A prospective multicenter study on the evaluation of antimicrobial resistance and molecular epidemiology of multidrug-resistant Acinetobacter baumannii infections in intensive care units with clinical and environmental features

Emergence of novel hypervirulent Acinetobacter baumannii strain and herpes simplex type 1 virus in a case of community-acquired pneumonia in China

BACKGROUND

A. baumannii is an important and common clinical pathogen, especially in the intensive care unit (ICU). This study aimed to characterize one hypervirulent A. baumannii strain in a patient with community-acquired pneumonia and herpes simplex type 1 virus infection.

METHODS

Minimum inhibitory concentrations (MICs) were determined using the Kirby-Bauer (K-B) and broth microdilution methods. Galleria mellonella infection model experiment was conducted. Whole-genome sequencing (WGS) was performed using the Illumina and Nanopore platforms. The resistance and virulence determinants were identified using the ABRicate program with ResFinder and the VFDB database. The capsular polysaccharide locus (K locus) and lipooligosaccharide outer core locus (OC locus) were identified using Kleborate with Kaptive. Phylogenetic analyses were conducted using the BacWGSTdb server.

RESULTS

A. baumannii XH2146 strain belongs to ST10Pas and ST447Oxf. The strain was resistant to cefazolin, ciprofloxacin, and trimethoprim/sulfamethoxazole (TMP-SMX). Bautype and Kaptive analyses showed that XH2146 contains OCL2 and KL49. WGS analysis revealed that the strain harbored blaADC-76, blaOXA-68, ant(3'')-IIa, tet(B), and sul2. Notably, tet(B) and sul2, both were located within a 114,700-bp plasmid (designated pXH2146-1). Virulence assay revealed A. baumannii XH2146 possessed higher virulence than A. baumannii AB5075 at 12 h. Comparative genomic analysis showed that A. baumannii ST447 strains were mainly isolated from the USA and exhibited a relatively close genetic relationship. Importantly, 11 strains were observed to carry blaOXA-58; blaOXA-23 was identified in 11 isolates and three ST447 A. baumannii strains harbored blaNDM-1.

CONCLUSIONS

Early detection of community-acquired hypervirulent Acinetobacter baumannii strains is recommended to prevent their extensive spread in hospitals.

Risk Factors Associated with Mortality in Acinetobacter baumannii Infections: Results of a Prospective Cohort Study in a Tertiary Public Hospital in Guayaquil, Ecuador

Antibiotic overuse and the resulting antimicrobial resistance pose significant global public health challenges, providing an avenue for opportunistic pathogens like Acinetobacter baumannii to thrive. This study will report the trends of Acinetobacter baumannii antimicrobial resistance patterns at the Hospital Teodoro Maldonado Carbo, Ecuador. An observational, analytical, longitudinal, and prospective study was conducted involving patients diagnosed with hospital-acquired infections. Antimicrobial susceptibility testing was performed, followed by molecular analysis of carbapenemase genes in Acinetobacter baumannii isolates. We included 180 patients aged from 16 to 93 years. The hospital mortality rate was 63/180 (35%). Invasive mechanical ventilation (IMV) was indicated in 91/180 patients (50.4%). The overall survival (OS) rate in patients on IMV was 49.5% (45/91), with a median survival of 65 days. The OS rate in patients not on IMV was 80.9% (72/89), with a median survival of 106 days (HR 2.094; 95% CI 1.174-3.737; p = 0.012). From multivariate analysis, we conclude that ventilator-associated pneumonia is the most related factor to OS.

Using time-series chest radiographs and laboratory data by machine learning for identifying pulmonary infection and colonization of Acinetobacter baumannii

BACKGROUND

Accurately distinguishing between pulmonary infection and colonization in patients with Acinetobacter baumannii is of utmost importance to optimize treatment and prevent antibiotic abuse or inadequate therapy. An efficient automated sorting tool could prompt individualized interventions and enhance overall patient outcomes. This study aims to develop a robust machine learning classification model using a combination of time-series chest radiographs and laboratory data to accurately classify pulmonary status caused by Acinetobacter baumannii.

METHODS

We proposed nested logistic regression models based on different time-series data to automatically classify the pulmonary status of patients with Acinetobacter baumannii. Advanced features were extracted from the time-series data of hospitalized patients, encompassing dynamic pneumonia indicators observed on chest radiographs and laboratory indicator values recorded at three specific time points.

RESULTS

Data of 152 patients with Acinetobacter baumannii cultured from sputum or alveolar lavage fluid were retrospectively analyzed. Our model with multiple time-series data demonstrated a higher performance of AUC (0.850, with a 95% confidence interval of [0.638-0.873]), an accuracy of 0.761, a sensitivity of 0.833. The model, which only incorporated a single time point feature, achieved an AUC of 0.741. The influential model variables included difference in the chest radiograph pneumonia score.

CONCLUSION

Dynamic assessment of time-series chest radiographs and laboratory data using machine learning allowed for accurate classification of colonization and infection with Acinetobacter baumannii. This demonstrates the potential to help clinicians provide individualized treatment through early detection.

Establishment and Validation of a Risk Prediction Model for Mortality in Patients with Acinetobacter baumannii Infection: A Retrospective Study

Purpose

This study aims to establish a valuable risk prediction model for mortality in patients with Acinetobacter baumannii (A. baumannii).

Patients and Methods

The 622 patients with A. baumannii infection from the First Affiliated Hospital of Anhui Medical University were enrolled as the study cohort. Univariate and multivariate logistic regression analysis was used to preliminarily screen the independent risk factors of death caused by A. baumannii infection, followed by LASSO regression analysis to determine the risk factors. According to the calculated regression coefficient, the Nomogram death prediction model is established. The area under the curve (AUC) and decision curve analysis (DCA) of the operating characteristic (ROC) curve of the subjects are used to evaluate the discrimination of the established prediction model. The calibration degree of the prediction model is represented by a calibration chart. A validation cohort that consisted of 477 patients admitted to the 901st Hospital was also included.

Results

Our results revealed that the source of infection, carbapenem-resistant A. baumannii, mechanical ventilation, serum albumin value, and Charlson comorbidity index were independent risk factors for death caused by A. baumannii infection. The AUC value of ROC curves of study cohort and validation cohort were 0.76 and 0.69, respectively. The probability range (30-80%) indicated a high net income of the modified model and strong capacity of discrimination. The calibration curve obtained by analysis swings up and down around the 45 diagonal line, which shows that the calibration degree of the prediction model is very high.

Conclusion

In this study, we have reconstructed a risk prediction model for mortality in patients with A. baumannii infections. This model provides useful information to predict the risk of death in patients with A. baumannii infection, but the specificity is not optimistic. If this prediction model is wanted to be applied to clinical practice, more analysis and research are necessary.

Safety and pharmacokinetics of SPR206 in subjects with varying degrees of renal impairment

SPR206 is a novel polymyxin derivative with potent in vitro activity against susceptible and multidrug-resistant strains of Acinetobacter baumannii, Pseudomonas aeruginosa, Klebsiella pneumoniae, Escherichia coli, and Enterobacter species. SPR206 is eliminated renally. The safety, tolerability, and pharmacokinetics (PK) of SPR206 were evaluated in healthy subjects with normal renal function (Cohort 1) and subjects with varying degrees of renal impairment (RI) (Cohorts 2-4) or end-stage renal disease (ESRD) on hemodialysis (HD) (Cohort 5). Subjects in Cohorts 1-4 received a 100-mg intravenous (IV) dose of SPR206. Subjects in Cohort 5 received a 100-mg IV dose within 2 h after HD on day 1 and 1 h before HD on day 5. Safety and PK analyses included 37 subjects. Mostly mild but no serious treatment-related adverse events were reported. Systemic exposure to SPR206 increased as renal function decreased, with mean area under the concentration-time curve from time 0 to the last quantifiable concentration (AUC0-last) values 39% to 239% greater in subjects with RI vs healthy subjects. Mean plasma clearance (CL) of SPR206 decreased with decreasing renal function (29% to 76% lower vs healthy subjects). In subjects with ESRD, AUC0-last decreased by 51%, and CL increased by 92% for dialyzed vs nondialyzed conditions. SPR206 was excreted in urine within 12 h in healthy subjects and subjects with mild RI (Cohort 2) but was prolonged in those with moderate and severe RI (Cohorts 3 and 4, respectively). In summary, SPR206 was generally safe and well tolerated, and the PK of SPR206 was well characterized in subjects with RI.

Amikacin-induced acute kidney injury in mechanically ventilated critically ill patients with sepsis

In this retrospective cohort study, we aimed to evaluate the incidence, risk factors and outcomes of amikacin-induced acute kidney injury (AKI) in critically ill patients with sepsis. A total of 311 patients were included in the study. Of them, 83 (26.7%) had amikacin-induced AKI. In model 1, the multivariable analysis demonstrated concurrent use of colistin (OR 25.51, 95%CI 6.99-93.05, p< 0.001), presence of septic shock during amikacin treatment (OR 4.22, 95%CI 1.76-10.11, p=0.001), and Charlson Comorbidity Index (OR 1.14, 95%CI 1.02-1.28, p=0.025) as factors independently associated with an increased risk of amikacin-induced AKI. In model 2, the multivariable analysis demonstrated concurrent use of at least one nephrotoxic agent (OR 1.95, 95%CI 1.10-3.45; p=0.022), presence of septic shock during amikacin treatment (OR 3.48, 95%CI 1.61-7.53; p=0.002), and Charlson Comorbidity Index (OR 1.12, 95%CI 1.01-1.26; p=0.037) as factors independently associated with an increased risk of amikacin-induced AKI. In conclusion, before amikacin administration, the risk of AKI should be considered, especially in patients with multiple complicated comorbid diseases, septic shock, and those receiving colistin therapy.

Does Emerging Carbapenem Resistance in Acinetobacter baumannii Increase the Case Fatality Rate? Systematic Review and Meta-Analysis

BACKGROUND

In the era of rising carbapenem resistance, we aimed to investigate the change in mortality rate and positivity of carbapenemase genes in Acinetobacter baumannii.

METHODS

Preferred Reporting Items for Systematic Review (PRISMA) guidelines were adopted in this systematic review. Our literature search included the Cochrane Library, Pubmed, Scopus, Web of Science, Medline, Tubitak TR Dizin, and Harman databases for studies dating back from 2003 to 2023 reporting bloodstream A. baumannii infections in Türkiye. A simple linear regression model was used to determine the association between resistance, mortality, and time.

RESULTS

A total of 1717 studies were identified through a literature search, and 21 articles were selected based on the availability of the data regarding mortality and resistance rate (four articles) or the molecular epidemiology of carbapenem-resistant A. baumannii (17 articles) in Türkiye. From 2007 to 2018, the carbapenem resistance rate increased (p = 0.025). The OXA-23 and OXA-58 positivities were inversely correlated (p = 0.025).

CONCLUSIONS

Despite the emergence of carbapenem resistance, mortality did not increase in parallel, which may be due to improved medical advancements or the fitness cost of bacteria upon prolonged antimicrobial exposure. Therefore, we suggest further global research with the foresight to assess clonal relatedness that might affect the carbapenem resistance rate.

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.

AamA-mediated epigenetic control of genome-wide gene expression and phenotypic traits in Acinetobacter baumannii ATCC 17978

Individual deletions of three genes encoding orphan DNA methyltransferases resulted in the occurrence of growth defect only in the aamA (encoding AcinetobacterAdenine Methylase A) mutant of A. baumannii strain ATCC 17978. Our single-molecule real-time sequencing-based methylome analysis revealed multiple AamA-mediated DNA methylation sites and proposed a potent census target motif (TTTRAATTYAAA). Loss of Dam led to modulation of genome-wide gene expression, and several Dam-target sites including the promoter region of the trmD operon (rpsP, rimM, trmD, and rplS) were identified through our methylome and transcriptome analyses. AamA methylation also appeared to control the expression of many genes linked to membrane functions (lolAB, lpxO), replication (dnaA) and protein synthesis (trmD operon) in the strain ATCC 17978. Interestingly, cellular resistance against several antibiotics and ethidium bromide through functions of efflux pumps diminished in the absence of the aamA gene, and the complementation of aamA gene restored the wild-type phenotypes. Other tested phenotypic traits such as outer-membrane vesicle production, biofilm formation and virulence were also affected in the aamA mutant. Collectively, our data indicated that epigenetic regulation through AamA-mediated DNA methylation of novel target sites mostly in the regulatory regions could contribute significantly to changes in multiple phenotypic traits in A. baumannii ATCC 17978.

Pharmacokinetics of SPR206 in Plasma, Pulmonary Epithelial Lining Fluid, and Alveolar Macrophages following Intravenous Administration to Healthy Adult Subjects

SPR206 is a next-generation polymyxin being developed for the treatment of multidrug-resistant (MDR) Gram-negative infections. This Phase 1 bronchoalveolar lavage (BAL) study was conducted to evaluate SPR206's safety and pharmacokinetics in plasma, pulmonary epithelial lining fluid (ELF), and alveolar macrophages (AM) in healthy volunteers. Subjects received a 100 mg intravenous (IV) dose of SPR206 infused over 1 h every 8 h for 3 consecutive doses. Each subject underwent 1 bronchoscopy with BAL at 2, 3, 4, 6, or 8 h after the start of the third IV infusion. SPR206 concentrations in plasma, BAL, and cell pellet were measured with a validated LC-MS/MS assay. Thirty-four subjects completed the study and 30 completed bronchoscopies. Mean SPR206 peak concentrations (Cmax) in plasma, ELF, and AM were 4395.0, 735.5, and 860.6 ng/mL, respectively. Mean area under the concentration-time curve (AUC0-8) for SPR206 in plasma, ELF, and AM was 20120.7, 4859.8, and 6026.4 ng*h/mL, respectively. The mean ELF to unbound plasma concentration ratio was 0.264, and mean AM to unbound plasma concentration ratio was 0.328. Mean SPR206 concentrations in ELF achieved lung exposures above the MIC for target Gram-negative pathogens for the entire 8-h dosing interval. Overall, SPR206 was well tolerated; 22 subjects (64.7%) reported at least 1 treatment-emergent adverse event (TEAE). Of the 40 reported TEAEs, 34 (85.0%) were reported as mild in severity. The most frequent TEAEs were oral paresthesia (10 subjects [29.4%]) and nausea (2 subjects [5.9%]). This study demonstrates pulmonary penetration of SPR206 and supports further development of SPR206 for the treatment of patients with serious infections caused by MDR Gram-negative pathogens.

Genome-wide identification and oxacillinase OXA distribution characteristics of Acinetobacter spp. based on a global database

Objective

To use genomic analysis to identify Acinetobacter spp. and to explore the distribution characteristics of ß-lactamase oxallicinases (blaOXA) among Acinetobacter species globally.

Methods

Genomes of global Acinetobacter spp. were downloaded from GenBank using Aspera batch. After quality check using CheckM and QUAST software, the genomes were annotated using Prokka software to investigate the distribution of blaOXAs across Acinetobacter spp.; a phylogenetic tree was constructed to explore the evolutionary relationship among the blaOXA genes in Acinetobacter spp. Average-nucleotide identification (ANI) was performed to re-type the Acinetobacter spp. BLASTN comparison analysis was implemented to determine the sequence type (ST) of Acinetobacter baumannii strain.

Results

A total of 7,853 genomes were downloaded, of which only 6,639 were left for further analysis after quality check. Among them, 282 blaOXA variants were identified from the genomes of 5,893 Acinetobacter spp.; blaOXA-23 (n = 3,168, 53.8%) and blaOXA-66 (2,630, 44.6%) were the most frequent blaOXAs, accounting for 52.6% (3,489/6639), and the co-carriage of blaOXA-23 and blaOXA-66 was seen in 2223 (37.7%) strains. The 282 blaOXA variants were divided into 27 clusters according to the phylogenetic tree. The biggest clade was blaOXA-51-family carbapenem-hydrolyzing enzymes composed of 108 blaOXA variants. Overall, 4,923 A. baumannii were identified out of the 6,639 Acinetobacter spp. strains and 291 distinct STs were identified among the 4,904 blaOXA-carrying A. baumannii. The most prevalent ST was ST2 (n = 3,023, 61.6%) followed by ST1 (n = 228, 4.6%).

Conclusion

OXA-like carbapenemases were the main blaOXA-type β-lactamase spread widely across Acinetobacter spp. Both blaOXA-23 and blaOXA-66 were the predominant blaOXAs, among all A. baumannii strains, with ST2 (belonging to CC2) being the main clone disseminated globally.

Drug‑resistant Acinetobacter baumannii: From molecular mechanisms to potential therapeutics (Review)

Bacterial drug resistance is increasingly becoming an important problem that needs to be solved urgently in modern clinical practices. Infection caused by Acinetobacter baumannii is a serious threat to the life and health of patients. The drug resistance rate of Acinetobacter baumannii strains is increasing, thus research on the drug resistance of Acinetobacter baumannii has also seen an increase. When patients are infected with drug-resistant Acinetobacter baumannii, the availability of suitable antibiotics commonly used in clinical practices is becoming increasingly limited and the prognosis of patients is worsening. Studying the molecular mechanism of the drug resistance of Acinetobacter baumannii is fundamental to solving the problem of drug-resistant Acinetobacter baumannii and potentially other 'super bacteria'. Drug resistance mechanisms primarily include enzymes, membrane proteins, efflux pumps and beneficial mutations. Research on the underlying mechanisms provides a theoretical basis for the use and development of antibiotics and the development of novel treatment methods.

A two-year retrospective study of multidrug-resistant Acinetobacter baumannii respiratory infections in critically Ill patients: Clinical and microbiological findings

BACKGROUND

Acinetobacter baumannii infection is a serious public health problem because it is highly resistant to antimicrobial therapy and causes a high fatality rate in critically ill patients. The aim of the study is to examine the demographics, microbiological findings, clinical presentation, and outcomes of multi-drug-resistant Acinetobacter baumannii respiratory infections in adult ICU intubated patients during COVID-19 pandemic.

METHODS

This study included 115 mechanically ventilated adult ICU patients who had multi-drug-resistant Acinetobacter baumannii retrieved from respiratory samples during the COVID-19 pandemic in Albaha, Saudi Arabia. The information was obtained from medical and laboratory files. Univariate analysis was used to compare gender, COVID-19 infection, and outcomes.

RESULTS

The rate of Acinetobacter baumanni respiratory infections among adult ICU patients was 6.2 %. Almost 93 % developed ventilator-associated pneumonia, and five of them developed bacteremia. The isolates had significant antibiotic resistance patterns, of which 3 % were pandrug-resistant bacteria. The death rate was 74 %, with major risk factors including sepsis, septic shock, VAP, liver diseases, and the use of inappropriate antibiotic therapy that lacked both colistin and tigecycline. Patients with COVID-19 coinfection had worse outcomes compared to non-COVID-19 patients.

CONCLUSIONS

The identification of MDR-AB as a threat highlights the importance of surveillance studies in this region.

Pathogen Distribution, Drug Resistance Risk Factors, and Construction of Risk Prediction Model for Drug-Resistant Bacterial Infection in Hospitalized Patients at the Respiratory Department During the COVID-19 Pandemic

Objective

To investigate the distribution and drug resistance of pathogens among hospitalized patients in the respiratory unit during the COVID-19 pandemic, analyze the risk factors of drug resistance, construct a risk prediction model.

Methods

This study isolated 791 strains from 489 patients admitted to the Affiliated Hospital of Chengdu University, who were retrospectively enrolled between December 2019 and June 2021. The patients were divided into training and validation sets based on a random number table method (8:2). The baseline information, clinical characteristics, and culture results were collected using an electronic database and WHONET 5.6 software and compared between the two groups. A risk prediction model for drug-resistant bacteria was constructed using multi-factor logistic regression.

Results

K. pneumoniae (24.78%), P. aeruginosa (17.19%), A. baumannii (10.37%), and E. coli (10.37%) were the most abundant bacterial isolates. 174 isolates of drug-resistant bacteria were collected, ie, Carbapenem-resistant organism-strains, ESBL-producing strains, methicillin-resistant S. aureus, multi-drug resistance constituting 38.51%, 50.57%, 6.32%, 4.60%, respectively. The nosocomial infection prediction model of drug-resistant bacteria was developed based on the combined use of antimicrobials, pharmacological immunosuppression, PCT>0.5 ng/mL, CKD stage 4-5, indwelling catheter, and age > 60 years. The AUC under the ROC curve of the training and validation sets were 0.768 (95% CI: 0.624-0.817) and 0.753 (95% CI: 0.657-0.785), respectively. Our model revealed an acceptable prediction demonstrated by a non-significant Hosmer-Lemeshow test (training set, p=0.54; validation set, p=0.88).

Conclusion

K. pneumoniae, P. aeruginosa, A. baumannii, and E. coli were the most abundant bacterial isolates. Antimicrobial resistance among the common isolates was high for most routinely used antimicrobials and carbapenems. COVID-19 did not increase the drug resistance pressure of the main strains. The risk prediction model of drug-resistant bacterial infection is expected to improve the prevention and control of antibacterial-resistant bacterial infection in hospital settings.

Molecular Characterization of Carbapenem-Resistant Acinetobacter baumannii with Special Reference to Carbapenemases: A Systematic Review

Carbapenemases are β-lactamase enzymes that hydrolyze a variety of β-lactams including carbapenem and belong to different Ambler classes (A, B, D). These enzymes can be encoded by plasmid or chromosomal-mediated genes. The major issues associated with carbapenemases-producing organisms are compromising the activity and increasing the resistance to carbapenems which are the last resort antibiotics used in treating serious infections. The global increase of pathogen, carbapenem-resistant A. baumannii has significantly threatened public health. Thus, there is a pressing need for a better understanding of this pathogen, to know the various carbapenem resistance encoding genes and dissemination of resistance genes from A. baumannii which help in developing strategies to overcome this problem. The horizontal transfer of resistant determinants through mobile genetic elements increases the incidence of multidrug, extensive drug, and Pan-drug resistant A. baumannii. Therefore, the current review aims to know the various mechanisms of carbapenem resistance, categorize and discuss carbapenemases encoding genes and various mobile genetic elements, and the prevalence of carbapenemase genes in recent years in A. baumannii from various geographical regions.

Risk factors for ventilator-associated pneumonia due to multi-drug resistant organisms after cardiac surgery in adults

Background

Ventilator-associated pneumonia (VAP) is one of the most common intensive care unit (ICU)-acquired infections, which can cause multiple adverse events. Due to bacterial mutation and overuse of antimicrobial drugs, multidrug-resistant organisms (MDRO) has become one of the major causes of postoperative VAP infections in cardiac patients. Therefore, this study aims to explore the risk factors for VAP with MDRO following cardiac surgery in adults.

Methods

The clinical data of adult VAP patients following cardiac surgery in the hospital from Jan 2017 to May 2021 were analyzed retrospectively, and the patients were divided into the MDRO VAP group and the non-MDRO VAP group. Univariable and multivariable logistic regression analyses were performed on risk factors in patients with MDRO VAP. The species and drug sensitivity of pathogens isolated from the VAP patients were also analyzed.

Results

A total of 61 VAP cases were involved in this study, with 34 cases in the MDRO VAP group (55.7%) and 27 cases in the non-MDRO VAP group (44.3%). Multivariable logistic regression analysis showed that independent risk factors for MDRO VAP included preoperative creatinine clearance rate (CCR) ≥ 86.6ml, intraoperative cardiopulmonary bypass (CPB) time ≥ 151 min, postoperative acute kidney injury (AKI) and nasal feeding. Gram-negative bacilli were the main pathogens in VAP patients (n = 54, 90.0%), with the highest rate of Acinetobacter baumannii (n = 24, 40.0%). Additionally, patients with MDRO VAP had a significantly longer postoperative intensive care unit (ICU) duration and higher hospitalization costs than non-MDRO VAP patients, but there was no notable difference in the 28-day mortality rate between the two groups.

Conclusion

Based on implementing measures to prevent VAP, clinicians should pay more attention to patients with kidney disease, longer intraoperative CPB time, and postoperative nasal feeding to avoid MDRO infections.

Molecular typing and antibiotic resistance patterns among clinical isolates of Acinetobacter baumannii recovered from burn patients in Tehran, Iran

Acinetobacter baumannii (A. baumannii) is now considered a highly resistant pathogen to various types of antibiotics. Therefore, tracking the source of its prevalence and continuous control is crucial. This study aimed to determine antibiotic resistance and perform various molecular typing methods on clinical isolates of A. baumannii isolated from hospitalized burn patients in Shahid Motahari Burn Hospital, Tehran, Iran. Hospital isolates were confirmed by phenotypic and molecular methods. Then the sensitivity to different antibiotics was determined using the minimum inhibitory concentration (MIC) method. In order to perform molecular typing, three-locus dual assay multiplex polymerase chain reaction (PCR), multiple-locus variable-number tandem repeat analysis (MLVA), and multilocus sequence typing (MLST) methods were used. Among the 60 isolates collected, the frequencies of multidrug-resistant (MDR) and extensively drug-resistant (XDR) isolates were 90 and 10%, respectively. The most effective antibiotics were colistin with 100% and tigecycline with 83.33% sensitivity. Isolates were 100% resistant to piperacillin/tazobactam and cephalosporins, and 68.3% were resistant to carbapenem. The results of multiplex PCR showed five groups that international clone I (IC I) and IC II were the most common. The MLVA method identified 34 MLVA types (MTs), 5 clusters, and 25 singletons. Multilocus sequence typing results for tigecycline-resistant isolates showed seven different sequence types (STs). Increasing antibiotic resistance in A. baumannii isolates requires careful management to control and prevent the occurrence of the pre-antibiotic era. The results of this study confirm that the population structure of A. baumannii isolates has a high diversity. More extensive studies are needed in Iran to better understand the epidemiology of A. baumannii.

Synergistic antibacterial activity of silver nanoparticles biosynthesized by carbapenem-resistant Gram-negative bacilli

Nanotechnology is being investigated for its potential to improve nanomedicine for human health. The purpose of this study was to isolate carbapenemase-producing Gram-negative bacilli (CPGB), investigate the presence of carbapenemase resistance genes, determine their antibiogram and ability to biosynthesise silver nanoparticles (Ag NPs), and estimate the antibacterial activity of Acinetobacter baumannii-biosynthesised Ag NPs on CPGB alone and in combination with antibiotics. A total of 51 CPGBs were isolated from various specimens in the study. The automated Vitek-2 system was used to identify and test these strains' antimicrobial susceptibilities. The carbapenemase resistance genes were identified using a polymerase chain reaction (PCR). Under the CPGB, A. baumannii could biosynthesise Ag NPs. X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), and field emission scanning electron were used to characterise Ag NPs. The antibacterial activity of Ag NP alone and in combination with antibiotics against CPGB was determined using the broth microdilution method, and their synergistic effect was determined using the checkerboard assay. bla_NDM and bla_OXA-48 were the most commonly reported, and 90% of the isolates produced multiple carbapenemase genes. Tigecycline proved to be the most effective anti-CPGB antibiotic. Isolates with more resistance genes were more resistant to antibiotics, and isolates with three genes (42%) had the most extensively drug-resistant patterns (38%). A significant relationship was discovered between genetic and antibiotic resistance patterns. Only A. baumannii produced Ag NPs out of all the isolates tested. Ag NPs with a size of 10 nm were confirmed by UV–visible spectroscopy, FT-IR, XRD, and TEM analysis. The Ag NPs were effective against CPGB, with minimum inhibitory concentrations ranging from 64 to 8 μg/ml on average. Surprisingly, the combination of Ag NPs and antibiotics demonstrated synergistic and partial synergistic activity (fractional inhibitory concentration between 0.13 and 0.56) against CPGB, as well as a significant reduction in antibiotic concentrations, particularly in the case of A. baumanii versus ceftriaxone (1024 to 4 μg/ml). The notable synergistic activity of Ag NPs with antibiotics represents a valuable nanomedicine that may find clinical application in the future as a combined remedy.

Description of a Rare Pyomelanin-Producing Carbapenem-Resistant Acinetobacter baumannii Strain Coharboring Chromosomal OXA-23 and NDM-1

Carbapenem-resistant Acinetobacter baumannii (CRAB), which belonged to global clones 1 (GC1) or 2 (GC2), has been widely reported and become a global threat. However, non-GC1 and non-GC2 CRAB strains are not well-studied, especially for those with rare phenotype. Here, one pyomelanin-producing CRAB strain (A. baumannii DETAB-R21) was isolated from oral swab in the ICU. Antimicrobial susceptibility testing showed it was resistant to carbapenems, ceftazidime, levofloxacin, and ciprofloxacin. DETAB-R21 was ST164_Pas and ST1418_Oxf with KL47 and OCL5, respectively. Whole-genome sequencing (WGS) analysis revealed chromosome contained three copies of bla_OXA-23 on three 4,805-bp Tn2006 composite transposons with various novel 9-bp target site duplications (TSD). A Tn125-like structure, including bla_NDM-1, a novel 4,343 bp composite transposon encoding bla_CARB-16, and three prophage regions were also identified. Importantly, hmgA was interrupted by a Tn2006 and contributed to pyomelanin production and further confirmed by hmgA overexpression. Furthermore, A. baumannii irradiated with UV light, DETAB-R21 showed a higher relatively survival rate compared to a control strain that did not produce pyomelanin. No effects of pyomelanin were observed on disinfectants susceptibility, growth, or virulence. In conclusion, pyomelanin-producing CRAB carrying the bla_NDM-1 and bla_OXA-23 genes embedded in the bacterial chromosome is of grave concern for health care settings, highlighting the need for effective measures to prevent further dissemination. IMPORTANCE Pyomelanin production is a quite rare phenotype in A. baumannii. Moreover, the mechanisms leading to the pyomelanin production was still unclear. Here, we for the first time, confirmed the mechanism of pyomelanin production, and further investigated the impact of pyomelanin on disinfectants susceptibility, growth, virulence, and UV irradiation. More importantly, many mobile genetic elements (MGEs), including three copies of Tn2006 composite transposons, one copy of bla_NDM-1 on the Tn125-like structure and three prophage regions, were identified in the chromosome, demonstrated strong plasticity of A. baumannii genome. Our study provides important insights into the new rare ST164_Pas A. baumannii strain with high level carbapenem resistance, which is of great threat for patients. These findings will provide important insights into the resistance gene transfer via transposition events and further spread in the clinic.

Carbapenem-resistant Gram-negative pathogens associated with septic shock: a review of 120 cases

This study aimed to evaluate the influencing variables for outcomes in patients with septic shock having culture-proven carbapenem-resistant Gram-negative pathogens. It included 120 patients (mean age 64.29 ± 1.35 years and 58.3% female). The mean Sequential Organ Failure Assessment score during septic shock diagnosis was found to be 11.22 ± 0.43 and 9 ± 0.79 among the patients with mortality and among the survivors, respectively (P = 0.017). The logistic regression analysis showed that empirical treatment as mono Gram-negative bacteria-oriented antibiotic therapy (P = 0.016, odds ratio (OR) = 17.730, 95% confidence interval (CI): 1.728-182.691), Charlson Comorbidity Index >2 (P = 0.032, OR = 7.312, 95% CI: 5.7-18.3), and systemic inflammatory response syndrome score 3 or 4 during septic shock diagnosis (P = 0.014, OR = 5.675, 95% CI: 1.424-22.619) were found as independent risk factors for day 30 mortality. Despite early diagnosis and effective management of patients with septic shock, the mortality rates are quite high in CRGNP-infected patients.

Genomic Analysis of Molecular Bacterial Mechanisms of Resistance to Phage Infection

To optimize phage therapy, we need to understand how bacteria evolve against phage attacks. One of the main problems of phage therapy is the appearance of bacterial resistance variants. The use of genomics to track antimicrobial resistance is increasingly developed and used in clinical laboratories. For that reason, it is important to consider, in an emerging future with phage therapy, to detect and avoid phage-resistant strains that can be overcome by the analysis of metadata provided by whole-genome sequencing. Here, we identified genes associated with phage resistance in 18 Acinetobacter baumannii clinical strains belonging to the ST-2 clonal complex during a decade (Ab2000 vs. 2010): 9 from 2000 to 9 from 2010. The presence of genes putatively associated with phage resistance was detected. Genes detected were associated with an abortive infection system, restriction–modification system, genes predicted to be associated with defense systems but with unknown function, and CRISPR-Cas system. Between 118 and 171 genes were found in the 18 clinical strains. On average, 26% of these genes were detected inside genomic islands in the 2000 strains and 32% in the 2010 strains. Furthermore, 38 potential CRISPR arrays in 17 of 18 of the strains were found, as well as 705 proteins associated with CRISPR-Cas systems. A moderately higher presence of these genes in the strains of 2010 in comparison with those of 2000 was found, especially those related to the restriction–modification system and CRISPR-Cas system. The presence of these genes in genomic islands at a higher rate in the strains of 2010 compared with those of 2000 was also detected. Whole-genome sequencing and bioinformatics could be powerful tools to avoid drawbacks when a personalized therapy is applied. In this study, it allows us to take care of the phage resistance in A. baumannii clinical strains to prevent a failure in possible phage therapy.

Assessment of In Vitro Cefiderocol Susceptibility and Comparators against an Epidemiologically Diverse Collection of Acinetobacter baumannii Clinical Isolates

Cefiderocol is a catechol-substituted siderophore cephalosporin combining rapid penetration into the periplasmic space with increased stability against β-lactamases. This study provides additional data on the in vitro antimicrobial activity of cefiderocol and commercially available comparators against an epidemiologically diverse collection of Acinetobacter baumannii clinical isolates. Antimicrobial susceptibility was tested using pre-prepared frozen 96-well microtiter plates containing twofold serial dilutions of: cefepime, ceftazidime/avibactam, imipenem/relebactam, ampicillin/sulbactam, meropenem, meropenem/vaborbactam, ciprofloxacin, minocycline, tigecycline, trimethoprim/sulfamethoxazole and colistin using the standard broth microdilution procedure in cation-adjusted Mueller–Hinton broth (CAMHB). For cefiderocol, iron-depleted CAMHB was used. A collection of 113 clinical strains of A. baumannii isolated from Argentina, Azerbaijan, Croatia, Greece, Italy, Morocco, Mozambique, Peru and Spain were included. The most active antimicrobial agents against our collection were colistin and cefiderocol, with 12.38% and 21.23% of non-susceptibility, respectively. A high proportion of multidrug-resistant (76.77%) and carbapenem-resistant (75.28%) A. baumannii isolates remained susceptible to cefiderocol, which was clearly superior to novel β-lactam/β-lactamase inhibitor combinations. Cefiderocol-resistance was higher among carbapenem-resistant isolates and isolates belonging to ST2, but could not be associated with any particular resistance mechanism or clonal lineage. Our data suggest that cefiderocol is a good alternative to treat infections caused by MDR A. baumanni, including carbapenem-resistant strains.

Prevalence and characterisation of carbapenemase encoding genes in multidrug-resistant Gram-negative bacilli

Background

Emerging worldwide in the past decade, there has been a significant increase in multidrug-resistant bacteria from serious nosocomial infections, especially carbapenemase-producing Gram-negative bacilli that have emerged worldwide. The objective of this study is to investigate carbapenem resistance in Gram-negative bacilli bacteria using phenotypic detection, antimicrobial resistance profiles and genotypic characterisation methods.

Methods

200 Gram-negative bacilli isolates were collected from different clinical specimens. All clinical samples were exposed to isolation and identification of significant pathogens applying bacteriological examination and an automated Vitek-2 system. The isolates were subjected to susceptibility tests by the Vitek-2 automated system and those isolates that were resistant to beta-lactam drugs, including carbapenems, third-generation cephalosporines or cefoxitin, were selected for phenotyping using Carba plus disc system assay for detection of carbapenemase-producing isolates. These isolates were further confirmed by molecular detection. PCR was used for the detection carbapenem-resistant genes (OXA-48, IMP, NDM, VIM, and KPC).

Results

110 (55%) of 200 Gram-negative bacilli were identified as beta-lactam-resistant isolates. The frequency of carbapenem-resistant isolates was calculated to be 30.9% (n = 34/110). A collection totalling 65/110 (59%) isolates were identified as carbapenemase producers by phenotypic method. Moreover, among the 65 carbapenemase-producing Gram-negative isolates with a positive phenotype-based result, 30 (46%), 20 (30%) and 18 (27%) isolates were positive for OXA-48, KPC and MBL enzymes, respectively, as well as the production of 27% of AmpC with porin loss. Tigecycline was the most effective antibiotic that affected 70% of MDR isolates, but high rates of resistance were detected to other tested antimicrobials. Of interest, a high incidence of MDR, XDR and PDR profiles were observed among all carbapenemase-producing isolates. 36% (24/65) of the tested isolates were MDR to 3 to 5 antimicrobial classes. 29% (17/65) of the recovered isolates were XDR to 6 to 7 antimicrobial classes. Alarmingly, 24% (16/65) of isolates displayed PDR to all the tested 8 antimicrobial classes. Genotype assay, including 53 phenotypically confirmed carbapenemase-producing isolates of Gram-negative bacilli, found 51(96%) isolates were harbouring one or more genes. The most common carbapenemase gene was bla_NDM 83% (44/53) followed by bla_OXA-48 75% (40/53), bla_VIM 49% (26/53) and bla_IMP 43% (23/53), while the gene bla_KPC was least frequent 7% (4/53). 92% (46/51) of isolates were involved in the production of more than one carbapenemase gene.

Conclusion

This study demonstrated the emergence of carbapenemase-producing Gram-negative pathogens implicated in healthcare-related infections. Accurate identification of carbapenem-resistant bacterial pathogens is essential for patient treatment, as well as the development of appropriate contamination control measures to limit the rapid spread of pathogens. Tigecycline exhibited potent antimicrobial activity against MDR, XDR and PDR-producing strains that establish a threatening alert which indicates the complex therapy of infections caused by these pathogens.

Antibiotic Resistance Pattern of Acinetobacter baumannii Strains: A Retrospective Study from Oman

Background:

Multidrug-resistant (MDR) Acinetobacter baumannii is of serious health concern and associated with high mortality. Data regarding the antibiotic resistance pattern of A. baumannii strains in Oman is limited.

Objectives:

To determine the antibiotic resistance pattern of A. baumannii from various clinical samples in a tertiary care hospital in the North-Batinah region of Oman.

Methods:

A. baumannii isolates recovered from various clinical samples in the Microbiology laboratory of Sohar Hospital, Oman, during 2015–2019 were retrospectively analyzed. Organism identification and their antibiotic resistance patterns were performed as recommended by the Clinical and Laboratory Standards Institute.

Results:

A total of 1890 A. baumannii nonduplicate isolates were found from clinical samples of 1326 patients. The isolates were more frequently isolated from elderly patients (40%) and in-patient department patients (67%). Infection/colonization was more common among patients treated in the medicine, intensive-care unit, and surgery departments. A. baumannii strains were highly resistant (50-83%) to most of the tested antibiotics, with the highest against ceftriaxone (83%) and ceftazidime (75%), and lowest against colistin (1%) and tigecycline (8%). Among the isolates, 67% (1265) were MDR strains. Of these, 22%, 32% and 16% were resistant to all six, five and four classes of the tested antibiotics.

Conclusion:

The study found that the frequency of isolation of MDR A. baumannii isolates in the northern region of Oman is high.

Virulence Potential and Treatment Options of Multidrug-Resistant (MDR) Acinetobacter baumannii

Acinetobacter baumannii is an opportunistic pathogen which is undoubtedly known for a high rate of morbidity and mortality in hospital-acquired infections. A. baumannii causes life-threatening infections, including; ventilator-associated pneumonia (VAP), meningitis, bacteremia, and wound and urinary tract infections (UTI). In 2017, the World Health Organization listed A. baumannii as a priority-1 pathogen. The prevalence of A. baumannii infections and outbreaks emphasizes the direct need for the use of effective therapeutic agents for treating such infections. Available antimicrobials, such as; carbapenems, tigecycline, and colistins have insufficient effectiveness due to the appearance of multidrug-resistant strains, accentuating the need for alternative and novel therapeutic remedies. To understand and overcome this menace, the knowledge of recent discoveries on the virulence factors of A. baumannii is needed. Herein, we summarized the role of various virulence factors, including; outer membrane proteins, efflux pumps, biofilm, penicillin-binding proteins, and siderophores/iron acquisition systems. We reviewed the recent scientific literature on different A. baumannii virulence factors and the effective antimicrobial agents for the treatment and management of bacterial infections.

Characteristics of and risk factors for biliary pathogen infection in patients with acute pancreatitis

Background

Infection in patients with acute pancreatitis, especially severe acute pancreatitis patients, is a common and important phenomenon, and the distributions and drug resistance profiles of bacteria causing biliary infection and related risk factors are dynamic. We conducted this study to explore the characteristics of and risk factors for bacterial infection in the biliary tract to understand antimicrobial susceptibility, promote the rational use of antibiotics, control multidrug-resistant bacterial infections and provide guidance for the treatment of acute pancreatitis caused by drug-resistant bacteria.

Methods

The distribution of 132 strains of biliary pathogenic bacteria in patients with acute pancreatitis from January 2016 to December 2020 were analyzed. We assessed drug resistance in the dominant Gram-negative bacteria and studied the drug resistance profiles of multidrug-resistant bacteria by classifying Enterobacteriaceae and nonfermentative bacteria. We then retrospectively analyzed the clinical data and risk factors associated with 72 strains of Gram-negative bacilli, which were divided into multidrug-resistant bacteria (50 cases) and non-multidrug-resistant bacteria (22 cases).

Results

The main bacteria were Escherichia coli, Acinetobacter baumannii, Klebsiella pneumoniae and Pseudomonas aeruginosa. Extended-spectrum beta-lactamase (ESBL)-producing Escherichia coli had a 66.67% detection rate. Acinetobacter baumannii had more than 50.00% drug resistance to carbapenems, ESBL-producing Klebsiella pneumoniae had 100.00% drug resistance, and Pseudomonas aeruginosa had 66.67% resistance to carbapenems. Multivariate logistic regression analysis suggested that the administration of third- or fourth-generation cephalosporins was an independent risk factor for Gram-negative multidrug-resistant biliary bacterial infection in acute pancreatitis patients.

Conclusion

Drug resistance among biliary pathogens in acute pancreatitis patients remains high; therefore, rational antimicrobial drug use and control measures should be carried out considering associated risk factors to improve diagnosis and treatment quality in acute pancreatitis patients.

Single- and Multiple-Ascending Dose Study of the Safety, Tolerability, and Pharmacokinetics of the Polymyxin Derivative, SPR206

Carbapenem-resistant Acinetobacter baumannii and Enterobacterales are identified as urgent threats, and multidrug-resistant (MDR) Pseudomonas aeruginosa and extended-spectrum beta-lactamase (ESBL)-producing pathogens are identified as serious threats by the Centers for Disease Control and Prevention (CDC). SPR206 is a novel polymyxin derivative with potent in vitro and in vivo activity against A. baumannii, P. aeruginosa, and multiple clinically important species of Enterobacterales, including multidrug- and extensively drug-resistant strains. This was a first-in-human (FIH) double-blind, placebo-controlled, single-, and multiple-ascending-dose study of the safety, tolerability, and pharmacokinetics (PK) of SPR206 in 94 healthy subjects. Following intravenous (i.v.) administration (1-h infusion) at single doses of 10 mg to 400 mg and multiple doses of 25 mg to 150 mg every 8 h (q8h) for 7 days and 100 mg q8h for 14 days, SPR206 was generally safe and generally well tolerated. While the incidence of adverse events increased with dose, most were of mild severity. Systemic exposure (maximum concentration of drug in serum [C_max] and area under the concentration-time curve [AUC]) to SPR206 was approximately dose proportional, time to peak concentrations ranged from 1.1 to 1.3 h, and half-life ranged from 2.4 to 4.1 h. No appreciable accumulation occurred with repeated dosing of SPR206, and trough concentrations suggest that steady state was achieved by day 2. Urinary excretion of unchanged SPR206 was dose dependent across single- (SAD) and multiple-ascending-dose (MAD) cohorts, and the percentage of dose excreted as SPR206 was up to >50%. Importantly, no evidence of nephrotoxicity was observed over 14 days of 100 mg q8h dosing of SPR206; a dosing regimen anticipated to exceed requirements for clinical efficacy. (This study has been registered at ClinicalTrials.gov under identifier NCT03792308.)

Detection of clinically important β-lactamases by using PCR

Increasing antimicrobial resistance of nosocomial pathogens is becoming a serious threat to public health. To control the spread of this resistance, it is necessary to detect β-lactamase-producing organisms in the clinical setting. The aims of the study were to design a PCR assay for rapid detection of clinically encountered β-lactamase genes described in Enterobacteriaceae and Gram-negative non-fermenting bacteria. The functionality of proposed primers was verified using eight reference strains and 17 strains from our collection, which contained 29 different β-lactamase genes. PCR products of the test strains were confirmed by Sanger sequencing. Sequence analysis was performed using bioinformatics software Geneious. Overall, 67 pairs of primers for detecting 12 members of the class C β-lactamase family, 15 members of class A β-lactamases, six gene families of subclass B1, one member each of subclasses B2, B3 and class D β-lactamases were designed, of which 43 pairs were experimentally tested in vitro. All 29 β-lactamase genes, including 10 oxacillinase subgroups, were correctly identified by PCR. The proposed set of primers should be able to specifically detect 99.7% of analyzed β-lactamase subtypes and more than 79.8% of all described β-lactamase genes.

Investigation of Acinetobacter baumannii Activity in Vascular Surgery Units through Epidemiological Management Based on the Analysis of Antimicrobial Resistance, Biofilm Formation and Genotyping

Background/Objectives: The genus Acinetobacter demonstrates resistance to antibiotics and has been shown to spread in the hospital environment causing epidemic outbreaks among hospitalized patients. The objectives of the present study was to investigate the antibiotic resistance, biofilm formation, and clonality among Acinetobacter baumannii strains. Materials and Methods: The study involved 6 (I Outbreak) and 3 (II Outbreak) A. baumannii strains isolated from patients hospitalized in vascular surgery unit. Results: All tested A. baumannii strains were extensively drug resistant (XDR) and all the isolates were carbapenem-resistant and among them, all carried the bla_OXA-51 gene, the bla_OXA-24 gene, as well as the bla_OXA-23 gene. All of the investigated strains had the ability to form a biofilm, but all of them produced less biofilm than the reference strain. Multi-locus sequence typing (MLST) showed that all strains belonged to the ST2 clone. Pulsed-field gel electrophoresis (PFGE) divided the tested outbreak strains into two clones (A and B). Conclusion: This study shows a nosocomial spread of XDR A. baumannii ST2 having the bla_OXA-51 gene, the bla_OXA-24 gene, as well as the bla_OXA-23 gene, low biofilm formers, that was prevalent in the vascular surgery unit. To identify the current situation of vascular surgery departments targeted epidemiological investigation was needed. Effective implementation of infection control prevented the spread of the epidemic outbreaks.

Molecular Characterization of Carbapenem-Resistant Acinetobacter baumannii Blood Culture Isolates from Three Hospitals in Turkey

We aimed to investigate the clonal relationships, common sequence types, and carbapenemase genes in 177 non-repetitive blood culture isolates of Acinetobacter baumannii collected from patients at three university hospitals in Turkey in 2016. Molecular epidemiological characteristics of the isolates were examined using pulsed-field gel electrophoresis (PFGE), and multilocus sequence typing (MLST) (Pasteur scheme-cpn60, fusA, gltA, pyrG, recA, rplB, and rpoB). Multiplex PCR was used to investigate the carbapenemase genes, including bla_OXA-23-like, bla_OXA-24-like, bla_OXA-48-like, bla_OXA-58-like, bla_IMP, bla_VIM, and bla_NDM. PFGE genotyping yielded 92 pulsotypes with a clustering ratio of 69.7%. As per a ≥85% similarity coefficient, 159 (90.9%) isolates were found to be clonally related. The bla_OXA-23-like and bla_OXA-58-like genes were identified in 100% and 28.2% of the isolates, respectively. The bla_NDM gene was identified in two isolates. The MLST analysis included 54 isolates with different pulsotypes, and 29 sequence types (STs). Most of the isolates (n = 36) belonged to the clonal complex (CC)2, one isolate belonged to CC1, and one isolate belonged to CC164. Sixteen new STs (ST1235-ST1250) were identified. Identifying both global ST2 and a large number of new STs, revealed high genetic diversity in A. baumannii isolates in the study population.

Antibiotic resistance assessment of Acinetobacter baumannii isolates from Tehran hospitals due to the presence of efflux pumps encoding genes (adeA and adeS genes) by molecular method

Objective

Acinetobacter baumannii (A. baumannii) has caused many problems in nosocomial infections. Efflux pumps are considered as one of the most important mechanisms of resistance in this bacterium and have the ability to excrete toxic substances such as antibiotics out of the cell.

Results

In this study, 60 isolates of A. baumannii were collected from patients in several hospitals in Tehran, Iran. After diagnosis using standard biochemical methods, the pattern of antibiotic susceptibility was determined using the disk diffusion method according to CLSI guidelines. The adeA and adeS genes were identified by PCR method. The highest resistance to Piperacillin and the lowest resistance to Gentamicin were observed (100% compared to 48.4%). 6.6% of the isolates had only adeA gene and adeS gene was observed in 8.4% of isolates and both genes were detected in 73.4% of the samples. Despite the high resistance of t A. baumannii o antibiotics and due to the high frequency of genes of adeA and adeS efflux pumps in A. baumannii isolates, it can be concluded that these efflux pumps may play an important role in resistance of this bacterium. By determining the pattern of antibiotic the resistance before treatment, the resistance of this pathogen can be prevented in societies.

Mutations at Novel Sites in pmrA/B and lpxA/D Genes and Absence of Reduced Fitness in Colistin-Resistant Acinetobacter baumannii from a Tertiary Care Hospital, India

Background: Colistin resistance in Acinetobacter baumannii, the last resort drug for serious infections, is emerging worldwide. There has been paucity of data on this aspect from India, which is one of the largest producers of colistin. We studied colistin resistance in A. baumannii and characterized the isolates with respect to resistance mechanisms and virulence. Methods: A total of 365 A. baumannii isolates were studied. Antimicrobial susceptibility testing was performed as per standards. Colistin resistance mechanisms were studied by mutation detection in pmrA/B and lpxA/C/D genes, phenotypic loss of lipopolysaccharide, presence of mcr1-5 genes, and carbonyl cyanide 3-chlorophenylhydrazone (CCCP) effects. Biofilm formation, desiccation survival, and growth kinetics were studied and statistically analyzed for colistin-resistant and colistin-susceptible isolates. Results: All the colistin-resistant isolates (9, 2.5%) showed multiple mutations at novel sites in pmrA/B and/or lpxA/D genes with reversion of resistance with CCCP. Majority of these isolates (6, 66.6%) were from patients without prior colistin therapy. All received prior carbapenems. The resistant isolates demonstrated no significant difference in biofilm formation and desiccation survival but were slow growers. Conclusion: Mutations in pmrA/B and/or lpxA/D genes were the main resistance mechanism in these colistin-resistant isolates that showed no reduction in fitness.

Oxacillinase Gene Distribution, Antibiotic Resistance, and Their Correlation with Biofilm Formation in Acinetobacter baumannii Bloodstream Isolates

Objectives: The limitations of treatment options in bloodstream infections caused by multidrug-resistant Acinetobacter baumannii (MDRAB) have been related to high morbidity and mortality. The aim of our present study was to determine antimicrobial susceptibility profiles, molecular resistance patterns, and biofilm properties of A. baumannii isolated from bloodstream infections. Materials and Methods: In the present study, a total of 44 A. baumannii bloodstream isolates were included. Antimicrobial susceptibility profiles and biofilm formation ability were assessed. The distribution of class D carbapenemases, ISAba1, ISAba1/blaOXA-23, blaNDM-1, mcr-1, and ompA was investigated by polymerase chain reaction (PCR). Arbitrarily primed-PCR (AP-PCR) was performed to evaluate clonal relationships. Results: A total of 32 isolates were MDRAB, whereas 6 isolates were also resistant to colistin without mcr-1 positivity. All isolates were harboring blaOXA-51 gene, whereas blaOXA-23 positivity was 63.6%. Fifty percent of the isolates had ISAba1. ISAba1 upstream of blaOXA-23 was determined in 18 isolates. None of the isolates were positive for blaNDM-1 gene. Majority of the strains were strong biofilm producers (86.8%). A total of 56.8% of the isolates were positive for ompA gene with no direct association with strong biofilm formation. However, blaOXA-51 + 23 genotype and trimethoprim-sulfamethoxazole resistance showed a significant relationship with biofilm formation. AP-PCR analysis revealed six distinct clusters of A. baumannii. Conclusions: Herein, majority of the A. baumannii blood isolates were characterized as blaOXA-51+OXA-23 carbapenemase genotype and were strong biofilm formers. None of the isolates were positive for blaNDM-1, which was promising. Resistant isolates were tended to form strong biofilms. Our results highlight the emergence of oxacillinase-producing MDRAB isolated from bloodstream with high biofilm formation ability.

In Vitro Evaluation of Antimicrobial Peptide Tridecaptin M in Combination with Other Antibiotics against Multidrug Resistant Acinetobacter baumannii

The rapid emergence of antimicrobial resistance in Acinetobacter baumannii coupled with the dried pipeline of novel treatments has driven the search for new therapeutic modalities. Gram-negative bacteria have an extra outer membrane that serves as a permeability barrier for various hydrophobic and/or large compounds. One of the popular approaches to tackle this penetration barrier is use of potentiators or adjuvants in combination with traditional antibiotics. This study reports the in vitro potential of an antimicrobial peptide tridecaptin M in combination with other antibiotics against different strains of A. baumannii. Tridecaptin M sensitized the bacteria to rifampicin, vancomycin, and ceftazidime. Further, we observed that a tridecaptin M and rifampicin combination killed the bacteria completely in 4 h in an ex vivo blood infection model and was superior to rifampicin monotherapy. The study also found that concomitant administration of both compounds is not necessary to achieve the antimicrobial effect. Bacteria pre-treated with tridecaptin M (for 2-4 h) followed by exposure to rifampicin showed similar killing as obtained for combined treatment. Additionally, this combination hampered the survival of persister development in comparison to rifampicin alone. These findings encourage the future investigation of this combination to treat severe infections caused by extremely drug-resistant A. baumannii.

Genotyping and molecular characterization of clinical Acinetobacter baumannii isolates from a single hospital in Southwestern Iran

ACINETOBACTER BAUMANNII

(A. baumannii) is a pathogen responsible for nosocomial infections among the hospitalized patients. The aim of this study was to investigate genotyping and molecular characterization and to examine the biofilm formation ability of A. baumannii isolates. In total, 70 A. baumannii isolates were collected from patients admitted to Imam Khomeini Hospital in Ahvaz, Southwestern Iran. Minimum inhibitory concentrations (MIC) test was performed using Vitek 2 system. The presence of genes encoding metallo-β-lactamases, oxacillinases, and integrase and the biofilm formation ability were then evaluated. Multiple locus variable-number tandem repeat (VNTR) analysis (MLVA) typing and multiplex PCR were performed to determine the genetic relationships. The blaOXA-23-like gene had the highest prevalence. The frequency of genes encoding blaSPM, blaIMP, and blaVIM among MDR A. baumannii isolates were 12 (17.1%), 18 (25.7%), and 22 (31.4%), respectively. Moreover, 46 isolates (75.4%) harbored class I integron and 10 isolates (16.39%) carried class II integron. The number of weak, moderate and strong biofilm-producing isolates were 3 (4.3%), 7 (10%), and 55 (78.5%), respectively. The results showed that 70 A. baumannii isolates were grouped into 12 distinct MLVA types with five clusters and four singleton genotypes. In addition, 25 (35.7%) isolates were assigned to international clone (IC) variants, 37 (52.8%) isolates belonged to group 1 (IC II), and 8  (11.4%) isolates belonged to group 2 (IC I). Our findings revealed that the population structure of the A. baumannii isolates was genetically diverse. More focus on genetic variation and antibiotic resistance of A. baumannii isolates are recommended.

Safety, Pharmacokinetics, and Drug-Drug Interaction Potential of Intravenous Durlobactam, a β-Lactamase Inhibitor, in Healthy Subjects

Durlobactam (DUR; also known as ETX2514) is a novel β-lactamase inhibitor with broad activity against Ambler class A, C, and D β-lactamases. Addition of DUR to sulbactam (SUL) in vitro restores SUL activity against clinical isolates of Acinetobacter baumannii. The safety and pharmacokinetics (PK) of DUR alone and with SUL and/or imipenem-cilastatin (IMI-CIL) were evaluated in healthy subjects. This was a randomized, placebo-controlled study. In part A, subjects, including a cohort of elderly subjects (which received DUR at 1 g), received single ascending doses of DUR ranging from 0.

Durlobactam (DUR; also known as ETX2514) is a novel β-lactamase inhibitor with broad activity against Ambler class A, C, and D β-lactamases. Addition of DUR to sulbactam (SUL) in vitro restores SUL activity against clinical isolates of Acinetobacter baumannii. The safety and pharmacokinetics (PK) of DUR alone and with SUL and/or imipenem-cilastatin (IMI-CIL) were evaluated in healthy subjects. This was a randomized, placebo-controlled study. In part A, subjects, including a cohort of elderly subjects (which received DUR at 1 g), received single ascending doses of DUR ranging from 0.25 to 8 g. In part B, multiple ascending doses of DUR ranging from 0.25 to 2 g were administered every 6 h (q6h) for 29 doses. In parts C and D, the drug-drug interaction (DDI) potential, including the safety, of DUR (1 g) with SUL (1 g) and/or IMI-CIL (0.5/0.5 g) was investigated after single and multiple doses. Plasma and urine concentrations of DUR, SUL, and IMI-CIL were determined. Among 124 subjects, DUR was generally safe and well tolerated when it was administered either alone or in combination with SUL and/or IMI-CIL. After single and multiple doses, DUR demonstrated linear dose-proportional exposure across the studied dose ranges. Renal excretion was a predominant clearance mechanism. No drug-drug interaction potential between DUR and SUL and/or IMI-CIL was identified. SUL-DUR at 1 g (of each component) administered q6h with a 3-h intravenous (i.v.) infusion is under development for the treatment of serious infections due to A. baumannii. (This study has been registered at ClinicalTrials.gov under identifier NCT02971423.)

Evaluating the antimicrobial resistance patterns and molecular frequency of bla oxa-48 and bla GES-2 genes in Pseudomonas aeruginosa and Acinetobacter baumannii strains isolated from burn wound infection in Tehran, Iran

The aim of this study is to evaluate the antimicrobial resistance patterns and molecular frequency of bla_GES-2 and bla_oxa-48 genes in Pseudomonas aeruginosa and Acinetobacter baumannii strains isolated from burn wound infection in Tehran, Iran. In this study, 50 isolates of A. baumannii and 48 isolates of P. aeruginosa were collected from the Burn Unit of Shahid Motahari Hospital at Tehran, Iran. Antibiotic susceptibility tests of all isolates were carried out using the disc diffusion method, and the production of extended-spectrum β-lactamases (ESBLs) in isolates was surveyed by the double disc synergy method and based on CLSI (2019 AST M100) criteria. Finally, the frequency of bla_GES-2 and bla_oxa-48 genes was surveyed by PCR. Antibiotic susceptibility tests showed that 48/48 (100%) of P. aeruginosa isolates and 49/50 (98%) of A. baumannii isolates were resistant to ceftriaxone and cefotaxime, respectively. Ceftazidime exhibited the lowest (26/48; 54.1%) resistance rates against P. aeruginosa isolates. The production of ESBLs was seen in 8/48 (16.6%) and 3/50 (6%) of P. aeruginosa and A. baumannii isolates, respectively. On the basis of conventional PCR and sequencing, the frequencies of the bla_GES-2 gene among P. aeruginosa and A. baumannii was 87.5% and 58%, respectively. Moreover, bla_oxa-48 gene was detected in 70.83% and 92% of P. aeruginosa and A. baumannii isolates, respectively. Results suggest that antibiotic-resistant A. baumannii and P. aeruginosa strains isolated from burn patients are frequently found; therefore, it is absolutely necessary to implement continuous screening and follow-up programmes for detecting antimicrobial resistance.

Genetic Diversity of Imipenem-Resistant Acinetobacter baumannii Infections at an Intensive Care Unit

Introduction. Imipenem-resistant Acinetobacter baumannii (IRAB) represents a major clinical threat. Dissemination in critical care areas necessitates effective action measures including genotyping tools to study the clonality of these strains and trace their origin. The main aim of this study is to assess the genetic relatedness between IRAB isolates in our institution intensive care units (ICU) which are at a particular risk of outbreaks.

Effect of chlorhexidine bathing on colonization or infection with Acinetobacter baumannii: a systematic review and meta-analysis

Healthcare-associated infections (HAIs) caused by multi-drug-resistant Gram-negative bacteria (MDRGNB) have increased prevalence in intensive care units (ICUs). A common strategy to prevent HAIs is bathing patients with chlorhexidine gluconate (CHG). However, the effectiveness of CHG bathing against multidrug-resistant Acinetobacter baumannii (MDRAB) is still controversial. The aim of this study was to perform a systematic review and meta-analysis of the effectiveness of CHG bathing on Acinetobacter baumannii colonization and infection in the ICU setting. A systematic literature search of PubMed, EMBASE, Web of Science and CINAHL was performed from inception through to June 2018. Randomized controlled trials (RCTs), pre-post studies, or interrupted time series (ITS) studies were included. The numbers of patients with/without colonization or infection of A. baumannii in the experimental or control groups were extracted from each study. Quality assessment was performed by the related instruments of National Institute of Health. Pooled risk ratios (RRs) were calculated using the random-effects model. One RCT and 12 pre-post or ITS studies comprising 18,217 patients were included, of which 8069 were in the CHG bathing arm and 9051 in the control arm. CHG bathing was associated with a reduced colonization of A. baumannii (RR, 0.66; 95% confidence interval: 0.57-0.77; P<0.001). Chlorhexidine at 4% showed a better effect than 2% chlorhexidine (meta-regression P=0.044). CHG bathing was associated with a non-significant reduction of infection (pooled RR 0.41, 95% CI: 0.13-1.25). This study suggests that CHG bathing significantly reduces colonization of A. baumannii in the ICU setting. However, more trials are needed to confirm whether CHG bathing can reduce infections with A. baumannii.