Clonal spread of multidrug-resistant Acinetobacter baumannii in eastern Taiwan

Acinetobacter baumannii in the critically ill: complex infections get complicated

Acinetobacter baumannii is increasingly associated with various epidemics, representing a serious concern due to the broad level of antimicrobial resistance and clinical manifestations. During the last decades, A. baumannii has emerged as a major pathogen in vulnerable and critically ill patients. Bacteremia, pneumonia, urinary tract, and skin and soft tissue infections are the most common presentations of A. baumannii, with attributable mortality rates approaching 35%. Carbapenems have been considered the first choice to treat A. baumannii infections. However, due to the widespread prevalence of carbapenem-resistant A. baumannii (CRAB), colistin represents the main therapeutic option, while the role of the new siderophore cephalosporin cefiderocol still needs to be ascertained. Furthermore, high clinical failure rates have been reported for colistin monotherapy when used to treat CRAB infections. Thus, the most effective antibiotic combination remains disputed. In addition to its ability to develop antibiotic resistance, A. baumannii is also known to form biofilm on medical devices, including central venous catheters or endotracheal tubes. Thus, the worrisome spread of biofilm-producing strains in multidrug-resistant populations of A. baumannii poses a significant treatment challenge. This review provides an updated account of antimicrobial resistance patterns and biofilm-mediated tolerance in A. baumannii infections with a special focus on fragile and critically ill patients.

Geographic patterns of Acinetobacter baumannii and carbapenem resistance in the Asia-Pacific Region: results from the Antimicrobial Testing Leadership and Surveillance (ATLAS) program, 2012-2019

OBJECTIVES

This study aimed to investigate the geographic distribution of carbapenem-resistant Acinetobacter baumannii (CR-AB) isolates in the Asia-Pacific region.

METHODS

We collected A. baumannii isolates using the Antimicrobial Testing Leadership and Surveillance program from 2012 to 2019. The minimum inhibitory concentrations (MICs) of the isolates were determined using the broth microdilution method. The major carbapenemase genes were identified using multiplex polymerase chain reaction assays for the isolates collected between 2012 and 2014. CR-AB was defined as isolates with meropenem MICs ≥8 mg/l.

RESULTS

In total, 2674 A. baumannii isolates were collected from 13 countries, of which 1918 (71.7%) were CR-AB. The carbapenem resistance rates among A. baumannii isolates were as low as 2.8% and 6.5% in Japan and Australia, respectively, but as high as 88% and 87.2% in South Korea and India, respectively. Of the 232 CR-AB isolates that underwent carbapenemase gene screening, 224 (96.6%) harbored at least one carbapenemase gene. A total of 226 carbapenemase genes were detected, with bla_OXA-23 (94.7%, 214/226) being the most dominant, followed by bla_OXA-72 (2.7%, 6/226), bla_OXA-58 (2.2%, 5/226), and bla_NDM-1 (0.4%, 1/226). CR-AB isolates had >80% resistance to amikacin, ampicillin/sulbactam, cefepime, ceftazidime, ciprofloxacin, levofloxacin, and piperacillin/tazobactam. The rates of CR-AB resistance to minocycline and colistin were 7.2% (31/429) and 1.7% (23/1368). For cefoperazone/sulbactam and tigecycline, 50.2% (527/1049) and 93.3% (1789/1918) of CR-AB isolates had an MIC ≤16 mg/l and ≤2 mg/l, respectively.

CONCLUSION

The prevalence of carbapenem resistance in A. baumannii showed significant differences among countries in the Asia-Pacific region, and the treatment options were limited.

Isolation of extensively drug resistant Acinetobacter baumannii from environmental surfaces inside intensive care units

BACKGROUND

Acinetobacter baumannii is a nosocomial pathogen that has emerged as a major threat in the health-care settings, particularly intensive care units (ICUs). The aim of this study was to investigate the prevalence of A. baumannii in the environment of intensive care and emergency units in 4 hospitals in Jordan.

METHODS

A total of 311 surface and 26 air samples were collected from 6 different ICUs and 2 emergency units. Examined high-touch surfaces included bed rails, sinks, food tables, trolley handles, ventilator inlets, blankets, sheets, door handles, light switches, bedside tables and drawers, curtains, normal saline stands and neonatal incubators. A. baumannii isolates were identified by CHROMagar and confirmed using 2 different PCR assays. All obtained isolates were characterized for their antibiotic resistance phenotypes, biofilm formation capacities and were typed by multi-locus sequence typing.

RESULTS

Of the 337 samples, 24 A. baumannii isolates were recovered, mostly from surfaces in the internal medicine ICUs. Among the 24 isolates, 10 isolates were classified as extensively-resistant (XDR), harbored the bla_OXA-23 like gene and able to form biofilms with varying capacities. ST2 was the most frequent sequence type, with all ST2 isolates classified as XDRs.

CONCLUSIONS

Our results showed that high-touch surfaces of adult and pediatric ICUs were contaminated with XDR A. baumannii isolates. Therefore, the cleaning practices of the surfaces and equipment surrounding ICU patients should be optimized, and health-care workers should continuously wash their hands and change their gloves constantly to control the spread of this pathogen.

Inhibition of the clinical isolates of Acinetobacter baumannii by Pseudomonas aeruginosa: In vitro assessment of a case-based study

BACKGROUND

The global rise in nosocomial infections associated with gram-negative bacteria and the spread of multi-drug resistant Acinetobacter baumannii (MDR-AB) pose public health concerns. This study investigates the inhibitory effects and possible inhibitory mechanism of Pseudomonas aeruginosa (PA) on selected clinical strains of A. baumannii (AB) isolated from Taiwanese patients.

METHODS

Four and eight clinical strains of AB and PA, respectively, were randomly selected from the bacterial collection of Feng-Yuan Hospital, Taiwan. Antimicrobial-susceptibility was performed on the AB strains. Inhibition potential of the PA strains against AB was assessed by measuring the inhibition zones. In vitro analysis using phenazine-1-carboxamide (PCN) was conducted to assess the possible inhibitory mechanism of PA, which was later confirmed in the clinical isolates by liquid chromatography-mass spectrometry.

RESULTS

All the clinical AB strains showed resistance to the eleven antibiotics and were classified as MDR-AB. The nine PA strains exert either a high (PA3596, PA3681, PA3772, and ATCC27853) or a low (PA3613, PA3625, PA3712, PA3715, and PA3744) degree of inhibition against AB strains. 0.25 mg/ml PCN had a clearer inhibition zone than 0.05 mg/ml PCN, suggesting a dose-dependent inhibition of PCN on the AB strains. The four PA strains that demonstrated a high degree of inhibition had a relatively high amount of PCN.

CONCLUSION

Selected strains of PA exert inhibitory actions on MDR-AB with PCN being a possible inhibitory agent. This finding raises the possibility of developing effective therapeutic antibiotics and disinfectant from specific components of PA for the treatment and control of Acinetobacter-associated infections in hospital settings.

New insights about the EptA protein and its correlation with the pmrC gene in polymyxin resistance in Pseudomonas aeruginosa

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Computational biology.

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Bacterial resistance.

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Pseudomonas aeruginosa.

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Gram-negative bacteria.

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Polymyxin.

Nowadays, clinical and scientific interest in antibiotics, as polymyxin, has increased due to the large number of reports of multiresistant Gram-negative bacteria, as Pseudomonas aeruginosa. The aim of this study was to investigate a related group of proteins for resistance to polymyxins, encoded by P. aeruginosa genome, through in silico analysis. The mobilized colistin resistance 1 (MCR₁) protein from Escherichia coli was used for comparison. Similar sequences to the protein MCR₁ in P. aeruginosa were analysed for physicochemical properties. 31 protein isoforms in P. aeruginosa (EptA) were found able to confer resistance to polymyxin showing protein lengths between 551 and 572 amino acids, with molecular mass values between 61.36 - 62. 80 kDa, isoelectric point between 6.10 to 7.17, instability index between 33.76 to 41.87, aliphatic index between 98.67 to 102.63 and the hydropathyindex between - 0.008 to 0.094. These proteins belong to the DUF₁₇₀₅ superfamily with bit-score values between 559.81 and 629.78. A high degree of similarity between EpTAs in P. aeruginosa was observed in relation to other proteins that confer resistance to polymyxins, present in Gram-negative bacteria species of clinical interest. Although, further studies are needed to identify the actual contribution of EptAs in P. aeruginosa species.

Multicenter surveillance of antimicrobial susceptibilities and resistance mechanisms among Enterobacterales species and non-fermenting Gram-negative bacteria from different infection sources in Taiwan from 2016 to 2018

OBJECTIVES

To explore the in vitro antimicrobial susceptibility among clinically important Gram-negative bacteria (GNB) in Taiwan.

METHODS

From 2016 through 2018, a total of 5458 GNB isolates, including Escherichia coli (n = 1545), Klebsiella pneumoniae (n = 1255), Enterobacter species (n = 259), Pseudomonas aeruginosa (n = 1127), Acinetobacter baumannii complex (n = 368), and Stenotrophomonas maltophilia (n = 179), were collected. The susceptibility results were summarized by the breakpoints of minimum inhibitory concentration (MIC) of CLSI 2020, EUCAST 2020 (for colistin), or published articles (for ceftolozane/tazobactam). The resistance genes among multidrug-resistant (MDR) or extensively drug-resistant (XDR)-GNB were investigated by multiplex PCR.

RESULTS

Significantly higher rates of non-susceptibility (NS) to ertapenem and carbapenemase production, predominantly KPC and OXA-48-like beta-lactamase, were observed in Enterobacterales isolates causing respiratory tract infection than those causing complicated urinary tract or intra-abdominal infection (12.7%/3.44% vs. 5.7%/0.76% or 7.7%/0.97%, respectively). Isolates of Enterobacter species showed higher rates of phenotypic extended-spectrum β-lactamase and NS to ertapenem than E. coli or K. pneumoniae isolates. Although moderate activity (54-83%) was observed against most potential AmpC-producing Enterobacterales isolates, ceftolozane/tazobactam exhibited poor in vitro (44.7-47.4%) activity against phenotypic AmpC Enterobacter cloacae isolates. Additionally, 251 (22.3%) P. aeruginosa isolates exhibited the carbapenem-NS phenotype, and their MDR and XDR rate was 63.3% and 33.5%, respectively. Fifteen (75%) of twenty Burkholderia cenocepacia complex isolates were inhibited by ceftolozane/tazobactam at MICs of ≤4 μg/mL.

CONCLUSIONS

With the increase in antibiotic resistance in Taiwan, it is imperative to periodically monitor the susceptibility profiles of clinically important GNB.

Antimicrobial Resistance Mechanisms and Virulence of Colistin- and Carbapenem-Resistant Acinetobacter baumannii Isolated from a Teaching Hospital in Taiwan

Acinetobacter baumannii, a Gram-negative bacterium, is an important nosocomial pathogen. Colistin-resistant A. baumannii is becoming a new concern, since colistin is one of the last-line antibiotics for infections by carbapenem-resistant A. baumannii. From 452 carbapenem-resistant isolates collected in a teaching hospital in Taipei, Taiwan, we identified seven that were resistant to colistin. Carbapenem resistance in these isolates is attributed to the presence of carbapenemase gene bla_OXA-23 in their genomes. Colistin resistance is presumably conferred by mutations in the sensor kinase domain of PmrB found in these isolates, which are known to result in modification of colistin target lipid A via the PmrB-PmrA-PmrC signal transduction pathway. Overexpression of pmrC, eptA, and naxD was observed in all seven isolates. Colistin resistance mediated by pmrB mutations has never been reported in Taiwan. One of the seven isolates contained three mutations in lpxD and exhibited an altered lipopolysaccharide profile, which may contribute to its colistin resistance. No significant difference in growth rates was observed between the isolates and the reference strain, suggesting no fitness cost of colistin resistance. Biofilm formation abilities of the isolates were lower than that of the reference. Interestingly, one of the isolates was heteroresistant to colistin. Four of the isolates were significantly more virulent to wax moth larvae than the reference.

Tigecycline antibacterial activity, clinical effectiveness, and mechanisms and epidemiology of resistance: narrative review

Tigecycline is unique glycylcycline class of semisynthetic antimicrobial agents developed for the treatment of polymicrobial infections caused by multidrug-resistant Gram-positive and Gram-negative pathogens. Tigecycline evades the main tetracycline resistance genetic mechanisms, such as tetracycline-specific efflux pump acquisition and ribosomal protection, via the addition of a glycyclamide moiety to the 9-position of minocycline. The use of the parenteral form of tigecycline is approved for complicated skin and skin structure infections (excluding diabetes foot infection), complicated intra-abdominal infections, and community-acquired bacterial pneumonia in adults. New evidence also suggests the effectiveness of tigecycline for the treatment of severe Clostridioides difficile infections. Tigecycline showed in vitro susceptibility to Coxiella spp., Rickettsia spp., and multidrug-resistant Neisseria gonnorrhoeae strains which indicate the possible use of tigecycline in the treatment of infections caused by these pathogens. Except for intrinsic, or often reported resistance in some Gram-negatives, tigecycline is effective against a wide range of multidrug-resistant nosocomial pathogens. Herein, we summarize the currently available data on tigecycline pharmacokinetics and pharmacodynamics, its mechanism of action, the epidemiology of tigecycline resistance, and its clinical effectiveness.

Genetic diversity of colistin resistance Nosocomial Acinetobacter baumannii strains from Iran

Background:

Drug-resistant Acinetobacter baumannii is a global health problem since its ability to acquire new resistance mechanisms. Here, we aimed to determine the association of common types of A. baumannii and assess their drug resistance of A. baumannii and contribution of integrons (Ints) and oxacillinase genes in Zanjan, Iran.

Materials and Methods:

Among 68 isolated Acinetobacters from patients, 48 isolates were A. baumannii strains. Antibiotic susceptibility pattern and colistin resistance were determined by disk diffusion and broth microdilution, respectively. The presence of Int I, II, III, and oxacillinase genes examined using polymerase chain reaction. The clonal relationship of clinical isolates of A. baumannii determined by Pulsed Field Gel Electrophoresis method.

Results:

The results showed the highest antibiotic susceptibility (58%) for colistin. 96% of isolates were considered as multidrug resistant, and 46% as extensively drug resistant, and 16% as pandrug resistant. Frequencies of Int I, II, III resistance genes were 60%, 28%, and 0%, respectively, and 12% of strains had no isoform of Ints. Frequencies of Carbapenem resistance genes were 74%, 24%, 100%, and 4% for blaOXA-23, blaOXA-24, blaOXA-51, and blaOXA-58, respectively. The above samples were group into 26 pulsotypes.

Conclusion:

The studied A. baumannii strains had several resistance genes, and the colistin resistance showed an extraordinary ascending tendency that could be a severe issue in nosocomial infections, and the presence of high genetic diversity indicated a variation in A. baumannii strains and possibly a variety of sources of contamination or infection.

Insight into Acinetobacter baumannii: pathogenesis, global resistance, mechanisms of resistance, treatment options, and alternative modalities

Acinetobacter baumannii, once considered a low-category pathogen, has emerged as an obstinate infectious agent. The scientific community is paying more attention to this pathogen due to its stubbornness to last resort antimicrobials, including carbapenems, colistin, and tigecycline, its high prevalence of infections in the hospital setting, and significantly increased rate of community-acquired infections by this organism over the past decade. It has given the fear of pre-antibiotic era to the world. To further enhance our understanding about this pathogen, in this review, we discuss its taxonomy, pathogenesis, current treatment options, global resistance rates, mechanisms of its resistance against various groups of antimicrobials, and future therapeutics.

Synergistic Effect of Colistin and Rifampin Against Multidrug Resistant Acinetobacter baumannii: A Systematic Review and Meta-Analysis

The existence of infections caused by multidrug resistant (MDR) Acinetobacter baumannii is a growing problem because of the difficulty to treat them. We examined the published literature and focused our analysis on the investigation of the synergism of colistin and rifampin against MDR A. baumannii isolates via systematic review and meta-analysis. A systematic literature search was performed using the following 4 databases (PubMed, Scopus, EMBASE and ISI Web of Sciences). The related articles were evaluated during the period from December 2014 to January 2015. Information based on resistance and sensitivity to antibiotics, the minimum inhibitory concentration and the effects of two antibiotics on each other including synergism, antagonism, relative synergism and additive antagonism were extracted. A meta-analysis of 17 studies including 448 samples was brought into process and 2% (95% CI 0-4%) and 72% (95% CI 56-89%) resistance to colistin and rifampin were observed, respectively. 42% of all isolates showed MIC = 4 µg/ml (95% CI 14-69%) to rifampin and 30% MIC= 2 µg/ml to colistin (95% CI 3.8-78%). MIC₅₀ and MIC₉₀ for both rifampin and colistin were 2 µg/ml and 4 µg/ml, respectively. 63% of the strains demonstrated synergy (95% CI 37-90%), 7% were highlighted as relative synergism (95% CI 0.0- 13%), 3% showed an additive effect (95% CI -0.0-7%) and 14% were indifferent (95% CI 6-23%). The antagonistic effect was not observed in this combination. Synergy rates of time-kill assay in rifampin and colistin combinations were generally higher than those of check bored microdilution and E-test method. The results demonstrated that the combination therapy could be more useful when compared to monotherapy and that this strategy might reduce the resistance rate to rifampin in MDR A. baumannii isolates.

Biology of Acinetobacter baumannii: Pathogenesis, Antibiotic Resistance Mechanisms, and Prospective Treatment Options

Acinetobacter baumannii is undoubtedly one of the most successful pathogens responsible for hospital-acquired nosocomial infections in the modern healthcare system. Due to the prevalence of infections and outbreaks caused by multi-drug resistant A. baumannii, few antibiotics are effective for treating infections caused by this pathogen. To overcome this problem, knowledge of the pathogenesis and antibiotic resistance mechanisms of A. baumannii is important. In this review, we summarize current studies on the virulence factors that contribute to A. baumannii pathogenesis, including porins, capsular polysaccharides, lipopolysaccharides, phospholipases, outer membrane vesicles, metal acquisition systems, and protein secretion systems. Mechanisms of antibiotic resistance of this organism, including acquirement of β-lactamases, up-regulation of multidrug efflux pumps, modification of aminoglycosides, permeability defects, and alteration of target sites, are also discussed. Lastly, novel prospective treatment options for infections caused by multi-drug resistant A. baumannii are summarized.

Antimicrobial susceptibility of Acinetobacter clinical isolates and emerging antibiogram trends for nosocomial infection management

INTRODUCTION

The drug resistant Acinetobacter strains are important causes of nosocomial infections that are difficult to control and treat. This study aimed to determine the antimicrobial susceptibility patterns of Acinetobacter strains isolated from different clinical specimens obtained from patients belonging to different age groups.

METHODS

In total, 716 non-duplicate Acinetobacter isolates were collected from the infected patients admitted to tertiary-care hospitals at Lahore, Pakistan, over a period of 28 months. The Acinetobacter isolates were identified using API 20E, and antimicrobial susceptibility testing was performed and interpreted according to Clinical and Laboratory Standards Institute (CLSI) guidelines.

RESULTS

The isolation rate of Acinetobacter was high from the respiratory specimens, followed by wound samples. Antibiotic susceptibility analyses of the isolates revealed that the resistance to cefotaxime and ceftazidime was the most common, in 710 (99.2%) specimens each, followed by the resistance to gentamicin in 670 (93.6%) isolates, and to imipenem in 651 (90.9%) isolates. However, almost all isolates were susceptible to tigecycline, colistin, and polymyxin B.

CONCLUSIONS

The present study showed the alarming trends of resistance of Acinetobacter strains isolated from clinical specimens to the various classes of antimicrobials. The improvement of microbiological techniques for earlier and more accurate identification of bacteria is necessary for the selection of appropriate treatments.

High prevalence of extensively drug-resistant and metallo beta-lactamase-producing clinical Acinetobacter baumannii in Iran

Acinetobacter species particularly Acinetobacter baumannii (A. baumannii) have been widely reported as broad-spectrum antibiotic resistant pathogens. Expression of various types of metallo beta-lactamases (MBL), classified as Ambler class B, has been associated with carbapenem resistance. Here, we attempted to assess the frequency of extensively drug-resistant (XDR) and MBL-producing A. baumannii among clinical isolates. 86 clinical A. baumannii strains were collected from 2014 to 2015 and their susceptibility to meropenem (10 μg), imipenem (10 μg), azteronem (30 μg), pipracillin (100 μg) tazobactam (110 μg), tobramycin (10 μg), fosfomycin (200 μg), rifampicin (5 μg), colistin (10 μg), tigecycline (15 μg), sulbactam/ampicillin (10 μg + 10 μg) and polymixin B (300 U) was evaluated using disk diffusion method. The MBL-producing isolates were screened using combined disc diffusion method. Furthermore, the presence of blaVIM, blaIMP, blaSPM, blaGIM, blaSIM and blaNDM was detected by PCR. 34.9% of isolates were recovered from bronchoalveolar lavage (BAL). 81 (94.2%) and 62 (71.2%) isolates were multidrug resistance (MDR) and XDR, respectively. 44 (51.2%) and 65 (75.6%) isolates were MBL-producing strains with resistance to imipenem and meropenem, respectively. 2 (2.3%), 13 (15.1%), 2 (2.3%), 4 (4.7%) and 2 (2.3%) isolates carried blaVIM, blaIMP, blaSPM, blaGIM and blaSIM genes, respectively. Our data showed that the rate of XDR and MBL A. baumannii is on the rise.

Improvement of in vivo antimicrobial activity of HBcARD peptides by D-arginine replacement

We previously identified a novel antimicrobial peptide with a broad spectrum bactericidal activity from human hepatitis B virus (HBV) core protein (HBc) arginine-rich domain (ARD). We compared the antimicrobial activities of HBcARD peptides from different hepadnaviruses which share similar amino acid sequences. In general, mammalian HBcARD peptides exhibited stronger antimicrobial activity than avian peptides. Using the strategy of D-amino acid substitutions, we improved the antimicrobial efficacy of human HBcARD peptide. This D-HBcARD peptide was much more resistant than L-HBcARD peptide to proteolytic degradation in vitro. Moreover, this D-HBcARD peptide maintained similar minimal bactericidal concentrations (MBC) against tested bacteria, and showed very low hemolytic activity. In the Staphylococcus aureus-infected mouse model, this D-HBcARD peptide was more protective than the L-HBcARD peptide. Repeated treatments with either L- or D-HBcARD peptides induced no significant immunogenicity. New derivatives of HBcARD peptides could serve as alternatives to the conventional antibiotics in clinical medicine in the future.

Impact of empirical antimicrobial therapy on the outcome of critically ill patients with Acinetobacter bacteremia

RATIONALE:

Empirical antimicrobial therapy (EAT) for Acinetobacter infections may not be appropriate as it tends to be multidrug-resistant. This study evaluated the relationship between appropriate EAT and the outcomes of Intensive Care Unit (ICU) patients with Acinetobacter bacteremia.

METHODS:

This is a retrospective study of patients admitted to a medical-surgical ICU (2005-2010) and developed Acinetobacter bacteremia during the stay. Patients were categorized according to EAT appropriateness, defined as administration of at least one antimicrobial agent to which the Acinetobacter was susceptible before susceptibility results were known. The relation between EAT appropriateness and outcomes was evaluated.

RESULTS:

Sixty patients developed Acinetobacter bacteremia in the 6-year period (age = 50 ± 19 years; 62% males; Acute Physiology and Chronic Health Evaluation II score = 28 ± 9; 98.3% with central lines; 67% in shock and 59% mechanically ventilated) on average on day 23 of ICU and day 38 of hospital stay. All isolates were resistant to at least three of the tested antimicrobials. Appropriate EAT was administered to 60% of patients, mostly as intravenous colistin. Appropriate EAT was associated with lower ICU mortality risk (odds ratio: 0.15; 95% confidence interval: 0.03-0.96) on multivariate analysis.

CONCLUSIONS:

In this 6-year cohort, Acinetobacter bacteremia was related to multidrug-resistant strains. Appropriate EAT was associated with decreased ICU mortality risk.

Phenotypic and molecular characterization of clinical isolates of Acinetobacter baumannii isolated from Delhi, India

Background

Acinetobacter has gained importance as a multi-drug resistant and hence a difficult to treat pathogen. This study was done to characterize our isolates with respect to drug resistance and presence of beta-lactamases which is a major mechanism of resistance and to type using RAPD and MLST so that comparison of our clones can be made with the existing international clones.

Methods

100 isolates recovered from clinical samples from two hospitals in Delhi were tested for their susceptibility against major groups of antimicrobials. The resistant isolates were screened and confirmed phenotypically for presence of ESBL, MBL and AmpC and MBLs also by PCR. The isolates were typed by RAPD and MLST.

Results

Out of the 100 isolates, 91, 78 and 2 % were MDR, XDR and PDR respectively. 97, 100 and 85 were screen positive for ESBL, AmpC and MBL respectively. Of these, 38.1 % were confirmed phenotypically to produce ESBL, 99 % produced AmpC and 29.4 % produced MBL comprising of GIM, VIM, SIM and IMP. MLST showed known STs 110, 188, 146, 69, 103, 108 and 194. Eight new STs were encountered. The RAPD showed a high degree of genetic variability among the isolates.

Conclusion

Majority of our isolates were MDR, producing one or more types of beta-lactamases. We encountered drug resistant international clones by MLST which are found in other continents there by confirming their spread to Indian sub continent. No data on ST types of other Indian isolates is available in the MLST database and hence comparison is not possible.

The Prevalence of IS Aba 1 and IS Aba 4 in Acinetobacter baumannii Species of Different International Clone Lineages Among Patients With Burning in Tehran, Iran

Background:

Multidrug resistant strains of Acinetobacter baumannii (MDR-AB) have emerged as alarming nosocomial pathogens among patients with burning.

Objectives:

The current study aimed to determine the susceptibility of A. baumannii species, carbapenems resistance patterns, and their association with IS_Aba1 and IS_Aba4 elements upstream of the bla_OXA-like genes, and the distribution of international clone (IC) of A. baumannii isolates among patients with burning in Tehran, Iran.

Materials and Methods:

In the current study, 62 A. baumannii species isolates from patients with burning in Tehran, Iran, in 2012 were evaluated for the antimicrobial susceptibility, genetic relationships, ICs, carbapenemase encoding genes, and insertion elements IS_Aba upstream of bla_OXA-like genes.

Results:

The highest rates of susceptibility were observed with colistin (88.7%) and tigecycline (82.2%). The extensively drug-resistance and pan drug-resistance were observed in 37.1% and 8.1% of the isolates, respectively. About 98.3% of 17 genotypes categorized into three distinct clusters. Thirty-six of the 62 isolates (58%) belonged to the IC II lineage. The most prevalent acquired OXA-type carbapenemase was bla_OXA-23-like (62.9%). IS_Aba1 and IS_Aba4 were detected upstream of bla_OXA-23-like genes in 45.1% and 12.9% of isolates, respectively. In 32.2% of all isolates, IS_Aba1 laid upstream of bla_OXA-51-like genes. The PCR results were negative for carbapenemase genes of Ambler class A and B, except bla_VIM-2. (1.6%).

Conclusions:

It was the first study that attempted to detect the insertion elements IS_Aba and IC lineages in MDR-AB species isolated from patients with burning in Iran.

Phenotypic and Molecular Epidemiology of Acinetobacter calcoaceticus baumannii Complex Strains Spread at Nemazee Hospital of Shiraz, Iran

Background

Acinetobacter calcoaceticus baumannii (ACB) complex are Gram-negative opportunistic bacteria with low virulence properties. Their resistance to antibiotics has become a matter of concern in hospital infections.

Objectives

The present study aimed to determine the prevalence and antimicrobial susceptibility of ACB isolates collected from the Nemazee hospital of Shiraz. In addition, Pulsed Field Gel Electrophoresis (PFGE) was used to determine the genetic patterns of these strains.

Patients and Methods

In this cross-sectional study, 93 strains of ACB complex were isolated from patients of Nemazee hospital, Shiraz, Iran. The antibiotic susceptibility patterns of the isolates to the following 15 antibiotics were determined: gentamicin, ticarcillin, ceftazidime, co-trimoxazole, imipenem, piperacillin tazobactam, amikacin, aztreonam, sulbactam, meropenem, tobramycin, cefotaxime, ceftriaxone, colistin, polymyxin B. Pulsed Field Gel Electrophoresis was used to determine the clonal relationship of these strains.

Results

Most of the isolates were found to be resistant to cefotaxime, co-trimoxazole, ceftriaxone, aztreonam, ceftazidime and ticarcillin (90%), and the least resistance was observed to colistin and polymyxin B. Among the 93 tested samples, 35 antimicrobial susceptibility patterns and 47 PFGE patterns were obtained.

Conclusions

High resistance to antibiotics was observed among the strains of ACB complex and the least resistance was towards colistin and polymyxin B, indicating that these antibiotics could be effective for treatment, in case there is no other choice. Using PFGE, the similarity between some strains of Acinetobacter was determined, which indicated epidemics in different parts of the hospital; such epidemics can in turn lead to increased incidence of Acinetobacter infections.

Antimicrobial resistance in Acinetobacter baumannii: From bench to bedside

Acinetobacter baumannii (A. baumannii) is undoubtedly one of the most successful pathogens in the modern healthcare system. With invasive procedures, antibiotic use and immunocompromised hosts increasing in recent years, A. baumannii has become endemic in hospitals due to its versatile genetic machinery, which allows it to quickly evolve resistance factors, and to its remarkable ability to tolerate harsh environments. Infections and outbreaks caused by multidrug-resistant A. baumannii (MDRAB) are prevalent and have been reported worldwide over the past twenty or more years. To address this problem effectively, knowledge of species identification, typing methods, clinical manifestations, risk factors, and virulence factors is essential. The global epidemiology of MDRAB is monitored by persistent surveillance programs. Because few effective antibiotics are available, clinicians often face serious challenges when treating patients with MDRAB. Therefore, a deep understanding of the resistance mechanisms used by MDRAB can shed light on two possible strategies to combat the dissemination of antimicrobial resistance: stringent infection control and antibiotic treatments, of which colistin-based combination therapy is the mainstream strategy. However, due to the current unsatisfying therapeutic outcomes, there is a great need to develop and evaluate the efficacy of new antibiotics and to understand the role of other potential alternatives, such as antimicrobial peptides, in the treatment of MDRAB infections.

Tigecycline resistance in Acinetobacter baumannii mediated by frameshift mutation in plsC, encoding 1-acyl-sn-glycerol-3-phosphate acyltransferase

Acinetobacter baumannii is an important pathogen of healthcare-associated infections and shows multidrug resistance. With the increasing application of tigecycline, isolates resistant to this antibiotic are of growing concern clinically. However, the definitive mechanism of tigecycline resistance remains unclear. To explore the mechanism of tigecycline resistance in A. baumannii, a tigecycline-resistant strain was obtained by increasing the concentration of the antimicrobial in liquid culture. Three mutations were identified by the whole genome comparison, including one synonymous substitution in a hypothetical protein and a frameshift mutation in plsC and omp38. The plsC gene was confirmed to cause decreased susceptibility to tigecycline by a complementation experiment and cellular membrane change was detected by flow cytometry. By measuring the relative growth rate, the fitness cost of plsC was estimated to be approximately 8 %. In conclusion, plsC was found to play an important role in tigecycline resistance in A. baumannii. The minor fitness cost of plsC indicates a high risk of the emergence and development of tigecycline resistance in A. baumannii.

Wide distribution of CC92 carbapenem-resistant and OXA-23-producing Acinetobacter baumannii in multiple provinces of China

Carbapenem-resistant Acinetobacter baumannii has spread rapidly across China and is currently reported to be a worldwide nosocomial menace. In light of its increasing clinical significance, this study aimed to investigate the molecular epidemiology of carbapenem-resistant and carbapenem-susceptible isolates obtained from multiple provinces of China. Antimicrobial susceptibility was determined by disk diffusion assay according to Clinical and Laboratory Standards Institute (CLSI) guidelines. Multilocus sequence typing (MLST) was used to investigate the molecular epidemiology of the isolates. In addition, a minimum spanning tree algorithm was applied to cluster sequence types (STs) into clonal complexes (CCs) in order to analyse their evolutionary relatedness. Generally, the average rate of resistance to most antibiotics in carbapenem-resistant isolates was extremely high (>85%), except for minocycline (20.45%). Analysis of MLST data confirmed that the genetic background of carbapenem-resistant isolates was relatively simple, with ST92 being the most prevalent clone, occurring in every province, followed by ST138, ST75 and ST381. In contrast, carbapenem-susceptible isolates had a more diverse genetic background. Furthermore, the most widely distributed CC of carbapenem-resistant isolates was bla(OXA-23)-like-producing and predominantly CC92, which incorporate ST136 and its several single-locus variants. Interestingly, isolates belonging to CC92 possessed higher antibiotic resistance rates compared with other STs. Overall, these observations suggest a wide distribution of carbapenem-resistant and bla(OXA-23)-like-producing clone CC92, especially ST92, ST75 and ST138, as the principal reason for the rapidly increasing carbapenem resistance rate in China.

Identification of a novel antimicrobial peptide from human hepatitis B virus core protein arginine-rich domain (ARD)

The rise of multidrug-resistant (MDR) pathogens causes an increasing challenge to public health. Antimicrobial peptides are considered a possible solution to this problem. HBV core protein (HBc) contains an arginine-rich domain (ARD) at its C-terminus, which consists of 16 arginine residues separated into four clusters (ARD I to IV). In this study, we demonstrated that the peptide containing the full-length ARD I–IV (HBc147-183) has a broad-spectrum antimicrobial activity at micro-molar concentrations, including some MDR and colistin (polymyxin E)-resistant Acinetobacter baumannii. Furthermore, confocal fluorescence microscopy and SYTOX Green uptake assay indicated that this peptide killed Gram-negative and Gram-positive bacteria by membrane permeabilization or DNA binding. In addition, peptide ARD II–IV (HBc153-176) and ARD I–III (HBc147-167) were found to be necessary and sufficient for the activity against P. aeruginosa and K. peumoniae. The antimicrobial activity of HBc ARD peptides can be attenuated by the addition of LPS. HBc ARD peptide was shown to be capable of direct binding to the Lipid A of lipopolysaccharide (LPS) in several in vitro binding assays. Peptide ARD I–IV (HBc147-183) had no detectable cytotoxicity in various tissue culture systems and a mouse animal model. In the mouse model by intraperitoneal (i.p.) inoculation with Staphylococcus aureus, timely treatment by i.p. injection with ARD peptide resulted in 100-fold reduction of bacteria load in blood, liver and spleen, as well as 100% protection of inoculated animals from death. If peptide was injected when bacterial load in the blood reached its peak, the protection rate dropped to 40%. Similar results were observed in K. peumoniae using an IVIS imaging system. The finding of anti-microbial HBc ARD is discussed in the context of commensal gut microbiota, development of intrahepatic anti-viral immunity and establishment of chronic infection with HBV. Our current results suggested that HBc ARD could be a new promising antimicrobial peptide.

Antibiotics-resistant pathogens have been a major problem to our public health. Recently, in our studies of human hepatitis B virus (HBV), we accidentally discovered potent and broad spectrum antimicrobial peptides from HBV core protein (HBc) arginine-rich domain (ARD). The peptides are mainly composed of SPRRR repeats and are effective against both Gram-positive and Gram-negative bacteria, as well as fungi. We found different bactericidal mechanisms of the ARD peptides, which involved LPS binding, DNA binding and membrane permeabilization in various tested bacteria, such as P. aeruginosa, K. pneumoniae, E. coli and S. aureus. We also found that this ARD peptide was effective for colistin-resistant A. baumannii. The peptides exhibited no hemolysis activity to human red blood cells and no cytotoxicity to human hepatoma cells and kidney cells. Furthermore, the ARD peptide was shown to be safe and protective in the animal model. Recently, intestinal flora was found to influence the development of immunity. We discussed here the potential involvement of the antimicrobial activity of HBc ARD in the establishment of HBV chronic infection in the newborns. We proposed here that the HBc ARD peptides could serve as an alternative to the conventional antibiotics in clinical medicine.

Bacteremia caused by Acinetobacter junii at a medical center in Taiwan, 2000-2010

We investigated the clinical characteristics and outcomes of 43 patients with Acinetobacter junii bacteremia at a 2,500-bed tertiary care center in northern Taiwan. These organisms were confirmed to the species level by an array assay and 16S rRNA gene sequence analysis. The antimicrobial susceptibilities of the 43 A. junii isolates to 13 agents were determined using the agar dilution method. Susceptibility testing for tigecycline was determined using the broth microdilution method. Most of the patients were hospital-acquired (n = 36, 83.7 %) or healthcare facility-related infections (n = 6, 13.9 %), and 55.8 % had impaired immunity. Central venous access devices were present in 35 (81.4 %) patients; among the total of 43 patients with A. junii bacteremia, 8 patients were diagnosed as catheter-related bloodstream infection and 19 patients were diagnosed as catheter-associated bloodstream infection. Shock requiring inotropic agents occurred in 2 patients (4.6 %). Most patients developed bacteremia in general wards (n = 36, 83.7 %). The overall in-hospital mortality rate was low (7 %), despite the low rate of removal of central venous devices, low rate of holding usage of original central venous devices, and high rate of inappropriate antimicrobial regimens. Carbapenems, fluoroquinolones, and amikacin had potent activity (>95 % susceptible rate) against A. junii isolates. Interestingly, 35 % of the A. junii isolates were resistant to colistin. Tigecycline exhibited low minimum inhibitory concentration (MIC) values (range, 0.06-2 μg/ml, MIC(90), 1 μg/ml) against the A. junii isolates.

Colistin resistance of Acinetobacter baumannii: clinical reports, mechanisms and antimicrobial strategies

Colistin is the last resort for treatment of multidrug-resistant Acinetobacter baumannii. Unfortunately, resistance to colistin has been reported all over the world. The highest resistance rate was reported in Asia, followed by Europe. The heteroresistance rate of A. baumannii to colistin is generally higher than the resistance rate. The mechanism of resistance might be loss of lipopolysaccharide or/and the PmrAB two-component system. Pharmacokinetic/pharmacodynamic studies revealed that colistin monotherapy is unable to prevent resistance, and combination therapy might be the best antimicrobial strategy against colistin-resistant A. baumannii. Colistin/rifampicin and colistin/carbapenem are the most studied combinations that showed promising results in vitro, in vivo and in the clinic. New peptides showing good activity against colistin-resistant A. baumannii are also being investigated.