Phenotypic and molecular characterization of Acinetobacter baumannii isolates causing lower respiratory infections among ICU patients

Application of LAMP assay for detection of carbapenem-resistant Acinetobacter calcoaceticus-Acinetobacter baumannii complex in ICU admitted sepsis patients: A rapid and cost-effective diagnostic tool

Carbapenem-resistant significant members of Acinetobacter calcoaceticus-Acinetobacter baumannii (CR-SM-ACB) complex have emerged as an important cause of sepsis, especially in ICUs. This study demonstrates the application of loop-mediated-isothermal-amplification (LAMP) assay for detection of CR-SM-ACB-complex from patients with sepsis. Whole-blood and culture-broths(CB) collected from patients with culture-positive sepsis were subjected to LAMP and compared with PCR, and RealAmp. Vitek-2 system and conventional PCR results were used as confirmatory references. The sensitivity and specificity of LAMP(97 % & 100 %) and RealAmp(100 % & 100 %) for detection of CR-SM-ACB-complex from CB were better than PCR(87 % & 100 %). Diagnostic accuracy of LAMP, RealAmp, and PCR for detection of SM-ACB-complex from CB was 98.5 %, 100 %, and 88.5 % respectively. Turnaround time of Culture, LAMP, PCR, and RealAmp was 28-53, 6-20, 9-23, and 6-20hours, respectively. LAMP is a simple, inexpensive tool that can be applied directly to positive CB and may be customized to detect emerging pathogens and locally-prevalent resistance genes and to optimize antimicrobial use.

Derivation and validation of a predictive mortality model of in-hospital patients with Acinetobacter baumannii nosocomial infection or colonization

PURPOSE

Acinetobacter baumannii (Ab) is a Gram-negative opportunistic bacterium responsible for nosocomial infections or colonizations. It is considered one of the most alarming pathogens due to its multi-drug resistance and due to its mortality rate, ranging from 34 to 44,5% of hospitalized patients. The aim of the work is to create a predictive mortality model for hospitalized patient with Ab infection or colonization.

METHODS

A cohort of 140 sequentially hospitalized patients were randomized into a training cohort (TC) (100 patients) and a validation cohort (VC) (40 patients). Statistical bivariate analysis was performed to identify variables discriminating surviving patients from deceased ones in the TC, considering both admission time (T0) and infection detection time (T1) parameters. A custom logistic regression model was created and compared with models obtained from the "status" variable alone (Ab colonization/infection), SAPS II, and APACHE II scores. ROC curves were built to identify the best cut-off for each model.

RESULTS

Ab infection status, use of penicillin within 90 days prior to ward admission, acidosis, Glasgow Coma Scale, blood pressure, hemoglobin and use of NIV entered the logistic regression model. Our model was confirmed to have a better sensitivity (63%), specificity (85%) and accuracy (80%) than the other models.

CONCLUSION

Our predictive mortality model demonstrated to be a reliable and feasible model to predict mortality in Ab infected/colonized hospitalized patients.

Evaluation of risk factors associated with hard-to-heal wound infection in a tertiary care hospital

OBJECTIVE

The incidence of hard-to-heal wound infection, especially as a result of multidrug-resistant Gram-negative organisms, has increased in recent years. The reason for the increase is multifactorial and the ability of these pathogenic isolates to form biofilms is one of the important risk factors in wound infection. This study aimed to evaluate the risk factors associated with such cases.

METHOD

This prospective analytical study, conducted over a period of two months, included pus or tissue samples from hospital inpatients with Gram-negative hard-to-heal wound infection. The samples were processed with conventional microbiological techniques. Patient demographic details and the presence of various risk factors were recorded. Biofilm production was detected by tissue culture plate method in the laboratory. The data were analysed using SPSS version 21 (IBM Ltd., US).

RESULTS

The experimental cohort comprised 200 patients. Klebsiella spp. was the most common identified organism, followed by Escherichia coli and Pseudomonas spp. Carbapenem resistance was observed in 106 (53%) strains. Almost 66% of the strains showed biofilm formation. On evaluation of associated risk factors, age (p=0.043), presence of biofilms (p=0.0001), diabetes (p=0.002), hypertension (p=0.02) and medical device use (p=0.008) had significant association, whereas sex, previous surgery and prior antibiotic use had no significant impact on the chronicity of the wound.

CONCLUSION

In this study, chronicity of wounds was observed to be associated with multiple risk factors, especially the biofilm-forming ability of the strain. Biofilms are difficult to eradicate and additional measures, such as physical debridement, are important for resolving chronicity. Knowledge about specific risk factors would also allow clinicians a better understanding of the healing process and drive appropriate wound care interventions.

DECLARATION OF INTEREST

A grant was received from the Indian Council of Medical Research (ICMR) for this work (grant ID: 2017-02686). The authors have no conflicts of interest to declare.

Epidemiology and antimicrobial resistance trends of Acinetobacter species in the United Arab Emirates: a retrospective analysis of 12 years of national AMR surveillance data

Introduction

Acinetobacter spp., in particular A. baumannii, are opportunistic pathogens linked to nosocomial pneumonia (particularly ventilator-associated pneumonia), central-line catheter-associated blood stream infections, meningitis, urinary tract infections, surgical-site infections, and other types of wound infections. A. baumannii is able to acquire or upregulate various resistance determinants, making it frequently multidrug-resistant, and contributing to increased mortality and morbidity. Data on the epidemiology, levels, and trends of antimicrobial resistance of Acinetobacter spp. in clinical settings is scarce in the Gulf Cooperation Council (GCC) and Middle East and North Africa (MENA) regions.

Methods

A retrospective 12-year analysis of 17,564 non-duplicate diagnostic Acinetobacter spp. isolates from the United Arab Emirates (UAE) was conducted. Data was generated at 317 surveillance sites by routine patient care during 2010-2021, collected by trained personnel and reported by participating surveillance sites to the UAE National AMR Surveillance program. Data analysis was conducted with WHONET.

Results

Species belonging to the A. calcoaceticus-baumannii complex were mostly reported (86.7%). They were most commonly isolated from urine (32.9%), sputum (29.0%), and soft tissue (25.1%). Resistance trends to antibiotics from different classes during the surveillance period showed a decreasing trend. Specifically, there was a significant decrease in resistance to imipenem, meropenem, and amikacin. Resistance was lowest among Acinetobacter species to both colistin and tigecycline. The percentages of multidrug-resistant (MDR) and possibly extensively drug-resistant (XDR) isolates was reduced by almost half between the beginning of the study in 2010 and its culmination in 2021. Carbapenem-resistant Acinetobacter spp. (CRAB) was associated with a higher mortality (RR: 5.7), a higher admission to ICU (RR 3.3), and an increased length of stay (LOS; 13 excess inpatient days per CRAB case), as compared to Carbapenem-susceptible Acinetobacter spp.

Conclusion

Carbapenem-resistant Acinetobacter spp. are associated with poorer clinical outcomes, and higher associated costs, as compared to carbapenem-susceptible Acinetobacter spp. A decreasing trend of MDR Acinetobacter spp., as well as resistance to all antibiotic classes under surveillance was observed during 2010 to 2021. Further studies are needed to explore the reasons and underlying factors leading to this remarkable decrease of resistance over time.

Molecular and virulence characteristics of carbapenem-resistant Acinetobacter baumannii isolates: a prospective cohort study

This study aimed to characterize the molecular features and virulence profiles of carbapenem-resistant Acinetobacter baumannii (CRAB) isolates. Clinical CRAB isolates were obtained from blood cultures of adult patients with CRAB bacteremia, collected between July 2015 and July 2021 at a Korean hospital. Real-time polymerase chain reaction was used to detect 13 virulence genes, genotyping was conducted via multilocus sequence typing (MLST), and a Tenebrio molitor infection model was selected for survival analysis. Herein, 170 patients, from whom CRAB isolates were collected, showed the in-hospital mortality rate of 57.6%. All 170 clinical CRAB isolates harbored blaOXA-23 and blaOXA-51. MLST genotyping identified 11 CRAB sequence types (STs), of which ST191 was predominant (25.7%). Virulence genes were distributed as follows: basD, 58.9%; espA, 15.9%; bap, 92.4%; and ompA, 77.1%. In the T. molitor model, ST195 showed a significantly higher mortality rate (73.3% vs. 66.7%, p = 0.015) than the other groups. Our findings provide insights into the microbiological features of CRAB blood isolates associated with high mortality. We suggest a potential framework for using a T. molitor infection model to characterize CRAB virulence. Further research is warranted to elucidate the mechanisms by which virulence improves clinical outcomes.

Phenotypic and Genotypic Investigation of Carbapenem-Resistant Acinetobacter baumannii in Maharaj Nakhon Si Thammarat Hospital, Thailand

(1) Background: Acinetobacter baumannii is well known as a causative agent of severe hospital-acquired infections, especially in intensive care units. The present study characterised the genetic traits of biofilm-forming carbapenem-resistant A. baumannii (CRAB) clinical isolates. Additionally, this study determined the prevalence of biofilm-producing A. baumannii isolates from a tertiary care hospital and investigated the association of biofilms with the distribution of biofilm-related and antibiotic resistance-associated genotypes. (2) Methods: The 995 non-duplicate A. baumannii isolates were identified, and their susceptibilities to different antibiotics were determined using the disk diffusion method. Using the modified microtiter plate assay, the CRAB isolates were investigated for their biofilm formation ability. Hemolysin and protease activities were determined. CRABs were subjected to polymerase chain reaction (PCR) assays targeting blaVIM, blaNDM, blaIMP, blaOXA-23-like, blaOXA-24-like, blaOXA-51-like, csuE and pgaB genes. Individual CRAB isolates were identified for their DNA fingerprint by repetitive element sequence-based (REP)-PCR. (3) Results: Among all A. baumannii isolates, 172 CRABs were identified. The major antibiotic resistance gene among the CRAB isolates was blaOXA-51-like (100%). Ninety-nine isolates (57.56%) were biofilm producers. The most prevalent biofilm gene was pgaB (79.65%), followed by csuE (76.74%). Evidence of virulence phenotypes revealed that all CRAB exhibited proteolytic activity; however, only four isolates (2.33%) were positive for the hemolytic-producing phenotype. REP-PCR showed that 172 CRAB isolates can be divided into 36-DNA fingerprint patterns. (4) Conclusions: The predominance of biofilm-producing CRAB isolates identified in this study is concerning. The characterisation of risk factors could aid in controlling the continual selection and spreading of the A. baumannii phenotype in hospitals, thereby improving patient care quality.

The Prevalence of Virulence Factor Genes among Carbapenem-Non-Susceptible Acinetobacter baumannii Clinical Strains and Their Usefulness as Potential Molecular Biomarkers of Infection

Healthcare-associated infections caused by multidrug-resistant Acinetobacter baumannii strains are a serious global threat. Therefore, it is important to expand the knowledge on the mechanisms of pathogenicity of these particular bacteria. The aim of this study was to assess the distribution of selected virulence factor genes (bap, surA1, omp33-36, bauA, bauS, and pld) among carbapenem-non-susceptible clinical A. baumannii isolates and to evaluate their potential usefulness as genetic markers for rapid diagnostics of A. baumannii infections. Moreover, we aimed to compare the virulence genes prevalence with the occurrence of carbapenemases genes. A total of 100 carbapenem-non-susceptible A. baumannii clinical isolates were included in the study. The presence of virulence factors and blaOXA genes was evaluated by real-time PCR. The occurrence of virulence factors genes was as follows: 100.0% for the bap and surA1 genes, 99.0% for the basD and pld genes. The bauA and omp33-36 genes were absent among the studied strains. The predominant genes (bap and surA1) are involved in biofilm formation and their presence among all clinical strains can be applied as a genetic marker to recognize A. baumannii infection. High frequencies of the basD gene—involved in siderophore biosynthesis and the gene encoding phospholipase D (pld)—were also noted among blaOXA-positive strains, showing their potential role in a pathogenicity of blaOXA-positive A. baumannii clinical strains.

Multidrug-resistant Acinetobacter baumannii in healthcare settings in Africa

The emergence of multidrug-resistant Acinetobacter baumannii is a major concern to healthcare providers and facilities in many parts of the world. This bacterial pathogen is commonly implicated in hospital-acquired infections, particularly in critically ill patients admitted to the intensive care unit (ICU). The extensive use of antibiotics, particularly in ICUs, and the lack of proper infection control interventions in many hospitals have led to an increased emergence of multidrug-resistant A. baumannii. Infections due to multidrug-resistant A. baumannii are associated with prolonged hospital stays and high morbidity and mortality, particularly among hospitalized ICU patients. The lack of antibiotic stewardship programmes in many healthcare facilities has exacerbated the burden of A. baumannii infections in many parts of Africa. This review discusses the prevalence and antibiotic-resistance pattern of the multidrug-resistant A. baumannii, and the possible ways to address or minimise its emergence in healthcare settings in Africa.

Genomic relatedness and dissemination of bla NDM-5 among Acinetobacter baumannii isolated from hospital environments and clinical specimens in Thailand

Background

Acinetobacter baumannii (A. baumannii) is an important cause of nosocomial infection, especially in intensive care units (ICUs). It has the propensity to tolerate various environments and multiple classes of antibiotics. Our study aimed to characterize the comparative genomes of A. baumannii from hospital environments and clinical isolates.

Methods

Clinical and environmental A. baumannii isolates were collected from a university hospital. Antibiotic susceptibility testing was performed, antibiotic resistance genes (ARGs) were characterized, and repetitive element palindromic-PCR (rep-PCR) typing was performed. Eight representative A. baumannii isolated from environmental and clinical samples from the same wards were selected for whole-genome sequencing (WGS) using the Illumina platform.

Results

A total of 106 A. baumannii isolates were obtained from 312 hospital environmental samples. A high percentage of samples with A. baumannii colonization were detected from AMBU bags (77.9%), followed by bedrails (66.7%) and suction tubes (66.7%). We found that 93.4% of the environmental isolates were multidrug-resistant A. baumannii (MDRAB), and 44.7% were extremely drug-resistant A. baumannii (XDRAB). bla _OXA-23 bla _NDM, and bla _OXA-58 were present in 80.2%, 78.3%, and 0.9% of all isolates, respectively. Sixty-one A. baumannii isolates were collected from patient specimens in the same ward. Among all A. baumannii clinical isolates, MDRAB and XDRAB accounted for 82% and 55.7%, respectively. The most dominant ARGs identified was bla _OXA-23 (80.3%), followed by bla _NDM (55.7%). The genetic diversity of all isolates using rep-PCR could be divided into 33 genotypes. The genome size of eight A. baumannii ranged from 3.78-4.01 Mb. We found six of eight strains to be bla _NDM-5-harboring A. baumannii. Mobile genetic elements (MGEs), such as integron1 (intl1), located upstream of bla _NDM-5 were observed. The phylogenomic relationship of the core and pan genomes as well as the single nucleotide polymorphism (SNP) count matrix revealed the genetic similarity of A. baumannii environmental and clinical strains obtained from the same ward.

Conclusion

This study confirmed that A. baumannii colonized in hospital environments were the main reservoir of nosocomial infection and provides critical information to guide the control of A. baumannii infection.

Carbapenem-resistant Acinetobacter baumannii: A challenge in the intensive care unit

Carbapenem-resistant Acinetobacter baumannii (CRAB) has become one of the leading causes of healthcare-associated infections globally, particularly in intensive care units (ICUs). Cross-transmission of microorganisms between patients and the hospital environment may play a crucial role in ICU-acquired CRAB colonization and infection. The control and treatment of CRAB infection in ICUs have been recognized as a global challenge because of its multiple-drug resistance. The main concern is that CRAB infections can be disastrous for ICU patients if currently existing limited therapeutic alternatives fail in the future. Therefore, the colonization, infection, transmission, and resistance mechanisms of CRAB in ICUs need to be systematically studied. To provide a basis for prevention and control countermeasures for CRAB infection in ICUs, we present an overview of research on CRAB in ICUs, summarize clinical infections and environmental reservoirs, discuss the drug resistance mechanism and homology of CRAB in ICUs, and evaluate contemporary treatment and control strategies.

Bacteriological profile of paediatric skin and soft tissue infections and their antibiogram at a tertiary care teaching hospital in north India

The increasing complexity of wound care in pediatric patients along with delay in the initiation of treatment predisposes these patients to many complications such as pressure ulcers, non-healing surgical wounds and skin damage. A retrospective study was conducted over a period of five years to gain insight into the etiology of pediatric wound infection. A total of 2819 wound culture positive cases were included. Most samples were from the burn ward (30.15%) followed by the general surgery ward (20.46%). Overall, the most common isolate was Staphylococcus aureus (39.73%) followed by Pseudomonas spp (19.12%). The prevalence of MRSA (Methicillin resistant S. aureus), CRE (Carbapenem-resistant Enterobacteriaceae), CRP (Carbapenem resistant Pseudomonas), CRAB (Carbapenem resistant Acinetobacter baumannii) was 47.3%, 62.5%, 70.5%, 96.4%, respectively. The high degree of resistance in children highlights the importance of regular surveillance for identification of common pathogens and optimization of antimicrobial treatment for multidrug resistant organisms.

3-indoleacetonitrile attenuates biofilm formation and enhances sensitivity to imipenem in Acinetobacter baumannii

Acinetobacter baumannii poses a global danger due to its ability to resist most of the currently available antimicrobial agents. Furthermore, the rise of carbapenem-resistant A. baumannii isolates has limited the treatment options available. In the present study, plant auxin 3-indoleacetonitrile was found to inhibit biofilm formation and motility of A. baumannii at sub-lethal concentration. Mechanistically, 3-indoleacetonitrile inhibited the synthesis of the quorum sensing signal 3-OH-C12-HSL by downregulating the expression of the abaI autoinducer synthase gene. 3-indoleacetonitrile was found to reduce MIC of A. baumannii ATCC 17 978 against imipenem, ofloxacin, ciprofloxacin, tobramycin, and levofloxacin, and significantly decreased persistence against imipenem. Inhibition of efflux pumps by down-regulating genes expression may be responsible for enhanced sensitivity and low persistence. 3-indoleacetonitrile reduced the resistance to imipenem in carbapenem-resistant A. baumannii isolates by down-regulating the expression of OXA β-lactamases (blaoxa-51 and blaoxa-23), outer membrane protein carO and transporter protein adeB. These findings demonstrate the therapeutic potential of 3-indoleacetonitrile which could be explored as an adjuvant with antibiotics for controlling A. baumannii infections.

Infections Due to Acinetobacter baumannii-calcoaceticus Complex: Escalation of Antimicrobial Resistance and Evolving Treatment Options

Bacteria within the genus Acinetobacter (principally A. baumannii-calcoaceticus complex [ABC]) are gram-negative coccobacilli that most often cause infections in nosocomial settings. Community-acquired infections are rare, but may occur in patients with comorbidities, advanced age, diabetes mellitus, chronic lung or renal disease, malignancy, or impaired immunity. Most common sites of infections include blood stream, skin/soft-tissue/surgical wounds, ventilator-associated pneumonia, orthopaedic or neurosurgical procedures, and urinary tract. Acinetobacter species are intrinsically resistant to multiple antimicrobials, and have a remarkable ability to acquire new resistance determinants via plasmids, transposons, integrons, and resistance islands. Since the 1990s, antimicrobial resistance (AMR) has escalated dramatically among ABC. Global spread of multidrug-resistant (MDR)-ABC strains reflects dissemination of a few clones between hospitals, geographic regions, and continents; excessive antibiotic use amplifies this spread. Many isolates are resistant to all antimicrobials except colistimethate sodium and tetracyclines (minocycline or tigecycline); some infections are untreatable with existing antimicrobial agents. AMR poses a serious threat to effectively treat or prevent ABC infections. Strategies to curtail environmental colonization with MDR-ABC require aggressive infection-control efforts and cohorting of infected patients. Thoughtful antibiotic strategies are essential to limit the spread of MDR-ABC. Optimal therapy will likely require combination antimicrobial therapy with existing antibiotics as well as development of novel antibiotic classes.

Pathogenic Characteristics and Risk Factors for ESKAPE Pathogens Infection in Burn Patients

Objective

This study aimed to determine the clinical manifestations, antimicrobial resistance, molecular characteristics, and risk factors for ESKAPE pathogens infection in burn patients.

Methods

A retrospective study of 187 burn patients infected with ESKAPE pathogens was conducted at the Department of Plastic and Burn Surgery of the Affiliated Hospital of Southwest Medical University (Luzhou, China) from October 2018 to June 2021. All strains were identified using a MicroScan WalkAway 96 Plus System, and antimicrobial susceptibilities were determined using the VITEK system or the disk diffusion method. The antimicrobial resistance genes of multi-drug resistant ESKAPE (MDR-ESKAPE) were detected by polymerase chain reaction (PCR). The multivariable logistic regression analysis was used to estimate the risk factors for ESKAPE infection and MDR-ESKAPE infection.

Results

A total of 255 strains were isolated in various types of clinical specimens from 187 burn patients, of which 47.5% were ESKAPE pathogens (121/255). Among these, MDR-ESKAPE pathogens accounted for 55% (67/121). Additionally, aph3ʹIII, mecA, bla_SHV, bla_TEM, bla_PDC, and bla_SHV were the most prevalent genes detected in Enterococcus faecalis, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter spp., respectively. The independent risk factors for ESKAPE infection were total body surface area (TBSA) >30–50% (odds ratio [OR] = 10.428; 95% confidence interval [CI], 2.047 to 53.108), TBSA >50% (OR = 15.534; 95% CI, 1.489 to 162.021), and parenteral nutrition (OR = 3.597; 95% CI, 1.098 to 11.787). No independent risk factors were found for MDR-ESKAPE infection.

Conclusion

Clinical staff should be alert to the risk of nosocomial infection with ESKAPE pathogens in burn patients receiving parenteral nutrition and under TBSA >30%. Full attention should also be paid to the ESKAPE resistance, strict adherence to infection control protocols for the rational use of antimicrobial agents, and enhanced clinical standardization of antimicrobial agents management.

Virulence Characteristics of Biofilm-Forming Acinetobacter baumannii in Clinical Isolates Using a Galleria mellonella Model

Acinetobacter baumannii is a Gram-negative coccobacillus responsible for severe hospital-acquired infections, particularly in intensive care units (ICUs). The current study was designed to characterize the virulence traits of biofilm-forming carbapenem-resistant A. baumannii causing pneumonia in ICU patients using a Galleria mellonella model. Two hundred and thirty patients with hospital-acquired or ventilator-associated pneumonia were included in our study. Among the total isolates, A. baumannii was the most frequently isolated etiological agent in ICU patients with pneumonia (54/165, 32.7%). All A. baumannii isolates were subjected to antimicrobial susceptibility testing by the Kirby–Bauer disk diffusion method, while the minimum inhibitory concentrations of imipenem and colistin were estimated using the broth microdilution technique. The biofilm formation activity of the isolates was tested using the microtiter plate technique. Biofilm quantification showed that 61.1% (33/54) of the isolates were strong biofilm producers, while 27.7% (15/54) and 11.1% (6/54) showed moderate or weak biofilm production. By studying the prevalence of carbapenemases-encoding genes among isolates, bla_OXA-23-_like was positive in 88.9% of the isolates (48/54). The Bla_NDM gene was found in 27.7% of the isolates (15/54 isolates). Bla_OXA-23-_like and bla_NDM genes coexisted in 25.9% (14/54 isolates). Bap and bla_PER-1 genes, the biofilm-associated genes, coexisted in 5.6% (3/54) of the isolates. For in vivo assessment of A. baumannii pathogenicity, a Galleria mellonella survival assay was used. G. mellonella survival was statistically different between moderate and poor biofilm producers (p < 0.0001). The killing effect of the strong biofilm-producing group was significantly higher than that of the moderate and poor biofilm producers (p < 0.0001 for each comparison). These findings highlight the role of biofilm formation as a powerful virulence factor for carbapenem-resistant A. baumannii that causes pneumonia in the ICU.

Case Commentary: Uncertainty in Evaluating Treatment Outcomes in Carbapenem-Resistant Acinetobacter baumannii Infections

Carbapenem-resistant Acinetobacter baumannii (CRAB) infections are challenging to treat and associated with poor clinical outcomes. In this issue, sulbactam-durlobactam, a novel β-lactam-β-lactamase inhibitor, was used with cefiderocol to successfully treat CRAB pneumonia. While this report and in vitro data are encouraging, determining the impact of treatment regimens on clinical outcomes after CRAB infections is not straightforward. Therefore, careful evaluation in pathogen-directed randomized controlled trials is needed to determine the optimal treatment of CRAB infections.

Development of Loop-Mediated Isothermal Amplification Assay for Detection of Clinically Significant Members of Acinetobacter calcoaceticus-baumannii Complex and Associated Carbapenem Resistance

Background:Acinetobacter calcoaceticus–baumannii (ACB) complex has emerged as an important nosocomial pathogen and is associated with life-threatening infections, especially among ICU patients, including neonates. Carbapenem resistance in Acinetobacter baumannii has emerged globally and is commonly mediated by bla_OXA-23. Clinically significant infections with carbapenem-resistant Acinetobacter baumannii (CRAB) are a major concern since therapeutic options are limited and associated mortality is high. Early diagnosis of both the pathogen and resistance is important to initiate the optimal therapy and prevent selection of resistance. In the current study, a loop-mediated isothermal amplification (LAMP) assay was developed for rapid detection of the ACB complex and carbapenem resistance mediated by bla_OXA-23.

Methodology: Universal LAMP primers were designed for the detection of significant members of the ACB complex and carbapenem resistance targeting the ITS 16S–23S rRNA and bla_OXA-23 gene respectively. The optimal conditions for the LAMP assay were standardized for each primer set using standard ATCC strains. The sensitivity of the LAMP assay was assessed based on the limit of detection (LOD) using different DNA concentrations and colony counts. The specificity of LAMP was determined using the non-ACB complex and non-Acinetobacter species. The results of the LAMP assay were compared with those of polymerase chain reaction (PCR).

Results: The optimal temperature for the LAMP assay was 65°C, and the detection time varied with various primers designed. Using the ITS Ab1 primer, LODs of LAMP and PCR assays were 100 pg/μl and 1 ng/μl of DNA concentration and 10⁴ cfu/ml and 10⁸ cfu/ml of colony count, respectively. The LAMP assay was 10- and 10⁴-fold more sensitive than PCR using DNA concentration and colony count, respectively. The LAMP assay was found to be specific for clinically important ACB complex species.

Significance of the study: The LAMP assay can be applied for early detection of significant species of the ACB complex from clinical samples and their carbapenem-resistant variants. Depending on the emerging pathogen and locally prevalent resistance genes, the LAMP assay can be modified for detection of colonization or infection by various resistant bugs.

Distribution of carbapenemase genes in clinical isolates of Acinetobacter baumannii & a comparison of MALDI-TOF mass spectrometry-based detection of carbapenemase production with other phenotypic methods

Background & objectives:

Carbapenemase-producing Acinetobacter baumannii (CRAB) poses a continuous threat to the current antimicrobial era with its alarming spread in critical care settings. The present study was conducted to evaluate the diagnostic potential of phenotypic methods for carbapenemase [carbapenem-hydrolyzing class D β-lactamases (CHDLs) and metallo-β-lactamases (MBLs)] production, by comparing with molecular detection of genes.

Methods:

One hundred and fifty clinical CRAB isolates collected between August 2013 and January 2014 were studied. Multiplex PCR was performed to identify the carbapenemases produced (class D bla_OXA-51, bla_OXA-23, bla_OXA-48,bla_OXA-58; class B bla_VIM, bla_NDM-1, bla_IMP; class A bla_KPC). Each isolate was evaluated for carbapenemase production by studying the pattern of imipenem hydrolysis using matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS).

Results:

The most commonly encountered carbapenemase genes were bla_OXA-51 (100%), bla_OXA-23 (98%), bla_VIM (49.3%), bla_NDM-1 (18.7%) and bla_OXA-58 (2%). MALDI-TOF MS was able to detect 30.6 per cent carbapenemases within three hours (P=0.001 for MBL and P>0.05 for CHDL) and 65.3 per cent within six hours (P=0.001 for MBL and P>0.05 for CHDL).

Interpretation & conclusions:

MALDI-TOF MS reliably detected carbapenemase activity within a short span of time, thus helping in tailoring patient therapy. MALDI-TOF MS, once optimized, can prove to be a useful tool for timely detection of carbapenemase production by A. baumannii and consequently in directing appropriate antimicrobial therapy.

Impact of an Intervention to Control Imipenem-Resistant Acinetobacter baumannii and Its Resistance Mechanisms: An 8-Year Survey

Background

This study aimed to examine the impact of an intervention carried out in 2011 to combat multi-drug resistance and outbreaks of imipenem-resistant Acinetobacter baumannii (IRAB), and to explore its resistance mechanism.

Methods

A total of 2572 isolates of A. baumannii, including 1673 IRAB isolates, were collected between 2007 and 2014. An intervention was implemented to control A. baumannii resistance and outbreaks. Antimicrobial susceptibility was tested by calculating minimal inhibitory concentrations (MICs), and outbreaks were typed using pulsed-field gel electrophoresis (PFGE). Resistance mechanisms were explored by polymerase chain reaction (PCR) and whole genome sequencing (WGS).

Results

Following the intervention in 2011, the resistance rates of A. baumannii to almost all tested antibiotics decreased, from 85.3 to 72.6% for imipenem, 100 to 80.8% for ceftriaxone, and 45.0 to 6.9% for tigecycline. The intervention resulted in a decrease in the number (seven to five), duration (8–3 months), and departments (five to three) affected by outbreaks; no outbreaks occurred in 2011. After the intervention, only bla_AMPC (76.47 to 100%) and bla_TEM–1 (75.74 to 96.92%) increased (P < 0.0001); whereas bla_GES–1 (32.35 to 3.07%), bla_PER–1 (21.32 to 1.54%), bla_OXA–58 (60.29 to 1.54%), carO (37.50 to 7.69%), and adeB (9.56 to 3.08%) decreased (P < 0.0001). Interestingly, the frequency of class B β-lactamase genes decreased from 91.18% (bla_SPM–1) and 61.03% (bla_IMP–1) to 0%, while that of class D bla_OXA–23 increased to 96.92% (P < 0.0001). WGS showed that the major PFGE types causing outbreaks each year (type 01, 11, 18, 23, 26, and 31) carried the same resistance genes (bla_KPC–1, bla_ADC–25, bla_OXA–66, and adeABC), AdeR-S mutations (G186V and A136V), and a partially blocked porin channel CarO. Meanwhile, plasmids harboring bla_OXA–23 were found after the intervention.

Conclusion

The intervention was highly effective in reducing multi-drug resistance of A. baumannii and IRAB outbreaks in the long term. The resistance mechanisms of IRAB may involve genes encoding β-lactamases, efflux pump overexpression, outer membrane porin blockade, and plasmids; in particular, clonal spread of bla_OXA–23 was the major cause of outbreaks. Similar interventions may also help reduce bacterial resistance rates and outbreaks in other hospitals.

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.

Graphene Oxide Coatings as Tools to Prevent Microbial Biofilm Formation on Medical Device

The clinical challenge on surface engineering of medical devices to prevent microorganisms adhesion and biofilm formation, has become an essential aspect for medical implants. Antibacterial properties of Graphene Oxide (GO) have been demonstrated across a broad spectrum of bacteria, and the different mechanisms of action with which this nanomaterial interacts with the microbial surface have been elucidated in detail. Innovative protective coatings based on graphene film and hydrogel could represent an innovative solution for the prevention of nosocomial pathogens colonization on implantable device. This brief review mainly focuses on the applications of graphene in nanomedicine with a particular deepening on the antibacterial properties of GO and GO-based nanomaterials. In order to evaluate the possible future applications of GO as an anti-biofilm coating material for medical devices, studies on the ability of graphene coated surface to prevent microbial adhesion are also discussed. A concise review on in vitro toxicity and in vivo safety is also presented.

Antigen Epitope Developed Based on Acinetobacter baumannii MacB Protein Can Provide Partial Immune Protection in Mice

Acinetobacter baumannii (A. baumannii) is an important opportunistic pathogen widely present in medical environment. Given its complex drug resistance, A. baumannii poses a serious threat to the safety of critically ill patients. Given the limited alternative antibiotics, nonantibiotic-based functional anti-A. baumannii infection proteins must be developed. In this study, we firstly used a series of biological software to predict potential epitopes in the MacB protein sequence and verified them by antibody recognition and lymphocyte proliferation tests. We finally screened out B cell epitope 2, CD8⁺ T cell epitope 7, and CD4⁺ T cell epitope 11 and connected them to construct a recombinant antigen epitope (RAE). The determination of IgG in the serum of immunised mice and cytokines in the supernatant of lymphocytes showed that the constructed epitope induced an immune response mediated by Th-1 cells. Finally, the challenge experiment of A. baumannii infection in mice confirmed that the epitope developed based on MacB, especially RAE, provided incomplete immune protection for mice.

Ultrastructural changes caused by the combination of intravenous immunoglobulin with meropenem, amikacin and colistin in multidrug-resistant Acinetobacter baumannii

Acinetobacter baumannii is an opportunistic pathogen associated with increased morbidity and mortality in Healthcare-associated infections (HAI). Combination antimicrobial therapy, meropenem, amikacin and colistin, has been used as an alternative in multidrug-resistant (MDR) A. baumannii infections due to reduced treatment options. However, these combinations are not always effective and exhibit high toxicity. Empiric therapy of intravenous immunoglobulin (IVIG) associated with antimicrobials has shown promising results in bacterial infections, considering the immunomodulatory action of IVIG. Thus, the aim of this study was to determine the combined antimicrobial action and to describe the ultrastructural changes caused in ten MDR A. baumannii isolates submitted to IVIG alone and in combination with colistin, meropenem and amikacin. Minimum Inhibitory Concentration (MIC) of antimicrobials and checkerboard were determined. Isolates were submitted to 4 mg/mL of IVIG alone and in combination with different synergistic sub-MIC of antimicrobials tested, and processed for scanning electron microscopy. Nine bacterial isolates showed meropenem-resistant, two isolates had colistin-intermediate, and four isolates were considered intermediate to amikacin. Synergism in five isolates for meropenem/amikacin and meropenem/colistin were observed. Bacterial cells submitted to IVIG and meropenem, amikacin and colistin presented several ultrastructural changes, such as cell elongation and rupture, membrane roughness, incomplete cell division, cell surface "bubbles" and "depression". A. baumannii isolates presented high resistance to meropenem and synergism among evaluated antimicrobials. In addition, it was possible to verify in vitro that IVIG associated with meropenem, amikacin and colistin is a promising alternative for MDR A. baumannii infections. Thus, these data support the continued empirical use and stimulate in vivo analyzes with IVIG to search for new therapeutic options for HAI.

Mortalidad y desenlaces clínicos en pacientes críticamente enfermos con infecciones por bacterias productoras de carbapenemasas en un hospital de alta complejidad en Bogotá, Colombia

Introducción: Los microorganismos capaces de producir carbapenemasas vienen incrementándose a nivel mundial y se han convertido en un problema de salud pública global. En Colombia actualmente la resistencia a carbapenémicos en las unidades de cuidado intensivo está aumentando y se desconoce su impacto en desenlaces clínicos. Objetivos: Determinar las características demográficas, clínicas, y los desenlaces de los pacientes adultos en estado crítico con infección por microorganismos productores de carbapenemasas en una unidad de cuidado intensivo polivalente de una institución de alta complejidad. Métodos: Estudio observacional, descriptivo y retrospectivo, incluyendo pacientes con infección por bacterias resistentes a carbapenémicos, ingresados a la unidad de cuidado intensivo entre el 1 de Enero de 2014 y el 1 de Enero de 2018. Se excluyeron los pacientes colonizados. Se evaluaron complicaciones clínicas, estancia en UCI y hospitalaria, así como la mortalidad en UCI y hospitalaria. Resultados: Se incluyó 58 pacientes. La mortalidad global fue de 67,2%, de los cuales 55,17% murió durante su estancia en la unidad de cuidado intensivo y 12.06% en hospitalización. La mediana de estancia en la unidad de cuidado intensivo fue de 18 días (RIQ 4-28). La causa más frecuente de mortalidad fue choque séptico en 51% y las complicaciones más comunes fueron lesión renal aguda y delirium en un 55,2% y 43,1%, respectivamente. La mediana de estancia en la UCI fue de 18 días (RIQ 4-28). Conclusiones: Las infecciones por bacterias resistentes a carbapenémicos en pacientes críticamente enfermos se relacionan con altas tasas de mortalidad, complicaciones y estancia prolongada en UCI

Rapid simultaneous detection of bla oxa-23, Ade-B, int-1, and ISCR-1 in multidrug-resistant Acinetobacter baumannii using single-tube multiplex PCR and high resolution melting assay

Objective: The aim of this study was to develop a multiplex PCR system for the rapid and simultaneous detection of bla_oxa-23, Ade-B, int-1, and ISCR-1 genes in multidrug-resistant Acinetobacter baumannii (MDRAB) using high resolution melting (HRM) assay.

Methods: Four pairs of primers were designed, and PCR amplification products were sequenced and compared with NCBI GeneBank sequences to ensure primer specificity. Multiplex PCR was performed using a dedicated HRM reagent, and melting curves and temperatures were able to distinguish the four genes. This method was subsequently used to detect these genes in 79 MDRAB isolates from the Third Affiliated Hospital of Southern Medical University in southern China.

Results: Using the HRM assay, 73 out of 79 isolates were found to carry both bla_oxa-23 and Ade-B, one isolate carried int-1, two isolates carried both int-1 and ISCR-1, and three isolates carried Ade-B, int-1, and ISCR-1. No isolates carried all four genes.

Conclusion: Compared with traditional resistance gene detection methods–PCR and agarose gel electrophoresis-based resistance gene detection methods–the multiplex PCR and HRM assay method was simple, rapid, highly efficient, and cost-effective. Our results showed that bla_oxa-23 and Ade-B were the main resistance genotypes in MDRAB.