Alcohol dehydrogenase modulates quorum sensing in biofilm formations of Acinetobacter baumannii

Comparative Proteomic Analysis of Protein Patterns of Stenotrophomonas maltophilia in Biofilm and Planktonic Lifestyles

Stenotrophomonas maltophilia is a clinically relevant bacterial pathogen, particularly in cystic fibrosis (CF) patients. Despite the well-known ability to form biofilms inherently resistant to antibiotics and host immunity, many aspects involved in S. maltophilia biofilm formation are yet to be elucidated. In the present study, a proteomic approach was used to elucidate the differential protein expression patterns observed during the planktonic-to-biofilm transition of S. maltophilia Sm126, a strong biofilm producer causing chronic infection in a CF patient, to identify determinants potentially associated with S. maltophilia biofilm formation. In all, 57 proteins were differentially (3-fold; p < 0.01) expressed in biofilm cells compared with planktonic counterparts: 38 were overexpressed, and 19 were down-expressed. It is worth noting that 34 proteins were exclusively found in biofilm, mainly associated with quorum sensing-mediated intercellular communication, augmented glycolysis, amino acid metabolism, biosynthesis of secondary metabolites, phosphate signaling, response to nutrient starvation, and general stress. Further work is warranted to evaluate if these proteins can be suitable targets for developing anti-biofilm strategies effective against S. maltophilia.

Overexpression of BIT33_RS14560 Enhances the Biofilm Formation and Virulence of Acinetobacter baumannii

Acinetobacter baumannii, a strictly aerobic, non-lactose fermented Gram-negative bacteria, is one of the important pathogens of nosocomial infection. Major facilitator superfamily (MFS) transporter membrane proteins are a class of proteins that widely exists in microbial genomes and have been revealed to be related to biofilm formation in a variety of microorganisms. However, as one of the MFS transporter membrane proteins, little is known about the role of BIT33_RS14560 in A. baumannii. To explore the effects of BIT33_RS14560 on biofilm formation of A. baumannii, the biofilm formation abilities of 62 isolates were firstly investigated and compared with their transcript levels of BIT33_RS14560. Then, this specific gene was over-expressed in a standard A. baumannii strain (ATCC 19606) and two isolates of extensively drug-resistant A. baumannii (XDR-Ab). Bacterial virulence was observed using a Galleria mellonella infection model. High-throughput transcriptome sequencing (RNA seq) was performed on ATCC 19606 over-expressed strain and its corresponding empty plasmid control strain. Spearman’s correlation analysis indicated a significant negative correlation (R = −0.569, p = 0.000) between the △CT levels of BIT33_RS1456 and biofilm grading of A. baumannii isolates. The amount of A. baumannii biofilm was relatively high within 12–48 h. Regardless of standard or clinical strains; the biofilm biomass in the BIT33_RS14560 overexpression group was significantly higher than that in the control group ( p < 0.0001). Kaplan–Meier survival curve analysis showed that the mortality of G. mellonella was significantly higher when infected with the BIT33_RS14560 overexpression strain (χ² = 8.462, p = 0.004). RNA-Seq showed that the mRNA expression levels of three genes annotated as OprD family outer membrane porin, glycosyltransferase family 39 protein, and glycosyltransferase family 2 protein, which were related to bacterial adhesion, biofilm formation, and virulence, were significantly upregulated when BIT33_RS14560 was over-expressed. Our findings provided new insights in identifying potential drug targets for the inhibition of biofilm formation. We also developed a practical method to construct an over-expressed vector that can stably replicate in XDR-Ab isolates.

Ketoprofen, Piroxicam and Indomethacin Suppressed Quorum Sensing and Virulence Factors in Acinetobacter baumannii

AIM

Quorum sensing (QS) inhibition is a promising strategy to suppress bacterial virulence, and control infection caused by Gram-negative and Gram-positive bacteria. This study explores the quorum sensing inhibiting activity of the non-steroidal anti-inflammatory drugs (NSAIDs) in Acinetobacter baumannii.

METHODS AND RESULTS

Ketoprofen, piroxicam, and indomethacin revealed QS inhibition via elimination of violacein production of the reporter strain Chromobacterium violaceum ATCC 12472 without affecting bacterial growth. The minimal inhibitory concentration (MIC) of ketoprofen, piroxicam, and indomethacin was determined against A. baumannii strains ATCC 17978, ATCC 19606, A1, A11, and A27 by the microbroth dilution method. The MICs of ketoprofen against tested isolates were 3.12-6.25 mg mL^-1 , piroxicam MICs were 1.25-2.5 mg mL^-1 , and indomethacin MICs were 3.12-12.5 mg mL^-1 . Those compounds significantly inhibited QS-associated virulence factors such as biofilm formation, and surface motility, as well as, significantly increased bacterial tolerance to oxidative stress without affecting bacterial growth. On the molecular level, the three compounds significantly inhibited the transcription of QS regulatory genes abaI/abaR, and biofilm regulated genes cusD, and pgaB. Molecular docking analysis revealed potent binding affinity of the three compounds with AbaI via hydrogen and/or hydrophobic bonds.

CONCLUSION

These results indicate that NSAIDs, ketoprofen, piroxicam, and indomethacin, could be potential inhibitors of the QS and could suppress the QS-related virulence factors of A. baumannii.

SIGNIFICANCE AND IMPACT

Ketoprofen, piroxicam, and indomethacin could provide promising implications and strategies for combating the virulence, and pathogenesis of A. baumannii.

Structural and Biochemical Analysis of the Furan Aldehyde Reductase YugJ from Bacillus subtilis

NAD(H)/NADP(H)-dependent aldehyde/alcohol oxidoreductase (AAOR) participates in a wide range of physiologically important cellular processes by reducing aldehydes or oxidizing alcohols. Among AAOR substrates, furan aldehyde is highly toxic to microorganisms. To counteract the toxic effect of furan aldehyde, some bacteria have evolved AAOR that converts furan aldehyde into a less toxic alcohol. Based on biochemical and structural analyses, we identified Bacillus subtilis YugJ as an atypical AAOR that reduces furan aldehyde. YugJ displayed high substrate specificity toward 5-hydroxymethylfurfural (HMF), a furan aldehyde, in an NADPH- and Ni²⁺-dependent manner. YugJ folds into a two-domain structure consisting of a Rossmann-like domain and an α-helical domain. YugJ interacts with NADP and Ni²⁺ using the interdomain cleft of YugJ. A comparative analysis of three YugJ structures indicated that NADP(H) binding plays a key role in modulating the interdomain dynamics of YugJ. Noticeably, a nitrate ion was found in proximity to the nicotinamide ring of NADP in the YugJ structure, and the HMF-reducing activity of YugJ was inhibited by nitrate, providing insights into the substrate-binding mode of YugJ. These findings contribute to the characterization of the YugJ-mediated furan aldehyde reduction mechanism and to the rational design of improved furan aldehyde reductases for the biofuel industry.

Therapeutic strategies against potential antibiofilm targets of multidrug-resistant Acinetobacter baumannii

Acinetobacter baumannii is the causative agent of various hospital-acquired infections. Biofilm formation is one of the various antimicrobial resistance (AMR) strategies and is associated with high mortality and morbidity. Hence, it is essential to review the potential antibiofilm targets in A. baumannii and come up with different strategies to combat these potential targets. This review covers different pathways involved in the regulation of biofilm formation in A. baumannii like quorum sensing (QS), cyclic-di-GMP signaling, two-component system (TCS), outer-membrane protein (ompA), and biofilm-associated protein (BAP). A newly discovered mechanism of electrical signaling-mediated biofilm formation and contact-dependent biofilm modulation has also been discussed. As biofilm formation and its maintenance in A. baumannii is facilitated by these potential targets, the detailed study of these targets and pathways can bring light to different therapeutic strategies such as anti-biofilm peptides, natural and synthetic molecule inhibitors, QS molecule degrading enzymes, and other strategies. These strategies may help in suppressing the lethality of biofilm-mediated infections. Targeting essential proteins/targets which are crucial for biofilm formation and regulation may render new therapeutic strategies that can aid in combating biofilm, thus reducing the recalcitrant infections and morbidity associated with the biofilm of A. baumannii.

Role of Iron-Containing Alcohol Dehydrogenases in Acinetobacter baumannii ATCC 19606 Stress Resistance and Virulence

Most bacteria possess alcohol dehydrogenase (ADH) genes (Adh genes) to mitigate alcohol toxicity, but these genes have functions beyond alcohol degradation. Previous research has shown that ADH can modulate quorum sensing in Acinetobacter baumannii, a rising opportunistic pathogen. However, the number and nature of Adh genes in A. baumannii have not yet been fully characterized. We identified seven alcohol dehydrogenases (NAD⁺-ADHs) from A. baumannii ATCC 19606, and examined the roles of three iron-containing ADHs, ADH3, ADH4, and ADH6. Marker-less mutation was used to generate Adh3, Adh4, and Adh6 single, double, and triple mutants. Disrupted Adh4 mutants failed to grow in ethanol-, 1-butanol-, or 1-propanol-containing mediums, and recombinant ADH4 exhibited strongest activity against ethanol. Stress resistance assays with inorganic and organic hydroperoxides showed that Adh3 and Adh6 were key to oxidative stress resistance. Virulence assays performed on the Galleria mellonella model organism revealed that Adh4 mutants had comparable virulence to wild-type, while Adh3 and Adh6 mutants had reduced virulence. The results suggest that ADH4 is primarily involved in alcohol metabolism, while ADH3 and ADH6 are key to stress resistance and virulence. Further investigation into the roles of other ADHs in A. baumannii is warranted.

S. aureus Biofilm Protein Expression Linked to Antimicrobial Resistance: A Proteomic Study

Simple Summary

Biofilm formation represents one of the most effective forms of bacterial persistence in surfaces where nutrients are available or in the tissues of living hosts as humans or animals. Such persistence is due to the high rate of antimicrobial resistance of this shell conformation. It often represents a burden when the pathogen colonizes niches from where it is not removable such as food facilities, farm facilities or parts of living organisms. In this study, we investigated biofilm formation mechanisms and enhanced antimicrobial resistance of 6 different S. aureus strains. The detected mechanisms were primarily related to the control of catabolites, the production of proteins with moonlighting activities and the detoxification of compounds with antimicrobial activities (i.e., alcohol). Glycolysis and aerobic metabolisms were found to be less active in the biofilm conformation. Consequently, less H₂O₂ production from aerobic metabolism was translated into a measurable under-representation of catalase protein.

Abstract

Antimicrobial resistance (AMR) represents one of the most critical challenges that humanity will face in the following years. In this context, a “One Health” approach with an integrated multidisciplinary effort involving humans, animals and their surrounding environment is needed to tackle the spread of AMR. One of the most common ways for bacteria to live is to adhere to surfaces and form biofilms. Staphylococcus aureus (S. aureus) can form biofilm on most surfaces and in a wide heterogeneity of environmental conditions. The biofilm guarantees the survival of the S. aureus in harsh environmental conditions and represents an issue for the food industry and animal production. The identification and characterization of biofilm-related proteins may provide interesting insights into biofilm formation mechanisms in S. aureus. In this regard, the aims of this study were: (i) to use proteomics to compare proteomes of S. aureus growing in planktonic and biofilm forms in order to investigate the common features of biofilm formation properties of different strains; (ii) to identify specific biofilm mechanisms that may be involved in AMR. The proteomic analysis showed 14 differentially expressed proteins among biofilm and planktonic forms of S. aureus. Moreover, three proteins, such as alcohol dehydrogenase, ATP-dependent 6-phosphofructokinase, and fructose-bisphosphate aldolase, were only differentially expressed in strains classified as high biofilm producers. Differentially regulated catabolites metabolisms and the switch to lower oxygen-related metabolisms were related to the sessile conformation analyzed.