Baumannii ATCC Research Articles

Expression of Biofilm-Related Genes in Extensively Drug-Resistant Acinetobacter baumannii

Background: Acinetobacter baumannii is an important cause of nosocomial pneumonia in patients requiring long-term mechanical ventilation. Besides, extensively drug-resistant (XDR) strains cause infection in intensive care unit (ICU) patients. Chronic infections of A. baumannii and antimicrobial resistance are associated with biofilm formation. Several virulence genes, such as blaPER-1, pgaA, and bap, are involved in biofilm formation. Objectives: The current study examines the expression levels of biofilm formation-related genes in pneumonia patients. Methods: The sputum samples were collected from patients hospitalized in the ICU, and A. baumannii ATCC 19606, the reference strain, was isolated and cultured on blood agar, eosin methylene blue agar, and chocolate agar medium. The media were then incubated at 37°C for 18 - 24 hours. Next, Gram-Thirty XDR A. baumannii isolates were collected from the sputum samples of ICU patients at Besat Hospital in Tehran, Iran. Bacterial isolates were characterized for antibiotic resistance patterns and biofilm-forming ability. Subsequently, RNA was extracted from the biofilm-forming isolates. A real-time polymerase chain reaction (PCR) assay was performed to evaluate the expression levels of the blaPER-1, pgaA, and bap genes. Transcripts were normalized to 16S rRNA as an internal control, and gene expression fold changes were calculated. Statistical analysis was performed using an unpaired two-tailed t-test (P < 0.05) with SPSS (V. 16). Results: The disk diffusion susceptibility test revealed that all 30 (100%) isolates were resistant to piperacillin-tazobactam, cefepime, ceftriaxone, ceftazidime, gentamicin, imipenem, meropenem, levofloxacin, and ciprofloxacin. All 30 isolates from ICU-admitted patients (100%) were classified as XDR, and 27 (90%) isolates demonstrated the ability to form biofilms. The obtained results indicated a significant difference in gene expression levels. The fold change in expression for blaPER-1, bap, and pgaA was 7.473, 11.964, and 5.277, respectively. Conclusions: In our study, XDR A. baumannii primarily caused ventilator-associated pneumonia, and an observed increase in the expression of biofilm-related genes was noted in these strains. Healthcare centers should implement appropriate infection control programs to manage nosocomial infections, particularly in the ICU.

Acinetobacter baumannii ATCC 17978 encodes a microcin system with antimicrobial properties for contact-independent competition.

Acinetobacter baumannii is a multidrug-resistant opportunistic pathogen that persists in the hospital environment and causes various clinical infections, primarily affecting immunocompromised patients. A. baumannii has evolved a wide range of mechanisms to compete with neighbouring bacteria. One such competition strategy depends on small secreted peptides called microcins, which exert antimicrobial effects in a contact-independent manner. Here, we report that A. baumannii ATCC 17978 (AB17978) encodes the class II microcin 17 978 (Mcc17978) with antimicrobial activity against closely related Acinetobacter, and surprisingly, also Escherichia coli strains. We identified the genetic locus encoding the Mcc17978 system in AB17978. Using classical bacterial genetic approaches, we determined that the molecular receptor of Mcc17978 in E. coli is the iron-catecholate transporter Fiu, and in Acinetobacter is Fiu's homolog, PiuA. In bacteria, the Ferric uptake regulator (Fur) positively regulates siderophore systems and microcin systems under iron-deprived environments. We found that the Mcc17978 system is upregulated under low-iron conditions commonly found in the host environment and identified a putative Fur binding site upstream of the mcc17978 gene. When we tested the antimicrobial activity of Mcc17978 under different levels of iron availability, we observed that low iron levels not only triggered transcriptional induction of the microcin, but also led to enhanced microcin activity. Taken together, our findings suggest that A. baumannii may utilize microcins to compete with other microbes for resources during infection.

Lysine Trimethylation in Planktonic and Pellicle Modes of Growth in Acinetobacter baumannii.

Over the past 30 years, Acinetobacter baumannii has been described as an important nosocomial pathogen due to frequent ventilator-associated infections. Many biological processes of A. baumannii remain elusive, such as the formation of an air-liquid biofilm (pellicle). Several studies demonstrated the importance of post-translational modifications (PTMs) in A. baumannii physiology. Here, we investigated K-trimethylation in A. baumannii ATCC 17978 in planktonic and pellicle modes using proteomic analysis. To identify the most high-confidence K-trimethylated peptides, we compared different sample preparation methods (i.e., strong cation exchange, antibody-capture) and processing software (i.e., different database search engines). We identified, for the first time, 84 K-trimethylated proteins, many of which are involved in DNA and protein synthesis (HupB, RplK), transporters (Ata, AdeB), or lipid metabolism processes (FadB, FadD). In comparison with previous studies, several identical lysine residues were observed acetylated or trimethylated, indicating the presence of proteoforms and potential PTM cross-talks. This is the first large-scale proteomic study of trimethylation in A. baumannii and will be an important resource for the scientific community (availability in Pride repository under accession PXD035239).

Emergence of tet(X2) in Acinetobacter pittii confers clinical resistance to tigecycline.

To characterize a novel transposon Tn7533 carrying the tet(X2) gene in a tigecycline-resistant Acinetobacter pittii BM4623 of clinical origin. Gene knockout and in vitro cloning were used to verify the function of tet(X2). WGS and comparative genomic analysis were used to explore the genetic characteristics and molecular evolution of tet(X2). Inverse PCR and electroporation experiments were used to evaluate the excision and integration capabilities of Tn7533. A. pittii BM4623 belonged to a novel ST, ST2232 (Pasteur scheme). Knockout of tet(X2) in BM4623 restored its susceptibility to tigecycline. Cloning of the tet(X2) gene into Escherichia coli DH5α and Acinetobacter baumannii ATCC 17978 resulted in 16-fold or more increases in MICs of tigecycline. Sequence analysis showed that the region upstream of tet(X2) exhibited a high degree of diversity, while there was a 145 bp conserved region downstream of tet(X2). tet(X2) in BM4623 was located on a novel composite transposon Tn7533, which also contains multiple resistance genes including blaOXA-58. Tn7533 could be excised from the chromosome to form a circular intermediate and transferred into A. baumannii ATCC 17978 by electroporation. Our study demonstrates that tet(X2) is a determinant conferring clinical resistance to tigecycline in Acinetobacter species. The emergence of Tn7533 may lead to the potential dissemination of tigecycline and carbapenem resistance in Acinetobacter, which requires continuous monitoring.

Diverse Repertoire and Relationship of Exopolysaccharide Genes in Cold-Adapted Acinetobacter sp. CUI-P1 Revealed by Comparative Genome Analysis.

This study focused on the exploration of microbial communities inhabiting extreme cold environments, such as the Passu and Pisan glaciers of Pakistan, and their potential utilization in industrial applications. Among the 25 initially screened strains, five were found to be suitable candidates for exopolysaccharide (EPS) production, with strain CUI-P1 displaying the highest yield of 7230.5 mg/L compared to the other four strains. The purified EPS from CUI-P1 was tested for its ability to protect probiotic bacteria and E. coli expressing green fluorescence protein (HriGFP) against extreme cold temperatures, and it exhibited excellent cryoprotectant and emulsification activity, highlighting its potential use in the biotechnological industry. Furthermore, the genome of Acinetobacter sp., CUI-P1 comprised 199 contigs, with a genome size of 10,493,143bp and a G + C content of 42%, and showed 98.197% nucleotide identity to the type genome of Acinetobacter baumannii ATCC 17978. These findings offer promising avenues for the application of EPS as a cryoprotectant, an essential tool in modern biotechnology.

Design, synthesis, and antibacterial activity of a new series of ciprofloxacin-thiadiazole hybrid

This study synthesized novel ciprofloxacin analogs bearing the 2-amino-1,3,4-thiadiazole ring, including tryptophan and different sulfonamides, to act as antimicrobial agents. Then, the activities of the synthesized hybrids were screened against 18 tested bacterial isolates from 4 standard strains (Escherichia coli ATCC 8739, Staphylococcus aureus ATCC 25,923, Acinetobacter baumannii ATCC 19,606, and Pseudomonas aeruginosa PAO1) and 14 clinical strains (2 Enterobacter cloacae and 12 Klebsiella pneumonia isolates). Investigations revealed that compound 2 showed better antimicrobial activities among the synthesized compounds than the standard drug, ciprofloxacin, demonstrated by its lower MIC and MBC values. We also notably observed that compared to ciprofloxacin, compound 2 maintained its activity for a longer time without inducing resistance in the tested bacterium. Hence, we conducted a time-to-kill assay and compared the results with its parent drug, followed by a molecular modeling simulation study through the docking of compound 2 into E. coli DNA gyrase enzyme active site to elucidate its binding modes to the receptor. Then, we compared these results with ciprofloxacin and calculated the physicochemical descriptors, ADME parameters, pharmacokinetic properties, and drug-like nature profile of compound 2 as the most potent were also calculated. Based on our findings, we conclude that with further modifications of compound 2, the design of a new and optimized fluoroquinolone generation should be possible.

Role of peptidoglycan recycling enzymes AmpD and AnmK in Acinetobacter baumannii virulence features.

Acinetobacter baumannii is an important causative agent of hospital acquired infections. In addition to acquired resistance to many currently-available antibiotics, it is intrinsically resistant to fosfomycin. It has previously been shown that AmpD and AnmK contribute to intrinsic fosfomycin resistance in A. baumannii due to their involvement in the peptidoglycan recycling pathway. However, the role that these two enzymes play in the fitness and virulence of A. baumannii has not been studied. The aim of this study was to characterize several virulence-related phenotypic traits in A. baumannii mutants lacking AmpD and AnmK. Specifically, cell morphology, peptidoglycan thickness, membrane permeability, growth under iron-limiting conditions, fitness, resistance to disinfectants and antimicrobial agents, twitching motility and biofilm formation of the mutant strains A. baumannii ATCC 17978 ΔampD::Kan and ΔanmK::Kan were compared to the wild type strain. Our results demonstrate that bacterial growth and fitness of both mutants were compromised, especially in the ΔampD::Kan mutant. In addition, biofilm formation was decreased by up to 69%, whereas twitching movement was reduced by about 80% in both mutants. These results demonstrate that, in addition to increased susceptibility to fosfomycin, alteration of the peptidoglycan recycling pathway affects multiple aspects related to virulence. Inhibition of these enzymes could be explored as a strategy to develop novel treatments for A. baumannii in the future. Furthermore, this study establishes a link between intrinsic fosfomycin resistance mechanisms and bacterial fitness and virulence traits.

Effectiveness Evaluation of a UV-C-Photoinactivator against Selected ESKAPE-E Pathogens.

Healthcare-associated infections (HAI) worldwide includes infections by ESKAPE-E pathogens. Environmental surfaces and fomites are important components in HAI transmission dynamics, and shoe soles are vectors of HAI. Ultraviolet (UV) disinfection is an effective method to inactivate pathogenic microorganisms. In this study, we investigated whether the SANITECH UV-C shoe sole decontaminator equipment that provides germicidal UV-C radiation could effectively reduce this risk of different pathogens. Six standard strains and four clinical MDR strains in liquid and solid medium were exposed to a UV-C System at specific concentrations at other times. Bacterial inactivation (growth and cultivability) was investigated using colony counts and resazurin as metabolic indicators. SEM was performed to assess the membrane damage. Statistically significant reduction in cell viability for all ATCCs strains occurred after 10 s of exposure to the UV-C system, except for S. enterica, which only occurred at 20 s. The cell viability of P. aeruginosa (90.9%), E. faecalis and A. baumannii (85.3%), S. enterica (82.9%), E. coli (79.2%) and S. aureus (71.9%) was reduced considerably at 20 s. In colony count, after 12 s of UV-C exposure, all ATCC strains showed a 100% reduction in CFU counts, except for A. baumannii, which reduced by 97.7%. A substantial reduction of colonies above 3 log10 was observed at 12 and 20 s in all bacterial strains tested, except for A. baumannii ATCC 19606 (12 s). The exposure of ATCCs bacterial strains to the UV-C system for only 2 s was able to reduce 100% in the colony forming units (CFU) count in all ATCCs strains, S. aureus, P. aeruginosa, E. coli, A. baumannii, E. faecalis, except the S. enterica strain which had a statistically significant reduction of 99.7%. In ATCC strains, there was a substantial decrease in colonies after 4 s (sec) of exposure to the UV-C system, with a reduction ranging from 3.78-4.15 log10 CFU/mL. This reduction was observed in MDR/ESKAPE-E strains within 10 s, showing that UV-C could eliminate above 3.84 log10 CFU/mL. SEM showed a reduction of pili-like appendages after UV-C treatment in all strains except for E. coli (ATCC 25922). The Sanitech UV-C shoe sole decontaminator equipment from Astech Serv. and Fabrication Ltd. (Petrópolis, Brazil), effectively killed in vitro a series of ATCCs and MDR/ESKAPE-E bacteria of sanitary interest, commonly found in the hospital environment.

Chitosan-Placental ECM Composite Thermos-Responsive Hydrogel as a Biomimetic Wound Dressing with Angiogenic Property.

Attempts are being made to develop an ideal wound dressing with excellent biomechanical and biological properties. Here, a thermos-responsive hydrogel is fabricated using chitosan (CTS) with various concentrations (1%, 2.5%, and 5% w/v) of solubilized placental extracellular matrix (ECM) and 20% β-glycerophosphate to optimize a smart wound dressing hydrogel with improved biological behavior. The thermo-responsive CTS (TCTS) alone or loaded with ECMs (ECM-TCTS) demonstrate uniform morphology using SEM. TCTS and ECM1%-TCTS and ECM2.5%-TCTS show a gelation time of 5min at 37°C, while no gel formation is observed at 4 and 25°C. ECM5%-TCTS forms gel at both 25 and 37°C. The degradation and swelling ratios increaseas the ECM content of the hydrogel increase. All the constructs show excellent biocompatibility in vitro and in vivo, however, the hydrogels with a higher concentration of ECM demonstrate better cell adhesion for fibroblast cells and induce expression of angiogenic factors (VEGF and VEGFR) from HUVEC. Only the ECM5%-TCTS has antibacterial activity against Acinetobacter baumannii ATCC 19606. The data obtained from the current study suggest the ECM2.5%-TCTS as an optimized smart biomimetic wound dressing with improved angiogenic properties now promises to proceed with pre-clinical and clinical investigations.

Transcriptome Analysis of Acinetobacter baumannii in Rapid Response to Subinhibitory Concentration of Minocycline.

The increasing emergence of multidrug-resistant Acinetobacter baumannii brings great threats to public health. Minocycline is a kind of semisynthetic derivative of the antibacterial drug tetracycline and is often used to treat infections caused by multidrug-resistant A. baumannii with other antibiotics. However, minocycline-resistant A. baumannii appears constantly. To rapidly explore the response of A. baumannii to minocycline stress, RNA-seq was carried out to compare the difference in the transcriptome of A. baumannii ATCC19606 in the presence or absence of minocycline. The results showed that 25 genes were differentially expressed, including 10 downregulated genes and 15 upregulated genes, and 24 sRNA were upregulated and 24 were downregulated based on the filter criteria (Log2FC > 1 or <−1 and FDR < 0.05). RtcB family protein and ABC transporter ATP-binding protein were upregulated by 2.6- and 11.3-fold, and molecular chaperone GroES, chaperonin GroL, class C beta-lactamase ADC-158, amino acid ABC transporter permease, and APC family permease were downregulated by at least two-fold in the presence of half-MIC minocycline. The differentially expressed genes are mainly involved in the stress response, the GroES/GroEL chaperonin system, and transport metabolic pathways. sRNA 1248 was significantly upregulated, and sRNA 1767, 5182, and 6984 were downregulated in a rapid response to minocycline. These results provide insights into the adaptive mechanism of A. baumannii to minocycline.

Identification of potential novel membrane drug targets of Acinetobacter baumannii ATCC 19606 using subtractive proteomics approach

Identification of potential novel membrane drug targets of Acinetobacter baumannii ATCC 19606 using subtractive proteomics approach

Growth kinetics of multiple Acinetobacter baumannii resistotype after meropenem-based antibiotic combination exposure.

Background: Carbapenems are the treatment of choice for multidrug-resistant (MDR) and extensively drug-resistant (XDR) Acinetobacter baumannii infections, but the emergence of carbapenem-resistant A. baumannii (CRAB) has rendered it ineffective in the vast majority of cases. Combination therapy has grown in popularity over the last decade; this study aims to analyze A.baumannii growth kinetics after exposure to meropenem and ampicillin-sulbactam compared with meropenem and amikacin antibiotic combinations in clinically relevant concentrations. Methods: This experimental laboratory study was conducted on the A. baumannii ATCC 19606 isolate and three clinical isolates that were intermediate or resistant to tested antibiotics. Meropenem and ampicillin-sulbactam, as well as meropenem and amikacin, were tested at four different concentrations against isolates. Turbidity measurements were taken at predetermined time points of 0, 1, 2, 4, 6, 8, and 24 hours following exposure; bacterial concentration was enumerated using the agar plate method, with the results plotted in a time-kill curve. Results: A bactericidal effect was achieved in isolates that were intermediate to ampicillin-sulbactam and resistant to meropenem after the administration of meropenem and ampicillin-sulbactam combination with a concentration of 4 µg/ml and 16/8 µg/ml, respectively. The combination of meropenem and ampicillin-sulbactam demonstrated bacteriostatic activity against isolates that were resistant to both antibiotics. Isolates treated with resistant antibiotics showed an increased growth rate compared to the growth control. Conclusion: The combination of meropenem and ampicillin-sulbactam could be a promising combination therapy in treating CRAB infections. The mechanism and degree of antibiotic resistance in the isolates affect the efficacy of antibiotic combinations; further research is needed to corroborate the findings of this study.

Complementary Regulation of BfmRS Two-Component and AbaIR Quorum Sensing Systems to Express Virulence-Associated Genes in Acinetobacter baumannii.

Acinetobacter baumannii expresses various virulence factors to adapt to hostile environments and infect susceptible hosts. This study investigated the regulatory network of the BfmRS two-component and AbaIR quorum sensing (QS) systems in the expression of virulence-associated genes in A. baumannii ATCC 17978. The ΔbfmS mutant exhibited a significant decrease in surface motility, which presumably resulted from the low expression of pilT and A1S_0112-A1S_0119 gene cluster. The ΔbfmR mutant displayed a significant reduction in biofilm and pellicle formation due to the low expression of csu operon. The deletion of abaR did not affect the expression of bfmR or bfmS. However, the expression of abaR and abaI was upregulated in the ΔbfmR mutant. The ΔbfmR mutant also produced more autoinducers than did the wild-type strain, suggesting that BfmR negatively regulates the AbaIR QS system. The ΔbfmS mutant exhibited no autoinducer production in the bioassay system. The expression of the A1S_0112-A1S_0119 gene cluster was downregulated in the ΔabaR mutant, whereas the expression of csu operon was upregulated in this mutant with a high cell density. In conclusion, for the first time, we demonstrated that the BfmRS-AbaIR QS system axis regulated the expression of virulence-associated genes in A. baumannii. This study provides new insights into the complex network system involved in the regulation of virulence-associated genes underlying the pathogenicity of A. baumannii.

Effect of some inorganic phosphate salts on Acinetobacter baumannii growth

Acinetobacter baumannii is considered as a gram-negative, ubiquitous nonmotile organism, it’s growth is limited by many conditions such as phosphate abundance. Phosphorus is the most essential element contributes too many biological processes like energy metabolism, the inheritance of genetic materials, intracellular signalling, and membrane integrity. In this study, different phosphorus sources and concentrations were used to detect the best source and the best concentration for bacterial growth. Serial concentrations (5,10.15,20,25,30,35 mg ml-1) of KH2 PO4 and K2HPO4 were used as inorganic phosphate source in nutrient broth to culture A. baumannii ATCC 17904 and A.baumannii HHR 1 The results showed that 5 mg ml-1of KH2 PO4 is the best source and best concentration for both isolates, where the bacterial growth was increased to OD600 of 1.596 for A. baumannii ATCC 17904 and 1.580 for A. baumannii HHR1 after 20 h, whereas, bacterial growth was slightly decreased when 35 mg ml-1 of KH2 PO4 was added to both isolates in comparison to the control. As for using of K2HPO4 , it was noticed that the growth of A. baumannii ATCC 17904 and A. baumannii HHR1 in the presence of 5 mg ml-1 (K2HPO4 ) increased the growth to approximately OD600 of 1.580 and 1.541 for both isolates respectively, compared to the control and other concentrations where the growth of both isolates slightly less than that of 5 mg ml-1.

Novel naphthalene-based bis-pyridinium compounds with pronounced antibacterial activity

Novel para-substituted bis-pyridinium compounds containing 2,7-dioxynaphthalene spacer were synthesized in two simple steps from the corresponding dihydroxy-naphthalene. The microbiological study on five reference (E. coli ATCC 25922, K. pneumoniae ATCC 70060, S. aureus ATCC 43300, P. aeruginosa ATCC27853, and A. baumannii ATCC 15308) and five clinical (E. coli B-3421/19,K. pneumoniae B-2523/18, S. aureus B-8648, P. aeruginosa B-2099/18 and A. baumannii B-2926/18) bacterial strains showed promising range of antibacterial properties for these biocides, compared to modern sanitizers.

Cinnamaldehyde derivatives act as antimicrobial agents against Acinetobacter baumannii through the inhibition of cell division.

Acinetobacter baumannii is a pathogen with high intrinsic antimicrobial resistance while multidrug resistant (MDR) and extensively drug resistant (XDR) strains of this pathogen are emerging. Treatment options for infections by these strains are very limited, hence new therapies are urgently needed. The bacterial cell division protein, FtsZ, is a promising drug target for the development of novel antimicrobial agents. We have previously reported limited activity of cinnamaldehyde analogs against Escherichia coli. In this study, we have determined the antimicrobial activity of six cinnamaldehyde analogs for antimicrobial activity against A. baumannii. Microscopic analysis was performed to determine if the compounds inhibit cell division. The on-target effect of the compounds was assessed by analyzing their effect on polymerization and on the GTPase activity of purified FtsZ from A. baumannii. In silico docking was used to assess the binding of cinnamaldehyde analogs. Finally, in vivo and in vitro safety assays were performed. All six compounds displayed antibacterial activity against the critical priority pathogen A. baumannii, with 4-bromophenyl-substituted 4 displaying the most potent antimicrobial activity (MIC 32 μg/mL). Bioactivity was significantly increased in the presence of an efflux pump inhibitor for A. baumannii ATCC 19606 (up to 32-fold) and significantly, for extensively drug resistant UW 5075 (greater than 4-fold), suggesting that efflux contributes to the intrinsic resistance of A. baumannii against these agents. The compounds inhibited cell division in A. baumannii as observed by the elongated phenotype and targeted the FtsZ protein as seen from the inhibition of polymerization and GTPase activity. In silico docking predicted that the compounds bind in the interdomain cleft adjacent to the H7 core helix. Di-chlorinated 6 was devoid of hemolytic activity and cytotoxicity against mammalian cells in vitro, as well as adverse activity in a Caenorhabditis elegans nematode model in vivo. Together, these findings present halogenated analogs 4 and 6 as promising candidates for further development as antimicrobial agents aimed at combating A. baumannii. This is also the first report of FtsZ-targeting compounds with activity against an XDR A. baumannii strain.

Transcriptomic analysis reveals the regulatory role of quorum sensing in the Acinetobacter baumannii ATCC 19606 via RNA-seq

BackgroundAcinetobacter baumannii has emerged as the major opportunistic pathogen in healthcare-associated infections with high-level antibiotic resistance and high mortality. Quorum sensing (QS) system is a cell-to-cell bacterial communication mediated by the synthesis, secretion, and binding of auto-inducer signals. It is a global regulatory system to coordinate the behavior of individual bacteria in a population. The present study focused on the QS system, aiming to investigate the regulatory role of QS in bacterial virulence and antibiotic resistance.MethodThe auto-inducer synthase gene abaI was deleted using the A. baumannii ATCC 19606 strain to interrupt the QS process. The RNA-seq was performed to identify the differentially expressed genes (DEGs) and pathways in the mutant (△abaI) strain compared with the wild-type (WT) strain.ResultsA total of 380 DEGs [the adjusted P value < 0.05 and the absolute value of log2(fold change) > log21.5] were identified, including 256 upregulated genes and 124 downregulated genes in the △abaI strain. The enrichment analysis indicated that the DEGs involved in arginine biosynthesis, purine metabolism, biofilm formation, and type VI secretion system (T6SS) were downregulated, while the DEGs involved in pathways related to fatty acid metabolism and amino acid metabolism were upregulated. Consistent with the expression change of the DEGs, a decrease in biofilm formation was observed in the △abaI strain compared with the WT strain. On the contrary, no obvious changes were found in antimicrobial resistance following the deletion of abaI.ConclusionsThe present study demonstrated the transcriptomic profile of A. baumannii after the deletion of abaI, revealing an important regulatory role of the QS system in bacterial virulence. The deletion of abaI suppressed the biofilm formation in A. baumannii ATCC 19606, leading to decreased pathogenicity. Further studies on the role of abaR, encoding the receptor of auto-inducer in the QS circuit, are required for a better understanding of the regulation of bacterial virulence and pathogenicity in the QS network.

Investigation the effects of silver nanoparticles and gold nanoparticles on expression of bap and csu genes in biofilm formation of Acinetobacter baumannii.

Acinetobacter baumannii is one of the main pathogens of the hospital and causes various infections. csu A/BABCDE involved in the initial surface attachment during biofilm formation and bap gene produces specific proteins at the cell surface that play a direct role in formation of biofilm and the infectivity of this bacterium. The aim of this study was to investigate the effect of silver nanoparticles and gold nanoparticles on the expression of bap and csu genes in the Acinetobacter baumannii biofilm formation. The susceptibility test was performed to determine the MIC of silver nanoparticles, gold nanoparticles and gold-vancomycin nanoparticles performed by broth dilution method on A. baumannii strains. The ability of biofilms formation in strains treated by MIC of silver nanoparticles and gold-vancomycin nanoparticles were evaluated by microtiter plate method and A. baumannii ATCC19606 used as control. Expression of the csu and bap genes were determinded by measuring the cognate mRNA level by real-time PCR. In present study, gold nanoparticles could not prevent the growth and biofilm formation of A. baumannii strains. The MIC concentration of silver nanoparticles and vancomycin- gold nanoparticles were 6.25 μg/ml and 0.625 μg/ml respectively and MBC concenteration of nanoparticles for 70% of strain was 12.5 μg/ml and 1.25 μg/ml respectively. Real-time PCR and data analysis, determined that the expression of bap, csuC and csuE genes in A. baumannii strains treated with MIC concentration (6.25 μg/ml) of silver nanoparticles decreased compared to control groups. Also, the expression of csuC and csuE genes in strains treated with MIC concentration (0.625 μg/ml) of vancomycin -gold nanoparticles increased, however the expression of bap was decreased compared to the control groups. Due to the inhibitory effect of silver nanoparticles and gold-vancomycin nanoparticles against A. baumannii biofilm formation and genes expression, they can probably be used for prevent of biofilm formation in medical instrument or can be use for treatment of infections with or without antibiotic.

3-indoleacetonitrile attenuates biofilm formation and enhances sensitivity to imipenem in Acinetobacter baumannii.

Acinetobacter baumannii poses a global danger due to its ability to resist most of the currently available antimicrobial agents. Furthermore, the rise of carbapenem-resistant A. baumannii isolates has limited the treatment options available. In the present study, plant auxin 3-indoleacetonitrile (3IAN) was found to inhibit biofilm formation and motility of A. baumannii at sublethal concentration. Mechanistically, 3IAN inhibited the synthesis of the quorum sensing signal 3-OH-C12-HSL by downregulating the expression of the abaI autoinducer synthase gene. 3IAN was found to reduce the minimum inhibitory concentration of A. baumannii ATCC 17978 against imipenem, ofloxacin, ciprofloxacin, tobramycin, and levofloxacin, and significantly decreased persistence against imipenem. Inhibition of efflux pumps by downregulating genes expression may be responsible for enhanced sensitivity and low persistence. 3IAN reduced the resistance to imipenem in carbapenem-resistant A. baumannii isolates by downregulating the expression of OXA β-lactamases (blaoxa-51 and blaoxa-23), outer membrane protein carO, and transporter protein adeB. These findings demonstrate the therapeutic potential of 3IAN, which could be explored as an adjuvant with antibiotics for controlling A. baumannii infections.

Histamine Produced by Gram-Negative Bacteria Impairs Neutrophil’s Antimicrobial Response by Engaging the Histamine 2 Receptor

We found that histamine (10−9 M) did not have any effect on the in vitro capture of Escherichia coli by neutrophils but accelerated its intracellular killing. In contrast, histamine (10−6 M) delayed the capture of Escherichia coli by neutrophils and reduced the amounts of pHrodo zymosan particles inside acidic mature phagosomes. Histamine acted through the H4R and the H2R, which are coupled to the Src family tyrosine kinases or the cAMP/protein kinase A pathway, respectively. The protein kinase A inhibitor H-89 abrogated the delay in bacterial capture induced by histamine (10−6 M) and the Src family tyrosine kinase inhibitor PP2 blocked histamine (10−9 M) induced acceleration of bacterial intracellular killing and tyrosine phosphorylation of proteins. To investigate the role of histamine in pathogenicity, we designed an Acinetobacter baumannii strain deficient in histamine production (hdc::TOPO). Galleria mellonella larvae inoculated with the wild-type Acinetobacter baumannii ATCC 17978 strain (1.1 × 105 CFU) died rapidly (100% death within 40 h) but not when inoculated with the Acinetobacter baumannii hdc::TOPO mutant (10% mortality). The concentration of histamine rose in the larval haemolymph upon inoculation of the wild type but not the Acinetobacter baumannii hdc::TOPO mutant, such concentration of histamine blocks the ability of hemocytes from Galleria mellonella to capture Candida albicans in vitro. Thus, bacteria-producing histamine, by maintaining high levels of histamine, may impair neutrophil phagocytosis by hijacking the H2R.