Acinetobacter baumannii Resistance: A Real Challenge for Clinicians

The Dissemination of NDM-1 in Acinetobacter baumannii Strains

Acinetobacter baumannii is a common pathogen in hospitals and usually causes bacteremia, pneumonia, meningitis, peritonitis and other diseases. Isolates carried NDM-1 gene can make several antibiotics such as carbapenems and other beta-lactams ineffective. Nowadays, the number of A. baumannii strains carrying NDM-1 has been climbing year by year in recent years. To characterise the transmission of NDM-1 in A. baumannii, we collected 2576 human-derived genomes of A. baumannii strains from NCBI database and found that 186 strains contained NDM-1 gene. The multi-locus sequence typing, phylogenetic tree, NDM-1 gene organization and the single nucleotide polymorphisms of NDM-1 were investigated. We hope that our work will provide a theoretical basis for the prevention of dissemination of NDM-1 in A. baumannii.

The antimicrobial cyclic peptide B2 combats multidrug resistant Acinetobacter baumannii infection

In silico methods were employed for the development of antimicrobial peptides against MDR A. baumannii by binding to BamA.

Molecular epidemiology of carbapenem-resistant Acinetobacter baumannii isolated from three major hospitals in Jordan

BACKGROUND

In the last decade, incidences of carbapenem-resistant Acinetobacter baumannii have been increasingly reported worldwide. Consequently, A. baumannii was included in the World Health Organization's new list of critical pathogens, for which new drugs are desperately needed. The objective of this research was to study the molecular epidemiology and antimicrobial susceptibility of clinical carbapenem-resistant A. baumannii isolated from Jordanian hospitals.

METHODS

A total of 78 A. baumannii and 8 Acinetobacter spp. isolates were collected from three major hospitals in Jordan during 2018. Disc diffusion and microdilution methods were used to test their susceptibility against 19 antimicrobial agents. Multilocus sequence typing (MLST) was performed using the Pasteur scheme, followed by eBURST analysis for all isolates. PCR was used to detect β-lactam resistance genes, bla_OXA-23-like , bla_OXA-51-like , and bla_NDM-1 .

RESULTS

Of the 86 tested isolates, 78 (90.6%) exhibited resistance to carbapenems, whereas no resistance was recorded to tigecycline or polymyxins. Based on the resistance profiles, 10.4% and 84.8% of isolates were classified into multidrug resistant (MDR) or extensively drug resistant (XDR), respectively. The most prevalent carbapenems resistance genes amongst isolates were bla_OXA-51-Like (89.5%), followed by bla_OXA-23-Like (88.3%) and bla_NDM-1 (10.4%). MLST revealed the presence of 19 sequence types (STs), belonging to eight different international complexes. The most commonly detected clonal complex (CC) was CC2, representing 64% of all typed isolates.

CONCLUSIONS

This is the first study to report the clonal diversity of A. baumannii isolates in Jordan. A high incidence of carbapenem resistance was detected in the isolates investigated. In addition, our findings provided evidence for the widespread of bla_OXA-23-like harbouring carbapenem-resistant A. baumannii and belonging to CC2. The number of XDR isolates identified in this study is alarming. Thus, periodic surveillance and molecular epidemiological studies of resistance factors are important to improve treatment outcomes and prevent the spread of A. baumannii infections.

Structural and functional analysis of the promiscuous AcrB and AdeB efflux pumps suggests different drug binding mechanisms

Upon antibiotic stress Gram-negative pathogens deploy resistance-nodulation-cell division-type tripartite efflux pumps. These include a H⁺/drug antiporter module that recognizes structurally diverse substances, including antibiotics. Here, we show the 3.5 Å structure of subunit AdeB from the Acinetobacter baumannii AdeABC efflux pump solved by single-particle cryo-electron microscopy. The AdeB trimer adopts mainly a resting state with all protomers in a conformation devoid of transport channels or antibiotic binding sites. However, 10% of the protomers adopt a state where three transport channels lead to the closed substrate (deep) binding pocket. A comparison between drug binding of AdeB and Escherichia coli AcrB is made via activity analysis of 20 AdeB variants, selected on basis of side chain interactions with antibiotics observed in the AcrB periplasmic domain X-ray co-structures with fusidic acid (2.3 Å), doxycycline (2.1 Å) and levofloxacin (2.7 Å). AdeABC, compared to AcrAB-TolC, confers higher resistance to E. coli towards polyaromatic compounds and lower resistance towards antibiotic compounds.

Antimicrobial, Immunomodulatory and Anti-Inflammatory Potential of Liposomal Thymoquinone: Implications in the Treatment of Bacterial Pneumonia in Immunocompromised Mice

Acinetobacter baumannii has recently been increasing as an aggressive pathogen in immunocompromised persons. In the present study, we determined the in vitro antibacterial and anti-biofilm activity of thymoquinone (TQ) against A. baumannii. A liposomal formulation of TQ (Lip-TQ) was prepared and its therapeutic potential was investigated in the treatment of A. baumannii infection in immunocompromised mice. Leukopenia was induced in mice by injecting cyclophosphamide (CYP) at a dose of 200 mg/kg and the leukopenic mice were infected with 1 × 10⁶ CFUs of A. baumannii. The effectiveness of free TQ or Lip-TQ against A. baumannii infection was assessed by analyzing the survival rate and bacterial burden. Moreover, the efficacy of Lip-TQ was also studied by examining the systemic inflammatory markers and the histological changes in the lung tissues. The results showed that the mice in the group treated with Lip-TQ at a dose of 10 mg/kg exhibited a 60% survival rate on day 40 post-infection, whereas all the mice treated with free TQ at the same dose died within this duration. Likewise, the lowest bacterial burden was found in the lung tissue of mice treated with Lip-TQ (10 mg/kg). Besides, Lip-TQ treatment remarkably alleviated the infection-associated inflammation, oxidative stress, and histological changes in the lung tissues. Based on the findings of the present study, we recommend considering Lip-TQ as a valuable therapeutic formulation in the treatment of A. baumannii-associated pneumonia in immunocompromised subjects.

Severe Pneumonia Caused by Infection With Tropheryma whipplei Complicated With Acinetobacter baumannii Infection: A Case Report Involving a Young Woman

Whipple's disease is a very rare systemic infectious disease, and very few cases have been reported. However, it can be fatal if not diagnosed and treated appropriately. The major clinical manifestations of this disease are usually digestive and nervous system symptoms. The majority of patients are male and between 40 and 50 years old. Although respiratory symptoms of this disease have rarely been reported, they pose a serious threat to the lives of the patients, especially when they progress to severe pneumonia. During admission to the hospital, Acinetobacter baumannii infection makes treatment more difficult. While most patients are middle-aged men, more attention should be given to the diagnosis and treatment of affected young women. To our knowledge, the case presented in the study is the first case of Tropheryma whipplei infection that resulted in severe pneumonia and was complicated by A. baumannii infection during treatment. We hope that our study can serve as a reference for the diagnosis and treatment of related cases in the future.

Comparative study of phenotypic-based detection assays for carbapenemase-producing Acinetobacter baumannii with a proposed algorithm in resource-limited settings

The increasing incidence of carbapenem resistance in Acinetobacter baumannii is a critical concern worldwide owing to the limitations of therapeutic alternatives. The most important carbapenem resistance mechanism for A. baumannii is the enzymatic hydrolysis mediated by carbapenemases, mostly OXA-type carbapenemases (class D) and, to a lesser extent, metallo-β-lactamases (class B). Therefore, early and accurate detection of carbapenemase-producing A. baumannii is required to achieve the therapeutic efficacy of such infections. Many methods for carbapenemase detection have been proposed as effective tests for A. baumannii; however, none of them are officially recommended. In this study, three carbapenemase detection methods, namely, CarbaAcineto NP test, modified carbapenem inactivation method (mCIM), and simplified carbapenem inactivation method (sCIM) were evaluated for phenotypic detection of clinically isolated A. baumannii. The MICs of imipenem, meropenem, and doripenem were determined for 123 clinically isolated A. baumannii strains before performing three phenotypic detections. The overall sensitivity and specificity values were 89.09%/100% for the carbAcineto NP test, 71.82%/100% for sCIM, and 32.73%/33.13% for mCIM. CarbAcineto NP test and sCIM performed excellently (100% sensitivity) when both Class B and Class D carbapenemases were present in the same isolate. Based on the results, the combined detection method of sCIM and CarbAcineto NP test was proposed to detect carbapenemase-producing A. baumannii rather than a single assay, significantly increasing the sensitivity of detection to 98.18%. The proposed algorithm was more reliable and cost-effective than the CarbAcineto NP test alone. It can be easily applied in routine microbiology laboratories for developing countries with limited resources.

In vitro activity of the antimicrobial peptides h-Lf1-11, MSI-78, LL-37, fengycin 2B, and magainin-2 against clinically important bacteria

We investigated the antibacterial activity of the antimicrobial peptides h-Lf1-11, MSI-78, LL-37, fengycin 2B, and magainin-2. The minimum inhibitory concentration (MIC) was determined by microdilution technique according to CLSI (M07-A9, 2012) against Escherichia coli, methicillin-resistant Staphylococcus aureus, Pseudomonas aeruginosa, carbapenem-resistant Klebsiella pneumoniae, and Acinetobacter baumannii. The MSI-78 showed potent bactericidal activity with MIC range of 1.25-40 mg/L against all bacterial strains. The h-Lf1-11, magainin-2, and LL-37 exhibited moderate activity (MIC range of 40-160, 80-160, and 40-160 mg/L, respectively) while the fengycin 2B did not show significant activity against all bacterial strains tested. These results revealed that MSI-78, h-Lf1-11, magainin-2, and LL-37 have great potential as antibacterial agents and their activity deserves to be more explored in further studies for the treatment of antibiotic-resistant bacteria.

Prevalence of β-lactamase-encoding genes and molecular typing of Acinetobacter baumannii isolates carrying carbapenemase OXA-24 in children

Background

β-Lactam antibiotics have been broadly used for the treatment of Acinetobacter baumannii infections, resulting in development of β-lactam inactivating β-lactamases. Here, we described antibiotic resistance rate, prevalence of β-lactamase-encoding genes, and clonal relationships of A. baumannii strains isolated from children referred to Children’s Medical Center in Tehran, Iran, during 2019–2020.

Methods

A total of 60 non-replicate A. baumannii isolates were recovered from clinical specimens of pediatric patients. Antibiotic susceptibility testing was done by the disc diffusion method. Colistin susceptibility of isolates was performed by the broth microdilution method. β-lactamase-encoding genes were characterized by PCR. The presence of ISAba1 element upstream of the several oxacillinase genes was also checked. Genetic relatedness of isolates was determined by using random amplification of polymorphic DNA (RAPD) typing.

Results

The antimicrobial susceptibility tests showed that 83.3% of A. baumannii isolates were MDR, and 40% XDR. Both MDR and XDR A. baumannii isolates were susceptible to colistin. The frequency of bla_OXA-51-like, bla_OXA-23-like, bla_TEM, bla_OXA-24-like, bla_PER, bla_SHV, bla_CTX-M, bla_OXA-58-like, and bla_IMP was 100, 93.33, 60, 36.67, 28.33, 8.33, 5, 3.33, and 1.67%, respectively. Coexistence of ISAba1/bla_OXA-23-like and ISAba1/bla_OXA-51-like was observed in 65% and 85% of isolates, respectively. RAPD analysis revealed 4 common types and 2 single types of A. baumannii isolates.

Conclusions

The multiple clones harboring bla_OXA-23-like, ISAba1-bla_OXA-51-like, and ISAba1-bla_OXA-23-like were responsible for the spread of A. baumannii isolates in our clinical wards. Dissemination of the well-established clones is worrisome and would become therapeutic challenges due to the possible transferring genetic elements associated with resistance.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12941-021-00480-5.

Bacterial Antibiotic Resistance: The Most Critical Pathogens

Antibiotics have made it possible to treat bacterial infections such as meningitis and bacteraemia that, prior to their introduction, were untreatable and consequently fatal. Unfortunately, in recent decades overuse and misuse of antibiotics as well as social and economic factors have accelerated the spread of antibiotic-resistant bacteria, making drug treatment ineffective. Currently, at least 700,000 people worldwide die each year due to antimicrobial resistance (AMR). Without new and better treatments, the World Health Organization (WHO) predicts that this number could rise to 10 million by 2050, highlighting a health concern not of secondary importance. In February 2017, in light of increasing antibiotic resistance, the WHO published a list of pathogens that includes the pathogens designated by the acronym ESKAPE (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter species) to which were given the highest "priority status" since they represent the great threat to humans. Understanding the resistance mechanisms of these bacteria is a key step in the development of new antimicrobial drugs to tackle drug-resistant bacteria. In this review, both the mode of action and the mechanisms of resistance of commonly used antimicrobials will be examined. It also discusses the current state of AMR in the most critical resistant bacteria as determined by the WHO's global priority pathogens list.

Bacterial Antibiotic Resistance: The Most Critical Pathogens

Antibiotics have made it possible to treat bacterial infections such as meningitis and bacteraemia that, prior to their introduction, were untreatable and consequently fatal. Unfortunately, in recent decades overuse and misuse of antibiotics as well as social and economic factors have accelerated the spread of antibiotic-resistant bacteria, making drug treatment ineffective. Currently, at least 700,000 people worldwide die each year due to antimicrobial resistance (AMR). Without new and better treatments, the World Health Organization (WHO) predicts that this number could rise to 10 million by 2050, highlighting a health concern not of secondary importance. In February 2017, in light of increasing antibiotic resistance, the WHO published a list of pathogens that includes the pathogens designated by the acronym ESKAPE (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter species) to which were given the highest "priority status" since they represent the great threat to humans. Understanding the resistance mechanisms of these bacteria is a key step in the development of new antimicrobial drugs to tackle drug-resistant bacteria. In this review, both the mode of action and the mechanisms of resistance of commonly used antimicrobials will be examined. It also discusses the current state of AMR in the most critical resistant bacteria as determined by the WHO's global priority pathogens list.

Identification of a novel plasmid-mediated tigecycline resistance-related gene, tet(Y), in Acinetobacter baumannii

OBJECTIVES

To characterize a novel plasmid-mediated tigecycline resistance-related gene, tet(Y), in a clinical Acinetobacter baumannii isolate from China.

METHODS

The tet(Y)-encoded tigecycline-resistant A. baumannii 2016GDAB1 was screened through antimicrobial susceptibility testing and WGS. The function of tet(Y) was verified by complementation of tet(Y). The plasmid transferability and stability were detected via plasmid conjugation and in vitro bacterial passaging. The 3D structure of Tet(Y) was predicted and docked using tFold and AutoDock Vina.

RESULTS

The tigecycline-resistant A. baumannii 2016GDAB1 was isolated from bronchoalveolar lavage fluid of a patient with hospital-acquired pneumonia. However, this strain did not harbour any common tigecycline resistance genes, determinants or mutations. 2016GDAB1 belongs to the non-epidemic clone ST355 (Oxford scheme), which has been mainly reported in animals. The tet(Y) gene was located on a 72 156 bp plasmid and genomic environment analysis revealed that Tn5393 may play a role in tet(Y) transmission, whereas phylogenetic analysis indicated the origin of tet(Y) as from Aeromonas. Overexpression of tet(Y) resulted in a 2- to 4-fold increase in tigecycline MIC. Introduction of the tet(Y)-harbouring plasmid p2016GDAB1 via electroporation resulted in a 16-fold increase in tigecycline MIC but failed to transfer into the tigecycline-susceptible A. baumannii recipient via conjugation. Isolates carrying the tet(Y) gene were vulnerable to tigecycline pressure and exhibited decreased susceptibility to tigecycline. A tet(Y)-carrying plasmid was stably maintained in the host strains.

CONCLUSIONS

This study identified the tigecycline resistance-related gene tet(Y) in A. baumannii. This gene conferred an increased tigecycline MIC and the transposable element Tn5393 may play a role in its transmission across isolates.

Whole-Genome Sequencing Elucidates the Epidemiology of Multidrug-Resistant Acinetobacter baumannii in an Intensive Care Unit

The nosocomial pathogen Acinetobacter baumannii is a frequent cause of healthcare-acquired infections, particularly in critically ill patients, and is of serious concern due to its potential for acquired multidrug resistance. Whole-genome sequencing (WGS) is increasingly used to obtain a high-resolution view of relationships between isolates, which helps in controlling healthcare-acquired infections. Here, we conducted a retrospective study to identify epidemic situations and assess the percentage of transmission in intensive care units (ICUs). Multidrug-resistant A. baumannii (MDR-AB) were continuously isolated from the lower respiratory tract of different patients (at the first isolation in our ICU). We performed WGS, pulsed-field gel electrophoresis (PFGE), and multilocus-sequence typing (MLST) analyses to elucidate bacterial relatedness and to compare the performance of conventional methods with WGS for typing MDR-AB. From June 2017 to August 2018, A. baumannii complex strains were detected in 124 of 796 patients during their ICU stays, 103 of which were MDR-AB. Then we subjected 70 available MDR-AB strains to typing with WGS, PFGE, and MLST. Among the 70 A. baumannii isolates, 38 (54.29%) were isolated at admission, and 32(45.71%) were acquisition isolates. MLST identified 12 unique sequence types, a novel ST (ST2367) was founded. PFGE revealed 16 different pulsotypes. Finally, 38 genotypes and 23 transmissions were identified by WGS. Transmission was the main mode of MDR-AB acquisition in our ICU. Our results demonstrated that WGS was a discriminatory technique for epidemiological healthcare-infection studies. The technique should greatly benefit the identification of epidemic situations and controlling transmission events in the near future.

Strategies for Rapid Identification of Acinetobacter baumannii Membrane Proteins and Polymyxin B's Effects

Acinetobacter baumannii, especially multidrug resistant Acinetobacter baumannii, is a notable source of pressure in the areas of public health and antibiotic development. To overcome this problem, attention has been focused on membrane proteins. Different digestion methods and extraction detergents were examined for membrane proteome sample preparation, and label-free quantitative and targeted proteome analyses of the polymyxin B-induced Acinetobacter baumannii ATCC 19606 membrane proteome were performed based on nano LC-MS/MS. Ultracentrifugation of proteins at a speed of 150,000×g, digestion by trypsin, filter-aided sample preparation, and detergents such as lauryldimethylamine-N-oxide were proved as a fast and effective way for identification of membrane proteome by nano LC-MS/MS. Upon treatment with polymyxin B, expression levels of 15 proteins related to membrane structure, transporters, cell surface, and periplasmic space were found to be significantly changed. Furthermore, targeted proteome was also used to confirm these changes. A relatively rapid membrane proteome preparation method was developed, and a more comprehensive view of changes in the Acinetobacter baumannii membrane proteome under polymyxin B pressure was obtained.

Mechanism Underlying the Role of LuxR Family Transcriptional Regulator abaR in Biofilm Formation by Acinetobacter baumannii

Our study attempted to explore the mechanism underlying the role of LuxR family transcriptional regulator abaR in biofilm formation by Acinetobacter baumannii. The abaR gene was knocked out in ATCC 17978 strain using homologous recombination method. The growth curve and biofilm formation were measured in the wild type and abaR gene knockdown strains. Transcriptome sequencing was performed in the wild type and abaR gene knockdown strains following 8 h of culture. The growth curve in the abaR gene knockdown strain was similar to that of the wild-type strain. Biofilm formation significantly declined in the abaR gene knockdown strain at 8 and 48 h after culture. A total of 137 differentially expressed genes (DEGs) were obtained including 20 downregulated DEGs and 117 upregulated DEGs. Genes with differential expression were closely related to viral procapsid maturation (GO:0046797), acetoin catabolism (GO:0045150), carbon metabolism (ko01200), and the glycolysis/gluconeogenesis (ko00010)-related pathways. The results of the eight verified expression DEGs were consistent with the results predicted by bioinformatics. AbaR gene knockdown significantly affected biofilm formation by A. baumannii ATCC 17978 strain. The glycolysis/gluconeogenesis pathways were significantly dysregulated and induced by abaR gene knockdown in A. baumannii.

Antibiogram Profile of Acinetobacterbaumannii Recovered from Selected Freshwater Resources in the Eastern Cape Province, South Africa

Acinetobacter species have been found in a variety of environments, including soil, food, plants, hospital environments and water. Acinetobacter baumannii is an opportunistic and emerging waterborne pathogen. It has been implicated in several nosocomial infections that demonstrate resistance to commonly administered antibiotics. We investigated phenotypic antibiotic resistance (PAR) and relevant antibiotic resistance genes (ARGs) in A. baumannii isolated from three freshwater resources in the Eastern Cape Province, South Africa; A. baumannii (410) was confirmed by the recA and gyrB genes of 844 suspected Acinetobacter species in the water samples. The PAR of the confirmed isolates was assessed using a panel of 11 antibiotics by the disc diffusion method, while ARGs were investigated in isolates exhibiting PAR. The A. baumannii isolates were resistant to piperacillin-tazobactam (11.2%), ceftazidime (12%), cefotaxime (18.8%), cefepime (8.8%), imipenem (2.7%), meropenem (4.15%), amikacin (2.4%), gentamicin (8.8%), tetracycline (16.8%), ciprofloxacin (11%) and trimethoprim/sulfamethoxazole (20.5%). For multidrug resistance (MDR), two isolates were resistant to all antibiotics and 28 isolates were resistant to imipenem and meropenem. Moreover, β-lactamases bla_TEM (64.4%) and bla_OXA-51 (28.70%) as well as sulphonamides sul1 (37.1%) and sul2 (49.4%) were common ARGs. Overall, PAR and ARGs had positive correlations (r) in all rivers. Detection of MDR-A. baumannii in freshwater resources could be linked to possible wastewater discharge from the nearby animal farms, indicating potential implications for public health.

Homeoviscous Adaptation of the Acinetobacter baumannii Outer Membrane: Alteration of Lipooligosaccharide Structure during Cold Stress

To maintain optimal membrane dynamics, cells from all domains of life must acclimate to various environmental signals in a process referred to as homeoviscous adaptation. Alteration of the lipid composition is critical for maintaining membrane fluidity, permeability of the lipid bilayer, and protein function under diverse conditions. It is well documented, for example, that glycerophospholipid content varies substantially in both Gram-negative and Gram-positive bacteria with changes in growth temperature. However, in the case of Gram-negative bacteria, far less is known concerning structural changes in lipopolysaccharide (LPS) or lipooligosaccharide (LOS) during temperature shifts. LPS/LOS is anchored at the cell surface by the highly conserved lipid A domain and localized in the outer leaflet of the outer membrane. Here, we identified a novel acyltransferase, termed LpxS, involved in the synthesis of the lipid A domain of Acinetobacter baumannii. A. baumannii is a significant, multidrug-resistant, opportunistic pathogen that is particularly difficult to clear from health care settings because of its ability to survive under diverse conditions. LpxS transfers an octanoate (C8:0) fatty acid, the shortest known secondary acyl chain reported to date, replacing a C12:0 fatty acid at the 2' position of lipid A. Expression of LpxS was highly upregulated under cold conditions and likely increases membrane fluidity. Furthermore, incorporation of a C8:0 acyl chain under cold conditions increased the effectiveness of the outer membrane permeability barrier. LpxS orthologs are found in several Acinetobacter species and may represent a common mechanism for adaptation to cold temperatures in these organisms. IMPORTANCE To maintain cellular fitness, the composition of biological membranes must change in response to shifts in temperature or other stresses. This process, known as homeoviscous adaptation, allows for maintenance of optimal fluidity and membrane permeability. Here, we describe an enzyme that alters the fatty acid content of A. baumannii LOS, a major structural feature and key component of the bacterial outer membrane. Although much is known regarding how glycerophospholipids are altered during temperature shifts, our understanding of LOS or LPS alterations under these conditions is lacking. Our work identifies a cold adaptation mechanism in A. baumannii, a highly adaptable and multidrug-resistant pathogen.

Diversity of International High-Risk Clones of Acinetobacter baumannii Revealed in a Russian Multidisciplinary Medical Center during 2017-2019

Acinetobacter baumannii is a dangerous bacterial pathogen possessing the ability to persist on various surfaces, especially in clinical settings, and to rapidly acquire the resistance to a broad spectrum of antibiotics. Thus, the epidemiological surveillance of A. baumannii within a particular hospital, region, and across the world is an important healthcare task that currently usually includes performing whole-genome sequencing (WGS) of representative isolates. During the past years, the dissemination of A. baumannii across the world was mainly driven by the strains belonging to two major groups called the global clones or international clones (ICs) of high risk (IC1 and IC2). However, currently nine ICs are already considered. Although some clones were previously thought to spread in particular regions of the world, in recent years this is usually not the case. In this study, we determined five ICs, as well as three isolates not belonging to the major ICs, in one multidisciplinary medical center within the period 2017-2019. We performed WGS using both short- and long-read sequencing technologies of nine representative clinical A. baumannii isolates, which allowed us to determine the antibiotic resistance and virulence genomic determinants, reveal the CRISPR/Cas systems, and obtain the plasmid structures. The phenotypic and genotypic antibiotic resistance profiles are compared, and the possible ways of isolate and resistance spreading are discussed. We believe that the data obtained will provide a better understanding of the spreading and resistance acquisition of the ICs of A. baumannii and further stress the necessity for continuous genomic epidemiology surveillance of this problem-causing bacterial species.

Efflux Pump Overexpression Profiling in Acinetobacter baumannii and Study of New 1-(1-Naphthylmethyl)-Piperazine Analogs as Potential Efflux Inhibitors

Overexpression of efflux pumps extruding antibiotics currently used for the treatment of Acinetobacter baumannii infections has been described as an important mechanism causing antibiotic resistance. The first aim of this work was to phenotypically evaluate the overexpression of efflux pumps on a collection of 124 ciprofloxacin-resistant A. baumannii strains. An overexpression of genes encoding one or more efflux pumps was obtained for 19 out of the 34 strains with a positive phenotypic efflux (56%). The most frequent genes overexpressed were those belonging to the RND family, with adeJ being the most prevalent (50%). Interestingly, efflux pump genes coding for MATE and MFS families were also overexpressed quite frequently: abeM (32%) and abaQ (26%). The second aim was to synthesize 1-(1-naphthylmethyl)-piperazine analogs as potential new efflux pump inhibitors and biologically evaluate them against strains with a positive phenotypic efflux. Quinoline and pyridine analogs were found to be more effective than their parent compound, 1-(1-naphthyl methyl)-piperazine. Stereochemistry also played an important part in the inhibitory activity, as quinoline derivative (R)-3a was identified as being the most effective and less cytotoxic. Its inhibitory activity was also correlated with the number of efflux pumps expressed by a strain. The results obtained in this work suggest that quinoline analogs of 1-(1-naphthylmethyl)-piperazine are promising leads in the development of new anti-Acinetobacter baumannii therapeutic alternatives in combination with antibiotics for which an efflux-mediated resistance is suspected.

Management of bacterial and fungal infections in cirrhosis: The MDRO challenge

Bacterial infections are frequent in cirrhotic patients with acute decompensation or acute-on-chronic liver failure and can complicate the clinical course. Delayed diagnosis and inappropriate empirical treatments are associated with poor prognosis and increased mortality. Fungal infections are much less frequent, usually nosocomial and associated with extremely high short-term mortality. Early diagnosis and adequate empirical treatment of infections is therefore key in the management of these patients. In recent decades, antibiotic resistance has become a major worldwide problem in patients with cirrhosis, warranting a more complex approach to antibiotic treatment that includes the use of broad-spectrum antibiotics, new administration strategies, novel drugs and de-escalation policies. Herein, we review epidemiological changes, the main types of multidrug-resistant organisms, mechanisms of resistance, new rapid diagnostic tools and currently available therapeutic options for bacterial and fungal infections in cirrhosis.

Antibiotic-Resistant Acinetobacter baumannii in Low-Income Countries (2000-2020): Twenty-One Years and Still below the Radar, Is It Not There or Can They Not Afford to Look for It?

Acinetobacter baumannii is an emerging pathogen, and over the last three decades it has proven to be particularly difficult to treat by healthcare services. It is now regarded as a formidable infectious agent with a genetic setup for prompt development of resistance to most of the available antimicrobial agents. Yet, it is noticed that there is a gap in the literature covering this pathogen especially in countries with limited resources. In this review, we provide a comprehensive updated overview of the available data about A. baumannii, the multi-drug resistant (MDR) phenotype spread, carbapenem-resistance, and the associated genetic resistance determinants in low-income countries (LIICs) since the beginning of the 21st century. The coverage included three major databases; PubMed, Scopus, and Web of Science. Only 52 studies were found to be relevant covering only 18 out of the 29 countries included in the LIC group. Studies about two countries, Syria and Ethiopia, contributed ~40% of the studies. Overall, the survey revealed a wide spread of MDR and alarming carbapenem-resistance profiles. Yet, the total number of studies is still very low compared to those reported about countries with larger economies. Accordingly, a discussion about possible reasons and recommendations to address the issue is presented. In conclusion, our analyses indicated that the reported studies of A. baumannii in the LICs is far below the expected numbers based on the prevailing circumstances in these countries. Lack of proper surveillance systems due to inadequate financial resources could be a major contributor to these findings.

Novel Acinetobacter baumannii Myovirus TaPaz Encoding Two Tailspike Depolymerases: Characterization and Host-Recognition Strategy

Acinetobacter baumannii, one of the most significant nosocomial pathogens, is capable of producing structurally diverse capsular polysaccharides (CPSs) which are the primary receptors for A. baumannii bacteriophages encoding polysaccharide-degrading enzymes. To date, bacterial viruses specifically infecting A. baumannii strains belonging to more than ten various capsular types (K types) were isolated and characterized. In the present study, we investigate the biological properties, genomic organization, and virus-bacterial host interaction strategy of novel myovirus TaPaz isolated on the bacterial lawn of A. baumannii strain with a K47 capsular polysaccharide structure. The phage linear double-stranded DNA genome of 93,703 bp contains 178 open reading frames. Genes encoding two different tailspike depolymerases (TSDs) were identified in the phage genome. Recombinant TSDs were purified and tested against the collection of A. baumannii strains belonging to 56 different K types. One of the TSDs was demonstrated to be a specific glycosidase that cleaves the K47 CPS by the hydrolytic mechanism.

Antimicrobial and Anti-Biofilm Peptide Octominin for Controlling Multidrug-Resistant Acinetobacter baumannii

Acinetobacter baumannii is a serious nosocomial pathogen with multiple drug resistance (MDR), the control of which has become challenging due to the currently used antibiotics. Our main objective in this study is to determine the antibacterial and antibiofilm activities of the antimicrobial peptide, Octominin, against MDR A. baumannii and derive its possible modes of actions. Octominin showed significant bactericidal effects at a low minimum inhibitory concentration (MIC) and the minimum bactericidal concentration (MBC) of 5 and 10 µg/mL, respectively. Time-kill kinetic analysis and bacterial viability tests revealed that Octominin showed a concentration-dependent antibacterial activity. Field-emission scanning electron microscopy (FE-SEM) analysis revealed that Octominin treatment altered the morphology and membrane structure of A. baumannii. Propidium iodide (PI) and reactive oxygen species (ROS) generation assays showed that Octominin increased the membrane permeability and ROS generation in A. baumannii, thereby causing bacterial cell death. Further, a lipopolysaccharides (LPS) binding assay showed an Octominin concentration-dependent LPS neutralization ability. Biofilm formation inhibition and eradication assays further revealed that Octominin inhibited biofilm formation and showed a high biofilm eradication activity against A. baumannii. Furthermore, up to a concentration of 100 µg/mL, Octominin caused no hemolysis and cell viability changes in mammalian cells. An in vivo study in zebrafish showed that the Octominin-treated group had a significantly higher relative percentage survival (54.1%) than the untreated group (16.6%). Additionally, a reduced bacterial load and fewer alterations in histological analysis confirmed the successful control of A. baumannii by Octominin in vivo. Collectively, these data suggest that Octominin exhibits significant antibacterial and antibiofilm activities against the multidrug-resistant A. baumannii, and this AMP can be developed further as a potent AMP for the control of antibiotic resistance.

Carbapenem resistance in Acinetobacter baumannii, and their importance in hospital-acquired infections: a scientific review

Carbapenem is an important therapy for serious hospital-acquired infections and for the care of patients affected by multidrug-resistant organisms, specifically Acinetobacter baumannii; however, with the global increase of carbapenem-resistant A. baumannii, this pathogen has significantly threatened public health. Thus, there is a pressing need to better understand this pathogen in order to develop novel treatments and control strategies for dealing with A. baumannii. In this review, we discuss an overview of carbapenem, including its discovery, development, classification and biological characteristics, and its importance in hospital medicine especially in critical care units. We also describe the peculiarity of bacterial pathogen, A. baumannii, including its commonly reported virulence factors, environmental persistence and carbapenem resistance mechanisms. In closing, we discuss various control strategies for overcoming carbapenem resistance in hospitals and for limiting outbreaks. With the appearance of strains that resist carbapenem, the aim of this review is to highlight the importance of understanding this increasingly problematic healthcare-associated pathogen that creates significant concern in the field of nosocomial infections and overall public health.

Mechanisms of Antibiotic Resistance in Important Gram-Positive and Gram-Negative Pathogens and Novel Antibiotic Solutions

Multidrug-resistant bacteria have on overwhelming impact on human health, as they cause over 670,000 infections and 33,000 deaths annually in the European Union alone. Of these, the vast majority of infections and deaths are caused by only a handful of species-multi-drug resistant Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, Enterococcus spp., Acinetobacter spp. and Klebsiella pneumoniae. These pathogens employ a multitude of antibiotic resistance mechanisms, such as the production of antibiotic deactivating enzymes, changes in antibiotic targets, or a reduction of intracellular antibiotic concentration, which render them insusceptible to multiple antibiotics. The purpose of this review is to summarize in a clinical manner the resistance mechanisms of each of these 6 pathogens, as well as the mechanisms of recently developed antibiotics designed to overcome them. Through a basic understanding of the mechanisms of antibiotic resistance, the clinician can better comprehend and predict resistance patterns even to antibiotics not reported on the antibiogram and can subsequently select the most appropriate antibiotic for the pathogen in question.

Acinetobacter baumannii Antibiotic Resistance Mechanisms

Acinetobacter baumannii is a Gram-negative ESKAPE microorganism that poses a threat to public health by causing severe and invasive (mostly nosocomial) infections linked with high mortality rates. During the last years, this pathogen displayed multidrug resistance (MDR), mainly due to extensive antibiotic abuse and poor stewardship. MDR isolates are associated with medical history of long hospitalization stays, presence of catheters, and mechanical ventilation, while immunocompromised and severely ill hosts predispose to invasive infections. Next-generation sequencing techniques have revolutionized diagnosis of severe A. baumannii infections, contributing to timely diagnosis and personalized therapeutic regimens according to the identification of the respective resistance genes. The aim of this review is to describe in detail all current knowledge on the genetic background of A. baumannii resistance mechanisms in humans as regards beta-lactams (penicillins, cephalosporins, carbapenems, monobactams, and beta-lactamase inhibitors), aminoglycosides, tetracyclines, fluoroquinolones, macrolides, lincosamides, streptogramin antibiotics, polymyxins, and others (amphenicols, oxazolidinones, rifamycins, fosfomycin, diaminopyrimidines, sulfonamides, glycopeptide, and lipopeptide antibiotics). Mechanisms of antimicrobial resistance refer mainly to regulation of antibiotic transportation through bacterial membranes, alteration of the antibiotic target site, and enzymatic modifications resulting in antibiotic neutralization. Virulence factors that may affect antibiotic susceptibility profiles and confer drug resistance are also being discussed. Reports from cases of A. baumannii coinfection with SARS-CoV-2 during the COVID-19 pandemic in terms of resistance profiles and MDR genes have been investigated.

A Multiepitope Peptide, rOmp22, Encapsulated in Chitosan-PLGA Nanoparticles as a Candidate Vaccine Against Acinetobacter baumannii Infection

Background

The development of vaccines is a promising and cost-effective strategy to prevent emerging multidrug-resistant (MDR) Acinetobacter baumannii (A. baumannii) infections. The purpose of this study was to prepare a multiepitope peptide nanovaccine and evaluate its immunogenicity and protective effect in BALB/c mice.

Methods

The B-cell and T-cell epitopes of Omp22 from A. baumannii were predicted using bioinformatics methods and identified by immunological experiments. The optimal epitopes were conjugated in series by 6-aminocaproic acid and chemically synthesized multiepitope polypeptide rOmp22. Then, rOmp22 was encapsulated by chitosan (CS) and poly (lactic-co-glycolic) acid (PLGA) to prepare CS-PLGA-rOmp22 nanoparticles (NPs). The immunogenicity and immunoprotective efficacy of the vaccine were evaluated in BALB/c mice.

Results

CS-PLGA-rOmp22 NPs were small (mean size of 272.83 nm) with apparently spherical structures, positively charged (4.39 mV) and nontoxic to A549 cells. A high encapsulation efficiency (54.94%) and a continuous slow release pattern were achieved. Compared with nonencapsulated rOmp22, CS-PLGA-rOmp22 immunized BALB/c mice induced higher levels of rOmp22-specific IgG in serum and IFN-γ in splenocyte supernatant. Additionally, lung injury and bacterial burdens in the lung and blood were suppressed, and potent protection (57.14%-83.3%) against acute lethal intratracheal A. baumannii challenge was observed in BALB/c mice vaccinated with CS-PLGA-rOmp22.

Conclusion

CS-PLGA-rOmp22 NPs elicited specific IgG antibodies, Th1 cellular immunity and protection against acute lethal intratracheal A. baumannii challenge. Our results indicate that this nanovaccine is a desirable candidate for preventing A. baumannii infection.

Impaired host response and the presence of Acinetobacter baumannii in the serum microbiome of type-II diabetic patients

Type II diabetes (T2D) affects over 10% of the US population and is a growing disease worldwide that manifests with numerous comorbidities and defects in inflammation. This dysbiotic host response allows for infection of the host by numerous microorganisms. In the course of T2D disease, individuals can develop chronic infections including foot ulcers and periodontitis, which lead to further complications and opportunistic infections in multiple body sites. In this study, we investigated the serum of healthy subjects and patients with T2D with (T2DP) or without periodontitis for both microbiome signatures in addition to cytokine profiles. Surprisingly, we detected the presence of Acinetobacter baumanii in the serum of 23% individuals with T2D/T2DP tested. In T2DP, IL-1β, TNF-α, MCP-1, IL-6, IL-8, and IFN-γ were significantly elevated in ABC-positive subjects. As an emerging pathogen, A. baumanii infection represents a risk for impaired inflammation and the development of comorbidities in subjects with T2D.

Successful Incidences of Controlling Multidrug-Resistant, Extensively Drug-Resistant, and Nosocomial Infection Acinetobacter baumannii Using Antibiotic Stewardship, Infection Control Programs, and Environmental Cleaning at a Chinese University Hospital

Objective

We estimated the efficacy of antimicrobial stewardship (AMS), infection control programs (ICP), and environmental cleaning (ENC) for controlling the resistance of Acinetobacter baumannii (AB) and controlling the incidence of multidrug-resistant AB (MDRAB), extensively drug-resistant AB (XDRAB), and nosocomial infection AB in the ICU (NIAB-ICU) at a university hospital.

Methods

The intervention included 4-year AMS+ICP and 3-year AMS+ICP+ENC between January 2012 and December 2019.

Results

A total of 2636 AB isolates were collected totally, and 64.98% of AB isolates were MDR and 29.97% were XDR. Preintervention and postintervention incidences of MDRAB, XDRAB, and NIAB-ICU by AMS+ICP measures ranged from 84.96% to 71.98%, 41.96% to 33.13%, and 45.6% to 38%, respectively. However, all of them were not statistically changed (P=0.085, 0.072, 0.061, separately). The preintervention and postintervention incidences of MDRAB, XDRAB, and NIAB-ICU by AMS+ICP+ENC measures ranged from 71.98% to 36.55%, 33.13% to 19.88%, and 38% to 22.5%, respectively. Statistically significant declines were observed (P=0.016, 0.041, 0.032, separately). The defined daily doses (DDD) per 1000 patient-days (PD) decreased from 45±3.3 to 30.81±1.5 per 1000 PD across from 2012 to 2019, and a statistical decline was seen (P=0.01). Concurrently, the alcohol-based hand gel (ABHG) consumption per 1000 PD increased from 0.6±0.05 L to 12.5±2.3 L per 1000 PD, and a statistical increase was observed (P=0.0001). A statistically positive correlation was revealed between the DDD and incidence of MDRAB, XDRAB, and NIAB-ICU (r=0.905 and p=0.002; r=0.939 and p=0.001; r=0.956 and p=0.0002; respectively). Simultaneously, a statistically negative correlation was showed between the ABHG and incidence of MDRAB, XDRAB, and NIAB-ICU (r=-0.858 and p=0.006; r=-0.888 and p=0.003; r=-0.882 and p=0.004, separately).

Conclusion

The AMS, ICP, and ENC may be one of the most effective and best measures to address the increasing incidence of MDRAB, XDRAB, and NIAB-ICU currently.