Characterization of carbapenem-resistant Acinetobacter baumannii isolates in a Chinese teaching hospital

Acinetobacter baumannii infection in intensive care unit: analysis of distribution and drug resistance

BACKGROUND

The isolation rate and drug resistance rate of Acinetobacter baumannii (A.baumannii) have increased over the years, which has become one of the main causes of infection and death in intensive care unit (ICU) patients. Analysis of the distribution characteristics, drug resistance and influencing factors of A.baumannii in ICU could provide basis and reference for the infection prevention and clinical treatment.

METHODS AND RESULTS

In this study, patients diagnosed with A.baumannii infection in ICU from January 2020 to December 2021 were selected. Samples of patients were collected for bacterial culture, drug sensitivity test analysis and drug resistant gene detection of A.baumannii. A total of 197 strains of A.baumannii were cultured in 2021, which was 18 strains more than in 2020. The specimens were mainly from lower respiratory tract secretions, and the isolated strains were multi-drug resistant. The resistance of isolates to tobramycin, gentamicin, and trimethoprim-sulfamethoxazole in 2021 showed a significant increase compared to 2020, while there were no significant differences observed in other resistance changes. The prevalence of multi-drug resistant A.baumannii in ICU remains high. Among them, all imipenem-resistant A.baumannii strains carried OXA-23 gene.

CONCLUSION

Clinical treatment should use antibiotics reasonably based on the characteristics of bacterial resistance, and strengthen the prevention and control of hospital infection, pay more attention to the disinfection and isolation to reduce the risk of cross infection.

Clonal relatedness of carbapenem-resistant Acinetobacter baumannii: high prevalence of ST136pas in a burn center

BACKGROUND

Carbapenem-resistant Acinetobacter baumannii (CRAB) is a global health crisis. This study aimed to determine the clonal relatedness of antibiotic-resistant A. baumannii isolates in hospitalized patients who suffered from burn wound infection.

METHODS

One hundred and six A. baumannii isolates from 562 patients with burn wound infections, were identified and examined for antimicrobial susceptibility. Detection and characterization of carbapenem-hydrolyzing class D OXA-type beta-lactamases (CHDLs) were performed by PCR assays. The clonal relatedness of A. baumannii isolates was determined by multilocus sequence typing (MLST) according to the Pasteur scheme, dual-sequence typing of bla_OXA-51-like and ampC genes, and RAPD-PCR method.

RESULTS

All isolates were carbapenem-resistant while susceptible to colistin, minocycline, doxycycline, and ampicillin-sulbactam. The intrinsic bla_OXA-51-like was detected in all isolates, and bla_OXA-23-like was identified in 92.5% of isolates. However, bla_OXA-143-like and bla_OXA-58-like genes were not detected among isolates. Four distinct bla_OXA-51-like alleles were determined as follows: bla_OXA-317 (67.0%), bla_OXA-90 (9.4%), bla_OXA-69 (17.0%), and bla_OXA-64 (6.6%) and four ampC (bla_ADC) allele types including ampC-25 (6.6%), ampC-39 (9.4%), ampC-1 (17.0%), and bla_ADC-88 (67.0%) were identified. MLST (Pasteur scheme) analysis revealed four ST types including ST136 (singleton), ST1 (CC1), ST25 (CC25), and ST78 (singleton) in 71, 18, 7, and 10 of A. baumannii strains, respectively. Five RAPD clusters including A (1.9%), B (26.4%), C (57.5%), D (7.5%), and E (1.9%) were characterized and 5 (4.7%) strains were found to be singletons.

CONCLUSION

The present study demonstrated that there was a high prevalence of bla_OXA-23-like producing CRAB in the clinical setting. The majority of isolates belonged to ST136 (singleton). However, bla_OXA-23-like producing multi-drug resistant international clones including ST1, and emerging lineages (e.g. ST25 and ST78) were also identified. Interestingly, in this study ST2 was not detected.

Effect of traditional Chinese medicine monomers interfering with quorum-sensing on virulence factors of extensively drug-resistant Acinetobacter baumannii

The antimicrobial resistance of Acinetobacter baumannii (A. baumannii) clinical isolates has emerged as a great threat to public health. Quorum sensing (QS) is one of the resistance mechanisms for drug-resistant A. baumannii. Interfering with QS is a promising strategy to combat infections caused by drug-resistant bacteria. This study explored the QS inhibition ability of thirty-four traditional Chinese medicine monomers (TCMMs) and assessed the effect of QS inhibitors (QSIs) on the virulence factors of twelve extensively drug-resistant A. baumannii (XDRAB) strains. Nine traditional Chinese medicine monomers, such as caffeic acid, cinnamic acid, and myricetin, were found to be able to inhibit the bacterial QS. Then, at 1/8 of the minimal inhibitory concentration, we found that these QSIs inhibited extensively drug-resistant A. baumannii adhesion and biofilm formation and downregulated the expression levels of virulence-associated genes (abaI, abaR, csuE, pgaA, and bap). In conclusion, nine traditional Chinese medicine monomers have QS inhibitory activity and may downregulate QS genes to interfere with the QS system, which could inhibit the expression of extensively drug-resistant A. baumannii virulence factors. These results suggest that traditional Chinese medicine monomers could develop as novel anti-virulence compounds to control extensively drug-resistant A. baumannii 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.

The Molecular Detection of Class B and Class D Carbapenemases in Clinical Strains of Acinetobacter calcoaceticus-baumannii Complex: The High Burden of Antibiotic Resistance and the Co-Existence of Carbapenemase Genes

The emergence of carbapenem-resistant Acinetobacter calcoaceticus-baumannii complex (CRACB) in clinical environments is a significant global concern. These critical pathogens have shown resistance to a broad spectrum of antibacterial drugs, including carbapenems, mostly due to the acquisition of various β-lactamase genes. Clinical samples (n = 1985) were collected aseptically from multiple sources and grown on blood and MacConkey agar. Isolates and antimicrobial susceptibility were confirmed with the VITEK-2 system. The modified Hodge test confirmed the CRACB phenotype, and specific PCR primers were used for the molecular identification of bla_OXA and bla_NDM genes. Of the 1985 samples, 1250 (62.9%) were culture-positive and 200 (43.9%) were CRACB isolates. Of these isolates, 35.4% were recovered from pus samples and 23.5% from tracheal secretions obtained from patients in intensive care units (49.3%) and medical wards (20.2%). An antibiogram indicated that 100% of the CRACB isolates were resistant to β-lactam antibiotics and β-lactam inhibitors, 86.5% to ciprofloxacin, and 83.5% to amikacin, while the most effective antibiotics were tigecycline and colistin. The CRACB isolates displayed resistance to eight different AWaRe classes of antibiotics. All isolates exhibited the bla_OXA-51 gene, while bla_OXA-23 was present in 94.5%, bla_VIM in 37%, and bla_NDM in 14% of the isolates. The bla_OXA-51, bla_OXA-23, and bla_OXA-24 genes co-existed in 13 (6.5%) isolates. CRACB isolates with co-existing bla_OXA-23, bla_OXA-24, bla_NDM, bla_OXA-51 and bla_VIM genes were highly prevalent in clinical samples from Pakistan. CRACB strains were highly critical pathogens and presented resistance to virtually all antibacterial drugs, except tigecycline and colistin.

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

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

Global Threat of Carbapenem-Resistant Gram-Negative Bacteria

Infections caused by multidrug-resistant (MDR) and extensively drug-resistant (XDR) Gram-negative bacteria (GNB), including carbapenem-resistant (CR) Enterobacterales (CRE; harboring mainly bla_KPC, bla_NDM, and bla_OXA-48-like genes), CR- or MDR/XDR-Pseudomonas aeruginosa (production of VIM, IMP, or NDM carbapenemases combined with porin alteration), and Acinetobacter baumannii complex (producing mainly OXA-23, OXA-58-like carbapenemases), have gradually worsened and become a major challenge to public health because of limited antibiotic choice and high case-fatality rates. Diverse MDR/XDR-GNB isolates have been predominantly cultured from inpatients and hospital equipment/settings, but CRE has also been identified in community settings and long-term care facilities. Several CRE outbreaks cost hospitals and healthcare institutions huge economic burdens for disinfection and containment of their disseminations. Parenteral polymyxin B/E has been observed to have a poor pharmacokinetic profile for the treatment of CR- and XDR-GNB. It has been determined that tigecycline is suitable for the treatment of bloodstream infections owing to GNB, with a minimum inhibitory concentration of ≤ 0.5 mg/L. Ceftazidime-avibactam is a last-resort antibiotic against GNB of Ambler class A/C/D enzyme-producers and a majority of CR-P. aeruginosa isolates. Furthermore, ceftolozane-tazobactam is shown to exhibit excellent in vitro activity against CR- and XDR-P. aeruginosa isolates. Several pharmaceuticals have devoted to exploring novel antibiotics to combat these troublesome XDR-GNBs. Nevertheless, only few antibiotics are shown to be effective in vitro against CR/XDR-A. baumannii complex isolates. In this era of antibiotic pipelines, strict implementation of antibiotic stewardship is as important as in-time isolation cohorts in limiting the spread of CR/XDR-GNB and alleviating the worsening trends of resistance.

A plethora of carbapenem resistance in Acinetobacter baumannii: no end to a long insidious genetic journey

Acinetobacter baumannii, notorious for causing nosocomial infections especially in patients admitted to intensive care unit (ICU) and burn units, is best at displaying resistance to all existing antibiotic classes. Consequences of high potential for antibiotic resistance has resulted in extensive drug or even pan drug resistant A. baumannii. Carbapenems, mainly imipenem and meropenem, the last resort for the treatment of A. baumannii infections have fallen short due to the emergence of carbapenem resistant A. baumannii (CRAB). Though enzymatic degradation by production of class D β-lactamases (Oxacillinases) and class B β-lactamases (Metallo β-lactamases) is the core mechanism of carbapenem resistance in A. baumannii; however over-expression of efflux pumps such as resistance-nodulation cell division (RND) family and variant form of porin proteins such as CarO have been implicated for CRAB inception. Transduction and outer membrane vesicles-mediated transfer play a role in carbapenemase determinants spread. Colistin, considered as the most promising antibacterial agent, nevertheless faces adverse effects flaws. Cefiderocol, eravacycline, new β-lactam antibiotics, non-β-lactam-β-lactamase inhibitors, polymyxin B-derived molecules and bacteriophages are some other new treatment options streamlined.

Predominance of international clone 2 multidrug-resistant Acinetobacter baumannii clinical isolates in Thailand: a nationwide study

BACKGROUND

Acinetobacter baumannii has emerged as one of the common multidrug resistance pathogens causing hospital-acquired infections. This study was conducted to elucidate the distribution of antimicrobial resistance genes in the bacterial population in Thailand. Multidrug-resistant A. baumannii (MDR A. baumannii) isolates were characterized phenotypically, and the molecular epidemiology of clinical isolates in 11 tertiary hospitals was investigated at a country-wide level.

METHODS

A total of 135 nonrepetitive MDR A. baumannii isolates collected from tertiary care hospitals across 5 regions of Thailand were examined for antibiotic susceptibility, resistance genes, and sequence types. Multilocus sequence typing (MLST) was performed to characterize the spread of regional lineages.

RESULTS

ST2 belonging to IC2 was the most dominant sequence type in Thailand (65.19%), and to a lesser extent, there was also evidence of the spread of ST164 (10.37%), ST129 (3.70%), ST16 (2.96%), ST98 (2.96%), ST25 (2.96%), ST215 (2.22%), ST338 (1.48%), and ST745 (1.48%). The novel sequence types ST1551, ST1552, ST1553, and ST1557 were also identified in this study. Among these, the blaoxa-23 gene was by far the most widespread in MDR A. baumannii, while the blaoxa-24/40 and blaoxa-58 genes appeared to be less dominant in this region. The results demonstrated that the predominant class D carbapenemase was blaOXA-23, followed by the class B carbapenemase blaNDM-like, while the mcr-1 gene was not observed in any isolate. Most of the MDR A. baumannii isolates were resistant to ceftazidime (99.23%), gentamicin (91.85%), amikacin (82.96%), and ciprofloxacin (97.78%), while all of them were resistant to carbapenems. The results suggested that colistin could still be effective against MDR A. baumannii in this region.

CONCLUSION

This is the first molecular epidemiological analysis of MDR A. baumannii clinical isolates at the national level in Thailand to date. Studies on the clonal relatedness of MDR A. baumannii isolates could generate useful data to understand the local epidemiology and international comparisons of nosocomial outbreaks.

Co-Existence of Carbapenemase-Encoding Genes in Acinetobacter baumannii from Cancer Patients

INTRODUCTION

Acinetobacter baumannii is an opportunistic pathogen, which can acquire new resistance genes. Infections by carbapenem-resistant A. baumannii (CRAB) in cancer patients cause high mortality.

METHODS

CRAB isolates from cancer patients were screened for carbapenemase-encoding genes that belong to Ambler classes (A), (B), and (D), followed by genotypic characterization by enterobacterial-repetitive-Intergenic-consensus-polymerase chain reaction (ERIC-PCR) and multilocus-sequence-typing (MLST).

RESULTS

A total of 94.1% of CRAB isolates co-harbored more than one carbapenemase-encoding gene. The genes blaNDM, blaOXA-23-like, and blaKPC showed the highest prevalence, with rates of 23 (67.7%), 19 (55.9%), and 17 (50%), respectively. ERIC-PCR revealed 19 patterns (grouped into 9 clusters). MLST analysis identified different sequence types (STs) (ST-268, ST-195, ST-1114, and ST-1632) that belong to the highly resistant easily spreadable International clone II (IC II). Genotype diversity indicated the dissemination of carbapenem-hydrolyzing, β-lactamase-encoding genes among genetically unrelated isolates. We observed a high prevalence of metallo-β-lactamase (MBL)-encoding genes (including the highly-resistant blaNDM gene that is capable of horizontal gene transfer) and of isolates harboring multiple carbapenemase-encoding genes from different classes.

CONCLUSION

The findings are alarming and call for measures to prevent and control the spread of MBL-encoding genes among bacteria causing infections in cancer patients and other immunocompromised patient populations.

Molecular characterization and antibiotic resistance of Acinetobacter baumannii in cerebrospinal fluid and blood

The increasing prevalence of carbapenem-resistant Acinetobacter baumannii (CRAB) caused nosocomial infections generate significant comorbidity and can cause death among patients. Current treatment options are limited. These infections pose great difficulties for infection control and clinical treatment. To identify the antimicrobial resistance, carbapenemases and genetic relatedness of Acinetobacter baumannii isolates from cerebrospinal fluid (CSF) and blood, a total of 50 nonrepetitive CSF isolates and 44 blood isolates were collected. The resistance phenotypes were determined, and polymerase chain reaction (PCR) was performed to examine the mechanisms of carbapenem resistance. Finally, multilocus sequence typing (MLST) was conducted to determine the genetic relatedness of these isolates. It was observed that 88 of the 94 collected isolates were resistant to imipenem or meropenem. Among them, the bla_OXA-23 gene was the most prevalent carbapenemase gene, with an observed detection rate of 91.5% (86/94), followed by the bla_OXA-24 gene with a 2.1% detection rate (2/94). Among all carbapenem-resistant Acinetobacter baumannii (CRAB) observations, isolates with the bla_OXA-23 gene were resistant to both imipenem and meropenem. Interestingly, isolates positive for the bla_OXA-24 gene but negative for the bla_OXA-23 gene showed an imipenem-sensitive but meropenem-resistant phenotype. The MLST analysis identified 21 different sequence types (STs), with ST195, ST540 and ST208 most frequently detected (25.5%, 12.8% and 11.7%, respectively). 80 of the 94 isolates (85.1%) were clustered into CC92 which showed a carbapenem resistance phenotype (except AB13). Five novel STs were detected, and most of them belong to CRAB. In conclusion, these findings provide additional observations and epidemiological data of CSF and blood A. baumannii strains, which may improve future infection-control measures and aid in potential clinical treatments in hospitals and other clinical settings.

Wza gene knockout decreases Acinetobacter baumannii virulence and affects Wzy-dependent capsular polysaccharide synthesis

To investigate the virulence of capsular polysaccharide export protein (Wza) in carbapenem-resistant Acinetobacter baumannii and its effect on capsule formation.

wza gene knockout and complementation strains were constructed, and changes in bacterial virulence were observed using in vitro adhesion, antiserum complement killing, anti-oxidation experiments, and infections in Galleria mellonella and mice. The effect of wza knockout on the genes wzb and wzc and wzi were assessed by RT-PCR.

We successfully constructed wza knockout and complementation strains. Compared with wild-type (WT) strains, wza knockout strains displayed lower adhesion to A549 cells (p = 0.044), lower antiserum complement killing ability (p = 0.001), and lower mortality of G. mellonella (p = 0.010) and mice (p = 0.033). Expression levels of wzb, wzc and wzi were decreased in wza knockout strains. The antioxidant capacity of Wza knockout bacteria was only slightly decreased. Complementation of the wza gene returned the adhesion ability, antiserum complement killing ability, and mortality of G. mellonella and mice to WT levels. Expression of wzb, wzc and wzi was also returned to WT levels following wza complementation.

The results clearly demonstrate that Wza is toxic. Wza affects the expression of other proteins of the Wzy capsule polysaccharide synthesis pathway, which affects the assembly, export, and extracellular fixation of capsular polysaccharide, resulting in synergistic effects that decrease bacterial virulence.

A catchment-scale assessment of the sanitary condition of treated wastewater and river water based on fecal indicators and carbapenem-resistant Acinetobacter spp

Urbanization and population growth have created considerable sanitation challenges in cities and communities in many parts of Europe and the world. As such, it is imperative to identify the most environmentally-harmful microbiological and chemical sources of pollution, these being wastewater treatment plants (WWTPs) which release wastewater of low quality. In the present manuscript, an extensive study was performed of the sanitary conditions of river water and treated wastewater from seventeen WWTPs of various sizes along the Pilica River catchment in central Poland, with the aim of identifying "hot spots" in terms of most serious sources of sanitary hazards. The bacteriological risk for the river, including fecal indicator bacteria (FIB) such as coliforms, E.coli, enterococci, C. perfringens, and carbapenem-resistant Acinetobacter spp. (CRA) were assessed using classical microbiological methods, and the physicochemical parameters were also tested. The WWTPs, particularly the small ones (<2000 people equivalent, PE) demonstrated significant variation regarding the physicochemical parameters. Carbapenem-resistant Acinetobacter spp. bacteria growing at 42 °C were found in the effluent wastewaters of all tested municipal WWTPs, and in most of the Pilica River water samples, presenting a potential hazard to public health. A positive correlation was identified between E. coli and CRA abundance in treated wastewater; however, no such relationship was found in river water. It was found that seven small treatment plants discharged wastewater with very different microbiological parameters. Moreover, three small treatment plants serving only 0.56% of the population in the studied area continuously released extremely high microbiological contamination, constituting as much as 54-82% of fecal indicator bacteria loads in the area studied. Our findings show that this type of comprehensive analysis may enable assessment of the use of the entire catchment area, thus identifying the most serious threats to surface water quality and guiding the actions needed to improve the worst operating WWTPs.

Prevalence of OXA-Type β-Lactamase Genes among Carbapenem-Resistant Acinetobacter baumannii Clinical Isolates in Thailand

Carbapenem-resistant Acinetobacter baumannii (CRAB) is a critical health concern for the treatment of infectious diseases. The aim of this study was to investigate the molecular epidemiology of CRAB emphasizing the presence of oxacillinase (OXA)-type β-lactamase-encoding genes, one of the most important carbapenem resistance mechanisms. In this study, a total of 183 non-repetitive CRAB isolates collected from 11 tertiary care hospitals across Thailand were investigated. As a result, the blaoxa-51-like gene, an intrinsic enzyme marker, was detected in all clinical isolates. The blaoxa-23-like gene was presented in the majority of isolates (68.31%). In contrast, the prevalence rates of blaoxa-40/24-like and blaoxa-58-like gene occurrences in CRAB isolates were only 4.92% and 1.09%, respectively. All isolates were resistant to carbapenems, with 100% resistance to imipenem, followed by meropenem (98.91%) and doripenem (94.54%). Most isolates showed high resistance rates to ciprofloxacin (97.81%), ceftazidime (96.72%), gentamicin (91.26%), and amikacin (80.87%). Interestingly, colistin was found to be a potential drug of choice due to the high susceptibility of the tested isolates to this antimicrobial (87.98%). Most CRAB isolates in Thailand were of ST2 lineage, but some belonged to ST25, ST98, ST129, ST164, ST215, ST338, and ST745. Further studies to monitor the spread of carbapenem-resistant OXA-type β-lactamase genes from A. baumannii in hospital settings are warranted.

In vitro activity of biofilm inhibitors in combination with antibacterial drugs against extensively drug-resistant Acinetobacter baumannii

Acinetobacter baumannii is a common pathogen of nosocomial infection, and its ability to form biofilms further contributes to its virulence and multidrug resistance, posing a great threat to global public health. In this study, we investigated the inhibitory effects of five biofilm inhibitors (BFIs) (zinc lactate, stannous fluoride, furanone, azithromycin, and rifampicin) on biofilm formation of nine extensively drug-resistant A. baumannii (XDRAB), and assessed the synergistic antibacterial effects of these BFIs when combined with one of four conventional anti-A. baumannii antibiotics (imipenem, meropenem, tigecycline, and polymyxin B). Each of the five BFIs tested was found to be able to significantly inhibit biofilm formation of all the clinical isolates tested under sub-minimal inhibitory concentrations. Then, we observed synergistic effects (in 22%, 56% and 11% of the isolates) and additive effects (56%, 44% and 44%) when zinc lactate, stannous fluoride and furanone were combined with tigecycline, respectively. When zinc lactate and stannous fluoride were each used with a carbapenem (imipenem or meropenem), in 33% and 56-67% of the isolates, they showed synergistic and additive effects, respectively. Additivity in > 50% of the isolates was detected when rifampicin was combined with imipenem, meropenem, tigecycline, or polymyxin B; and a 100% additivity was noted with azithromycin-polymyxin B combination. However, antagonism and indifference were noted for polymyxin B in its combination with zinc lactate and stannous fluoride, respectively. In conclusion, five BFIs in combination with four antibacterial drugs showed different degrees of in vitro synergistic and additive antibacterial effects against XDRAB.

Trends and Development in the Antibiotic-Resistance of Acinetobacter baumannii: A Scientometric Research Study (1991-2019)

Objective

Data visualization software were used to display and analyze the research status, hotspot and development trend of the antibiotic-resistance of Acinetobacter baumannii objectively and comprehensively, so as to provide guidance and reference for the research of the antibiotic-resistant Acinetobacter baumannii.

Materials and Methods

The data of relevant publications on antibiotic-resistant Acinetobacter baumanii from 1991 to 2019 were retrieved from Web of Science (WOS) Core database. VOSviewer and CiteSpace software were used to conduct co-citation visualization network rendering and cluster analysis on the publications’ years, authors, countries, institutions, keywords and citations.

Results

A total of 3915 valid records on the study of antibiotic-resistant Acinetobacter baumanii were retrieved. The number of relevant publications was increasing year after year. The United States is the most influential country in the field, which works closely with other countries and publishes most of the papers. University of Sydney is the leading institution in this area. Bonomo Robert A publishes most of the papers. There are the highest number of publications in the research areas of antimicrobial agents and chemotherapy. “Nucleotide sequence” and “outbreak” were once the hotspots in this field, but recently “bacteriophage”, “biofilm” and “colistin resistance” have become the research hotspots.

Conclusion

Since 1991, the number of publications on antibiotic-resistant Acinetobacter baumannii has grown rapidly, and various countries and institutions have paid close attention to the problem of antibiotic resistance. Countries, institutions and researchers, which have strong influential power, collaborate with each other closely. The future research direction of antibiotic-resistant Acinetobacter baumannii should lie in the further breakthrough of antibacterial peptides, bacteriophage therapy, CRISPR system and various combined therapies.

Molecular Characterization and Survival of Carbapenem-Resistant Acinetobacter baumannii Isolated from Hospitalized Patients in Mostar, Bosnia and Herzegovina

Increasingly difficult treatment of multidrug-resistant (MDR) bacteria has become a global problem of the 21st century. Within a group of multiresistant bacteria, the Acinetobacter baumannii convincingly occupies the position at the top of the group designated as ESKAPE pathogens. In this study, 61 isolates of A. baumannii were recovered from different samples originating from various departments of the University Clinical Hospital Mostar during 2018. All of the isolates were identified using conventional phenotypic methods and the VITEK^® 2 Compact System, and were confirmed by MALDI-TOF mass spectrometry. The minimum inhibitory concentrations (MICs) were determined by the microbroth dilution method using MICRONAUT-S MDR MRGN-Screening and VITEK 2 Compact System. All strains were resistant to carbapenems and classified in eight different resistotypes according to their antibiotic resistance and macrorestriction pulsed-field gel electrophoresis profiles, with all belonging to IC II. One isolate displayed resistance to colistin (MIC ≥16 mg/L). The presence of blaOXA genes encoding OXA-type carbapenemases was investigated by multiplex PCR and the Eazyplex^® SuperBugAcineto system and showed 100% compatibility with the detection of acquired oxacillinases. Molecular characterization of the isolates tested in this study revealed the OXA-23- and OXA-40-like groups of acquired oxacillinases. Sequencing of two PCR products of the OXA-40-like group confirmed the presence of OXA-72. Survival assays with two selected isolates of A. baumannii encoding different mechanisms of carbapenem resistance revealed that one isolate was able to survive on a fragment of white laboratory coat during 90 days of monitoring. To the best of our knowledge, this is the first article to present the results of a comprehensive phenotypic, genotypic, and molecular analysis of A. baumannii isolates from the leading clinical hospital center in the southwestern part of Bosnia and Herzegovina, including data for the survival of this pathogen on the white laboratory coats used as compulsory medical clothing.

Survey on Genetic Diversity, Biofilm Formation, and Detection of Colistin Resistance Genes in Clinical Isolates of Acinetobacter baumannii

Introduction

Acinetobacter baumannii is an opportunistic pathogen responsible for nosocomial infections. The emergence of colistin-resistant A. baumannii is a significant threat to public health. The aim of this study was to investigate the molecular characterization and genotyping of clinical A. baumannii isolates in Southwestern Iran.

Methods

A total of 70 A. baumannii isolates were collected from patients admitted to Imam Khomeini Hospital in Ahvaz, Southwestern Iran. Minimum inhibitory concentration test was conducted by using Vitek 2 system. The presence of biofilm-forming genes and colistin resistance-related genes were evaluated by PCR. The isolates were also examined for their biofilm formation ability and the expression of pmrA and pmrB genes. Finally, multilocus sequence typing (MLST) and PCR-based sequence group were used to determine the genetic relationships of the isolates.

Results

Overall, 61 (87.1%) and 9 (12.8%) isolates were multidrug-resistant (MDR) and extensively drug-resistant (XDR), respectively. Colistin and tigecycline with 2 (2.8%) and 32 (45.7%) resistance rates had the highest effect. Among all the isolates, 55 (78.5%), 7 (10%), and 3 (4.3%) were strong, moderate, and weak biofilm producers, respectively. The frequency rates of biofilm-related genes were 64 (91.4%), 70 (100%), 56 (80%), and 22 (31.42%) for bap, ompA, csuE, and bla_PER1, respectively. Overexpression of pmrA and pmrB genes was observed in two colistin-resistance isolates, but the expression of these genes did not change in colistin-sensitive isolates. Additionally, 37 (52.8%) and 8 (11.4%) isolates belonged to groups 1 (ICII) and 2 (IC I), respectively. MLST analysis revealed a total of nine different sequence types that six isolates belonged to clonal complex 92 (corresponding to ST801, ST118, ST138, ST 421, and ST735). Other isolates were belonging to ST133 and ST216, and two colistin-resistant (Ab4 and Ab41) isolates were belonging to ST387 and ST1812.

Conclusion

The present study revealed the presence of MDR and XDR A. baumannii isolates harboring biofilm genes and emergence of colistin-resistant isolates in Southwestern Iran. These isolates had high diversity, which was affirmed by typing techniques. The control measures and regular surveillance are urgently needed to preclude the spread of these isolates.

Development and Evaluation of a Loop-Mediated Isothermal Amplification Assay for Rapid and Specific Identification of Carbapenem-Resistant Acinetobacter baumannii Strains Harboring blaOXA-23, and the Epidemiological Survey of Clinical Isolates

Acinetobacter baumannii is an important nosocomial pathogen in hospital-acquired infections, and carbapenem resistance has been increasingly observed worldwide. Oxacillinase production by bla_OXA-23 is a predominant and prevalent carbapenem resistance mechanism of A. baumannii, especially in China. Rapid and specific detection of bla_OXA-23 may offer valuable insight for administration of directed antimicrobial therapy. In this study, we aimed to develop a loop-mediated isothermal amplification (LAMP)-based method for identifying carbapenem-resistant A. baumannii (CRAB) harboring the bla_OXA-23 gene. High-specificity primers for screening bla_OXA-23 were designed and synthesized, and the LAMP reactions were performed. Clinical A. baumannii strains isolated from the Former 307th Hospital of People's Liberation Army were used to determine the sensitivity and specificity of this method compared with those of phenotypic antimicrobial susceptibility testing and the traditional PCR method. Multilocus sequence typing (MLST) was performed to investigate the epidemiology of the A. baumannii bacterial population. Compared with antimicrobial susceptibility testing, the sensitivity and specificity of LAMP in detecting bla_OXA-23 were 88.4% and 97.7%, respectively. However, the LAMP method is much simpler and less time-consuming (within 60 minutes) than conventional PCR and phenotypic susceptibility testing. The 113 isolates could be clustered into 30 sequence types, and most strains (83/113) belonged to clonal complex (CC) 92, which is also the dominant CC in China. The LAMP-based method detected bla_OXA-23 in a simpler manner and could provide rapid results for identifying CRAB. Consequently, bla_OXA-23 may serve as a surrogate marker for the presence of CRAB in patients with serious infections in clinical practice.

Decreased carO gene expression and OXA-type carbapenemases among extensively drug-resistant Acinetobacter baumannii strains isolated from burn patients in Tehran, Iran

A major challenge in the treatment of infections has been the rise of extensively drug resistance (XDR) and multidrug resistance (MDR) in Acinetobacter baumannii. The goals of this study were to determine the pattern of antimicrobial susceptibility, blaOXA and carO genes among burn-isolated A. baumannii strains. In this study, 100 A. baumannii strains were isolated from burn patients and their susceptibilities to different antibiotics were determined using disc diffusion testing and broth microdilution. Presence of carO gene and OXA-type carbapenemase genes was tested by PCR and sequencing. SDS-PAGE was done to survey CarO porin and the expression level of carO gene was evaluated by Real-Time PCR. A high rate of resistance to meropenem (98%), imipenem (98%) and doripenem (98%) was detected. All tested A. baumannii strains were susceptible to colistin. The results indicated that 84.9% were XDR and 97.9% of strains were MDR. In addition, all strains bore blaOXA-51 like and blaOXA-23 like and carO genes. Nonetheless, blaOXA-58 like and blaOXA-24 like genes were harbored by 0 percent and 76 percent of strains, respectively. The relative expression levels of the carO gene ranged from 0.06 to 35.01 fold lower than that of carbapenem-susceptible A. baumannii ATCC19606 and SDS - PAGE analysis of the outer membrane protein showed that all 100 isolates produced CarO. The results of current study revealed prevalence of blaOXA genes and changes in carO gene expression in carbapenem resistant A.baumannii.

Molecular Surveillance of Multidrug-Resistant Acinetobacter baumannii

Acinetobacter baumannii, a bacterial strain which demonstrates an elevated wide range multidrug resistance to commonly prescribed antibiotics, has been linked to recent major global outbreaks, raising a major clinical concern. Its reduced antibiotic susceptibility is closely related to the acquisition of a potent carbapenemase and/or intrinsic gene "over expression" through insertion sequences. Hence, this study aimed at investigating the antimicrobial susceptibility and molecular mechanisms underlying β-lactam resistance in A. baumannii, isolated at an academic medical centre. To understand the basis of resistance, 103 multidrug-resistant (MDR) A. baumannii isolates were collected, their antibiotic susceptibility was tested phenotypically, and then molecular analyses were performed, by testing a range of commonly encountered carbapenemases-OXA-51, OXA-23, NDM, VIM, and KPC. All strains demonstrated pan-resistance to most of the advanced antibiotics tested, including piperacillin/tazobactam, ceftazidime, cefepime, and ciprofloxacin. Moreover, majority of isolates exhibited resistance to imipenem (98.1%) and trimethoprim (90.3%). Approximately 50% of the strains showed meropenem, amikacin, and gentamycin resistance; however, lower resistance rate to tigecycline (4.9%) was noted. Moreover, isolates contained potent carbapenemases such as the intrinsic OXA-51 (89.3%), as well as the acquired resistant genes OXA-23 (68.9%), NDM (84.5%), and VIM (88.3%). The insertion sequence element ISAba1 was only detected in 35.9% of the strains. Potent resistant genes known to be carried on mobile genetic elements that aid the spread of highly resistant phenotypes were observed in a majority of isolates. These findings enforce the need for vigilant infection control measures and continuous surveillance.

Coagulation factors VII, IX and X are effective antibacterial proteins against drug-resistant Gram-negative bacteria

Infections caused by drug-resistant “superbugs” pose an urgent public health threat due to the lack of effective drugs; however, certain mammalian proteins with intrinsic antibacterial activity might be underappreciated. Here, we reveal an antibacterial property against Gram-negative bacteria for factors VII, IX and X, three proteins with well-established roles in initiation of the coagulation cascade. These factors exert antibacterial function via their light chains (LCs). Unlike many antibacterial agents that target cell metabolism or the cytoplasmic membrane, the LCs act by hydrolyzing the major components of bacterial outer membrane, lipopolysaccharides, which are crucial for the survival of Gram-negative bacteria. The LC of factor VII exhibits in vitro efficacy towards all Gram-negative bacteria tested, including extensively drug-resistant (XDR) pathogens, at nanomolar concentrations. It is also highly effective in combating XDR Pseudomonas aeruginosa and Acinetobacter baumannii infections in vivo. Through decoding a unique mechanism whereby factors VII, IX and X behave as antimicrobial proteins, this study advances our understanding of the coagulation system in host defense, and suggests that these factors may participate in the pathogenesis of coagulation disorder-related diseases such as sepsis via their dual functions in blood coagulation and resistance to infection. Furthermore, this study may offer new strategies for combating Gram-negative “superbugs”.

Using WGS to identify antibiotic resistance genes and predict antimicrobial resistance phenotypes in MDR Acinetobacter baumannii in Tanzania

BACKGROUND

Reliable phenotypic antimicrobial susceptibility testing can be a challenge in clinical settings in low- and middle-income countries. WGS is a promising approach to enhance current capabilities.

AIM

To study diversity and resistance determinants and to predict and compare resistance patterns from WGS data of Acinetobacter baumannii with phenotypic results from classical microbiological testing at a tertiary care hospital in Tanzania.

METHODS AND RESULTS

MLST using Pasteur/Oxford schemes yielded eight different STs from each scheme. Of the eight, two STs were identified to be global clones 1 (n = 4) and 2 (n = 1) as per the Pasteur scheme. Resistance testing using classical microbiology determined between 50% and 92.9% resistance across all drugs. Percentage agreement between phenotypic and genotypic prediction of resistance ranged between 57.1% and 100%, with coefficient of agreement (κ) between 0.05 and 1. Seven isolates harboured mutations at significant loci (S81L in gyrA and S84L in parC). A number of novel plasmids were detected, including pKCRI-309C-1 (219000 bp) carrying 10 resistance genes, pKCRI-43-1 (34935 bp) carrying two resistance genes and pKCRI-49-1 (11681 bp) and pKCRI-28-1 (29606 bp), each carrying three resistance genes. New ampC alleles detected included ampC-69, ampC-70 and ampC-71. Global clone 1 and 2 isolates were found to harbour ISAba1 directly upstream of the ampC gene. Finally, SNP-based phylogenetic analysis of the A. baumannii isolates revealed closely related isolates in three clusters.

CONCLUSIONS

The validity of the use of WGS in the prediction of phenotypic resistance can be appreciated, but at this stage is not sufficient for it to replace conventional antimicrobial susceptibility testing in our setting.

Outbreak of carbapenem-resistant Acinetobacter baumannii carrying the carbapenemase OXA-23 in ICU of the eastern Heilongjiang Province, China

Background

To investigate the carbapenem resistance mechanisms and clonal relationship of carbapenem-resistant Acinetobacter baumannii (CRAB) strains isolated in the intensive care unit (ICU) of the First Affiliated Hospital of Jiamusi University, management approaches to ICU clonal CRAB outbreaks were described.

Methods

The sensitivity of the antibiotic was determined using the VITEK-2 automated system. Carbapenemase genes (bla_TEM, bla_SHV, bla_KPC, bla_NDM, bla_IMP-4, bla_VIM, bla_OXA-23, bla_OXA-24, bla_OXA-51, and bla_OXA-58), AmpC enzyme genes (bla_ACC, bla_DHA, bla_ADC), and ISAba1 were assessed for all collected isolates using polymerase chain reaction (PCR). The transfer of resistance genes was investigated via conjugation experiments. The clonal relationship of isolates was determined via enterobacterial repetitive intergenic consensus (ERIC)-PCR and multilocus sequence typing (MLST). When the detection rate of CRAB increased from 25% in 2010 to 92% in 2014, a number of actions were initiated, including enhanced infection control, staff education, and the cleaning of the hospital environment.

Results

Clinical isolates were positive for the following genes: bla_OXA23, bla_OXA51, bla_OXA24, bla_ADC, bla_TEM, ISAba1, ISA-23, and ISA-ADC; however, bla_OXA58, ISA-51, bla_NDM, bla_IMP, bla_KPC, bla_TEM, bla_SHV, bla_VIM, and bla_ACC were not detected. Four carbapenem-resistant isolates successfully transferred plasmids from A. baumannii isolates to E. coli J53. MLST showed that all strains belonged to ST2 except for one isolate, which belonged to the new genotype ST1199. The ERIC-PCR method found the following three genotypes: type A in 8, type B in 12, type C in 1, and two profiles (A, B) belonged to ST2. After taking control measures, the prevalence of CRAB isolates decreased, and the discovery rate of CRAB dropped to 11.4% in 2017.

Conclusion

The obtained result suggests that bla_OXA-23-producing CC2 isolates were prevalent in the ICU of the First Affiliated Hospital of Jiamusi University. Targeted surveillance was implemented to identify the current situation of the ICU and the further implementation of infection control effectively prevented the spread of nosocomial infection.

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

BACKGROUND

Multi-drug resistant Acinetobacter baumannii has emerged as important nosocomial pathogen associated with various infections including lower respiratory tract. Limited therapeutic options contribute to increased morbidity and mortality. Acinetobacter baumannii has the ability to persist in the environment for prolonged periods. Breach in infection control practices increases the chances of cross transmission between patients and inter/intraspecies transmission of resistance elements. The present prospective work was conducted among patients with lower respiratory tract infections (LRTI) in the intensive care unit (ICU) to study the etiology with special reference to Acinetobacter baumannii and the role of immediate patient environment in the ICU as possible source of infection. Acinetobacter baumannii were characterized for antimicrobial susceptibility, mechanism of carbapenem resistance and virulence determinants. Molecular typing of the clinical and environmental isolates was undertaken to study the probable modes of transmission.

MATERIALS AND METHODS

Appropriate respiratory samples from 107 patients with LRTI admitted to ICU during September 2016 to March 2017 were studied for likely bacterial pathogens. Environmental samples (n = 71) were also screened. All the samples were processed using conventional microbiological methods. Consecutive Acinetobacter spp. isolated from clinical and environmental (health care workers and environment from ICU) samples were included in the study. Antimicrobial susceptibility was performed as per CLSI guidelines. Carbapenem resistance, mediated by carbapenemase genes (bla_OXA-23-like,bla_OXA-24-like,bla_OXA-58-like and bla_NDM-1) were studied by PCR. Biofilm forming ability was tested phenotypically using microtitre plate method. Pulse Field Gel Electrophoresis (PFGE) was used to study clonality of the clinical and environmental isolates.

RESULTS

The prevalence of Acinetobacter baumannii was 26.2% (28/107) and 11.26% (8/71) among patients with LRTI and environmental samples respectively. The carbapenem resistance was high, 96.42% (27/28) and 87.5% (7/8) in clinical and environmental isolates respectively. The most common carbapenemase associated with resistance was bla_OXA-23-like gene followed by bla_NDM-1 among both the clinical and environmental isolates. All isolates were sensitive to colistin (MIC ≤ 1 μg/ml). Biofilm production was observed among all clinical (n = 28) and 87.5% (7/8) of the environmental isolates. Line listing of the cases suggests the occurrence of infections throughout the study period with no significant clustering. On PFGE, 12 clusters were observed and 16/36 isolates were present in one single cluster that included both clinical and environmental isolates which were either carbapenem resistant or sensitive.

DISCUSSION

Carbapenem resistant Acinetobacter baumannii (CRAB) is an important cause of LRTI in the ICU. PFGE suggests spread of carbapenem resistant isolates via cross transmission among patients and the environment. The detection of bla_NDM-1 gene among Acinetobacter baumannii and existence of carbapenem resistant and sensitive isolates within the same clones suggests horizontal transmission of resistant genes among various bacterial species. The ability of Acinetobacter baumannii to form biofilms may contribute to its persistence in the environment. This along with breach in infection control practices are the likely factors contributing to this transmission. This information can be used to strengthen and monitor infection control (IC) and the hospital cleaning and disinfection practices to prevent spread of resistant organisms within the ICU. Colistin remains drug of choice for management of CRAB.

Prevalence and Mechanisms of Carbapenem Resistance Among Acinetobacter baumannii Clinical Isolates in Egypt

The increasing number of carbapenem-resistant Acinetobacter baumannii clinical isolates is a major concern, which restricts therapeutic options for treatment of serious infections caused by this emerging pathogen. The aim of this work is to assess the antimicrobial resistance profile and identify the molecular mechanisms involved in carbapenem resistance in A. baumannii isolated from different clinical sources in Mansoura University Hospitals, Egypt. Antimicrobial susceptibility testing has shown that resistance to carbapenem has dramatically increased (98%) with concomitant elevated levels of resistance to quinolones, trimethoprim/sulfamethoxazole, and aminoglycosides. Polymyxin B and colistin are considered the last resort. Random amplified polymorphic DNA (RAPD) typing method revealed great diversity among A. baumannii isolates. Coexistence of diverse intrinsic and acquired carbapenem-hydrolyzing β-lactamases has been detected in the tested isolates: Ambler class A: bla_KPC (56%) and bla_GES (48%), and Ambler class B: bla_NDM (30%), bla_SIM (28%), bla_VIM (20%), and bla_IMP (10%). Most isolates (94%) carried bla_OXA-23-like and bla_OXA-51-like simultaneously. bla_OXA-23-like was preceded by ISAba1 providing a potent promoter activity for its expression. Sequencing analysis revealed that ISAba1 has been also inserted in carbapenem resistance-associated outer membrane protein (OMP) (carO) gene in three isolates, two of which were clonal based on RAPD typing, leading to interruption of its expression as confirmed by SDS-PAGE analysis of OMP fractions. Carbapenem resistance genes are widely distributed among A. baumannii clinical isolates from different clinical sources. Therefore, enhanced infection control measures, effective barriers, and rational use of antimicrobials should be enforced in hospitals for minimizing the widespread resistance to carbapenems and all other antibiotics.

Distribution of virulence-associated genes and antimicrobial susceptibility in clinical Acinetobacter baumannii isolates

Acinetobacter baumannii is undoubtedly one of the most clinically significant pathogens. The multidrug resistance and virulence potential of A. baumannii are responsible for hospital-acquired nosocomial infections. Unlike numerous investigations on the drug-resistant epidemiology of A. baumanni, virulence molecular epidemiology is less studied. Here, we collected 88 A. baumannii clinical isolates, tested their antimicrobial susceptibility to 10 commonly used antibiotics and analyzed the distribution of 9 selected virulence-associated genes, aims to investigate the primary characteristics of the virulence-associated genes that exist in clinically multidrug resistant (MDR) and non-MDR isolates of A. baumannii. The MIC results showed the resistance rates of ciprofloxacin (68.2%, 60/88), gentamicin (67.0%, 59/88), amikacin (58.0%, 51/88), tobramycin (58.0%, 51/88), doxycycline (67.0%, 59/88), meropenem (54.5%, 48/88) and imipenem (65.9%, 58/88) were all above 50%, except for levofloxacin (34.1%, 30/88), minocycline (1.1%, 1/88) and polymyxin B (0%, 0/88). The Pulsed field gel electrophoresis (PFGE) analysis revealed that the resistance rate of MDR A. baumannii isolates in the Epidemic group was predominant (79.5%, 44/58), but in the Sporadic group was only 6.7% (2/30). Further investigation on the distribution of virulence genes showed the virulence genes bap (95.5%), surA1 (92.0%), BasD (92.0%), paaE (88.6%), pld (87.5%), BauA (62.5%), omp33-36 (59.1%) and pglC (53.4%) were accounted for high proportion, except for traT (0%). Overall, our results revealed that MDR isolates predominated in the Epidemic A. baumannii isolates, and contained a very high proportion of virulence genes, which may lead to high risk, high pathogenicity and high treatment challenge.

Molecular Characterization and Antibiotic Susceptibility Pattern of Acinetobacter Baumannii Isolated in Intensive Care Unit Patients in Al-Hassa, Kingdom of Saudi Arabia

Background:

Acinetobacter baumannii, is an emerging nosocomial multidrug resistance pathogen with the rapid spread of clones being reported in health-care settings and hospitals worldwide. Carbapenem resistance in this bacterium has been attributed to D OXA β-lactamases with OXA-51-like β-lactamase, being present in all A. baumannii isolate. The present study looks into the antibiotics susceptibility and molecular characterization of clinical A. baumannii isolates from Intensive Care Unit (ICU) samples in Al-Hofuf, South-eastern region of Saudi Arabia.

Materials and Methods:

Eleven strains of ICU A. baumanni i isolates were used for the investigation. Bacteria isolation was by basic microbiological techniques. Organisms identification and antibiogram susceptibility testing was by the BioMerieux VITEK 2 compact automated system (BioMerieux, Marcy I'Etoile France), according to the manufacturers guidelines. Confirmation of A. baumannii was by the presence of the OX-51 gene, also, carbapenemase encoding resistant genesbla_OXA-23, bla_OXA-40, and bla_OXA-51, were analyzed using multiplex PCR. The Student's t test was used to analyze the obtained data for between group comparisons with statistically significance level set at P < 0.05.

Results:

Eight of the isolates were confirmed to be A. baumannii. Five of which were resistant to the carbapenems against which they had been tested. One isolate was resistant to tigecycline, whereas three tested intermediate to the drug. OXA-23 was detected in isolates 1, 4, 5, 6, and 7.

Conclusion:

It can, therefore, be concluded that the probable predominate carbapenems resistant genes in ICU isolates from the present investigation, are those associated with OXA-23.

Molecular Characterization of Reduced Susceptibility to Biocides in Clinical Isolates of Acinetobacter baumannii

Active efflux is regarded as a common mechanism for antibiotic and biocide resistance. However, the role of many drug efflux pumps in biocide resistance in Acinetobacter baumannii remains unknown. Using biocide-resistant A. baumannii clinical isolates, we investigated the incidence of 11 known/putative antimicrobial resistance efflux pump genes (adeB, adeG, adeJ, adeT1, adeT2, amvA, abeD, abeM, qacE, qacEΔ1, and aceI) and triclosan target gene fabI through PCR and DNA sequencing. Reverse transcriptase quantitative PCR was conducted to assess the correlation between the efflux pump gene expression and the reduced susceptibility to triclosan or chlorhexidine. The A. baumannii isolates displayed high levels of reduced susceptibility to triclosan, chlorhexidine, benzalkonium, hydrogen peroxide, and ethanol. Most tested isolates were resistant to multiple antibiotics. Efflux resistance genes were widely distributed and generally expressed in A. baumannii. Although no clear relation was established between efflux pump gene expression and antibiotic resistance or reduced biocide susceptibility, triclosan non-susceptible isolates displayed relatively increased expression of adeB and adeJ whereas chlorhexidine non-susceptible isolates had increased abeM and fabI gene expression. Increased expression of adeJ and abeM was also demonstrated in multiple antibiotic resistant isolates. Exposure of isolates to subinhibitory concentrations of triclosan or chlorhexidine induced gene expression of adeB, adeG, adeJ and fabI, and adeB, respectively. A point mutation in FabI, Gly95Ser, was observed in only one triclosan-resistant isolate. Multiple sequence types with the major clone complex, CC92, were identified in high level triclosan-resistant isolates. Overall, this study showed the high prevalence of antibiotic and biocide resistance as well as the complexity of intertwined resistance mechanisms in clinical isolates of A. baumannii, which highlights the importance of antimicrobial stewardship and resistance surveillance in clinics.

Characterization of a blaNDM‑1‑harboring plasmid from a Salmonella enterica clinical isolate in China

The plasmid-mediated transmission of antibiotic resistance genes has been reported to be involved in the development of antibiotic resistance in bacteria, and poses a serious threat for the success of bacterial infection treatment and human health worldwide. The present study used a 454 GS-FLX pyrosequencing system to determine the ~140 kb nucleotide sequence of plasmid pHS36-NDM, which was identified in a Salmonella Stanley isolate from the stool sample of an 11-month-old girl at Lishui Central Hospital, China, and which contains a New Delhi metallo-β-lactamase-1 (NDM-1) carbapenem resistance gene (bla_NDM-1). The 181 open reading frames encode proteins with functions including replication, stable inheritance, antibiotic resistance and mobile genetic elements. Both horizontal transfer and passage stability-related genes were identified in pHS36-NDM, including a conserved type 4 secretion system and stbA (stable plasmid inheritance protein A). Two multidrug resistance gene islands were identified: The ISEcp1-bla_CMY transposition unit which contains a CMY-6 β-lactamase gene (bla_CMY-6) and a quaternary ammonium compound resistance gene (sugE); and the intI1-ISCR27 accessory region, which contained a trimethoprim resistance gene (dfrA12), two aminoglycoside resistance genes (aadA2 and rmtC), a truncated quaternary ammonium compound resistance gene (qacE∆1), a sulfonamide resistance gene (sul1), the bla_NDM-1 carbapenemase and a bleomycin resistance gene (ble_MBL). pHS36-NDM shared high homology with other bla_NDM-1-containing plasmids reported in Sweden, Italy and Japan. However, no previous international travel history was documented for the patient and her family, even to neighboring cities. Furthermore, pHS36-NDM is of a different incompatibility group to other published bla_NDM-1-carrying plasmids reported in China, with low homology in the surrounding structure of bla_NDM-1. The present study will facilitate the understanding of the underlying resistance and dispersal mechanism of pHS36-NDM, and will deepen our recognition of the ongoing spread of the bla_NDM-1-containing plasmids.

Molecular epidemiology of bla OXA-23 -producing carbapenem-resistant Acinetobacter baumannii in a single institution over a 65-month period in north China

BACKGROUND

Carbapenem-resistant Acinetobacter baumannii poses a significant threat to hospitalized patients, as few therapeutic options remain. Thus, we investigated the molecular epidemiology and mechanism of resistance of carbapenem-resistant A.baumannii isolates in Beijing, China.

METHODS

Carbapenem-resistant A.baumannii isolates (n = 101) obtained between June 2009 and November 2014 were used. Multilocus sequence typing (MLST) and PCR assays for class C and D β-lactamase were performed on all isolates. S1 nuclease pulsed-field gel electrophoresis (PFGE) and Southern blot hybridization were performed to identify the resistance gene location.

RESULTS

All 101 A.baumannii isolates were highly resistant to frequently used antimicrobials, and were considered multidrug resistant. A total of 12 sequence types (STs) were identified, including 10 reported STs and 2 novel STs. Eighty-seven isolates were classified to clonal complex 92 (CC92), among which ST191 and ST195 were the most common STs. The bla _OXA-23 gene was positive in most (n = 95) of the A.baumannii isolates. Using S1-nuclease digestion PFGE and Southern blot hybridization, 3 patterns of plasmids carrying bla _OXA-23 were confirmed. ST191 and ST195 (both harboring bla _OXA-23 ) caused outbreaks during the study period, and this is the first report of outbreaks caused by ST191 and ST195 in north China.

CONCLUSION

bla _OXA-23 -producing A.baumannii ST191 and ST 195 isolates can disseminate in a hospital and are potential nosocomial outbreak strains. Surveillance of imipenem-resistant A.baumannii and antimicrobial stewardship should be strengthened.

Prevalence of carbapenemases among high-level aminoglycoside-resistant Acinetobacter baumannii isolates in a university hospital in China

The prevalence of aminoglycoside resistant enzymes has previously been reported and extended-spectrum β-lactamase among Acinetobacter baumannii. To track the risk of multidrug-resistant A. baumannii, the present study aimed to determine the prevalence of carbapenemases in high-level aminoglycoside resistant A. baumannii over two years. A total of 118 strains of A. baumannii were consecutively collected in the First Affiliated Hospital of Chengdu Medical College, Chengdu, China. These isolates were investigated on the genetic basis of their resistance to aminoglycosides. The results showed that 75 (63.56%) isolates were high-level resistant to aminoglycosides, including gentamicin and amikacin (minimum inhibitory concentration, ≥256 µg/ml). Aminoglycoside-resistant genes ant(2″)-Ia, aac(6′)-Ib, aph(3′)-Ia, aac(3)-Ia, aac(3)-IIa, armA, rmtA, rmtB, rmtC, rmtD, rmtE, rmtF, rmtG, rmtH and npmA, and carbapenem-resistant genes bla_OXA-23, bla_OXA-24, bla_OXA-51, bla_OXA-58, bla_SIM, bla_IMP, bla_NDM-1 and bla_KPC, were analyzed using polymerase chain reaction. The positive rate of ant(2″)-Ia, aac(6′)-Ib, aph(3′)-Ia, aac(3)-Ia and aac(3)-IIa was 66.95, 69.49, 42.37, 39.83 and 14.41%, respectively. armA was present in 72.0% (54/75) of A. baumannii isolates with high-level resistance to aminoglycosides. The remaining nine 16S ribosomal RNA methlyase genes (rmtA, rmtB, rmtC, rmtD, rmtE, rmtF, rmtG, rmtH and npmA) and aminoglycoside-modifying enzyme gene aac(6′)-Ib-cr were not detected. Among the 54 armA-positive isolates, the prevalence of the carbapenem resistant bla_OXA-23 and bla_OXA-51 genes was 79.63 and 100%, respectively. armA, ant(2″)-Ia and aac(6′)-Ib were positive in 43 isolates. The results of multilocus sequence typing revealed 31 sequence types (STs) in all clinical strains. Among these STs, the high-level aminoglycoside-resistant A. baumannii ST92, which mostly harbored bla_OXA-23, was the predominant clone (29/75). In conclusion, A. baumannii harboring carbapenemases and aminoglycoside-resistant enzymes are extremely prevalent in western China, emphasizing the need to adopt surveillance programs to solve the therapeutic challenges that this presents.

Epidemiology and resistance features of Acinetobacter baumannii isolates from the ward environment and patients in the burn ICU of a Chinese hospital

Acinetobacter baumannii is an important opportunistic pathogen that causes severe nosocomial infections, especially in intensive care units (ICUs). Over the past decades, an everincreasing number of hospital outbreaks caused by A. baumannii have been reported worldwide. However, little attention has been directed toward the relationship between A. baumannii isolates from the ward environment and patients in the burn ICU. In this study, 88 A. baumannii isolates (26 from the ward environment and 62 from patients) were collected from the burn ICU of the Southwest Hospital in Chongqing, China, from July through December 2013. Antimicrobial susceptibility testing results showed that drug resistance was more severe in isolates from patients than from the ward environment, with all of the patient isolates being fully resistant to 10 out of 19 antimicrobials tested. Isolations from both the ward environment and patients possessed the β-lactamase genes bla OXA-51, bla OXA-23, bla AmpC, bla VIM, and bla PER. Using pulsed-field gel electrophoresis (PFGE) and multi-locus sequence typing (MLST), these isolates could be clustered into 4 major PFGE types and 4 main sequence types (ST368, ST369, ST195, and ST191) among which, ST368 was the dominant genotype. Epidemiologic and molecular typing data also revealed that a small-scale outbreak of A. baumannii infection was underway in the burn ICU of our hospital during the sampling period. These results suggest that dissemination of β-lactamase genes in the burn ICU might be closely associated with the high-level resistance of A. baumannii, and the ICU environment places these patients at a high risk for nosocomial infection. Cross-contamination should be an important concern in clinical activities to reduce hospitalacquired infections caused by A. baumannii.

Intranasal treatment with bacteriophage rescues mice from Acinetobacter baumannii-mediated pneumonia

AIM

With the emergence of drug-resistant bacteria, finding alternative agents to treat antibiotic-resistant bacterial infections is imperative.

MATERIALS & METHODS

A mouse pneumonia model was developed by combining cyclophosphamide pretreatment and Acinetobacter baumannii challenge, and a lytic bacteriophage was evaluated for its therapeutic efficacy in this model by examining the survival rate, bacterial load in the lung and lung pathology.

RESULTS

Intranasal instillation with bacteriophage rescued 100% of mice following lethal challenge with A. baumannii. Phage treatment reduced bacterial load in the lung. Microcomputed tomography indicated a reduction in lung inflammation in mice given phage.

CONCLUSION

This research demonstrates that intranasal application of bacteriophage is viable, and could provide complete protection from pneumonia caused by A. baumannii.