Metabolomics responses and tolerance of Pseudomonas aeruginosa under acoustic vibration stress.

Sound has been shown to impact microbial behaviors. However, our understanding of the chemical and molecular mechanisms underlying these microbial responses to acoustic vibration is limited. In this study, we used untargeted metabolomics analysis to investigate the effects of 100-Hz acoustic vibration on the intra- and extracellular hydrophobic metabolites of P. aeruginosa PAO1. Our findings revealed increased levels of fatty acids and their derivatives, quinolones, and N-acylethanolamines upon sound exposure, while rhamnolipids (RLs) showed decreased levels. Further quantitative real-time polymerase chain reaction experiments showed slight downregulation of the rhlA gene (1.3-fold) and upregulation of fabY (1.5-fold), fadE (1.7-fold), and pqsA (1.4-fold) genes, which are associated with RL, fatty acid, and quinolone biosynthesis. However, no alterations in the genes related to the rpoS regulators or quorum-sensing networks were observed. Supplementing sodium oleate to P. aeruginosa cultures to simulate the effects of sound resulted in increased tolerance of P. aeruginosa in the presence of sound at 48 h, suggesting a potential novel response-tolerance correlation. In contrast, adding RL, which went against the response direction, did not affect its growth. Overall, these findings provide potential implications for the control and manipulation of virulence and bacterial characteristics for medical and industrial applications.

Boesenbergia rotunda (L.) Mansf. extract potentiates the antibacterial activity of some ß-lactams against ß-lactam-resistant staphylococci.

OBJECTIVES: The purpose of this study was to investigate the effect of Boesenbergia rotunda (L.) Mansf. extract (BRE) and peptidoglycan inhibitor antibiotics, alone and in combination, against ß-lactam-resistant staphylococci. METHODS: Antibacterial and synergistic activities of BRE alone and in combination with ampicillin (AMP), cloxacillin (CLX), cefazolin (CZO) or vancomycin (VAN) were evaluated against two ß-lactam-resistant Staphylococcus aureus (BRSA) isolates and one ß-lactam-resistant Staphylococcus epidermidis (BRSE) isolate. The activities were confirmed by killing curve assays. The preliminary antimicrobial action was elucidated by transmission electron microscopy (TEM) and cytoplasmic membrane (CM) permeability assay. RESULTS: All tested staphylococci were inhibited by BRE at a minimum inhibitory concentration (MIC) of 16µg/mL. Two BRSA strains showed high resistance to CLX, AMP and CZO, whilst BRSE was resistant to CLX and AMP. All tested isolates remained susceptible to VAN. Chequerboard assay demonstrated a fractional inhibitory concentration index (FICI) of 0.50 for the BRE+CLX combination against the BRSA strains. Killing curve determinations confirmed the antibacterial and synergistic activities. TEM revealed collapse of the CM in BRE-treated cells and damage both of the CM and peptidoglycan (PG) in BRE+CLX-treated cells. The CM permeability assay showed that either BRE or nisin alone as well as BRE+CLX significantly induced leakage of OD260nm-absorbing materials. CONCLUSIONS: BRE potentiated the activity of ß-lactams, particularly CLX, against ß-lactam-resistant staphylococci by damaging the CM and PG layer, leading to leakage of intracellular material. Combination of BRE and ß-lactams provides a potential way forward in developing novel antistaphylococcal agents.

Evaluation of resazurin microtiter plate assay and HPLC- photodiode array analysis of the roots of Asparagus adscendens.

Asparagus adscendens Roxb. (Asparagaceae), is native to the Himalayas. The present study, for the first time, was undertaken to explore the antimicrobial potential, to determine the minimum inhibitory concentration (MIC) values of the methanol extract of the roots of A. adscendens and its solid-phase extraction (SPE) fractions using resazurin microtitre assay against Gram-positive and negative bacterial-registered strains and to carry out HPLC-photodiode array analysis of the SPE fractions. The methanol extract and all SPE exhibited considerable level of antibacterial potential against Gram-positive bacteria (MIC: 2.5-0.009 mg/mL) than against Gram-negative bacteria (MIC: 1.25-2.5 mg/mL). The use of microtitre plates has the advantage of lower cost, fast and quantitative results. Like other Asparagus species, the presence of phenolic compounds in all SPE fractions was evident in the HPLC-PDA data.