associations between the isolate type (clinical vs. non-clinical) and resistance to four antimicrobials (ampicillin, tetracycline, gentamicin, and nalidixic acid) per animal category in Germany and France. Additional statistical analyses comparing clinical and non-clinical isolates were performed with the available data on the same antimicrobial panel and animal categories from the UK and Norway. Higher resistance prevalence was found in clinical isolates compared to non-clinical isolates from calves to all antimicrobials included in Germany and France. It was also found for gentamicin in broilers from France. In contrast, in broilers and turkeys from Germany and France and in broilers from the UK, a higher resistance level to ampicillin and tetracycline in non-clinical isolates was encountered. This was also found in resistance to gentamicin in isolates from turkeys in Germany. Resistance differed within countries and across years, which was partially in line with differences in antimicrobial use patterns. Differences in AMR between clinical and non-clinical isolates of Escherichia coli are associated with animal category (broiler, calf, and turkey) and specific antimicrobials. The NRI method allowed comparing results of non-harmonized AMR systems and might be useful until international harmonization is achieved.

Treatment outcomes of Acinetobacter baumannii -associated pneumonia and/or bacteraemia at the intensive care unit of Universitas Academic Hospital, Bloemfontein, South Africa

Background

Nosocomial infection with multidrug-resistant (MDR) Acinetobacterbaumannii is associated with high mortality rates and the optimal treatment regimen is uncertain.

Objectives

To compare outcomes, as well as ICU and in-hospital survival rates of patients with A. baumannii pneumonia and/or bacteraemia who were treated with colistin monotherapy v. colistin/tigecycline combination therapy

Methods

This was a retrospective cross-sectional study of patients admitted to the multidisciplinary ICU of Universitas Academic Hospital, Bloemfontein, South Africa, between 1 January 2018 and 31 December 2019.

Results

Sixteen patients were included in the study. Nine patients were treated with a combination of colistin and tigecycline, while 7 patients were treated with colistin only. Seven out of 9 (77.8%) patients in the colistin/tigecycline combination therapy group were treated successfully and survived until discharge from ICU, as opposed to 2 out of 7 (28.6%) in the colistin monotherapy group (relative risk (RR) 2.7; 95% CI 0.80 - 9.24). Five out of 9 (55.6%) in the colistin/tigecycline combination therapy group v. 2 out of 7 (28.6%) in the colistin monotherapy group survived until discharge from hospital (RR 1.94; 95% CI 0.53 - 7.20).

Conclusion

Although ICU survival in patients with A. baumannii infection was better when treated with colistin/tigecycline combination therapy compared with colistin monotherapy, a statistically significant difference could not be detected. Adequately powered prospective clinical trials are required to detect statistically significant differences in treatment outcomes.

Evaluation of the Clinical Systems for Polymyxin Susceptibility Testing of Clinical Gram-Negative Bacteria in China

OBJECTIVES

The performance of mainstream commercial antimicrobial susceptibility testing systems on polymyxins has not been well evaluated in China. In this study, three antimicrobial susceptibility testing systems were evaluated for polymyxin B and colistin.

METHODS

The MICs of 257 Gram-negative strains collected from clinical cases and livestock were determined and analyzed. Using Broth Microdilution as the gold standard, the performance of VITEK 2® COMPACT, PhoenixTM M50, and Bio-kont AST System were evaluated. Essential agreement (EA), category agreement (CA), very major error (VME), and major error (ME) were calculated for comparison. The results of mcr-1 positive strains were separately discussed.

RESULTS

The EA, CA, VME, and ME to polymyxin B for Bio-kont were 83.5, 95.6, 13.1, and 0.6%, respectively. The EAs, CAs, VMEs, and MEs to colistin were as follows: Bio-kont, 86.7%/96.5%/7.2%/1.7%; Vitek 2, 64.2%/86.8%/41.0%/0%, and Phoenix M50, 92.9%/92.9%/21.7%/0%. The performance of Bio-kont to polymyxin B and colistin for Pseudomonas spp. (EA, CA < 90%, VME > 1.5%, ME = 5.6%/10%) and Enterobacter spp. (EA, CA < 90%, VME > 1.5% and ME = 0%), Vitek to colistin for most genera, and Phoenix to colistin for Enterobacter spp. (EA, CA < 90%, VME > 1.5%, ME = 0%) were unsatisfactory compared with other genera. The performance of Bio-kont to polymyxins for Escherichia spp. and Phoenix to colistin for Citrobacter spp., Escherichia spp., and Klebsiella spp., which all met the CLSI standard, were satisfactory. When the susceptibility of mcr-1 positive E. coli was tested, Bio-kont and Phoenix M50 presented excellent performance with no category errors, while Vitek 2 performed a high VME (25.5%).

CONCLUSION

With relatively more accurate results for polymyxin B and colistin and lower VME, Bio-kont has an advantage in polymyxin antimicrobial susceptibility testing, especially for Escherichia spp., Klebsiella spp., Citrobacter spp. and Acinetobacter spp.

Simple Phenotypic Tests To Improve Accuracy in Screening Chromosomal and Plasmid-Mediated Colistin Resistance in Gram-Negative Bacilli

CLSI and EUCAST recommend that only broth microdilution (BMD) should be used for routine colistin susceptibility testing; however, this technique can be difficult to perform in resource-poor settings. The purpose of this study was to evaluate the accuracy of a colistin agar spot test (COL-AS) and a colistin drop test (COL-DT) compared to BMD. COL-AS and COL-DT were assessed with a collection of 271 Gram-negative bacilli clinical isolates: 195 Enterobacterales (including 63 mcr-1 positive strains), 37 Acinetobacter spp., and 39 Pseudomonas aeruginosa For COL-AS, 3.0 μg/ml (final concentration) of colistin was added to a Mueller-Hinton agar plate and subsequently swabbed with a 0.5 McFarland standard suspension of the tested strain within a 1 cm² spot. For COL-DT, 10 μl of a 16 μg/ml colistin solution was dripped on the surface of a Mueller-Hinton agar plate, previously inoculated with a lawn of the tested strain (0.5 McFarland standard). Colistin solution was made either by dissolving powder or by disk elution in cation-adjusted Mueller-Hinton broth (CA-MHB). Overall, 141/271 (52%) isolates were categorized as colistin resistant by reference BMD. COL-AS yielded a categorical agreement (CA) of 95.5% compared to BMD, with 0.7% very major errors and 3.8% major errors. COL-DT yielded a CA of 96.2% compared to BMD, with 0.7% and 0% very major errors and 3.1% and 3.8% major errors, for colistin powder and disk elution solutions, respectively. Most major errors occurred for mcr-1 strains with MICs that fluctuated from 2 to 4 μg/ml according to the method used. In conclusion, we developed and validated methods suited to the systematic screening of resistance to colistin in Gram-negative bacilli.

Affordable automated phenotypic antibiotic susceptibility testing method based on a contactless conductometric sensor

User-friendly phenotypic antibiotic susceptibility testing (AST) methods are urgently needed in many fields including clinical medicine, epidemiological studies and drug research. Herein, we report a convenient and cost-effective phenotypic AST method based on online monitoring bacterial growth with a developed 8-channel contactless conductometric sensor (CCS). Using E. coli and V. parahaemolyticus as microorganism models, as well as enoxacin, florfenicol, ampicillin, kanamycin and sulfadiazine as antibiotic probes. The minimum inhibitory concentration (MIC) determination was validated in comparison with standard broth microdilution (BMD) assay. The total essential agreements between the CCS AST assays and the reference BMD AST assays are 68.8–92.3%. The CCS has an approximate price of $9,000 (USD). Requiring neither chemical nor biotic auxiliary materials for the assay makes the cost of each sample < $1. The MICs obtained with the automated CCS AST assays are more precise than those obtained with the manual BMD. Moreover, in 72 percent of the counterpart, the MICs obtained with the CCS AST assays are higher than that obtained with the BMD AST assays. The proposed CCS AST method has advantages in affordability, accuracy, sensitivity and user-friendliness.

Tigecycline Versus Colistin in the Treatment of Carbapenem-resistant Acinetobacter baumannii Complex Osteomyelitis

Background: Acinetobacter baumannii complex is an increasingly important cause of osteomyelitis. It is considered a difficult to treat agent, due to increasing antimicrobial resistance and few available therapeutic options. Objective: To compare effectiveness and tolerability of tigecycline and colistin in patients with osteomyelitis caused by carbapenem-resistant A. baumannii complex (CRABC). Methods: This retrospective review included all patients admitted to a 150-bed tertiary hospital from 2007 to 2015 with microbiologically confirmed CRABC osteomyelitis for which they received tigecycline or colistin. Data on demographic and clinical characteristics, adverse events, and outcomes 12 months after the end of antimicrobial treatment were analysed and stratified according to the antimicrobial used. Results: 65 patients were included, 34 treated with colistin and 31 with tigecycline. There were significantly more men (P = 0.028) in the colistin group, and more smokers (P = 0.021) and greater occurrence of chronic osteomyelitis (P = 0.036) in the tigecycline treatment group. Median duration of therapy was 42.5 days for colistin and 42 days for tigecycline, with no significant difference. Overall incidence of adverse events was higher in the colistin group (P = 0.047). In particular, incidence of renal impairment was also higher in this group (P = 0.003). Nausea and vomiting were more frequent with tigecycline (P = 0.046). There were no significant differences between groups in relapse, amputation, or death. Conclusions: Tigecycline had a better safety profile than colistin in the treatment of osteomyelitis due to CRABC, with no significant difference in outcomes after 12 months of follow-up.

How should we treat acinetobacter pneumonia?

PURPOSE OF REVIEW

To describe recent data about Acinetobacter baumannii pneumonia epidemiology and the therapeutic options including adjunctive nebulized therapy.

RECENT FINDINGS

A. baumannii is a major cause of nosocomial pneumonia in certain geographic areas affecting mainly debilitated patients, with prolonged hospitalization and broad-spectrum antimicrobials. Inappropriate empirical treatment has clearly been associated with increased mortality in A. baumannii pneumonia. Carbapenems may not be considered the treatment of choice in areas with high rates of carbapenem-resistant A. baumannii. Nowadays, polymyxins are the antimicrobials with the greatest level of in-vitro activity. Colistin is the antimicrobial most widely used although polymyxin B is associated with less renal toxicity. It is clear that lung concentrations of polymyxins are suboptimal in a substantial proportion of patients. This issue has justified the use of combination therapy or adjunctive nebulized antibiotics. Current evidence does not allow us to recommend combination therapy for A. baumannii pneumonia. Regarding nebulized antibiotics, it seems reasonable to use in patients who are nonresponsive to systemic antibiotics or A. baumannii isolates with colistin minimum inhibitory concentrations close to the susceptibility breakpoints. Cefiderocol, a novel cephalosporin active against A. baumannii, may represent an attractive therapeutic option if ongoing clinical trials confirm preliminary results.

SUMMARY

The optimal treatment for multidrug-resistant A. baumannii pneumonia has not been established. New therapeutic options are urgently needed. Well designed, randomized controlled trials must been conducted to comprehensively evaluate the effectiveness and safety of nebulized antibiotics for the treatment of A. baumannii pneumonia.

Managing Acinetobacter baumannii infections

PURPOSE OF REVIEW

We reviewed recent data about epidemiology of Acinetobacter baumannii, resistance mechanisms, and therapeutic options for severe infections caused by multidrug-resistant strains.

RECENT FINDINGS

A. baumannii is a major cause of nosocomial infections affecting mainly to debilitating patients in the ICU, although the spread to regular wards and to long-term care facilities is increasing. It is characterized by its great persistence in the environment and to have an extraordinary capability to develop resistance to all antimicrobials.Carbapenems may not be considered the treatment of choice in areas with high rates of carbapenem-resistant A. baumannii. Nowadays, polymyxins are the antimicrobials with the greatest level of in-vitro activity against A. baumannii. Colistin is the most widely used in clinical practice although polymyxin B seems to be associated with less renal toxicity. Colistin is administered intravenously as its inactive prodrug colistimethate. A loading dose of 9 million IU and subsequently high, extended-interval maintenance doses (4.5 million IU/12 h) are recommended. Combination therapy instead of monotherapy increases the rates of microbiological eradication although no clinical study has demonstrated a reduction in clinical outcomes (mortality or length of stay).

SUMMARY

The optimal treatment for multidrug-resistant A. baumannii nosocomial infections has not been established. There are no compelling data to recommend combination therapy for severe A. baumannii infections.

Polymyxin Susceptibility Testing and Interpretive Breakpoints: Recommendations from the United States Committee on Antimicrobial Susceptibility Testing (USCAST)

The polymyxins are important agents for carbapenem-resistant Gram-negative bacilli. The United States Committee on Antimicrobial Susceptibility Testing breakpoint recommendations for colistin and polymyxin B are that isolates of Pseudomonas aeruginosa, Acinetobacter baumannii, and Enterobacteriaceae are considered susceptible at MIC values of ≤2 mg/liter. These recommendations are contingent upon dosing and testing strategies that are described in this commentary. Importantly, these recommendations are not applicable to lower respiratory tract infections, for which we recommend no breakpoints. Furthermore, there is no breakpoint recommendation for polymyxin B for lower urinary tract infections.

Emergence and nosocomial spread of ST11 carbapenem-resistant Klebsiella pneumoniae co-producing OXA-48 and KPC-2 in a regional hospital in Taiwan

Purpose. Carbapenem-resistant Klebsiella pneumoniae (CRKP) has emerged as a major challenge for global healthcare systems. The objectives of this study were to determine the nosocomial spread of CRKP clones and analyse the molecular characteristics of CRKP in our hospital.Methodology. Ninety-eight non-duplicated clinical CRKP isolates were collected from March 2014-June 2015. Clinical, demographic and microbiological data of patients with CRKP were reviewed. Pulsed-field gel electrophoresis (PFGE) and multi-locus sequence typing were applied to investigate the genetic relationship between the 98 isolates. Antibiotic resistance genes were identified by conventional PCR-sequencing.Results. PFGE patterns were grouped into 26 clusters. Two main PFGE clusters were identified: L (53 isolates, belonging to ST11) and N (11 isolates, belonging to ST11). The most dominant ST was ST11 (79 %, 77/98), followed by ST273 (5 %, 5/98). KPC-2 (n=82) was the predominant carbapenemase followed by OXA-48 (n=64). Fifty isolates (51 %, 50/98) harboured bla _KPC-2 and bla _OXA-48 simultaneously, and three of these isolates were detected with the third carbapenemase genes (bla _IMP-8 or bla _VIM-1).Conclusion. The clonal spread of K. pneumoniae ST11 expressing OXA-48, KPC-2 and CTX-M-14 β-lactamases was the cause of an outbreak of CRKP. To the best of our knowledge, a single strain harbouring A-, B- and D-class carbapenemase genes has not previously been identified. There is a high prevalence of plasmid-encoded KPC-2- and OXA-48-producing CRKP in our hospital; most isolates were members of ST11, which may be representative of a high-risk CRKP clone disseminating in central Taiwan.

The added value of the selective SuperPolymyxin™ medium in detecting rectal carriage of Gram-negative bacteria with acquired colistin resistance in intensive care unit patients receiving selective digestive decontamination

The objective of this study was to determine the value of using SuperPolymyxin™ selective medium (ELITech Group, Puteaux, France) in addition to conventional non-selective inoculation methods in the detection of acquired colistin resistance in a Dutch intensive care unit (ICU) that routinely uses selective decontamination of the digestive tract (SDD). We performed a cross-sectional study with prospective data collection in a tertiary-care ICU. All consecutive surveillance rectal swabs of ICU-patients receiving SDD were included and cultured in an observer-blinded approach using (1) a conventional culture method using non-selective media and (2) SuperPolymyxin™ selective medium. MIC values for colistin of non-intrinsically colistin-resistant Gram-negative isolates were determined with broth microdilution (BMD) using Sensititre™ and colistin resistance was confirmed using BMD according to EUCAST guidelines. One thousand one hundred five rectal swabs of 428 unique ICU-patients were inoculated using both culture methods, yielding 346 and 84 Gram-negative isolates for BMD testing with the conventional method and SuperPolymyxin™ medium, of which 308 and 80 underwent BMD, respectively. The number of identified rectal carriers of isolates with acquired colistin resistance was 3 (0.7%) for the conventional method, 4 (0.9%) for SuperPolymyxin™, and 5 (1.2%) for both methods combined. The number of isolates with acquired colistin resistance was 4 (1.0%) for the conventional method, 8 (2.1%) for SuperPolymyxin™ and 9 (2.3%) for both methods combined. In a surveillance setting of low prevalence of acquired colistin resistance in patients that receive SDD in a Dutch tertiary-care ICU, SuperPolymyxin™ had a higher diagnostic yield than conventional inoculation methods, but the combination of both had the highest diagnostic yield.

Performance of three commercial assays for colistin susceptibility in clinical isolates and Mcr-1 carrying reference strain

Objective

Commercially available antibiotic susceptibility tests (cAST) for colistin are reported to shows variable performance. The current controversy on the colistin susceptibility testing and scarce data from India has left the clinical laboratories in a dilemma on the appropriate and practical approach to tackle the colistin antimicrobial susceptibility testing (AST) issue. This study was aimed to evaluate the performance of commonly used cAST for colistin against broth microdilution (BMD) as the reference method in the clinical isolates.

Materials and Methods

Colistin AST was performed on 225 nonduplicate isolates of Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa and Acinetobacter baumannii by BMD as the reference method and compared with Vitek-2, Micronaut-S and E-test. The accuracy of the various cASTs was analysed by assessing categorical and essential agreement (EA).

Results

We observed an overall categorical agreement of 98.2%, 99.6% and 96.4% and EA of 92%, 92.4% and 72% for Vitek-2, Micronaut-S and E-test, respectively. Unacceptable rates of major error (10.5%) and very major error (21%) were observed for P. aeruginosa with Vitek-2 and E-test, respectively. All the categorical errors (CEs) (7.7%) with Vitek-2 were seen for minimum inhibitory concentrations ranging within two-fold dilution breakpoint of 2 mg/L.

Conclusion

Micronaut-S was found to be an acceptable method for colistin AST. In contrast, E-test was unreliable in terms of EA. Vitek-2 was found to be reliable for colistin AST, although it was more prone to CE near the colistin breakpoints.

In vitro activity of eravacycline in combination with colistin against carbapenem-resistant A. baumannii isolates

The synergistic activity of eravacycline in combination with colistin on carbapenem-resistant A. baumannii (CRAB) isolates was evaluated in this study. Minimum inhibitory concentrations (MICs) of eravacycline and colistin were determined by the broth microdilution method. MICs values ranged between 1 to 4 mg and 0.5 to 256 mg l^-1 for eravacycline and colistin, respectively. In vitro synergy between eravacycline and colistin was evaluated by using the chequerboard methodology. Synergistic activity was found in 10% of the strains, and additive effect in 30%. No antagonism was detected. Similar activity was also observed in colistin-resistant CRAB isolates. The result of this study indicates that eravacycline and colistin combination may be a potential therapeutic option for the treatment of CRAB related infections.

Treatment of infections caused by multidrug-resistant Gram-negative bacteria: report of the British Society for Antimicrobial Chemotherapy/Healthcare Infection Society/British Infection Association Joint Working Party

The Working Party makes more than 100 tabulated recommendations in antimicrobial prescribing for the treatment of infections caused by multidrug-resistant (MDR) Gram-negative bacteria (GNB) and suggest further research, and algorithms for hospital and community antimicrobial usage in urinary infection. The international definition of MDR is complex, unsatisfactory and hinders the setting and monitoring of improvement programmes. We give a new definition of multiresistance. The background information on the mechanisms, global spread and UK prevalence of antibiotic prescribing and resistance has been systematically reviewed. The treatment options available in hospitals using intravenous antibiotics and in primary care using oral agents have been reviewed, ending with a consideration of antibiotic stewardship and recommendations. The guidance has been derived from current peer-reviewed publications and expert opinion with open consultation. Methods for systematic review were NICE compliant and in accordance with the SIGN 50 Handbook; critical appraisal was applied using AGREE II. Published guidelines were used as part of the evidence base and to support expert consensus. The guidance includes recommendations for stakeholders (including prescribers) and antibiotic-specific recommendations. The clinical efficacy of different agents is critically reviewed. We found there are very few good-quality comparative randomized clinical trials to support treatment regimens, particularly for licensed older agents. Susceptibility testing of MDR GNB causing infection to guide treatment needs critical enhancements. Meropenem- or imipenem-resistant Enterobacteriaceae should have their carbapenem MICs tested urgently, and any carbapenemase class should be identified: mandatory reporting of these isolates from all anatomical sites and specimens would improve risk assessments. Broth microdilution methods should be adopted for colistin susceptibility testing. Antimicrobial stewardship programmes should be instituted in all care settings, based on resistance rates and audit of compliance with guidelines, but should be augmented by improved surveillance of outcome in Gram-negative bacteraemia, and feedback to prescribers. Local and national surveillance of antibiotic use, resistance and outcomes should be supported and antibiotic prescribing guidelines should be informed by these data. The diagnosis and treatment of both presumptive and confirmed cases of infection by GNB should be improved. This guidance, with infection control to arrest increases in MDR, should be used to improve the outcome of infections with such strains. Anticipated users include medical, scientific, nursing, antimicrobial pharmacy and paramedical staff where they can be adapted for local use.

Evaluation of six commercial products for colistin susceptibility testing in Enterobacterales

OBJECTIVES

The recommended technique for colistin susceptibility testing by both EUCAST and CLSI is broth microdilution (BMD). However, many routine laboratories still use other methods such as gradient strips or semi-automated systems. The objective of this study was to compare six of the most widespread commercial products for colistin susceptibility testing in Europe with in-house prepared BMD.

METHODS

A collection of 325 carbapenemase-producing Enterobacterales was tested for colistin susceptibility with three semi-automated systems (Vitek 2, BD Phoenix, MicroScan WalkAway), one gradient-strip test (Etest®) and two commercial BMD products (MICRONAUT-S, TREK Sensititre). BMD, in-house prepared according to ISO standard 20776-1, served as reference.

RESULTS

The MICRONAUT-S BMD performed best with only one false-resistant (major error, ME) and four false-susceptible (very major error, VME) results while the TREK BMD performed poorer with 16 ME and seven VME. The semi-automated systems Vitek 2 and Phoenix performed poorly with 31 and 26 VME, respectively. The WalkAway semi-automated system showed 16 and 13 false results, depending on the inoculation method. The Etest® showed six ME and 10 VME.

CONCLUSIONS

This study shows that colistin susceptibility testing remains a challenging task for laboratories. It emphasizes the need for selecting the most reliable test method to advocate proper treatment and shows that critical evaluation and precautious usage of colistin susceptibility testing results is constantly required.

Antimicrobial Susceptibility Testing for Polymyxins: Challenges, Issues, and Recommendations

Polymyxins, including polymyxin B and polymyxin E (colistin), are now increasingly being used worldwide to treat patients with multidrug-resistant (MDR) Gram-negative bacterial infections. This necessitates that laboratories employ an accurate and reliable method for the routine performance of polymyxin susceptibility testing. A number of reasons have accounted for the difficulties with susceptibility testing for the polymyxins, including their multicomponent composition, poor diffusion in the agar medium, adsorption to microtiter plates, the lack of a reliable susceptibility test, the lack of a specific breakpoint from professional organizations, the synergistic effect of polysorbate 80, and the development of heteroresistance. This minireview discusses such problems that impact the results of currently available susceptibility testing methods. We also provide emerging concepts on mechanisms of polymyxin resistance, including chromosomally and plasmid-mediated mcr-related resistance. Broad-range investigations on such critical issues in relation to polymyxins can be beneficial for the implementation of effective treatment against MDR Gram-negative bacterial infections.

Development of New Tools to Detect Colistin-Resistance among Enterobacteriaceae Strains

The recent discovery of the plasmid-mediated mcr-1 gene conferring resistance to colistin is of clinical concern. The worldwide screening of this resistance mechanism among samples of different origins has highlighted the urgent need to improve the detection of colistin-resistant isolates in clinical microbiology laboratories. Currently, phenotypic methods used to detect colistin resistance are not necessarily suitable as the main characteristic of the mcr genes is the low level of resistance that they confer, close to the clinical breakpoint recommended jointly by the CLSI and EUCAST expert systems (S ≤ 2 mg/L and R > 2 mg/L). In this context, susceptibility testing recommendations for polymyxins have evolved and are becoming difficult to implement in routine laboratory work. The large number of mechanisms and genes involved in colistin resistance limits the access to rapid detection by molecular biology. It is therefore necessary to implement well-defined protocols using specific tools to detect all colistin-resistant bacteria. This review aims to summarize the current clinical microbiology diagnosis techniques and their ability to detect all colistin resistance mechanisms and describe new tools specifically developed to assess plasmid-mediated colistin resistance. Phenotyping, susceptibility testing, and genotyping methods are presented, including an update on recent studies related to the development of specific techniques.

Combining VITEK® 2 with colistin agar dilution screening assist timely reporting of colistin susceptibility

OBJECTIVES

The rise in carbapenem resistance among Gram-negative bacteria has renewed interest in colistin. Recently, the EUCAST-CLSI Polymyxin Breakpoints Working Group declared that broth microdilution (BMD) is the only valid method for colistin susceptibility testing. BMD is not easily incorporated into the routine work of clinical laboratories, and usually this test is incorporated serially, resulting in delayed susceptibility reporting. We tested a strategy of combining VITEK^® 2 with a 2 μg/mL colistin agar dilution (VITEK^® 2/AD) screening plate to improve performance and time to reporting of colistin susceptibility.

METHODS

Colistin susceptibility for 364 clinical isolates was determined by VITEK^® 2/AD and compared with the reference standard BMD according to the ISO 20776-1:2007 and CLSI guidelines. The EUCAST colistin susceptibility breakpoint of ≤2 μg/mL was used. Escherichia coli NCTC 13846 served as quality control strain. Agreement, very major error (VME) and major error rates were determined using ISO 20776-2:2007.

RESULTS

The VME rate for VITEK^® 2 alone was 30.6% (15/49, 95% CI 18.3-45.4%), and was reduced to 10.2% (5/49, 95% CI 3.4-22.2%) using the VITEK^® 2/AD combined testing. The combined testing had categorical agreement with BMD of 97% (354/364, 95% CI 95.0-98.7%), and a major error (ME) rate of 1.6% (5/315, 95% CI 0.5-3.7%). Using the combined testing, even against challenging strains, 349 (95.8%, 95% CI 93.3-97.7%) colistin susceptibility results could be reported, and only 15 isolates required further analysis by BMD.

DISCUSSION

Our method is simple to apply and allows rapid reporting of colistin susceptibility.

Multicenter Evaluation of the Accelerate PhenoTest BC Kit for Rapid Identification and Phenotypic Antimicrobial Susceptibility Testing Using Morphokinetic Cellular Analysis

We describe results from a multicenter study evaluating the Accelerate Pheno system, a first of its kind diagnostic system that rapidly identifies common bloodstream pathogens from positive blood cultures within 90 min and determines bacterial phenotypic antimicrobial susceptibility testing (AST) results within ∼7 h. A combination of fresh clinical and seeded blood cultures were tested, and results from the Accelerate Pheno system were compared to Vitek 2 results for identification (ID) and broth microdilution or disk diffusion for AST. The Accelerate Pheno system accurately identified 14 common bacterial pathogens and two Candida spp. with sensitivities ranging from 94.6 to 100%. Of fresh positive blood cultures, 89% received a monomicrobial call with a positive predictive value of 97.3%. Six common Gram-positive cocci were evaluated for ID. Five were tested against eight antibiotics, two resistance phenotypes (methicillin-resistant Staphylococcus aureus and Staphylococcus spp. [MRSA/MRS]), and inducible clindamycin resistance (MLSb). From the 4,142 AST results, the overall essential agreement (EA) and categorical agreement (CA) were 97.6% and 97.9%, respectively. Overall very major error (VME), major error (ME), and minor error (mE) rates were 1.0%, 0.7%, and 1.3%, respectively. Eight species of Gram-negative rods were evaluated against 15 antibiotics. From the 6,331 AST results, overall EA and CA were 95.4% and 94.3%, respectively. Overall VME, ME, and mE rates were 0.5%, 0.9%, and 4.8%, respectively. The Accelerate Pheno system has the unique ability to identify and provide phenotypic MIC and categorical AST results in a few hours directly from positive blood culture bottles and support accurate antimicrobial adjustment.

High incidence of pandrug-resistant Acinetobacter baumannii isolates collected from patients with ventilator-associated pneumonia in Greece, Italy and Spain as part of the MagicBullet clinical trial

OBJECTIVES

To investigate the molecular epidemiology, antimicrobial susceptibility and carbapenem resistance determinants of Acinetobacter baumannii isolates from respiratory tract samples of patients diagnosed with ventilator-associated pneumonia (VAP) who were enrolled in the MagicBullet clinical trial.

METHODS

A. baumannii isolates were prospectively cultured from respiratory tract samples from 65 patients from 15 hospitals in Greece, Italy and Spain. Susceptibility testing was performed by broth microdilution. Carbapenem resistance determinants were identified by PCR and sequencing. Molecular epidemiology was investigated using rep-PCR (DiversiLab) and international clones (IC) were identified using our in-house database.

RESULTS

Of 65 isolates, all but two isolates (97%) were resistant to imipenem and these were always associated with an acquired carbapenemase, OXA-23 (80%), OXA-40 (4.6%), OXA-58 (1.5%) or OXA-23/58 (1.5%). Resistance to colistin was 47.7%. Twenty-two isolates were XDR, and 20 isolates were pandrug-resistant (PDR). The majority of isolates clustered with IC2 (n = 54) with one major subtype comprising isolates from 12 hospitals in the three countries, which included 19 XDR and 16 PDR isolates.

CONCLUSIONS

Carbapenem resistance rates were very high in A. baumannii recovered from patients with VAP. Almost half of the isolates were colistin resistant, and 42 (64.6%) isolates were XDR or PDR. Rep-PCR confirmed IC2 is the predominant clonal lineage in Europe and suggests the presence of an epidemic XDR/PDR A. baumannii clone that has spread in Greece, Italy and Spain. These data highlight the difficulty in empirical treatment of patients with A. baumannii VAP in centres with a high prevalence of carbapenem-resistant A. baumannii.