Detection of carbapenemase producing Acinetobacter baumannii ST19 from Georgia and Ukraine carrying bla OXA-23, bla OXA-72, and/or bla NDM-5, December 2019 to June 2023.

In 2003-2023, amid 5,436 Acinetobacter baumannii isolates collected globally through the Multidrug-Resistant Organism Repository and Surveillance Network, 97 were ST19PAS, 34 of which carbapenem-resistant. Strains (n = 32) sampled after 2019 harboured either bla OXA-23, bla OXA-72, and/or bla NDM-5. Phylogenetic analysis of the 97 isolates and 11 publicly available ST19 genomes revealed three sub-lineages of carbapenemase-producing isolates from mainly Ukraine and Georgia, including an epidemic clone carrying all three carbapenemase genes. Infection control and global surveillance of carbapenem-resistant A. baumannii remain important.

Phage-Bacterial Interaction Alters Phenotypes Associated with Virulence in Acinetobacter baumannii.

Bacteriophages exert strong selection on their bacterial hosts to evolve resistance. At the same time, the fitness costs on bacteria following phage resistance may change their virulence, which may affect the therapeutic outcomes of phage therapy. In this study, we set out to assess the costs of phage resistance on the in vitro virulence of priority 1 nosocomial pathogenic bacterium, Acinetobacter baumannii. By subjecting phage-resistant variant Ev5-WHG of A. baumannii WHG40004 to several in vitro virulence profiles, we found that its resistance to phage is associated with reduced fitness in host microenvironments. Also, the mutant exhibited impaired adhesion and invasion to mammalian cells, as well as increased susceptibility to macrophage phagocytosis. Furthermore, the whole-genome sequencing of the mutant revealed that there exist multiple mutations which may play a role in phage resistance and altered virulence. Altogether, this study demonstrates that resistance to phage can significantly alter phenotypes associated with virulence in Acinetobacter baumannii.

Enhancing the Antibacterial Impact of Lipopeptide Extracted from Bacillus licheniformis as a Probiotic against MDR Acinetobacter baumannii.

BACKGROUND: The antibiotic resistance of microorganisms is escalating rapidly. Infections caused by opportunistic pathogens in immunocompromised individuals have prompted researchers to seek for potent and safe antibacterial agents. The purpose of this investigation was to explore the suppression of virulence gene expression, specifically the pga operon genes responsible in biofilm formation in Acinetobacter baumannii, through the utilization of metabolites obtained from probiotic bacteria. METHODS: To assess the antimicrobial properties, standard strains of five probiotic bacteria were tested against a standard strain of multidrug-resistant (MDR) A. baumannii employing the agar gel diffusion technique. Following the identification of the most potent probiotic strain (Bacillus licheniformis), the existence of its LanA and LanM genes was confirmed using the polymerase chain reaction (PCR) test. High-performance liquid chromatography (HPLC) and fourier-transform infrared spectroscopy (FTIR) techniques were employed to identify the intended metabolite, which was found to be a lipopeptide nature. The minimum inhibitory concentration (MIC) values and anti-biofilm activity of the targeted metabolite were determined using a dilution method in 96-well microplates and field emission scanning electron microscopy (FE-SEM). Real-time PCR (qPCR) was utilized for comparing the expression of pga operon genes, including pgaABCD, in A. baumannii pre- and post-exposure to the derived lipopeptide. RESULTS: The MIC results indicated that the probiotic product inhibited the growth of A. baumannii at concentrations lower than those needed for conventional antibiotics. Furthermore, it was observed that the desired genes' expression decreased due to the effect of this substance. CONCLUSIONS: This research concludes that the B. licheniformis probiotic product could be a viable alternative for combating drug resistance in A. baumannii.

Structural and Dynamic Features of Acinetobacter baumannii OXA-66 ß-Lactamase Explain Its Stability and Evolution of Novel Variants.

OXA-66 is a member of the OXA-51 subfamily of class D ß-lactamases native to the Acinetobacter genus that includes Acinetobacter baumannii, one of the ESKAPE pathogens and a major cause of drug-resistant nosocomial infections. Although both wild type OXA-66 and OXA-51 have low catalytic activity, they are ubiquitous in the Acinetobacter genomes. OXA-51 is also remarkably thermostable. In addition, newly emerging, single and double amino acid variants show increased activity against carbapenems, indicating that the OXA-51 subfamily is growing and gaining clinical significance. In this study, we used molecular dynamics simulations, X-ray crystallography, and thermal denaturation data to examine and compare the dynamics of OXA-66 wt and its gain-of-function variants: I129L (OXA-83), L167V (OXA-82), P130Q (OXA-109), P130A, and W222L (OXA-234). Our data indicate that OXA-66 wt also has a high melting temperature, and its remarkable stability is due to an extensive and rigid hydrophobic bridge formed by a number of residues around the active site and harbored by the three loops, P, Ω, and ß5-ß6. Compared to the WT enzyme, the mutants exhibit higher flexibility only in the loop regions, and are more stable than other robust carbapenemases, such as OXA-23 and OXA-24/40. All the mutants show increased rotational flexibility of residues I129 and W222, which allows carbapenems to bind. Overall, our data support the hypothesis that structural features in OXA-51 and OXA-66 promote evolution of multiple highly stable variants with increased clinical relevance in A. baumannii.

Establishment of a Multiplex Detection Method for Common Bacteria in Blood Based on Human Mannan-Binding Lectin Protein-Conjugated Magnetic Bead Enrichment Combined with Recombinase-Aided PCR Technology.

Objective: Recombinase-aided polymerase chain reaction (RAP) is a sensitive, single-tube, two-stage nucleic acid amplification method. This study aimed to develop an assay that can be used for the early diagnosis of three types of bacteremia caused by Staphylococcus aureus (SA), Pseudomonas aeruginosa (PA), and Acinetobacter baumannii (AB) in the bloodstream based on recombinant human mannan-binding lectin protein (M1 protein)-conjugated magnetic bead (M1 bead) enrichment of pathogens combined with RAP. Methods: Recombinant plasmids were used to evaluate the assay sensitivity. Common blood influenza bacteria were used for the specific detection. Simulated and clinical plasma samples were enriched with M1 beads and then subjected to multiple recombinase-aided PCR (M-RAP) and quantitative PCR (qPCR) assays. Kappa analysis was used to evaluate the consistency between the two assays. Results: The M-RAP method had sensitivity rates of 1, 10, and 1 copies/µL for the detection of SA, PA, and AB plasmids, respectively, without cross-reaction to other bacterial species. The M-RAP assay obtained results for < 10 CFU/mL pathogens in the blood within 4 h, with higher sensitivity than qPCR. M-RAP and qPCR for SA, PA, and AB yielded Kappa values of 0.839, 0.815, and 0.856, respectively ( P < 0.05). Conclusion: An M-RAP assay for SA, PA, and AB in blood samples utilizing M1 bead enrichment has been developed and can be potentially used for the early detection of bacteremia.

Lytic Capsule-Specific Acinetobacter Bacteriophages Encoding Polysaccharide-Degrading Enzymes.

The genus Acinetobacter comprises both environmental and clinically relevant species associated with hospital-acquired infections. Among them, Acinetobacter baumannii is a critical priority bacterial pathogen, for which the research and development of new strategies for antimicrobial treatment are urgently needed. Acinetobacter spp. produce a variety of structurally diverse capsular polysaccharides (CPSs), which surround the bacterial cells with a thick protective layer. These surface structures are primary receptors for capsule-specific bacteriophages, that is, phages carrying tailspikes with CPS-depolymerizing/modifying activities. Phage tailspike proteins (TSPs) exhibit hydrolase, lyase, or esterase activities toward the corresponding CPSs of a certain structure. In this study, the data on all lytic capsule-specific phages infecting Acinetobacter spp. with genomes deposited in the NCBI GenBank database by January 2024 were summarized. Among the 149 identified TSPs encoded in the genomes of 143 phages, the capsular specificity (K specificity) of 46 proteins has been experimentally determined or predicted previously. The specificity of 63 TSPs toward CPSs, produced by various Acinetobacter K types, was predicted in this study using a bioinformatic analysis. A comprehensive phylogenetic analysis confirmed the prediction and revealed the possibility of the genetic exchange of gene regions corresponding to the CPS-recognizing/degrading parts of different TSPs between morphologically and taxonomically distant groups of capsule-specific Acinetobacter phages.

Assessment of three antibiotic combination regimens against Gram-negative bacteria causing neonatal sepsis in low- and middle-income countries.

Gram-negative bacteria (GNB) are a major cause of neonatal sepsis in low- and middle-income countries (LMICs). Although the World Health Organization (WHO) reports that over 80% of these sepsis deaths could be prevented through improved treatment, the efficacy of the currently recommended first- and second-line treatment regimens for this condition is increasingly affected by high rates of drug resistance. Here we assess three well known antibiotics, fosfomycin, flomoxef and amikacin, in combination as potential antibiotic treatment regimens by investigating the drug resistance and genetic profiles of commonly isolated GNB causing neonatal sepsis in LMICs. The five most prevalent bacterial isolates in the NeoOBS study (NCT03721302) are Klebsiella pneumoniae, Acinetobacter baumannii, E. coli, Serratia marcescens and Enterobacter cloacae complex. Among these isolates, high levels of ESBL and carbapenemase encoding genes are detected along with resistance to ampicillin, gentamicin and cefotaxime, the current WHO recommended empiric regimens. The three new combinations show excellent in vitro activity against ESBL-producing K. pneumoniae and E. coli isolates. Our data should further inform and support the clinical evaluation of these three antibiotic combinations for the treatment of neonatal sepsis in areas with high rates of multidrug-resistant Gram-negative bacteria.

Resistance to bacteriophage incurs a cost to virulence in drug-resistant Acinetobacter baumannii.

Introduction . Acinetobacter baumannii is a critical priority pathogen for novel antimicrobials (World Health Organization) because of the rise in nosocomial infections and its ability to evolve resistance to last resort antibiotics. A. baumannii is thus a priority target for phage therapeutics. Two strains of a novel, virulent bacteriophage (LemonAid and Tonic) able to infect carbapenem-resistant A. baumannii (strain NCTC 13420), were isolated from environmental water samples collected through a citizen science programme.Gap statement. Phage-host coevolution can lead to emergence of host resistance, with a concomitant reduction in the virulence of host bacteria; a potential benefit to phage therapy applications.Methodology. In vitro and in vivo assays, genomics and microscopy techniques were used to characterize the phages; determine mechanisms and impact of phage resistance on host virulence, and the efficacy of the phages against A. baumannii.Results. A. baumannii developed resistance to both viruses, LemonAid and Tonic. Resistance came at a cost to virulence, with the resistant variants causing significantly reduced mortality in a Galleria mellonella larval in vivo model. A replicated 8 bp insertion increased in frequency (~40 % higher frequency than in the wild-type) within phage-resistant A. baumannii mutants, putatively resulting in early truncation of a protein of unknown function. Evidence from comparative genomics and an adsorption assay suggests this protein acts as a novel phage receptor site in A. baumannii. We find no evidence linking resistance to changes in capsule structure, a known virulence factor. LemonAid efficiently suppressed growth of A. baumanni in vitro across a wide range of titres. However, in vivo, while survival of A. baumannii infected larvae significantly increased with both remedial and prophylactic treatment with LemonAid (107 p.f.u. ml-1), the effect was weak and not sufficient to save larvae from morbidity and mortality.Conclusion. While LemonAid and Tonic did not prove effective as a treatment in a Galleria larvae model, there is potential to harness their ability to attenuate virulence in drug-resistant A. baumannii.

Molecular epidemiology and molecular typing methods of Acinetobacter baumannii: An updated review.

The aim of this study was to go through the molecular methods used for typing of carbapenem-resistant Acientobacter baumannii (CRAB) isolates for investigating the molecular epidemiology all over the world. Multiple typing techniques are required to understand the source and nature of outbreaks caused by Acientobacter baumannii (A. baumannii) and acquired resistance to antimicrobials. Nowadays, there is gradual shift from traditional typing methods to modern molecular methods to study molecular epidemiology and infection control. Molecular typing of A. baumannii strains has been revolutionized significantly in the last 2 decades. A few sequencing-based techniques have been proven as a breakthrough and opened new prospects, which have not been achieved by the traditional methods. In this review, discussed different pre-existing and recently used typing methods to explore the molecular epidemiology of A. baumannii pertaining in context with human infections.

Genomic Landscape Reveals Chromosomally-Mediated Antimicrobial Resistome and Virulome of a High-Risk International Clone II Acinetobacter baumannii AB073 from Thailand.

This study utilized integrative bioinformatics' tools together with phenotypic assays to understand the whole-genome features of a carbapenem-resistant international clone II Acinetobacter baumannii AB073. Overall, we found the isolate to be resistant to seven antibiotic classes, penicillins, ß-lactam/ß-lactamase inhibitor combinations, cephalosporins, carbapenems, aminoglycosides, fluoroquinolones, and folate pathway antagonists. These resistance phenotypes are related to various chromosomal-located antibiotic resistance determinants involved in different mechanisms such as reduced permeability, antibiotic target protection, antibiotic target alteration, antibiotic inactivation, and antibiotic efflux. IC2 A. baumannii AB073 could not transfer antibiotic resistance by conjugation experiments. Likewise, mobilome analysis found that AB073 did not carry genetic determinants involving horizontal gene transfer. Moreover, this isolate also carried multiple genes associated with the ability of iron uptake, biofilm formation, immune invasion, virulence regulations, and serum resistance. In addition, the genomic epidemiological study showed that AB073-like strains were successful pathogens widespread in various geographic locations and clinical sources. In conclusion, the comprehensive analysis demonstrated that AB073 contained multiple genomic determinants which were important characteristics to classify this isolate as a successful international clone II obtained from Thailand.

Lactate metabolism promotes in vivo fitness during Acinetobacter baumannii infection.

Acinetobacter baumannii is one of the most prevalent causes of nosocomial infections worldwide. However, a paucity of information exists regarding the connection between metabolic capacity and in vivo bacterial fitness. Elevated lactate is a key marker of severe sepsis. We have previously shown that the putative A. baumannii lactate permease gene, lldP, is upregulated during in vivo infection. Here, we confirm that lldP expression is upregulated in three A. baumannii strains during a mammalian systemic infection. Utilising a transposon mutant disrupted for lldP in the contemporary clinical strain AB5075-UW, and a complemented strain, we confirmed its role in the in vitro utilisation of l-(+)-lactate. Furthermore, disruption of the lactate metabolism pathway resulted in reduced bacterial fitness during an in vivo systemic murine competition assay. The disruption of lldP had no impact on the susceptibility of this strain to complement mediated killing by healthy human serum. However, growth in biologically relevant concentrations of lactate observed during severe sepsis, led to bacterial tolerance to killing by healthy human blood, a phenotype that was abolished in the lldP mutant. This study highlights the importance of the lactate metabolism pathway for survival and growth of A. baumannii during infection.

[Analysis of the virulence and genetic differences of carbapenem-resistant Acinetobacter baumannii epidemic clones].

Objective: To evaluate the virulence levels of carbapenem-resistant Acinetobacter baumannii ST191, ST195, and ST208, and to analyze the differences in virulence factors among these epidemic clones. Methods: The study involved the genomic sequencing of 233 Acinetobacter baumannii strains that were isolated from the Fifth Medical Center of the Chinese People's Liberation Army General Hospital (North Hospital) between 2011 and 2019. The genomic data was cross-referenced with the Virulence Factor Database (VFDB) to examine the presence of virulence genes in the strains. Furthermore, a Galleria mellonella infection survival model was used to evaluate the virulence levels of the strains, and the association between virulence levels and virulence genes was analyzed. Results: The study included 38 strains of the ST191 clone, 104 strains of the ST195 clone, and 91 strains of the ST208 clone. In the Galleria mellonella infection survival experiment, the average mortality rate for ST191 was 23.0%, with 3 (7.9%) highly virulent strains. For ST195, the average mortality rate was 53.0%, with 34 (32.7%) highly virulent strains. For ST208, the average mortality rate was 47.0%, with 20 (21.9%) highly virulent strains. There was a significant statistical difference in mortality rates between ST191 and ST195 (χ2=13.9, P<0.001) as well as between ST191 and ST208 (χ2=15.2, P<0.001). A comparison of the strains with the VFDB revealed significant differences in the virulence genes carried by the clones. Specifically, the type Ⅵ secretion system-related genes (clpV/tssH, hcp/tssD, tagX, tssA, tssB, tssC, tssE, tssF, tssG, tssK, ssL, tssM) and the sugar transferase gene ACICU_RS00475 were found to be universally absent in ST191 strains (0%) while being prevalent in ST195 (100.0%) and ST208 (>82.0%) strains. Statistical analysis revealed an association between the mortality rate of the clones and the presence of virulence genes(clpV/tssH P<0.001, hcp/tssD P=0.001, tagX P<0.001, tssA P<0.001, tssB P=0.001, tssC P=0.001, tssE P=0.001, tssF P=0.001, tssG P<0.001, tssK P<0.001, tssL P<0.001, tssM P=0.001, ACICU_RS00475 P=0.001). Conclusion: Among the carbapenem-resistant epidemic clones of Acinetobacter baumannii, the ST191 clone shows lower mortality rates in Galleria mellonella, possibly because of the lack of type Ⅵ secretion system and sugar transferase genes.

Implications of deduplication on the detection rates of multidrug-resistant organism (MDRO) in various specimens: insights from the hospital infection surveillance program.

BACKGROUND: Currently, different guidelines recommend using different methods to determine whether deduplication is necessary when determining the detection rates of multidrug-resistant organisms (MDROs). However, few studies have investigated the effect of deduplication on MDRO monitoring data. In this study, we aimed to investigate the influence of deduplication on the detection rates of MDROs in different specimens to assess its impact on infection surveillance outcomes. METHODS: Samples were collected from hospitalized patients admitted between January 2022 and December 2022; four types of specimens were collected from key monitored MDROs, including sputum samples, urine samples, blood samples, and bronchoalveolar lavage fluid (BALF) samples. In this study, we compared and analysed the detection rates of carbapenem-resistant Klebsiella pneumoniae (CRKP), carbapenem-resistant Escherichia coli (CRECO), carbapenem-resistant Acinetobacter baumannii (CRAB), carbapenem-resistant Pseudomonas aeruginosa (CRPA), and methicillin-resistant Staphylococcus aureus (MRSA) under two conditions: with and without deduplication. RESULTS: When all specimens were included, the detection rates of CRKP, CRAB, CRPA, and MRSA without deduplication (33.52%, 77.24%, 44.56%, and 56.58%, respectively) were significantly greater than those with deduplication (24.78%, 66.25%, 36.24%, and 50.83%, respectively) (all P < 0.05). The detection rates in sputum samples were significantly different between samples without duplication (28.39%, 76.19%, 46.95%, and 70.43%) and those with deduplication (19.99%, 63.00%, 38.05%, and 64.50%) (all P < 0.05). When deduplication was not performed, the rate of detection of CRKP in urine samples reached 30.05%, surpassing the rate observed with deduplication (21.56%) (P < 0.05). In BALF specimens, the detection rates of CRKP and CRPA without deduplication (39.78% and 53.23%, respectively) were greater than those with deduplication (31.62% and 42.20%, respectively) (P < 0.05). In blood samples, deduplication did not have a significant impact on the detection rates of MDROs. CONCLUSION: Deduplication had a significant effect on the detection rates of MDROs in sputum, urine, and BALF samples. Based on these data, we call for the Infection Prevention and Control Organization to align its analysis rules with those of the Bacterial Resistance Surveillance Organization when monitoring MDRO detection rates.

Exploring the evolutionary and pathogenic role of Acinetobacter baumannii biofilm-associated protein (Bap) through in silico structural modeling.

Acinetobacter species encode for extracellularly secreted Biofilm-associated protein (Bap), a multi-domain protein with variable molecular weights reaching several hundred kilodaltons. Bap is crucial for the development of multi-dimensional structures of mature biofilms. In our investigation, we analyzed 7338 sequences of A. baumannii from the NCBI database and found that Bap or Bap-like protein (BLP) was present in 6422 (87.52%) isolates. Further classification revealed that 12.12% carried Type-1 Bap, 68.44% had Type-2, 6.91% had Type-3, 0.05% had Type-6 or SDF-Type, and 12.51% lacked Bap or BLP. The majority of isolates with Type-1, Type-2, and Type-3 Bap belonged to ST1, ST2, and ST25, respectively. Phylogenetic analysis suggested that Type-1 Bap is the most ancient, while Type-3 and SDF-Type have evolved recently. Studying the interaction of predicted Bap structures with human CEACAM-1 and PIgR showed that Bap with its BIg13 and BIg6 domains interact with the N-terminal domain of CEACAM-1, involving Arg43 and Glu40, involved in CEACAM-1 dimerization. Also, we found that recently evolved Type-3 and SDF-Type Bap showed greater interaction with CEACAM-1 and PIgR. It can be asserted that the evolution of Bap has conferred enhanced virulence characteristics to A. baumannii with increased interaction with CEACAM-1 and PIgR. Using in silico approaches, this study explores the evolutionary, physicochemical, and structural features of A. baumannii Bap and unravels its crucial role in mediating interaction with human CEACAM-1 and PIgR through detailed structure modelling. These findings advance our understanding of A. baumannii Bap and highlight its role in pathogenesis.

Exposure to imipenem at sub-minimum inhibitory concentration leads to altered expression of major outer membrane proteins in Acinetobacter baumannii.

AIMS: Acinetobacter baumannii is a nosocomial pathogen known to be multidrug-resistant (MDR), especially to drugs of the carbapenem class. Several factors contribute to resistance, including efflux pumps, ß-lactamases, alteration of target sites, and permeability defects. In addition, outer membrane proteins (OMPs), like porins are involved in the passage of antibiotics, and their alteration could lead to resistance development. This study aimed to explore the possible involvement of porins and OMPs in developing carbapenem resistance due to differential expression. METHODS AND RESULTS: The antibiotic-susceptible and MDR isolates of A. baumannii were first studied for differences in their transcriptional levels of OMP expression and OMP profiles. The antibiotic-susceptible isolates were further treated with imipenem, and it was found that the omp genes were differentially expressed. Six of the nine genes studied were upregulated at 1 h of exposure to imipenem. Their expression gradually decreased with time, further confirmed by their OMP profile and two-dimensional gel electrophoresis. CONCLUSIONS: This study could identify OMPs that were differentially expressed on exposure to imipenem. Hence, this study provides insights into the role of specific OMPs in antibiotic resistance in A. baumannii.

[Characteristics of drug resistance and biofilm formation in carbapenem-resistant Acinetobacter baumannii in hospitalized children]. / 住院患儿耐碳青霉烯类鲍曼不动杆菌的耐药及生物膜特征分析.

OBJECTIVES: To study the distribution, drug resistance, and biofilm characteristics of carbapenem-resistant Acinetobacter baumannii (CRAB) isolated from hospitalized children, providing a reference for the prevention and treatment of CRAB infections in hospitalized children. METHODS: Forty-eight CRAB strains isolated from January 2019 to December 2022 were classified into epidemic and sporadic strains using repetitive extragenic palindromic sequence-based polymerase chain reaction. The drug resistance, biofilm phenotypes, and gene carriage of these two types of strains were compared. RESULTS: Both the 22 epidemic strains and the 26 sporadic strains were producers of Class D carbapenemases or extended-spectrum ß-lactamases with downregulated outer membrane porins, harboring the VIM, OXA-23, and OXA-51 genes. The biofilm formation capability of the sporadic strains was stronger than that of the epidemic strains (P<0.05). Genes related to biofilm formation, including Bap, bfs, OmpA, CsuE, and intI1, were detected in both epidemic and sporadic strains, with a higher detection rate of the intI1 gene in epidemic strains (P<0.05). CONCLUSIONS: CRAB strains are colonized in the hospital, with sporadic strains having a stronger ability to form biofilms, suggesting the potential for forming new clonal transmissions in the hospital. Continuous monitoring of the epidemic trends of CRAB and early warning of the distribution of epidemic strains are necessary to reduce the risk of CRAB infections in hospitalized children.

PmrAB, the two-component system of Acinetobacter baumannii, controls the phosphoethanolamine modification of lipooligosaccharide in response to metal ions.

Acinetobacter baumannii is highly resistant to antimicrobial agents, and XDR strains have become widespread. A. baumannii has developed resistance to colistin, which is considered the last resort against XDR Gram-negative bacteria, mainly caused by lipooligosaccharide (LOS) phosphoethanolamine (pEtN) and/or galactosamine (GalN) modifications induced by mutations that activate the two-component system (TCS) pmrAB. Although PmrAB of A. baumannii has been recognized as a drug resistance factor, its function as TCS, including its regulatory genes and response factors, has not been fully elucidated. In this study, to clarify the function of PmrAB as TCS, we elucidated the regulatory genes (regulon) of PmrAB via transcriptome analysis using pmrAB-activated mutant strains. We discovered that PmrAB responds to low pH, Fe2+, Zn2+, and Al3+. A. baumannii selectively recognizes Fe2+ rather than Fe3+, and a novel region ExxxE, in addition to the ExxE motif sequence, is involved in the environmental response. Furthermore, PmrAB participates in the phosphoethanolamine modification of LOS on the bacterial surface in response to metal ions such as Al3+, contributing to the attenuation of Al3+ toxicity and development of resistance to colistin and polymyxin B in A. baumannii. This study demonstrates that PmrAB in A. baumannii not only regulates genes that play an important role in drug resistance but is also involved in responses to environmental stimuli such as metal ions and pH, and this stimulation induces LOS modification. This study reveals the importance of PmrAB in the environmental adaptation and antibacterial resistance emergence mechanisms of A. baumannii. IMPORTANCE: Antimicrobial resistance (AMR) is a pressing global issue in human health. Acinetobacter baumannii is notably high on the World Health Organization's list of bacteria for which new antimicrobial agents are urgently needed. Colistin is one of the last-resort drugs used against extensively drug-resistant (XDR) Gram-negative bacteria. However, A. baumannii has become increasingly resistant to colistin, primarily by modifying its lipooligosaccharide (LOS) via activating mutations in the two-component system (TCS) PmrAB. This study comprehensively elucidates the detailed mechanism of drug resistance of PmrAB in A. baumannii as well as its biological functions. Understanding the molecular biology of these molecules, which serve as drug resistance factors and are involved in environmental recognition mechanisms in bacteria, is crucial for developing fundamental solutions to the AMR problem.

Carbapenemase genes in clinical and environmental isolates of Acinetobacter spp. from Quito, Ecuador.

Carbapenem-resistant Acinetobacter spp. is associated with nosocomial infections in intensive care unit patients, resulting in high mortality. Although Acinetobacter spp. represent a serious public health problem worldwide, there are a few studies related to the presence of carbapenemases in health care facilities and other environmental settings in Ecuador. The main aim of this study was to characterize the carbapenem-resistant Acinetobacter spp. isolates obtained from four hospitals (52) and from five rivers (27) close to Quito. We used the disc diffusion and EDTA sinergy tests to determine the antimicrobial susceptibility and the production of metallo ß-lactamases, respectively. We carried out a multiplex PCR of gyrB gene and the sequencing of partial rpoB gene to bacterial species identification. We performed molecular screening of nine carbapenem-resistant genes (blaSPM, blaSIM, blaGIM, blaGES, blaOXA-23, blaOXA-24, blaOXA-51, blaOXA-58, and blaOXA-143) by multiplex PCR, followed by identification using sequencing of blaOXA genes. Our findings showed that carbapenem-resistant A. baumannii were the main species found in health care facilities and rivers. Most of the clinical isolates came from respiratory tract samples and harbored blaOXA-23, blaOXA-366, blaOXA-72, blaOXA-65, blaOXA-70, and blaOXA-143-like genes. The river isolates harbored only the blaOXA-51 and probably blaOXA-259 genes. We concluded that the most predominant type of carbapenem genes among isolates were both blaOXA-23 and blaOXA-65 among A. baumannii clinical isolates.