Carbapenem-resistant Acinetobacter Baumannii Strains Research Articles

Mobile genetic elements carrying aminoglycoside resistance genes in Acinetobacter baumannii isolates belonging to global clone 2.

Aminoglycosides are used to treat infections caused by carbapenem-resistant Acinetobacter baumannii (CRAB) strains. However, resistance to aminoglycosides has increased remarkably in the last few years. Here, we aimed to determine the mobile genetic elements (MGEs) associated with resistance to aminoglycosides in the global clone 2 (GC2) A. baumannii. Among the 315 A. baumannii isolates, 97 isolates were identified as GC2, and 52 of GC2 isolates (53.6%) were resistant to all the aminoglycosides tested. The AbGRI3s carrying armA were detected in 88 GC2 isolates (90.7%), and of them, 17 isolates (19.3%) carried a new variant of AbGRI3 (AbGRI3ABI221). aphA6 was located in TnaphA6 of 30 isolates out of 55 aphA6-harboring isolates, and 20 isolates were found to harbor TnaphA6 on a RepAci6 plasmid. Tn6020 carrying aphA1b was detected in 51 isolates (52.5%), which was located within AbGRI2 resistance islands. The pRAY* carrying the aadB gene was detected in 43 isolates (44.3%), and no isolate was found to contain a class 1 integron harboring this gene. The GC2 A. baumannii isolates contained at least one MGE carrying the aminoglycoside resistance gene, located mostly either in the chromosome within AbGRIs or on the plasmids. Thus, it is likely that these MGEs play a role in the dissemination of aminoglycoside resistance genes in GC2 isolates from Iran.

Genomic Characterization of Carbapenem-Resistant Acinetobacter baumannii (CRAB) in Mechanically Ventilated COVID-19 Patients and Impact of Infection Control Measures on Reducing CRAB Circulation during the Second Wave of the SARS-CoV-2 Pandemic in Milan, Italy.

COVID-19 has significantly affected hospital infection prevention and control (IPC) practices, especially in intensive care units (ICUs). This frequently caused dissemination of multidrug-resistant organisms (MDROs), including carbapenem-resistant Acinetobacter baumannii (CRAB). Here, we report the management of a CRAB outbreak in a large ICU COVID-19 hub Hospital in Italy, together with retrospective genotypic analysis by whole-genome sequencing (WGS). Bacterial strains obtained from severe COVID-19 mechanically ventilated patients diagnosed with CRAB infection or colonization between October 2020 and May 2021 were analyzed by WGS to assess antimicrobial resistance and virulence genes, along with mobile genetic elements. Phylogenetic analysis in combination with epidemiological data was used to identify putative transmission chains. CRAB infections and colonization were diagnosed in 14/40 (35%) and 26/40 (65%) cases, respectively, with isolation within 48 h from admission in 7 cases (17.5%). All CRAB strains belonged to Pasteur sequence type 2 (ST2) and 5 different Oxford STs and presented blaOXA-23 gene-carrying Tn2006 transposons. Phylogenetic analysis revealed the existence of four transmission chains inside and among ICUs, circulating mainly between November and January 2021. A tailored IPC strategy was composed of a 5-point bundle, including ICU modules' temporary conversion to CRAB-ICUs and dynamic reopening, with limited impact on ICU admission rate. After its implementation, no CRAB transmission chains were detected. Our study underlies the potentiality of integrating classical epidemiological studies with genomic investigation to identify transmission routes during outbreaks, which could represent a valuable tool to ensure IPC strategies and prevent the spread of MDROs. IMPORTANCE Infection prevention and control (IPC) practices are of paramount importance for preventing the spread of multidrug-resistant organisms (MDROs) in hospitals, especially in the intensive care unit (ICU). Whole-genome sequencing (WGS) is seen as a promising tool for IPC, but its employment is currently still limited. COVID-19 pandemics have posed dramatic challenges in IPC practices, causing worldwide several outbreaks of MDROs, including carbapenem-resistant Acinetobacter baumannii (CRAB). We present the management of a CRAB outbreak in a large ICU COVID-19 hub hospital in Italy using a tailored IPC strategy that allowed us to contain CRAB transmission while preventing ICU closure during a critical pandemic period. The analysis of clinical and epidemiological data coupled with retrospective genotypic analysis by WGS identified different putative transmission chains and confirmed the effectiveness of the IPC strategy implemented. This could be a promising approach for future IPC strategies.

Evaluation of combination therapies with colistin in an experimental mouse pneumonia model induced by carbapenem-resistant Acinetobacter baumannii strain.

The treatment options are limited in Acinetobacter baumannii infections. In this study, the effectiveness of colistin monotherapy and combinations of colistin with different antibiotics were investigated in an experimental pneumonia model induced by carbapenem-resistant A.baumannii strain. Mice in the study were divided into five groups as control (no treatment), colistin monotherapy, colistin + sulbactam, colistin + imipenem, and colistin + tigecycline combinations. The modified experimental surgical pneumonia model of Esposito and Pennington was applied to all groups. The presence of bacteria in blood and lung samples was investigated. Results were compared. In blood cultures, while there was no difference between the control and colistin groups, there was a statistical difference between the control and the combination groups (P = 0.029). When the groups were compared in terms of lung tissue culture positivity, there was a statistical difference between the control group and all treatment groups (colistin, colistin + sulbactam, colistin + imipenem, and colistin + tigecycline) (P = 0.026, P < 0.001, P < 0.001, and P = 0.002, respectively). The number of microorganisms that grew in the lung tissue was found to be statistically significantly lower in all treatment groups in comparison with the control group (P = 0.001). Both monotherapy and combination therapies of colistin were found to be effective in the treatment of carbapenem-resistant A.baumannii pneumonia, but the superiority of combination therapies over colistin monotherapy has not been demonstrated.

Emergence and Evolution of OXA-23-Producing ST46Pas-ST462Oxf-KL28-OCL1 Carbapenem-Resistant Acinetobacter baumannii Mediated by a Novel ISAba1-Based Tn7534 Transposon

Carbapenem-resistant Acinetobacter baumannii (CRAB) isolates of global clone 1 (GC1) and global clone 2 (GC2) have been widely reported. Nevertheless, non-GC1 and non-GC2 CRAB strains have been studied less. In particular, no reports concerning sequence type 46 (ST46Pas) CRAB strains have been described thus far. In this work, the genomic features and possible evolution mechanism of ST46Pas OXA-23-producing CRAB isolates from clinical specimens are reported for the first time. Antimicrobial susceptibility testing of three ST46Pas strains revealed identical resistance profiles (resistance to imipenem, meropenem, ciprofloxacin and the combination of cefoperazone/sulbactam at a 2:1 ratio). They were found to belong to ST46Pas and ST462Oxf with capsular polysaccharide 28 (KL28) and lipooligosaccharide 1 (OCL1), respectively. Whole-genome sequencing (WGS) revealed that all contained one copy of chromosomal blaOXA-23, which was located in a novel ISAba1-based Tn7534 composite transposon. In particular, another copy of the Tn7534 composite transposon was identified in an Hgz_103-type plasmid with 9 bp target site duplications (TSDs, ACAACATGC) in the A. baumannii ZHOU strain. As the strains originated from two neighboring intensive care units (ICUs), ST46Pas OXA-23-producing CRAB strains may have evolved via transposition events or a pdif module. Based on the GenBank database, ST46Pas strains were collected from various sources; however, most were collected in Hangzhou (China) from 2014 to 2021. Pan-genome analysis revealed 3276 core genes, 0 soft-core genes, 768 shell genes and 443 cloud genes shared among all ST46Pas strains. In conclusion, the emergence of ST46Pas CRAB strains might present a new threat to healthcare settings; therefore, effective surveillance is required to prevent further dissemination.

Detection and homology analysis of carbapenem resistant Acinetobacter baumannii resistance gene.

To explore the carrying status and homology of carbapenem resistant Acinetobacter baumannii (CRAB) in our hospital. From January 2015 to December 2017, 52 strains of acinetobacter baumannii isolated from the bacteria room of the clinical laboratory of Baogang hospital in Inner Mongolia were selected as the research object. K-B disk diffusion method and Vitek-2 were used to determine the drug sensitivity of Acinetobacter baumannii. The drug resistance gene was detected by polymerase chain reaction (PCR) and its homology was analyzed by pulsed field gel electrophoresis (PFGE). Except for Cefoperazone/sulbactam, other antibiotics were resistant to ab. The detection rate of drug resistance gene class C β-lactamases (ADC) was 100%, and the higher detection rates of other drug resistance genes were class D β-lactamases (OXA)-51 (36 strains, 90.0%),disinfectant gene qacE△1-sull (32 strains, 80.0%), and klebsiella pneumoniae carbapenemase (KPC) gene was not detected. 2-8 drug resistance genes were detected in each CRAB strain, and the strains with 6 drug resistance genes were the most (15 strains, 37.5%); Among the detected drug-resistant gene combinations, ADC+OXA-23 + OXA-51 gene was detected at the same time (29 strains, 72.5%), followed by ADC+ intl1 + qacE △ 1-sull gene (26 strains, 65.0%), ADC + qacE △ 1-sull + ant (3 '') -i gene (19 strains, 47.5%), and 11 strains (27.5%). There were 19 different types in PFGE homology test, each type was 1-9 strains, including 9 strains of A5 type and 8 strains of A18 type, mainly from intensive care unit. CRAB in the hospital is highly resistant to common clinical antibiotics. OXA-23 and OXA-51 genes are most likely to be the main factors causing drug resistance of Acinetobacter baumannii in the hospital. Homology analysis showed that there was CRAB nosocomial infection transmission in different wards of the hospital.

Molecular epidemiology of carbapenem-resistant Acinetobacter baumannii isolates in Turkiye: Systematic review.

The World Health Organization has designated carbapenem-resistant Acinetobacter baumannii (CRAB) as a "critical" pathogen on the global priority list of antibiotic-resistant bacteria. This study aims to discuss the molecular epidemiology of CRAB isolates in Turkiye in the last 12 years and the prevalence of gene regions associated with resistance or pathogenesis using a systematic review method. Our study consists of a literature search, determination of eligibility and exclusion criteria, qualitative analysis of studies, data extraction, and statistical analysis. All studies were analyzed according to the Preferred Reporting Items for Systematic Reviews and Meta-Analysis Guidelines. The incidence rates of blaOXA-23, blaOXA-23-like, blaOXA-24/40, blaOXA-24/40-like, blaOXA-51, blaOXA-51-like, blaOXA-58, and blaOXA-58-like genes in CRAB strains were 76.4%, 68.6%, 1.2%, 3.4%, 97.0%, 98.6%, 8.4%, and 17.1%, respectively. It was determined that the prevalence of the blaOXA-23 and blaOXA-58 gene regions showed a statistically significant change over the years. Due to the high prevalence of A. baumannii strains carrying the blaOXA-23 variant, it is necessary to follow its geographical distribution and transposon and plasmid movements. Based on available data, molecular surveillance of CRAB strains should be standardized. In addition, sterilization and disinfection processes applied within the scope of an effective struggle against CRAB strains that can remain live on surfaces for a long time should be reviewed frequently.

Vaccination with a combination of planktonic and biofilm virulence factors confers protection against carbapenem-resistant Acinetobacter baumannii strains

Acinetobacter baumannii is a multi-drug resistant pathogen with the ability to switch between planktonic and biofilm phenotypes. Although there is no vaccine against A. baumannii infections, many attempts have been made to develop vaccines using planktonic or biofilm antigens. To cover the different phenotypes of A. baumannii during growth and attachment, we combined planktonic upregulated antigens of iron receptors with biofilm upregulated antigens of pilus rods and evaluated immune responses and protective efficacies of the combined vaccine using lethal and sub-lethal murine sepsis models. The results showed that the combined vaccine elicited high IgG antibody titers and conferred protection against lethal doses of two Carbapenem-resistant high adherent A. baumannii strains. Complete bacterial clearance from all the affected tissues of the mice challenged with A. baumannii was an excellent achievement with our quadrivalent immunogen. These results demonstrate both planktonic and biofilm antigens are important during antigen selection for vaccine design.

Genomic Analysis of Carbapenem-Resistant Acinetobacter baumannii Strains Recovered from Chilean Hospitals Reveals Lineages Specific to South America and Multiple Routes for Acquisition of Antibiotic Resistance Genes.

ABSTRACTCarbapenem-resistant Acinetobacter baumannii (CRAb) is a public health threat accounting for a significant number of hospital-acquired infections. Despite the importance of this pathogen, there is scarce literature on A. baumannii molecular epidemiology and evolutionary pathways relevant to resistance emergence in South American strains. We analyzed the genomic context of 34 CRAb isolates recovered from clinical samples between 2010 and 2013 from two hospitals in Santiago, Chile, using whole-genome sequencing. Several Institut Pasteur scheme sequence types (STs) were identified among the 34 genomes studied here, including ST1, ST15, ST79, ST162, and ST109. No ST2 (the most widespread sequence type) strain was detected. Chilean isolates were phylogenetically closely related, forming lineages specific to South America (e.g., ST1, ST79, and ST15). The genomic contexts of the resistance genes were diverse: while genes were present in a plasmid in ST15 strains, all genes were chromosomal in ST79 strains. Different variants of a small Rep_3 plasmid played a central role in the acquisition of the oxa58 carbapenem and aacC2 aminoglycoside resistance genes in ST1, ST15, and ST79 strains. The aacC2 gene along with blaTEM were found in a novel transposon named Tn6925 here. Variants of Tn7 were also found to play an important role in the acquisition of the aadA1 and dfrA1 genes. This work draws a detailed picture of the genetic context of antibiotic resistance genes in a set of carbapenem-resistant A. baumannii strains recovered from two Chilean hospitals and reveals a complex evolutionary picture of antibiotic resistance gene acquisition events via multiple routes involving several mobile genetic elements.IMPORTANCE Treating infections caused by carbapenem-resistant A. baumannii (CRAb) has become a global challenge given that CRAb strains are also often resistant to a wide range of antibiotics. Analysis of whole-genome sequence data is now a standard approach for studying the genomic context of antibiotic resistance genes; however, genome sequence data from South American countries are scarce. Here, phylogenetic and genomic analyses of 34 CRAb strains recovered from 2010 to 2013 from two Chilean hospitals revealed a complex picture leading to the generation of resistant lineages specific to South America. From these isolates, we characterized several mobile genetic elements, some of which are described for the first time. The genome sequences and analyses presented here further our understanding of the mechanisms leading to multiple-drug resistance, extensive drug resistance, and pandrug resistance phenotypes in South America. Therefore, this is a significant contribution to elucidating the global molecular epidemiology of CRAb.

Extensively drug-resistant Acinetobacter baumannii co-producing VIM-2 and OXA-23 in intensive care units: Results of a one-day point prevalence in a Tunisian hospital

ObjectiveThe main objective of this study was to identify carbapenem resistance mechanisms among clinical, commensal and environmental carbapenem-resistant Acinetobacter baumannii (CRAB) strains isolated in 5 Tunisian intensive care units (ICUs). Materials and MethodsCRAB isolates were recovered from different sources: clinical specimens, rectal and environmental swabs. Bacterial identification was carried out using conventional methods and susceptibility testing according to EUCAST recommendations. Evaluation of phenotypic carbapenemase production of was performed using seven different methods, and molecular detection of carbapenemase-coding genes (blaOXA23, blaOXA24, blaOXA58, blaNDM, blaGES, blaOXA48, blaIMP, blaVIM and blaKPC) was done by PCR. The genetic relationships between CRAB isolates were analyzed by pulsed-field gel electrophoresis. ResultsAll in all, 46 CRAB isolates were identified in clinical specimens (n = 26/26), rectal swabs (n = 17/36) and environmental swabs (n = 3/63). Most of them (n = 41/46) were clonally related and found in the different ICUs. All of the CARB isolates harbored blaOXA-51-like and blaOXA-23 genes, while blaVIM-2 gene was detected in 42 isolates (91.3 %). Phenotypic carbapenemase activity was found in all 46 strains, using the CIM-Tris test with 100 % sensitivity for OXA-23 and VIM-carbapenemase detection, thereby justifying its routine use. ConclusionThe emergence and diffusion of clonal CRAB strains inducing high mortality rates in ICUs is a major public health concern. Enhanced infection control practices and mandatory staff education are needed to control the spread of these multidrug-resistant bacteria.

Risk factors and resistance patterns of invasive Acinetobacter Baumannii infection in Children

Objective: To understand the risk factors and antibiotics-resistant patterns of invasive Acinetobacter baumannii infection in Children. Methods: This retrospective study was conducted in 6 tertiary hospitals from January 2016 to December 2018. The basic information, clinical data and the results of antimicrobial susceptibility testing were collected from the 98 pediatric inpatients with Acinetobacter baumannii isolated from blood or cerebrospinal fluid and analyzed. According to the susceptibility of the infected strains to carbapenems, they were divided into carbapenem-sensitive Acinetobacter baumannii (CSAB) group and carbapenem-resistant Acinetobacter baumannii (CRAB) group. According to the possible sources of infection, they were divided into nosocomial infection group and community infection group. Chi-square test or Fisher exact test were used to analyze categorical variables and rank sum test were used to analyze continuous variables. The risk factors of invasive CRAB infection in children were analyzed by Logistic regression. Result: There were 56 males and 42 females in 98 cases. The onset age of patients was 8 (2, 24) months. There were 62 cases (63%) from rural area. A total of 87 cases (89%) were confirmed with bloodstream infection, and 12 cases (12%) confirmed with meningitis (1 case was accompanied with bloodstream infection). In these patients, 66 cases (67%) received invasive medical procedures or surgery, 54 cases (55%) received carbapenems-containing therapy. Twenty-four cases were infected with CRAB, and 74 cases with CSAB. The onset age of cases in CRAB group was lower than that in CSAB group (4 (1, 9) vs. 10 (4, 24) months, Z=-2.16, P=0.031). The proportions of hospitalization in intensive care unit, carbapenem antibiotics using, pneumonia and adverse prognosis in CRAB group were higher than those in CSAB group (6 cases (25%) vs. 4 cases (5%), 18 cases (75%) vs. 36 cases (49%), 17 cases (71%) vs. 17 cases (23%), 6 cases (25%) vs. 4 cases (5%), χ2=5.61, 5.09, 18.32, 5.61, all P<0.05). Seventy-seven cases were nosocomial infection and 21 cases were hospital-acquired infection. The proportion of children hospitalized in high-risk wards for nosocomial infections, length of hospitalization, number of antimicrobial therapy received and duration of antimicrobial therapy were higher in the hospital associated infection group than those in the community acquired infection group (all P<0.05). Logistic regression analysis showed that children from rural area (OR=8.42, 95%CI 1.45-48.88), prior mechanical ventilation (OR=12.62, 95%CI 1.31-121.76), and prior antibiotic therapy (OR=4.90, 95%CI 1.35-17.72) were independent risk factors for CRAB infection. The resistance percentage of CSAB isolates to many classes of antibiotics was <6% except to gentamicin, which was as high as 20% (13/65). All CRAB isolates of resistant to ampicillin-sulbactam (20/20), cefepime (23/23), piperacillin (17/17), meropenem (23/23) and imipenem (24/24) were 100%. The resistance percentage to other antibiotics were up to 42%-96%. Conclusions: Most of invasive Acinetobacter baumannii infection in children in China are hospital-acquired. The outcome of invasive CRAB infection was poorer than that of CSAB infection. The drug resistance rate of CRAB strains isolated is high. Living in rural area, prior invasive mechanical ventilation and prior antibiotic therapy were independent risk factors for invasive CRAB infection. The prevention and control of nosocomial infection and appropriate use of antibiotics to reduce Acinetobacter baumannii infection.

Comprehensive Surveillance and Sampling Reveal Carbapenem-Resistant Organism Spreading in Tertiary Hospitals in China.

PurposeCarbapenem-resistant organisms (CROs) have posed a great threat to antibiotic use and induce multi-drug resistance. Contamination of the hospital environment and infection of healthcare workers (HCWs) are reported as sources of nosocomial infections. Here, we performed a comprehensive environment sampling and timely epidemiological investigation during outbreaks to investigate the role of the environment and HCWs in CRO transmission.Patients and MethodsWe enrolled carbapenem-resistant organism outbreaks in ICU-1 of Huashan Hospital from January 2019 to March 2019, and ICU-2 located at west branch of Huashan Hospital from October 2019 to November 2019. Carbapenem-resistant Klebsiella pneumoniae (CRKP) and carbapenem-resistant Acinetobacter baumannii (CRAB) isolates were collected from the patients. We performed a real-time comprehensive environmental and HCW sampling in the two ICUs. Isolated strains from patients and the positive colonies from the screening were sent for whole-genome sequencing. Finally, phylogenetic trees were constructed.ResultsCRAB and CRKP outbreaks simultaneously occurred in ICU-1; the outbreak involved 13 patients. Meanwhile, the CRKP outbreak in ICU-2 included 11 patients. Twelve out of 146 environment and HCWs samples in ICU-1 were carbapenem-resistant bacteria, including six CRKP and six CRAB strains. For ICU-2, hospital surfaces and HCWs were negative for CRKP. Phylogenetic analyses showed that CRKP strains in ICU-1 were classified into two clades: Clade 1 and Clade 2, sharing a high similarity of isolates from the environment and HCWs. The same phenomenon was observed in CRAB.ConclusionA timely comprehensive sampling combined with genome-based investigation may aid in tracking the transmission route of and controlling the infections. The environment and HCWs could be contaminated during CRO transmission, which calls for strengthened prevention and control measures.

Epidemiological and genetic characteristics of clinical carbapenem-resistant Acinetobacter baumannii strains collected countrywide from hospital intensive care units (ICUs) in China

ABSTRACT Acinetobacter baumannii is one of the key Gram-negative pathogens that can cause serious nosocomial infections. In China, a large proportion of clinical A. baumannii strains are multidrug resistant, among which strains resistant to carbapenems are particularly worrisome, as infections caused by such strains may limit the choice of existing antibiotics. We conducted a nationwide and genome-based surveillance on the prevalence and antibiotic susceptibility profile of carbapenem-resistant A. baumannii (CRAB) strains collected from intensive care units (ICUs) in hospitals in different provinces and investigated the routes of transmission and mechanism of resistance by whole-genome sequencing and phylogenetic analysis. We found that CRAB strains were prevalent in 71.4% (55/77) of the ICUs surveyed. Clonal spread of CRAB was found in 37.6% (29/77) of ICUs and a total of 22 different clones were identified. Most clones were transmissible within one ICU, but up to six clones could be detected in at least three hospitals. In addition, carbapenem-hydrolysing class D β-lactamases (CHDL) were found to be mainly responsible for carbapenem-resistance in A. baumannii and the ST2 global-clone is the predominant type of CRAB in China. Importantly, we found that CRAB isolates currently exhibited an extremely low rate of resistance to colistin (0.4%) and tigecycline (2.5%), but a high rate of resistance to ceftazidime–avibactam (70.2%). Findings in this work shall facilitate development of appropriate antimicrobial regimens for treatment of CRAB infections. Further surveillance and research on the evolutionary and epidemiological features of clinical CRAB strains are necessary.

Prevalence of Extended-Spectrum β-Lactamase Genes and Antibiotic Resistance Pattern in Clinical Isolates of Acinetobacter baumannii from Patients Hospitalized in Mashhad, Iran

Background: Carbapenem-resistant Acinetobacter baumannii strains are one of the most severe factors in hospital infection worldwide, in which the beta-lactamase enzyme is one of the main resistance mechanisms. Objectives: This study aimed to evaluate the presence of carbapenem-resistant beta-lactamase genes and determine antibiotic resistance patterns in the clinical isolates of A. baumannii from patients hospitalized in the Shahid Kamyab Hospital, Mashhad, Iran. Methods: Out of 286 collected isolates from patients hospitalized in Shahid Kamyab Hospital (from March 2017 to June 2017), 31 isolates were confirmed to be A. baumannii using biochemical tests. Antibiotic susceptibility testing was conducted using the disc diffusion method according to the CLSI standard protocols. The presence of beta-lactamase genes, namely blaVEB, blaPER, blaAmpC, blaVIM, blaIMP, blaSHV, and blaTEM, was detected using polymerase chain reaction. Results: In this study, 31 isolates were identified as A. baumannii, all of which revealed high resistance to ceftazidime, cefixime, ceftriaxone, meropenem, imipenem, cefotaxime and cephalexin. In this case, the lowest resistance (19.35%) was observed against polymixin B. Moreover, blaAmpC, blaTEM, blaSHV, blaPER, and blaVIM were observed in 93.54% (29), 51.61% (16), 48.38% (15), 41.93% (13), and 77% (24) of the isolates, respectively. However, blaVEB and blaIMP were observed in none of the isolates. Conclusions: The results showed high carbapenem resistance and high frequency of beta-lactamase resistance genes among the clinical isolates of A. baumannii.

Minocycline Susceptibility and tetB Gene in Carbapenem-Resistant Acinetobacter baumannii in Taiwan.

PurposeIn this study, we evaluated the minocycline susceptibility rate in carbapenem-resistant Acinetobacter baumannii (CRAB) clinical strains, and the association between tetB carriage and minocycline susceptibility in CRAB.Patients and MethodsA total of 100 genetically unrelated CRAB clinical strains from bloodstream infection were randomly collected from a medical center in Taiwan. An argument for a new minocycline susceptibility breakpoint of 1 mg/L was suggested based on pharmacokinetic (PK) and pharmacodynamic (PD) studies. Strains with minocycline minimum inhibitory concentrations (MICs) of >1 mg/L were classified as PK-PD non-susceptible. TetB carriage was detected by polymerase chain reaction (PCR).ResultsFifty-five (55%) CRAB strains were susceptible to minocycline according to the Clinical and Laboratory Standards Institute (CLSI) criteria, among which 98.2% (54/55) were PK-PD non-susceptible. The minocycline MIC50/90 was 4/16 mg/L. Ninety-seven (97%) strains carried tetB. All of the tetB-positive strains and 66.7% (2/3) of the tetB-negative strains were PK-PD non-susceptible. By statistical analysis, tetB carriage was significantly correlated with PK-PD non-susceptibility (P = 0.03) and a higher minocycline MIC (P = 0.02). The sensitivity and specificity of the tetB PCR for predicting PK-PD non-susceptibility were 98% and 100%, respectively.ConclusionAt our institute, most CRAB strains were PK-PD non-susceptible and most carried tetB gene. Recognizing the minocycline MIC and tetB status may be essential when using minocycline to treat CRAB-related infections.

Polymyxin B Combined with Minocycline: A Potentially Effective Combination against blaOXA-23-harboring CRAB in In Vitro PK/PD Model.

Polymyxin-based combination therapy is commonly used to treat carbapenem-resistant Acinetobacter baumannii (CRAB) infections. In the present study, the bactericidal effect of polymyxin B and minocycline combination was tested in three CRAB strains containing blaOXA-23 by the checkerboard assay and in vitro dynamic pharmacokinetics/pharmacodynamics (PK/PD) model. The combination showed synergistic or partial synergistic effect (fractional inhibitory concentration index ≤0.56) on the tested strains in checkboard assays. The antibacterial activity was enhanced in the combination group compared with either monotherapy in in vitro PK/PD model. The combination regimen (simultaneous infusion of 0.75 mg/kg polymyxin B and 100 mg minocycline via 2 h infusion) reduced bacterial colony counts by 0.9–3.5 log10 colony forming units per milliliter (CFU/mL) compared with either drug alone at 24 h. In conclusion, 0.75 mg/kg polymyxin B combined with 100 mg minocycline via 2 h infusion could be a promising treatment option for CRAB bloodstream infections.

Clonal Relationships and Antibiotic Resistance Profiles of Carbapenem-Resistant Acinetobacter baumannii Strains Associated with Healthcare-Related Infections in Eastern Anatolia Region, Turkey

Clonal Relationships and Antibiotic Resistance Profiles of Carbapenem-Resistant Acinetobacter baumannii Strains Associated with Healthcare-Related Infections in Eastern Anatolia Region, Turkey

Phylogenetic analysis of carbapenem-resistant Acinetobacter baumannii isolated from different sources using Multilocus Sequence Typing Scheme.

The emergence and worldwide distribution of carbapenem-resistant Acinetobacter baumannii strains has become a major public health threat. The objective of this study was to investigate the clonal relatedness of A. baumannii isolates collected from clinical and extra-hospital environments in Mthatha, South Africa. Forty carbapenem-resistant isolates comprising of clinical (20) and extra-hospital (20) were identified and tested for antimicrobial susceptibility. Detection of carbapenemase encoding genes was performed by Real-time PCR. The clonal relationship of clinical isolates relative to extra-hospital isolates was determined via multilocus sequence typing (MLST). All isolates (clinical and extra-hospital) were resistant to most common antibiotics including carbapenems (imipenem; MIC ≥32μg/mL and meropenem; MIC ≥32μg/mL) with the only exception being amikacin (with 3 isolates susceptible), tigecycline (14 isolates susceptible) and colistin (all isolates susceptible). The bla OXA-23-like and the intrinsic bla OXA-51 -like genes were detected in all the isolates tested. The bla OXA-58-like and bla IMP-type genes were detected in 2 clinical isolates whilst the bla OXA-24-like, bla VIM-type, bla NDM-1, bla SIM, and bla AmpC were not detected. The bla OXA-24-like, bla OXA-58-like, bla IMP-type, bla VIM-type, bla NDM-1, bla SIM, and bla AmpC were negative in the extra-hospital isolates. Co-occurrence of bla OXA-23 -like, bla OXA-58-like and bla IMP-type was observed in 2 clinical isolates. The MLST performed on 33 isolates identified 5 existing sequence types (ST) (ST1, ST2, ST25, ST85 and ST215) in clinical isolates and 2 existing STs (ST1 and ST2) in extra-hospital isolates. The most dominant ST was ST2 accounting for 68.8% of the clinical isolates and 82.4% of the extra-hospital isolates. The study demonstrated high prevalence and potential clonal spread of globally-disseminated clonal complex 2 carrying bla OXA-23-like within our local settings. However, ST25 might be an emerging lineage carrying the bla OXA-23-like . Continuous monitoring is important in limiting the spread of these strains in other healthcare settings and the community.

In vitro and in vivo Activity of Combinations of Polymyxin B with Other Antimicrobials Against Carbapenem-Resistant Acinetobacter baumannii.

PurposeTo study the in vitro and in vivo antibacterial activities of polymyxin B (PB) and other five antimicrobial agents, including imipenem (IMP), meropenem (MEM), tigecycline (TGC), sulbactam (SUL), and rifampicin (RIF), alone or in combination against carbapenem-resistant Acinetobacter baumannii (CRAB).MethodsMicrobroth dilution method was used to determine the minimum inhibitory concentration (MIC) of ten strains of CRAB against six antibacterial drugs, and the checkerboard method was used to determine the fractional inhibitory concentration index (FICI). A mouse pneumonia model was established by intranasal instillation of Ab5075 to evaluate the antibacterial activity in vivo.ResultsThe resistance rate of ten CRAB strains to IMP, MEM, and SUL was 100%, that to PB and TGC was 0%, and that to RIF was 20%. When PB was used in combination with the other five antibiotics in vitro, it mainly showed synergistic and additive effects on CRAB. The synergistic effect of PB and RIF was maximal, followed by MEM and IMP but was weak with SUL and TGC. In vivo, compared to the model group (untreated with antibiotics), treatment group (six antibiotics alone and PB combined with the other five antibiotics) reduced the bacterial load in the lung tissue and the serum inflammatory factors (IL-1β, IL-6, and TNF-α). The bacterial load and the inflammatory factors of the combined group decreased significantly than that of the single group (P<0.05). The IL-6 and TNF-α values of the PB combined with the RIF group were significantly lower than the two drugs used individually.ConclusionThe combination of PB and IMP, MEM, and RIF exerted robust in vitro synergistic effects on CRAB isolates. The combination of PB and the other five antimicrobial agents had a better effect in the mouse pneumonia model than single agent, while the combination of PB and RIF had the best effect.

Molecular Epidemiology of Carbapenem-Resistant Acinetobacter baumannii Strains Isolated at the German Military Field Laboratory in Mazar-e Sharif, Afghanistan.

The study was performed to provide an overview of the molecular epidemiology of carbapenem-resistant Acinetobacter baumannii in Afghanistan isolated by the German military medical service during the Afghanistan conflict. A total of 18 isolates were collected between 2012 and 2018 at the microbiological laboratory of the field hospital in Camp Marmal near Mazar-e Sharif, Afghanistan, from Afghan patients. The isolates were subjected to phenotypic and genotypic differentiation and antimicrobial susceptibility testing as well as to a core genome multi-locus sequence typing (cgMLST) approach based on whole-genome next-generation sequence (wgNGS) data. Next to several sporadic isolates, four transmission clusters comprising strains from the international clonal lineages IC1, IC2, and IC9 were identified. Acquired carbapenem resistance was due to blaOXA-23 in 17/18 isolates, while genes mediating resistance against sulfonamides, macrolides, tetracyclines, and aminoglycosides were frequently identified as well. In conclusion, the assessment confirmed both the frequent occurrence of A. baumannii associated with outbreak events and a variety of different clones in Afghanistan. The fact that acquired carbapenem resistance was almost exclusively associated with blaOXA-23 may facilitate molecular resistance screening based on rapid molecular assays targeting this resistance determinant.

Increased Capsule Thickness and Hypermotility Are Traits of Carbapenem-Resistant Acinetobacter baumannii ST3 Strains Causing Fulminant Infection.

BackgroundAcinetobacter baumannii is a successful nosocomial pathogen, causing severe, life-threatening infections in hospitalized patients, including pneumonia and bloodstream infections. The spread of carbapenem-resistant Acinetobacter baumannii (CRAB) strains is a major health threat worldwide. The successful spread of CRAB is mostly due to its highly plastic genome. Although some virulence factors associated with CRAB have been uncovered, many mechanisms contributing to its success are not fully understood.MethodsHere we describe strains of CRAB that were isolated from fulminant cases in 2 hospitals in Israel. These isolates show a rare hypermucoid (HM) phenotype and were investigated using phenotypic assays, comparative genomics, and an in vivo Galleria mellonella model. ResultsThe 3 isolates belonged to the ST3 international clonal type and were closely related to each other, as shown by Fourier-transform infrared spectroscopy and phylogenetic analyses. These isolates possessed thickened capsules and a dense filamentous extracellular polysaccharides matrix as shown by transmission electron microscopy (TEM), and overexpressed the capsule polysaccharide synthesis pathway-related wzc gene. ConclusionsThe HM isolates possessed a unique combination of virulence genes involved in iron metabolism, protein secretion, adherence, and membrane glycosylation. HM strains were more virulent than control strains in 2 G. mellonella infection models. In conclusion, our findings demonstrated several virulence factors, all present in 3 CRAB isolates with rare hypermucoid phenotypes.