Demonstration of an outer membrane protein that is antigenically specific for Acinetobacter baumannii

Acinetobacter baumannii is an emerging nosocomial pathogen that is resistant to many types of antibiotics, and hence, a fast, sensitive, specific, and economical test for its rapid diagnosis is needed. Development of such a test requires a specific antigen, and outer membrane proteins (OMPs) are the prime candidates. The goal of this study was to find a specific OMP of A. baumannii and demonstrate the presence of specific IgM, IgA, and IgG against the candidate protein in human serum. OMPs of A. baumannii ATCC 19606 and 16 other clinical isolates of A. baumannii were extracted from an overnight culture grown at 37?°C. Protein profiles were obtained using sodium dodecyl sulfate polyacrylamide gel electrophoresis, and Western blot analysis was performed to detect the presence of IgM, IgA, and IgG against the OMP in host serum. An antigenic 34.4-kDa OMP was uniquely recognized by IgM, IgA, and IgG from patients with A. baumannii infection, and it did not cross-react with sera from patients with other types of infection. The band was also found in the other 16 A. baumannii isolates. This 34.4-kDa OMP is a prime candidate for development of a diagnostic test for the presence of A. baumannii.     

Whole-genome pyrosequencing of an epidemic multidrug-resistant Acinetobacter baumannii strain belonging to the European clone II group

The whole-genome sequence of an epidemic, multidrug-resistant Acinetobacter baumannii strain (strain ACICU) belonging to the European clone II group and carrying the plasmid-mediated bla(OXA)(-)(58) carbapenem resistance gene was determined. The A. baumannii ACICU genome was compared with the genomes of A. baumannii ATCC 17978 and Acinetobacter baylyi ADP1, with the aim of identifying novel genes related to virulence and drug resistance. A. baumannii ACICU has a single chromosome of 3,904,116 bp (which is predicted to contain 3,758 genes) and two plasmids, pACICU1 and pACICU2, of 28,279 and 64,366 bp, respectively. Genome comparison showed 86.4% synteny with A. baumannii ATCC 17978 and 14.8% synteny with A. baylyi ADP1. A conspicuous number of transporters belonging to different superfamilies was predicted for A. baumannii ACICU. The relative number of transporters was much higher in ACICU than in ATCC 17978 and ADP1 (76.2, 57.2, and 62.5 transporters per Mb of genome, respectively). An antibiotic resistance island, AbaR2, was identified in ACICU and had plausibly evolved by reductive evolution from the AbaR1 island previously described in multiresistant strain A. baumannii AYE. Moreover, 36 putative alien islands (pAs) were detected in the ACICU genome; 24 of these had previously been described in the ATCC 17978 genome, 4 are proposed here for the first time and are present in both ATCC 17978 and ACICU, and 8 are unique to the ACICU genome. Fifteen of the pAs in the ACICU genome encode genes related to drug resistance, including membrane transporters and ex novo acquired resistance genes. These findings provide novel insight into the genetic basis of A. baumannii resistance.     

First Report of an OXA-23 Carbapenemase-Producing Acinetobacter baumannii Clinical Isolate Related to Tn2006 in Spain

A carbapenem-resistant Acinetobacter baumannii clinical isolate belonging to European clone II and sequence type 2 was recovered from a patient in the Son Espases hospital in Mallorca, Spain. Genetic analysis showed the presence of the bla_OXA-23 gene in association with the widely disseminated transposon Tn2006. This is the first reported identification of A. baumannii carrying bla_OXA-23 in Spain.     

In Vitro Potential of Lycosin-I as an Alternative Antimicrobial Drug for Treatment of Multidrug-Resistant Acinetobacter baumannii Infections

The resistance of multidrug-resistant Acinetobacter baumannii (MDRAB) isolates to most traditional antibiotics results in huge challenges for infection therapy. We investigated the in vitro activities of both l- and d-lycosin-I against MDRAB. These two compounds displayed high antibacterial activities and rapid bactericidal effects against MDRAB. Moreover, the compounds retained their activity even at high salt (Mg²⁺ or Ca²⁺) concentrations. These results demonstrate the potential of lycosin-I to be developed as a new antibiotic.     

Screening of antibiotics resistance to Enterobacteriaceae, Pseudomonas aeruginosa, and Acinetobacter baumannii by an advanced expert system

The VITEK2 advanced expert system (AES) gives information about the antibiotics-resistance mechanisms based on the biological validation derived from the VITEK2 susceptibility result. In this study, we investigated whether or not this system correctly categorized the β-lactamase resistance mechanism data derived from the VITEK2 susceptibility result using the testing card, AST-N025, with Enterobacteriaceae, Pseudomonas aeruginosa, and Acinetobacter baumannii. We used 131 strains, and their phenotypes were determined according to the biological and genetic screening. The AES analysis result matched the phenotype testing in 120 (91.6%) of the 131 strains. Incorrect findings were found in six strains, including three strains of Serratia marcescens. The resistance mechanism could not be determined in five strains, including three strains of Providencia rettgeri. The analysis of those phenotypes agreed in 34 (97.1%) among 35 strains with extended spectrum β-lactamase (ESBL), and in 27 (96.4%) among 28 strains with high-level cephalosporinase. The agreement ratio in the phenotype was very high as we expected. The incorrect and nondeterminable samples were strains with relatively high cephalosporinase that has variation of outer membrane protein. The AES was able to detect the phenotype for carbapenemase. The AES is a clinically useful system that allows taking prompt measures to treat patients because it can provide information about the resistance mechanism in less than half a day after starting the analysis.     

AbeM, an H+-coupled Acinetobacter baumannii multidrug efflux pump belonging to the MATE family of transporters

We cloned a gene, abeM, for a multidrug efflux pump from Acinetobacter baumannii using Escherichia coli as the host. Sequence analysis revealed that AbeM is a member of the MATE family of pumps. AbeM was found to be an H(+)-coupled multidrug efflux pump and a unique member of the MATE family.     

Agar Shake Tube Technique for Simultaneous Determination of Aerobic and Anaerobic Susceptibility to Antibiotics

The broth dilution method of determining the minimum inhibitory concentration (MIC) of antibiotics has been adapted to an agar shake tube technique with semisolid media. This permits the simultaneous determination of the aerobic and anaerobic MICs for facultatively anaerobic bacteria such as staphylococci.     

Vitek 2 Compact全自动微生物仪检测鲍曼不动杆菌对阿米卡星敏感性误差的原因

目的探讨为什么不能用Vitek 2 Compact全自动微生物分析仪检测鲍曼不动杆菌对阿米卡星的敏感性。方法收集用Vitek 2 Compact检测对阿米卡星敏感的鲍曼不动杆菌60株,用K-B法和琼脂稀释法复检,PCR法扩增4种氨基糖苷类修饰酶基因aac(6’)-Ⅰ、aac(3’)-Ⅰ、aph(3’)-Ⅵ及aac(3’)-Ⅱ和3种16S rRNA甲基化酶基因armA、rmtB及rmtC。结果 K-B法和琼脂稀释法的药敏结果一致,与仪器法有差异;50株(83.3%)仪器法敏感的菌株,K-B法表型为阿米卡星双圈耐药,该50株菌均扩增出armA,未扩增出rmtB及rmtC;其中47株(94.0%)扩增出aac(6’)-Ⅰ基因,35株(70.0%)扩增出aac(3’)-Ⅰ基因,10株(20.0%)扩增出aph(3’)-Ⅵ基因,8株(16.0%)扩增出aac(3’)-Ⅱ基因;有9株(15.0%)3种药敏方法的结果一致,均对阿米卡星敏感,未扩增出相关耐药基因;另有1株(1.7%)仪器法敏感、K-B法阿米卡星为非双圈耐药,未扩增出16SrRNA甲基化酶相关基因,仅扩增出aac(6’)-Ⅰ基因。结论用Vitek 2 Compact检测鲍曼不动杆菌对阿米卡星会出现假敏感现象,可能由16S rRNA甲基化酶基因armA表达介导。     

Adjunctive therapy of intravenous colistin to intravenous tigecycline for adult patients with non-bacteremic post-surgical intra-abdominal infection due to carbapenem-resistant Acinetobacter baumannii

Post-surgical intra-abdominal infections (IAIs) due to carbapenem-resistant Acinetobacter baumannii (CRAB) are difficult to treat due to suboptimal peritoneal penetrations of several antimicrobial agents. Tigecycline has favorable outcomes of treating IAIs due to multidrug-resistant organisms but occurrence of breakthrough bacteremia has been observed because this agent has low serum level. Colistin has in vitro activity against CRAB but data on treatment of IAIs is limited due to poor peritoneal penetration. The purpose of this retrospective study is to explore the outcomes of adjunctive intravenous (IV) colistin to IV tigecycline in the treatment of IAIs caused by CRAB. Of 28 patients with non-bacteremic post-surgical IAIs due to CRAB, 14 patients received IV tigecycline alone and 14 patients received IV tigecycline with IV colistin. The 14-day, 30-day, in-hospital mortality rates, the rate of breakthrough bacteremia and the rate of bacterial eradication were not significantly different. The adjunctive therapy of IV colistin was associated with significantly higher rates of renal complications (10/14) than those receiving IV tigecycline alone (3/14) (P value = 0.023). In addition, the patients receiving adjunctive IV colistin had significantly more unfavorable non-clinical outcomes including longer length of hospital stay (P value = 0.049) and higher antimicrobial cost (P value = 0.008) and non-antimicrobial costs (P value = 0.037). In this study, adjunctive IV colistin to conventional IV tigecycline in the treatment of non-bacteremic post-surgical IAIs caused by CRAB did not yield clinical benefit but caused higher renal complication and unfavorable non-clinical outcomes.     

Pharmacodynamics of the Antibacterial Effect of and Emergence of Resistance to Doripenem in Pseudomonas aeruginosa and Acinetobacter baumannii in an In Vitro Pharmacokinetic Model

An in vitro dilutional pharmacokinetic model of infection was used to study the pharmacodynamics of doripenem in terms of the ability to kill Pseudomonas aeruginosa or Acinetobacter baumannii and also changes in their population profiles. In dose-ranging studies, the cumulative percentages of a 24-h period that the drug concentration exceeds the MIC under steady-state pharmacokinetic conditions (T(MIC)s) required for doripenem to produce a 24-h bacteriostatic effect and a -2-log-unit reduction in viable count were 25% ± 11% and 35% ± 13%, respectively, for P. aeruginosa (MIC range, 0.24 to 3 mg/liter) and 20% ± 11% and 33% ± 12%, respectively, for Acinetobacter spp. (MIC range, 0.45 to 3.0 mg/liter). A T(MIC) of >40 to 50% produced a maximum response with both species at 24 h or 48 h of exposure. After 24 h of exposure to doripenem at a T(MIC) in the range of 12.5 to 37.5%, P. aeruginosa and A. baumannii population profiles revealed mutants able to grow on 4× MIC-containing medium; such changes were further amplified by 48 h of exposure. Dose-fractionation experiments targeting T(MIC)s of 12.5%, 25%, or 37.5% as six exposures, two exposures, or a single exposure over 48 h with a single strain of P. aeruginosa indicated that changes in population profiles were greatest with multiple exposures at T(MIC) targets of 12.5 or 25%. In contrast, multiple exposures at 37.5% T(MIC) most effectively suppressed total bacterial counts and changes in population profiles. Simulations of human doses of doripenem of 500 mg, 1,000 mg, 2,000 mg, and 3,000 mg every 8 h over 96 h showed marked initial killing up to 6 h but growback thereafter. Changes in population profiles occurred only in the regimen of 500 mg every 8 h against P. aeruginosa but occurred with all dose regimens for A. baumannii strains. A doripenem T(MIC) of ≥40 to 50% is maximally effective in killing P. aeruginosa or A. baumannii and suppressing changes in population profiles in short-term experiments for up to 48 h; however, a T(MIC) of 12.5 to 25% amplifies population changes, especially with exposures every 8 h. In longer-term experiments, up to 96 h, even doripenem doses of 4 to 6 times those used in human studies proved incapable of pathogen eradication and prevention of changes in population profiles. The association of a T(MIC) of 25 to 37.5% with changes in population profiles has implications in terms of future clinical breakpoint setting.     

Wall painting following terminal cleaning with a chlorine solution as part of an intervention to control an outbreak of carbapenem-resistant Acinetobacter baumannii in a neurosurgical intensive care unit in Israel

BackgroundTo describe the use of wall painting as part of an intervention to control an outbreak of carbapenem-resistant Acinetobacter baumannii (CRAB).MethodsAn interrupted time-series analysis was performed analyzing an intervention in a neurosurgical intensive care unit (NSICU) and an inpatient hematology department in a tertiary level medical center in Israel. The intervention involved wall painting using a water based acrylic paint following patient discharge and terminal cleaning with sodium troclosene as part of an infection control bundle for an outbreak of CRAB in a NSICU and concurrent outbreaks of carbapenem-resistant Enterobacteriaceae (CRE) colonization/infection in the same NSICU and the hematology department.ResultsBetween January 2013 and December 2018, 122 patients hospitalized in the NSICU were identified with new CRAB colonization/infection. The median incidence in the periods prior to/post intervention were 2.24/1000 HD (interquartile range [IQR] 0.84–2.90/1000) vs. 0/1000 HD (IQR 0–0.49/1000), respectively. Poisson regression indicated a decrease of 92% in the CRAB incidence following the intervention onset (relative risk [RR] 0.080, 95% confidence interval [CI] 0.037–0.174, p < 0.001). Forty-seven patients in the NSICU and 110 in the hematology department were colonized/infected with CRE in the same time period; a significant change was not observed following the start of the intervention in either department (for NSICU RR 1.236, 95% CI 0.370–4.125, p = 0.731; for hematology RR 0.658, 95% CI 0.314–1.378, p = 0.267).ConclusionsA. baumannii is able to survive on environmental surfaces despite decontamination efforts; wall-painting as part of a bundle may be a successful infection control measure.     

Anidulafungin and Micafungin MIC Breakpoints Are Superior to That of Caspofungin for Identifying FKS Mutant Candida glabrata Strains and Echinocandin Resistance

By CLSI interpretive criteria, anidulafungin and micafungin MICs determined by various methods were sensitive (60 to 70%) and highly specific (94 to 100%) for identifying FKS mutations among 120 Candida glabrata isolates. Anidulafungin and micafungin breakpoints were more specific than CLSI''s caspofungin breakpoint in identifying FKS mutant strains and patients with invasive candidiasis who were likely to fail echinocandin treatment (P ≤ 0.0001 for both). Echinocandin MICs were most useful clinically when interpreted in the context of prior echinocandin exposure.