Acinetobacter junii: an emerging One Health pathogen

Acinetobacter junii is an opportunistic human and animal pathogen severely understudied. Here, we conducted the largest genomic epidemiological study on this pathogen to date. Our data show that this bacterium has spread globally. Also, we found that some human and non-human isolates are not well differentiated from one another, implying transmission between clinical and non-clinical, non-human settings. Remarkably, human but also some non-human isolates have clinically important antibiotic resistance genes, and some of these genes are located in plasmids. Given these results, we put forward that A. junii should be considered an emerging One Health problem. In this regard, future molecular epidemiological studies about this species will go beyond human isolates and will consider animal-, plant-, and water-associated environments.

IMPORTANCE

Acinetobacter baumannii is the most well-known species from the genus Acinetobacter. However, other much less studied Acinetobacter species could be important opportunistic pathogens of animals, plants and humans. Here, we conducted the largest genomic epidemiological study of A. junii, which has been described as a source not only of human but also of animal infections. Our analyses show that this bacterium has spread globally and that, in some instances, human and non-human isolates are not well differentiated. Remarkably, some non-human isolates have important antibiotic resistance genes against important antibiotics used in human medicine. Based on our results, we propose that this pathogen must be considered an issue not only for humans but also for veterinary medicine.

Earliest observation of the tetracycline destructase tet(X3)

Tigecycline is an antibiotic of last resort for infections with carbapenem-resistant Acinetobacter baumannii. Plasmids harboring variants of the tetracycline destructase gene tetX promote rising tigecycline resistance rates. We report the earliest observation of tet(X3) in a clinical strain predating tigecycline's commercialization, suggesting selective pressures other than tigecycline contributed to its emergence.

IMPORTANCE

We present the earliest observation of a tet(X3)-positive bacterial strain, predating by many years the earliest reports of this gene so far. This finding is significant as tigecycline is an antibiotic of last resort for carbapenem-resistant Acinetobacter baumannii (CRAB), which the World Health Organization ranks as one of its top three critical priority pathogens, and tet(X3) variants have become the most prevalent genes responsible for enabling CRAB to become tigecycline resistant. Moreover, the tet(X3)-positive strain we report is the first and only to be found that predates the commercialization of tigecycline, an antibiotic that was thought to have contributed to the emergence of this resistance gene. Understanding the factors contributing to the origin and spread of novel antibiotic resistance genes is crucial to addressing the major global public health issue, which is antimicrobial resistance.

Emergence of Colistin-Resistant Acinetobacter junii in China

The increasing number of multidrug-resistant Gram-negative bacteria presents a serious threat to global health. However, colistin-resistant Acinetobacter junii has rarely been reported. We identified a colistin-resistant A. junii clinical isolate, AJ6079, in blood. The colony of AJ6079 presented a dry phenotype, and it was difficult to form a bacterial suspension, whilst transmission electron microscopy revealed that AJ6079 possessed a thick outer membrane. The phenotypic and genomic comparisons were conducted with one colistin-susceptible A. junii, which had the same antibiotic susceptibility profile except for colistin, and had the same KL25 capsule biosynthesis locus. The AJ6079 exhibited a slower growth rate, indicating that colistin-resistant A. junii possesses a higher fitness cost. The genome of AJ6079 had a G+C content of 38.7% and contained one 3,362,966 bp circular chromosome with no plasmid or mobile colistin resistance (mcr) gene. Comparative genomic analysis revealed that the AJ6079 contained several previously unreported point mutations in colistin-resistance-related genes involving amino acid substitutions in PmrB (N5K, G147C), LpxA (I107F, H131Y), and LpxD (F20I, K263R), which might be correlated with colistin resistance in A. junii. Further research is needed for verification as the genetic background was not exactly the same between the two isolates.

Carbapenem Resistance in Acinetobacter nosocomialis and Acinetobacter junii Conferred by Acquisition of blaOXA-24/40 and Genetic Characterization of the Transmission Mechanism between Acinetobacter Genomic Species

Carbapenem resistance is increasing among Gram-negative bacteria, including the genus Acinetobacter. This study aimed to characterize, for the first time, the development of carbapenem resistance in clinical isolates of Acinetobacter junii and Acinetobacter nosocomialis conferred by the acquisition of a plasmid-borne bla_OXA-24/40 gene and also to characterize the dissemination of this gene between species of Acinetobacter. Carbapenem-resistant A. nosocomialis HUAV-AN66 and A. junii HUAV-AJ77 strains were isolated in the Arnau de Vilanova Hospital (Spain). The genomes were sequenced, and in silico analysis were performed to characterize the genetic environment and the OXA-24/40 transmission mechanism. Antibiotic MICs were determined, and horizontal transfer assays were conducted to evaluate interspecies transmission of OXA-24/40. Carbapenems MICs obtained were ≥64 mg/L for HUAV-AN66 and HUAV-AJ77. Genome analysis revealed the presence in both strains of a new plasmid, designated pHUAV/OXA-24/40, harboring the carbapenem-resistance gene bla_OXA-24/40 and flanked by sequences XerC/XerD. pHUAV/OXA-24/40 was successfully transferred from A. nosocomialis and A. junii to a carbapenem-susceptible A. baumannii strain, thus conferring carbapenem resistance. A second plasmid (pHUAV/AMG-R) was identified in both clinical isolates for the successful horizontal transfer of pHUAV/OXA-24/40. bla_OXA-24/40-carrying plasmids of the GR12 group and showing high identity with pHUAV/OXA-24/40 were identified in at least 8 Acinetobacter species. In conclusion the carbapenemase OXA-24/40 is described for the first time in A. nosocomialis and A. junii. In both isolates the bla_OXA-24/40 gene was located in the GR12 pHUAV/OXA-24/40 plasmid. GR12 plasmids are implicated in the dissemination and spread of carbapenem resistance among Acinetobacter species. IMPORTANCE Acinetobacter baumannii is one of the most relevant pathogens in terms of antibiotic resistance. The main resistance mechanisms are the carbapenem-hydrolyzing class D β-lactamases (CHDLs), especially OXA-23 and OXA-24/40. In addition to A. baumannii, there are other species within the genus Acinetobacter, which in general exhibit much lower resistance rates. In this work we characterize for the first time two clinical isolates of Acinetobacter nosocomialis and Acinetobacter junii, isolated in the same hospital, carrying the carbapenemase OXA-24/40 and displaying high resistance rates to carbapenems. By means of bioinformatics analysis we have also been able to characterize the mechanism by which this carbapenemase is horizontally transferred interspecies of Acinetobacter spp. The dissemination of carbapenemase OXA-24/40 between non-baumannii Acinetobacter species is concerning since it prevents the use of most β-lactam antibiotics in the fight against these resistant isolates.

Novel Polyherbal Nanocolloids to Control Bovine Mastitis

Mastitis is a widespread disease in dairy cattle occurring throughout the world. The increased use of antibiotics brings about the development of antibiotic-resistant microbes. The application of antibiotics in dairy farming led to increased antibiotic resistance and represents a major obstacle for the treatment of mastitis. Recent advancements in nanotechnology led to the development of nanocolloids to overcome disadvantages posed by conventional antimicrobial agents. Hence, a novel, environmentally friendly, cost-effective, biocompatible, and long-term antibacterial represents a promising solution for medicine and farming. Hence, polyherbal nanocolloids (PHNc) was formulated by using the extracts of Syzygium aromaticum, Cinnamomum verum, Emblica officinalis, Terminalia belerica, Terminalia chebula, and Cymbopogon citratus and physicochemically characterized. From mastitis milk samples, microorganisms were isolated including Acinetobacter junii, Klebsiella pneumoniae, Pseudomonas stutzeri, and Acinetobacter baumannii and screened for antibiotic susceptibility. All the isolated strains were tested with PHNc and compared with antibiotics. Minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), and biofilm assays were performed at different concentrations, and antibacterial effects were quantified. In our results, PHNc showed potent bacteriostatic, bactericidal, and antibiofilm activity against all the strains. Our results indicated that PHNc can reduce the virulence factors responsible for infection by different bacterial strains. This study confirmed that PHNc had the potential to inhibit the growth of pathogenic Gram-negative and Gram-positive strains and could be utilized as an alternative to antibiotics to inhibit multidrug-resistant microbial pathogens in cattle.

Acinetobacter junii as a rare pathogen of urinary tract infection

Acinetobacter junii is one of more than 50 different species belonging to the genus Acinetobacter. This bacterium is rarely reported to cause human infections. Here we described a rare case of Acinetobacter junii, which grew in urine culture approximately one month after the patient was discharged from the hospital with antibiotics for a urinary tract infection, which caused left obstructing renal calculi requiring nephrostomy tube placement.

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Acinetobacter is often considered to be ubiquitous in nature.

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Acinetobacter junii is rarely reported to cause human infections.

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A rare case of Acinetobacter junii, which grew in urine culture, was described.

Antimicrobial, anti-biofilm, and anti-proliferative activities of lipopeptide biosurfactant produced by Acinetobacter junii B6

Lipopeptide biosurfactants (LPBs) are amphiphilic compounds produced by microorganisms exhibiting various biological activities. The main aim of the present study was to assess the in vitro antimicrobial, anti-biofilm, and cytotoxic effects of LPB produced by Acinetobacter junii (AjL). We determined AjL minimum inhibitory concentration (MIC) against both Gram-positive and Gram-negative bacteria as well as two fungal strains. Also, the anti-biofilm activity of AjL against the biofilm produced by clinically isolated bacterial strains was investigated. The AjL non-selectively showed activity against both Gram-positive and Gram-negative bacterial strains. The obtained results of the present study exhibited that the AjL in concentrations nearly below critical micelle concentration (CMC) has an effective antibacterial activity. It was found that the MIC values of AjL were lower than standard antifungal and it exhibited nearly 100% inhibition against Candida utilis. The attained results of the biofilm formation revealed that AjL disrupted the biofilm of Proteus mirabilis, Staphylococcus aureus, and Pseudomonas aeruginosa at 1250 μg/ml and 2500 μg/ml concentrations. The attained results of cytotoxic effect (determined by WST-1 assay) of the AjL revealed IC₅₀ of 7.8 ± 0.4 mg/ml, 2.4 ± 0.5 mg/ml, and 5.7 ± 0.1 mg/ml, against U87, KB, and HUVEC cell lines, respectively. The results indicated that AjL has a potential application in the relatively new field of biomedicine.

Evaluation of the cytotoxicity and interaction of lead with lead resistant bacterium Acinetobacter junii Pb1

This study explores the potential of lead resistant bacterium Acinetobacter junii Pb1 for adsorption/accumulation of lead using various techniques. In the present work, growth of A. junii Pb1 was investigated in the presence of a range of Pb(II) concentrations (0, 100, 250, 500, and 1000 mg l^-1). Lead was found to have no toxic effect on the growth of A. junii Pb1 at 100 and 250 mg l^-1 concentrations. However, further increase in Pb(II) concentration (500 mg l^-1) showed increase in lag phase, though growth remained unaffected and significant growth inhibition was observed when concentration was increased to 1000 mg l^-1. Same was confirmed by the observations of flow cytometry. Further, the effect of Pb(II) on A. junii Pb1 was evaluated by using fluorescence microscopy, spectrofluorimetry, and flow cytometry. The spectrofluorimetry and fluorescence microscopy results revealed the accumulation of Pb(II) inside the bacterial cells as evident by green fluorescence due to lead binding fluorescent probe, Leadmium Green AM dye. Flow cytometry observations indicate an increase in cell size and granularity of exposure to lead. Thus, present work provides a new understanding of Pb(II) tolerance in A. junii Pb1 and its potential use in remediation of lead from contaminated soil.

Efficient phosphate accumulation in the newly isolated Acinetobacter junii strain LH4

Phosphate (PO₄^3-) accumulation associated with bacteria contributes to efficient remediation of eutrophic waters and has attracted attention due to its low cost, high removal efficiency and environmental friendliness. In the present study, we isolated six strains from sludge with high concentrations of chemical oxygen demand, total nitrogen and total phosphorus levels. Among them, strain LH4 exhibited the greatest PO₄^3- removal ability. Strain LH4 is typical of Acinetobacter junii based on physiological, biochemical, and molecular analyses and is a PO₄^3--accumulating organism (PAO) based on toluidine blue staining. The strain grew quickly when subjected to aerobic medium after pre-incubation under anaerobic condition, with a maximum OD₆₀₀ of 1.429 after 8 h and PO₄^3- removal efficiency of 99%. Our data also indicated that this strain preferred utilizing the carbon (C) sources sodium formate and sodium acetate and the nitrogen (N) sources NH₄Cl and (NH₄)₂SO₄ over other compounds. To achieve optimal PO₄^3- removal efficiency, a C:N ratio of 5:1, inoculation concentration of 3%, solution pH of 6, incubation temperature of 30 °C, and shaking speed of 100 rpm were recommended for A. junii strain LH4. By incubating this strain with different concentrations of PO₄^3-, we calculated that its relative PO₄^3- removal capacity ranged from 0.67 to 3.84 mg L^-1 h^-1, ranking in the top three among reported PAOs. Our study provided a new PO₄^3--accumulating bacterial strain that holds promise for remediating eutrophic waters, and its potential for large-scale use warrants further investigation.

Investigation of the structural, physicochemical properties, and aggregation behavior of lipopeptide biosurfactant produced by Acinetobacter junii B6

In the present study the produced biosurfactant of Acinetobacter junii B6 (recently isolated from Iranian oil excavation site) were partially purified and identified by high performance thin layer chromatography (HPTLC), Fourier transform infrared spectroscopy (FTIR), and proton nuclear magnetic resonance (¹H NMR). Elemental analysis of the biosurfactant by energy dispersive X-ray spectroscopy (EDS) revealed that the biosurfactant was anionic in nature. The physiochemical properties of the lipopeptide biosurfactant were evaluated by determination of its critical micelle concentration (CMC) and hydrophile-lipophile balance (HLB). The produced biosurfactant decreased the surface tension of water to 36mNm^-1 with the CMC of approximately 300mg/l. Furthermore, the solubility properties of the biosurfactant (dissolved in phosphate-buffer saline solution, pH7.4) were investigated by turbidity examination, dynamic light scattering (DLS) measurements, and transmission electron microscopy (TEM) inspection. It could be concluded that the biosurfactant showed the spherical-shaped vesicles at a concentration higher than its CMC and the circular dichroism (CD) spectra showed that the secondary structure of the biosurfactant vesicles is dominated by the β sheet.

Pb1 isolated from coal mine dump

A lead-resistant bacterial strain was isolated from coal mine dump and identified as Acinetobacter junii Pb1 on basis of 16S rRNA (ribosomal ribonucleic acid) gene sequencing. The minimum inhibitory concentration of lead for the strain was 16,000 mg l^-1 and it showed antibiotic and multi metal resistance. In aqueous culture, at an initial lead (Pb(II)) concentration of 100 and 500 mg l^-1, lead adsorption and accumulation by the isolate was 100 and 60%, at pH 7 at 30 °C after 48 and 120 h, respectively. The two fractions of exopolysaccharide (EPS), loosely associated EPS (laEPS) and bound EPS (bEPS), and whole cells (devoid of EPS) showed high binding affinity towards Pb(II). The binding affinity of laEPS towards Pb(II) (1071 mg Pb g^-1) was three times higher than that of bEPS (321.5 mg Pb g^-1) and 6.5 times higher than that of whole cells (165 mg Pb g^-1). The binding affinity of EPS and whole cells with Pb(II), reported in the current study, is considerably higher as compared to that reported in the literature, till date. SEM analysis, showed an increase in thickness of cells on exposure to Pb(II) and TEM analysis, revealed its accumulation (interior of cell) and its adsorption (with the external cell surface). The isolate was also found to be positive for indole acetic acid (IAA) and 1-aminocyclopropane-1-carboxylate (ACC) deaminase production which helps in promoting plant growth. Thus, this study provides a new understanding towards Pb(II) uptake by A. junii Pb1, highlighting its potential on the restoration of Pb(II) contaminated repositories.

Rhamnolipids Produced by Indigenous Acinetobacter junii from Petroleum Reservoir and its Potential in Enhanced Oil Recovery

Biosurfactant producers are crucial for incremental oil production in microbial enhanced oil recovery (MEOR) processes. The isolation of biosurfactant-producing bacteria from oil reservoirs is important because they are considered suitable for the extreme conditions of the reservoir. In this work, a novel biosurfactant-producing strain Acinetobacter junii BD was isolated from a reservoir to reduce surface tension and emulsify crude oil. The biosurfactants produced by the strain were purified and then identified via electrospray ionization-Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR-MS). The biosurfactants generated by the strain were concluded to be rhamnolipids, the dominant rhamnolipids were C26H48O9, C28H52O9, and C32H58O13. The optimal carbon source and nitrogen source for biomass and biosurfactant production were NaNO3 and soybean oil. The results showed that the content of acid components increased with the progress of crude oil biodegradation. A glass micromodel test demonstrated that the strain significantly increased oil recovery through interfacial tension reduction, wettability alteration and the mobility of microorganisms. In summary, the findings of this study indicate that the newly developed BD strain and its metabolites have great potential in MEOR.