Antibiotic-resistant Acinetobacter Baumannii Research Articles

Current status of Acinetobacter baumannii infection and antibiotic selection in children

Acinetobacter baumannii is an important pathogen of clinical infection in critically ill patients.The clinical detection rate of Acinetobacter baumannii is increasing and the drug resistance is becoming more and more serious.The selection of antibiotics to antibiotic-resistant Acinetobacter baumannii is very limited, particularly in children with the special age and physiological characteristics, which aggravates the clinical burden.This article reviewed the status of Acinetobacter baumannii infection, especially on different diseases including pneumonia, bloodstream infections, intracranial infections and antibiotics using. Key words: Acinetobacter baumannii; Drug resistance; Children; Antibiotics

Temporal Variation in Antibiotic Resistance of Acinetobacter baumannii in a Teaching Hospital in Tunisia: Correlation with Antimicrobial Consumption

Background: To investigate the potential correlation between the rates of antimicrobial drug consumption and the prevalence of antimicrobial resistance among clinical Acinetobacter baumannii recovered in a tertiary care hospital in Tunisia. Methods: The microbiological and epidemiological profiles of A. baumannii infections at the Hospital Sahloul, Sousse, were investigated between 2001 to 2004 and 2012 to 2015 along with the consumption record of broad-spectrum antibiotics. Results: Our data showed that extensively drug-resistant A. baumannii (XDRAb) isolates increased from 11.2% to 30.5% between 2012 and 2015 and disseminated endemically for a long time. Furthermore, we evidenced a drastic increase of carbapenem-resistant A. baumannii isolates from 29.5% in 2001 up to 88.6% in 2015 (612/691). This rise could be paralleled with a significant increase in antibiotic consumption over the last 15 years, especially with the sharp increase in the annual consumption of imipenem (r = 0.816 and p <103). A noteworthy correlation between carbapenem use and resistance rate (r = 0.778, p<0.001) was evidenced. Conclusion: Feedback of these data to clinicians and decision-makers in the local setting was crucial to promote the rational use of antimicrobials and to raise awareness to strictly implement hygiene measures to limit the spread of these XDRAb isolates, to prevent colonization and subsequent infection.

Antibiotic resistance in Acinetobacter baumannii as agent of surgery infection and approaches to its overcoming by means of deca-methoxinum antiseptic

Introduction. Non-fermenting Gram-negative bacilli are known as one of the most frequent causative agents of hospital-acquired infections. Acinetobacter baumannii, as causative agent of infection complications of different localization, has obtained recently high resistance to anti-biotics and has belonged to ESKAPE group of pathogens. Antimicrobials, recommended for the prophylaxis and therapy of hospital-acquired infections, have been failing in their effectiveness and lead to selection of antibiotic resistant strains of A. baumannii.
 The aim of this research was to substantiate the way of overcoming of resistance in clinical strains of A. baumannii, by means of synergic antimicrobial activity of antibiotics and antiseptic decamethoxinum®.
 Material and methods. The research was carried out on 190 clinical strains of A. baumannii, isolated from patients with burn disease during the period 2011–2015. The sensitivity of clinical strains of A. baumannii was determined to such antibiotics as ampicillin/sulbactam, cefoperazone, cefoperazone/sulbactam, meropenem, imipenem, amikacin, ciprofloxacin, gatifloxacin and antiseptic decamethoxinum® (DCM; Registration certificate No UA/14444/01/01 since 24.06.2015. Order of the Ministry of Health of Ukraine No 373). The sensitivity of A. baumannii to antibiotics and DCM was determined by means of disk diffusion test and serial dilution (Order of the Ministry of Health of Ukraine No167 since 05.04.2007; EUCAST expert rules).The study of the influence of antiseptic DCM on the sensitivity of acinetobacteria to antibiotics was studied on 35 clinical strains of A. baumannii, drafted from the general number of isolates enrolled in the research. For this, the sensitivity of A. baumannii to antibiotics in the presence of sub-minimal inhibitory concentrations (subMIC) of DCM was identified. The received experimental data were analyzed by “Statistica 6.0”.
 Results and discussion. The changes of antibiotic sensitivity profile of A. baumannii for five years were shown. It was found that the sensitivity of A. baumannii to majority of antibiotics, selected for study, decreased significantly. But the only ampicillin/sulbactam was found to have vice versa tendency. We found the rising quantity of antibiotic resistant strains of A. baumannii. At the same time, high resistance of acinetobacteria to fluoroquinolones (ciprofloxacin– 96,1%; gatifloxacin– 95,8%) was found in 2015.
 The in vitro research of combined activity of DCM antiseptic remedy and early mentioned antibiotics against clinical strains of A. baumannii demonstrated the reveal antibiotic effectiveness. As follows, minimal inhibitory concentrations of antibiotics decreased in 1.5–4 times in the mediums which contained subMIC of DCM. Especially this tendency was found in resistant clinical strains.
 Conclusion. Under selective influence of antibiotics protected by β-lactamase inhibitors, carbapenems, fluoroquinolones aminoglycosides increase the antibiotic resistance in A. baumannii, causative agents of infectious complications in patients with burn disease. The antiseptic remedy decamethoxinum® helps to improve antibiotic sensitivity in resistant A. baumannii.

Intestinal carriage of antibiotic resistant Acinetobacter baumannii among newborns hospitalized in Moroccan neonatal intensive care unit.

This study was conducted in order to assess the acquisition rate of Acinetobacter baumannii by newborn screening, on admission and during the discharge process of neonatal intensive care unit. (NICU). Furthermore, we investigated risk factors for potential colonization and molecular epidemiology of isolated resistant bacteria. This prospective study was conducted in the neonatal unit of Hassan II University Hospital of Fez from February 2013 to July 2015. During this period, all consecutive admitted neonates were screened for A. baumannii intestinal carriage, on admission and during the discharge process. Bacteriological and molecular tests were evaluated according to the international standards. This study examines the screening on admission of 455 newborns, 59% of whom were male. The average gestational age and birth weight were 35.2 weeks and 2612.1 g respectively. In total, 277 patients were included in the acquisition study on admission. The prevalence of multi-drug resistant (MDR) A. baumannii strain carriage was 6.5%, while the acquisition rate during the hospital recovery was 13.7%. In this study, 68 MDR A. baumannii isolates were collected. The resistance rates to different antibiotic classes including, Ceftazidime, Gentamycin and Ciprofloxacin varied between 92 and 100%. Moreover, 13% of MDR A. baumannii isolates were carbapenemase producers and 88% harbored blaOXA-23 gene. On admission, three risk factors were significantly associated with A. baumannii colonization: age (OR, 2.803; IC95%, 1.191–6.596; P = 0.01), gender (OR, 0.382; IC95%, 0.158–0.921; P = 0.03) and the delivery birth at the Maternity of University Hospital (MUH), (OR, 0.196; IC95%, 0.071–0.540; P = 0.002). However during hospitalization, the only risk factor associated with acquisition of A. baumannii was the respiratory distress (OR, 2.270; IC95%, 1.055–4.881; P = 0.03). A high intestinal carriage rate of A. baumannii and multiple antibiotic resistance were found in our NICU. Thus, the spread of MDR A. baumannii should be monitored by an active surveillance strategy.

CpaA Is a Glycan-Specific Adamalysin-like Protease Secreted by Acinetobacter baumannii That Inactivates Coagulation Factor XII.

Antibiotic-resistant Acinetobacter baumannii is increasingly recognized as a cause of difficult-to-treat nosocomial infections, including pneumonia, wound infections, and bacteremia. Previous studies have demonstrated that the metalloprotease CpaA contributes to virulence and prolongs clotting time when added to human plasma as measured by the activated partial thromboplastin time (aPTT) assay. Here, we show that CpaA interferes with the intrinsic coagulation pathway, also called the contact activation system, in human as well as murine plasma, but has no discernible effect on the extrinsic pathway. By utilizing a modified aPTT assay, we demonstrate that coagulation factor XII (fXII) is a target of CpaA. In addition, we map the cleavage by CpaA to two positions, 279-280 and 308-309, within the highly glycosylated proline-rich region of human fXII, and show that cleavage at the 308-309 site is responsible for inactivation of fXII. At both sites, cleavage occurs between proline and an O-linked glycosylated threonine, and deglycosylation of fXII prevents cleavage by CpaA. Consistent with this, mutant fXII (fXII-Thr309Lys) from patients with hereditary angioedema type III (HAEIII) is protected from CpaA inactivation. This raises the possibility that individuals with HAEIII who harbor this mutation may be partially protected from A. baumannii infection if CpaA contributes to human disease. By inactivating fXII, CpaA may attenuate important antimicrobial defense mechanisms such as intravascular thrombus formation, thus allowing A. baumannii to disseminate.IMPORTANCE Ventilator-associated pneumonia and catheter-related bacteremia are the most common and severe infections caused by Acinetobacter baumannii Besides the capsule, lipopolysaccharides, and the outer membrane porin OmpA, little is known about the contribution of secreted proteins to A. baumannii survival in vivo Here we focus on CpaA, a potentially recently acquired virulence factor that inhibits blood coagulation in vitro We identify coagulation factor XII as a target of CpaA, map the cleavage sites, and show that glycosylation is a prerequisite for CpaA-mediated inactivation of factor XII. We propose adding CpaA to a small, but growing list of bacterial proteases that are specific for highly glycosylated components of the host defense system.

Genetic structure of four plasmids found in Acinetobacter baumannii isolate D36 belonging to lineage 2 of global clone 1.

Four plasmids ranging in size from 4.7 to 44.7 kb found in the extensively antibiotic resistant Acinetobacter baumannii isolate D36 that belongs to lineage 2 of global clone 1 were examined. D36 includes two cryptic plasmids and two carrying antibiotic resistance genes. The smallest plasmid pD36-1 (4.7 kb) carries no resistance genes but includes mobA and mobC mobilisation genes related to those found in pRAY* (pD36-2, 6,078 bp) that also carries the aadB gentamicin, kanamycin and tobramycin resistance gene cassette. These two plasmids do not encode a Rep protein. Plasmid pRAY* was found to be mobilised at high frequency by the large conjugative plasmid pA297-3 but a pRAY* derivative lacking the mobA and mobC genes was not. The two larger plasmids, pD36-3 and pD36-4, encode Rep_3 family proteins (Pfam1051). The cryptic plasmid pD36-3 (6.2 kb) has RepAci1 and pD36-4 (44.7 kb) encodes two novel Rep_3 family proteins suggesting a co-integrate. Plasmid pD36-4 includes the sul2 sulfonamide resistance gene, the aphA1a kanamycin/neomycin resistance gene in Tn4352::ISAba1 and a mer module in a hybrid Tn501/Tn1696 transposon conferring resistance to mercuric ions. New examples of dif modules flanked by pdif sites (XerC-XerD binding sites) that are part of many A. baumannii plasmids were also identified in pD36-3 and pD36-4 which carry three and two dif modules, respectively. Homologs of three dif modules, the sup sulphate permease module in pD36-3, and of the abkAB toxin-antitoxin module and the orf module in pD36-4, were found in different contexts in diverse Acinetobacter plasmids, consistent with module mobility. A novel insertion sequence named ISAba32 found next to the pdif site in the abkAB dif module is related to members of the ISAjo2 group which also are associated with the pdif sites of dif modules. Plasmids found in D36 were also found in some other members of GC1 lineage 2.

Pseudaminic Acid on Exopolysaccharide of Acinetobacter baumannii Plays a Critical Role in Phage-Assisted Preparation of Glycoconjugate Vaccine with High Antigenicity.

Pseudaminic acid (Pse) has been known for participating in crucial bacterial virulence and thus is an attractive target in the development of glycoconjugate vaccine. Particularly, this therapeutic alternative was suggested to be a potential solution against antibiotic resistant Acinetobacter baumannii that poses a serious global health threat. Also, Pse was found to be involved in the exopolysaccharide (EPS) of mild antibiotic resistant A. baumannii strain 54149 ( Ab-54149) of which specific glycosyl linkage can be depolymerized by phage ΦAB6 tailspike protein (ΦAB6TSP). In this study, we found that the antibodies induced by Ab-54149 EPS was capable of recognizing a range of EPS of other clinical A. baumannii strains, and deemed as a great potential material for vaccination. To efficiently acquire homogeneous EPS-derived oligosaccharide with significant immunogenic activity for the production of glycoconjugate, we used the ΦAB6TSP for the fragmentation of Ab-54149 EPS instead of chemical methods. Moreover, insight into the ligand binding characterization of ΦAB6TSP suggested the branched Pse on the Ab-54149 EPS served as a recognition site of ΦAB6TSP. The serum boosted by ΦAB6TSP-digested product and carrier protein CRM197 conjugate complex displayed specific sensitivity toward Ab-54149 EPS with bacterial killing activity. Strikingly, Pse is an ideal epitope with strong antigenicity, profiting the application of the probe for pathogen detection and glyco-based vaccine.

Substrate Specificities and Efflux Efficiencies of RND Efflux Pumps of Acinetobacter baumannii.

Antibiotic-resistant Acinetobacter baumannii causes infections that are extremely difficult to treat. A significant role in these resistance profiles is attributed to multidrug efflux pumps, especially those belonging to the resistance-nodulation-cell division (RND) superfamily of transporters. In this study, we analyzed functions and properties of RND efflux pumps in A. baumannii ATCC 17978. This strain is susceptible to antibiotics and does not contain mutations that are commonly selected upon exposure to high concentrations of antibiotics. We constructed derivatives of ATCC 17978 lacking chromosomally encoded RND pumps and complemented these strains by the plasmid-borne genes. We analyzed the substrate selectivities and efficiencies of the individual pumps in the context of native outer membranes and their hyperporinated variants. Our results show that inactivation of AdeIJK provides the strongest potentiation of antibiotic activities, whereas inactivation of AdeFGH triggers the overexpression of AdeAB. The plasmid-borne overproduction complements the hypersusceptible phenotypes of the efflux deletion mutants to the levels of the parental ATCC 17978. Only a few antibiotics strongly benefitted from the overproduction of efflux pumps and antibacterial activities of some of those depended on the synergistic interaction with the low permeability barrier of the outer membrane. Either overproduction or inactivation of efflux pumps change dramatically the lipidome of ATCC 17978. We conclude that efflux pumps of A. baumannii are tightly integrated into physiology of this bacterium and that clinical levels of antibiotic resistance in A. baumannii isolates are unlikely to be reached solely due to the overproduction of RND efflux pumps.IMPORTANCE RND-type efflux pumps are important contributors in development of clinical antibiotic resistance in A. baumannii However, their specific roles and the extent of contribution to antibiotic resistance remain unclear. We analyzed antibacterial activities of antibiotics in strains with different permeability barriers and found that the role of active efflux in antibiotic resistance of A. baumannii is limited to a few select antibiotics. Our results further show that the impact of efflux pump overproduction on antibiotic susceptibility is significantly lower than the previously reported for clinical isolates. Additional mechanisms of resistance, in particular those that improve the permeability barriers of bacterial cells and act synergistically with active efflux pumps are likely involved in antibiotic resistance of clinical A. baumannii isolates.

Antibiotic Resistance in Acinetobacter baumannii Isolated from Patients with Urinary Tract Infections in Zabol, Iran

Background: Acinetobacter baumannii are opportunistic pathogens that are found in abundance in Zabol. Due to their unique capability for long-term survival in the hospital environment, the chances of becoming infected with the bacteria are very high. Therefore, identifying potential sources of infection in the donor is very important. The aim of this study was to determine antibiotic resistance in Acinetobacter isolates. Methods: A cross sectional study was performed to evaluate 30 strains of Acinetobacter baumannii, isolated from urine culture of hospitalized patients (Amir- Al- Momenin Hospital, Zabol, South Eastern Iran) with urinary tract infections during a period of 6 months and antibiotic resistance was determined by the disk diffusion method and minimum inhibitory concentration for the antibiotic gentamicin was found with the microdilution method. Results: The results showed that in this study, all antibiotics used on Acinetobacter were effective antimicrobial agents, and only four positions (13.33%) and 26 sensitive points (86.66%) to these antibiotics have been accessed. After chloramphenicol, gentamicin was found as the most active antibiotic in a way that 7 sensitive samples (23.33%) and 23 officials (76.66%) were observed. Results of minimum inhibitory concentration (MIC) showed that four strains of Acinetobacter could grow at all concentrations of gentamicin, while the highest MIC was equal to 1024 micrograms per milliliter. Conclusions: This study demonstrates the increasing resistance of many strains of Acinetobacter baumannii, thus new antibiotics and new treatments are needed.

Antibiotic Combinations That Enable One-Step, Targeted Mutagenesis of Chromosomal Genes.

Targeted modification of bacterial chromosomes is necessary to understand new drug targets, investigate virulence factors, elucidate cell physiology, and validate results of -omics-based approaches. For some bacteria, reverse genetics remains a major bottleneck to progress in research. Here, we describe a compound-centric strategy that combines new negative selection markers with known positive selection markers to achieve simple, efficient one-step genome engineering of bacterial chromosomes. The method was inspired by the observation that certain nonessential metabolic pathways contain essential late steps, suggesting that antibiotics targeting a late step can be used to select for the absence of genes that control flux into the pathway. Guided by this hypothesis, we have identified antibiotic/counterselectable markers to accelerate reverse engineering of two increasingly antibiotic-resistant pathogens, Staphylococcus aureus and Acinetobacter baumannii. For S.aureus, we used wall teichoic acid biosynthesis inhibitors to select for the absence of tarO and for A.baumannii, we used colistin to select for the absence of lpxC. We have obtained desired gene deletions, gene fusions, and promoter swaps in a single plating step with perfect efficiency. Our method can also be adapted to generate markerless deletions of genes using FLP recombinase. The tools described here will accelerate research on two important pathogens, and the concept we outline can be readily adapted to any organism for which a suitable target pathway can be identified.

Changes in antimicrobial resistance of clinical isolates of Acinetobacter baumannii group isolated in Greece, 2010-2015.

In recent years, hospitals in southeastern Europe have faced dramatically high rates of antibiotic-resistant Acinetobacter baumannii. We analysed the evolution of resistance among clinical isolates of A. baumannii group obtained from nine tertiary hospitals throughout Greece over 6 years (2010-2015). Identification and antimicrobial susceptibility testing were performed using Vitek 2 or Microscan walkaway automated systems. Between 2010 and 2015, resistance to ampicillin/sulbactam increased from 46.2 to 88.2 % (P=0.021), resistance to gentamicin increased from 69.3 to 86.4 % (P=0.014) and resistance to tobramycin increased from 59.8 to 76.8 % (P=0.011). Imipenem resistance rates were consistently very high, ranging from 90.3 % in 2010 to 94.5 % in 2015 (P=0.198), while meropenem resistance rates increased from 82.6 % in 2010 to 94.8 % in 2015 (P=0.006). Resistance rates to trimethoprim/sulfamethoxazole showed a remarkable decreasing trend, declining from 90.2 % in 2010 to 69.1 % in 2015 (P=0.035). These evolutions render the treatment of A. baumannii infections particularly challenging and underline the need for enhanced infection control measures.

First report of OXA-143-lactamase producing Acinetobacter baumannii in Qom, Iran.

Objective(s):Antibiotic resistance in Acinetobacter baumannii and outbreaks caused by this organism have been reported from several areas of the world. The present study aimed at determining the antibiotic susceptibility profiles and the distribution of OXA-type beta-lactamases among Iranian Acinetobacter baumannii isolates from Qom of Iran.Materials and Methods:For this study, 108 non-duplicate A. baumannii isolates were obtained from clinical specimens in four teaching hospitals in Qom in the central of Iran. The antimicrobial susceptibility of isolates was tested by standard disk diffusion and prevalence of bla OXA genes was investigated by PCR method.Results:Among 97 carbapenem non-susceptible isolates of A. baumannii, 90.72% (88 isolates) isolates showed extensive drug resistance to multiple antibiotics. Among carbapenem resistant isolates, 100% carried blaOXA-51-like, 82.47% carried blaOXA-23-like, 55.67% carried blaOXA-58-like, 22.68% carried blaOXA-40-like and 14.43% had blaOXA-143-like resistance genes.Conclusion:This study demonstrated high genetic diversity of OXA genes among isolates of A. baumannii in Qom, Iran.

5,7-Di-N-acetyl-8-epiacinetaminic acid: A new non-2-ulosonic acid found in the K73 capsule produced by an Acinetobacter baumannii isolate from Singapore

Nonulosonic acids are found in the surface polysaccharides of many bacterial species and are often implicated in pathogenesis. Here, the structure of a novel 5,7-diacetamido-3,5,7,9-tetradeoxynon-2-ulosonic acid recovered from the capsular polysaccharide of a multiply antibiotic resistant Acinetobacter baumannii isolate was determined. The isolate carries a sugar synthesis module that differs by only a single gene from the module for the synthesis of 5,7-diacetamido-3,5,7,9-tetradeoxy-L-glycero-L-altro-non-2-ulosonic acid or 5,7-di-N-acetylacinetaminic acid, recently discovered in the capsule of another A. baumannii isolate. The new monosaccharide is the C8-epimer of acinetaminic acid (8eAci; 5,7-diacetamido-3,5,7,9-tetradeoxy-D-glycero-L-altro-non-2-ulosonic acid) and the C7-epimer of legionaminic acid. This monosaccharide had not previously been detected in a biological sample but had been synthesized chemically.

A large plasmid, pD46-4, carrying a complex resistance region in an extensively antibiotic-resistant ST25 Acinetobacter baumannii.

A large plasmid, pD46-4, carrying a complex resistance region in an extensively antibiotic-resistant ST25 Acinetobacter baumannii.

Clinical Antibiotic-resistant Acinetobacter baumannii Strains with Higher Susceptibility to Environmental Phages than Antibiotic-sensitive Strains

Antibiotic-resistant Acinetobacter baumannii is associated with nosocomial infections worldwide. Here, we used clinically isolated A. baumannii strains as models to demonstrate whether antibiotic resistance is correlated with an increased susceptibility to bacteriophages. In this study, 24 active phages capable of infecting A. baumannii were isolated from various environments, and the susceptibilities of both antibiotic-sensitive and antibiotic-resistant strains of A. baumannii to different phages were compared. In our study, a total of 403 clinically isolated A. baumannii strains were identified. On average, the phage infection percentage of the antibiotic-resistant A. baumannii strains was 84% (from 81–86%), whereas the infection percentage in the antibiotic-sensitive A. baumannii strains was only 56.5% (from 49–64%). In addition, the risk of phage infection for A. baumannii was significantly increased in the strains that were resistant to at least four antibiotics and exhibited a dose-dependent response (p-trend < 0.0001). Among all of the A. baumannii isolates, 75.6% were phage typeable. The results of phage typing might also reveal the antibiotic-resistant profiles of clinical A. baumannii strains. In conclusion, phage susceptibility represents an evolutionary trade-off in A. baumannii strains that show adaptations for antibiotic resistance, particularly in medical environments that have high antibiotic use.

Detection of antibiotic resistant Acinetobacter baumannii in various hospital environments: potential sources for transmission of Acinetobacter infections

BackgroundAntibiotic resistant Acinetobacter baumannii has emerged as one of the most problematic hospital acquired pathogens around the world. This study was designed to investigate the presence of antibiotic resistant A. baumannii in various hospital environments.MethodsAir, water and inanimate surface samples were taken in different wards of four hospitals and analyzed for the presence of A. baumannii. Confirmed A. baumannii isolates were analyzed for antimicrobial susceptibility and also screened for the presence of three most common OXA- type carbapenemase-encoding genes.ResultsA. baumannii was detected in 11% (7/64) of air samples with the highest recovery in intensive care units (ICUs). A. baumannii was also detected in 17% (7/42) and 2% (1/42) of surface and water samples, respectively. A total of 40 A. baumannii isolates were recovered and analysis of antimicrobial susceptibility showed the highest resistance towards ceftazidime (92.5%, 37/40). 85% (34/40) and 80% (32/40) of the isolates were also resistant to imipenem and gentamicin, respectively. Resistance genes analysis showed that 77.5% (31/40) strains contained OXA-23 and 5% (2/40) strains contained OXA-24, but OXA-58 was not detected in any of the strains.ConclusionDetection of antibiotic resistant A. baumannii in various samples revealed that hospital environments could act as a potential source for transmission of A. baumannii infections especially in ICUs. These results emphasize the importance of early detection and implementation of control measures to prevent the spread of A. baumannii in hospital environments.

RCH51, a multiply antibiotic-resistant Acinetobacter baumannii ST103IP isolate, carries resistance genes in three plasmids, including a novel potentially conjugative plasmid carrying oxa235 in transposon Tn6252.

To determine the identity and context of genes conferring antibiotic resistance in a sporadic multiply antibiotic-resistant Acinetobacter baumannii recovered at Royal Children's Hospital, Brisbane. The antibiotic resistance phenotype for 23 antibiotics was determined using disc diffusion or MIC determination. The whole-genome sequence of RCH51 was determined using the Illumina HiSeq platform. Antibiotic resistance determinants were identified using ResFinder. Plasmids were recovered by transformation. Isolate RCH51 belongs to the uncommon STs ST103 IP (7-3-2-1-7-1-4) and ST514 OX (1-52-29-28-18-114-7). It was found to be resistant to sulfamethoxazole, tetracycline, gentamicin, tobramycin and kanamycin and also exhibited reduced susceptibility to imipenem (MIC 2 mg/L) and meropenem (MIC 6 mg/L). RCH51 carries the oxa235 , sul2 , floR , aadB and tet39 resistance genes, all located on plasmids. The largest of the three plasmids, pRCH51-3, is 52 789 bp and carries oxa235 in the ISAba1-bounded transposon Tn 6252 , as well as sul2 and floR . pRCH51-3 represents a new A. baumannii plasmid family that is potentially conjugative as it contains several genes predicted to encode transfer functions. However, conjugation of pRCH51-3 was not detected. The aadB and tet39 resistance genes were each found in small plasmids identical to the known plasmids pRAY*-v1 and pRCH52-1, respectively. The resistance gene complement of RCH51 was found in three plasmids. pRCH51-3, which carries the oxa235 , sul2 and floR resistance genes, represents a new, potentially conjugative A. baumannii plasmid type.

The KL24 gene cluster and a genomic island encoding a Wzy polymerase contribute genes needed for synthesis of the K24 capsular polysaccharide by the multiply antibiotic resistant Acinetobacter baumannii isolate RCH51.

The whole-genome sequence of the multiply antibiotic resistant Acinetobacter baumannii isolate RCH51 belonging to sequence type ST103 (Institut Pasteur scheme) revealed that the set of genes at the capsule locus, KL24, includes four genes predicted to direct the synthesis of 3-acetamido-3,6-dideoxy-d-galactose (d-Fuc3NAc), and this sugar was found in the capsular polysaccharide (CPS). One of these genes, fdtE, encodes a novel bifunctional protein with an N-terminal FdtA 3,4-ketoisomerase domain and a C-terminal acetyltransferase domain. KL24 lacks a gene encoding a Wzy polymerase to link the oligosaccharide K units to form the CPS found associated with isolate RCH51, and a wzy gene was found in a small genomic island (GI) near the cpn60 gene. This GI is in precisely the same location as another GI carrying wzy and atr genes recently found in several A. baumannii isolates, but it does not otherwise resemble it. The CPS isolated from RCH51, studied by sugar analysis and 1D and 2D 1H and 13C NMR spectroscopy, revealed that the K unit has a branched pentasaccharide structure made up of Gal, GalNAc and GlcNAc residues with d-Fuc3NAc as a side branch, and the K units are linked via a β-d-GlcpNAc-(1→3)-β-d-Galp linkage formed by the Wzy encoded by the GI. The functions of the glycosyltransferases encoded by KL24 were assigned to formation of specific bonds. A correspondence between the order of the genes in KL24 and other KL and the order of the linkages they form was noted, and this may be useful in future predictions of glycosyltransferase specificities.

Genomic sequencing of a strain of Acinetobacter baumannii and potential mechanisms to antibiotics resistance

Acinetobacter baumannii has been becoming a great challenge to clinicians due to their resistance to almost all available antibiotics. In this study, we sequenced the genome from a multiple antibiotics resistant Acinetobacter baumannii stain which was named A. baumannii-1isolated from China by SMRT sequencing technology to explore its potential mechanisms to antibiotic resistance. We found that several mechanisms might contribute to the antibiotic resistance of Acinetobacter baumannii. Specifically, we found that SNP in genes associated with nucleotide excision repair and ABC transporter might contribute to its resistance to multiple antibiotics; we also found that specific genes associated with bacterial DNA integration and recombination, DNA-mediated transposition and response to antibiotics might contribute to its resistance to multiple antibiotics; Furthermore, specific genes associated with penicillin and cephalosporin biosynthetic pathway and specific genes associated with CHDL and MBL β-lactamase genes might contribute to its resistance to multiple antibiotics. Thus, the detailed mechanisms by which Acinetobacter baumannii show extensive resistance to multiple antibiotics are very complicated. Such a study might be helpful to develop new strategies to control Acinetobacter baumannii infection.

Genetic Regulation of Virulence and Antibiotic Resistance in Acinetobacter baumannii

Multidrug resistant microorganisms are forecast to become the single biggest challenge to medical care in the 21st century. Over the last decades, members of the genus Acinetobacter have emerged as bacterial opportunistic pathogens, in particular as challenging nosocomial pathogens because of the rapid evolution of antimicrobial resistances. Although we lack fundamental biological insight into virulence mechanisms, an increasing number of researchers are working to identify virulence factors and to study antibiotic resistance. Here, we review current knowledge regarding the regulation of virulence genes and antibiotic resistance in Acinetobacter baumannii. A survey of the two-component systems AdeRS, BaeSR, GacSA and PmrAB explains how each contributes to antibiotic resistance and virulence gene expression, while BfmRS regulates cell envelope structures important for pathogen persistence. A. baumannii uses the transcription factors Fur and Zur to sense iron or zinc depletion and upregulate genes for metal scavenging as a critical survival tool in an animal host. Quorum sensing, nucleoid-associated proteins, and non-classical transcription factors such as AtfA and small regulatory RNAs are discussed in the context of virulence and antibiotic resistance.