Antibacterial Screening of Isoespintanol, an Aromatic Monoterpene Isolated from Oxandra xylopioides Diels

Abstract

The incidence of nosocomial infections, as well as the high mortality and drug resistance expressed by nosocomial pathogens, especially in immunocompromised patients, poses significant medical challenges. Currently, the efficacy of plant compounds with antimicrobial potential has been reported as a promising alternative therapy to traditional methods. Isoespintanol (ISO) is a monoterpene with high biological activity. Using the broth microdilution method, the antibacterial activity of ISO was examined in 90 clinical isolates, which included 14 different species: (Escherichia coli (38), Pseudomonas aeruginosa (12), Klebsiella pneumoniae (13), Acinetobacter baumannii (3), Proteus mirabilis (7), Staphylococcus epidermidis (3), Staphylococcus aureus (5), Enterococcus faecium (1), Enterococcus faecalis (1), Stenotrophomonas maltophilia (2), Citrobacter koseri (2), Serratia marcescens (1), Aeromonas hydrophila (1), and Providencia rettgeri (1). MIC90 minimum inhibitory concentration values ranged from 694.3 to 916.5 µg/mL and MIC50 values from 154.2 to 457.3 µg/mL. The eradication of mature biofilms in P. aeruginosa after 1 h of exposure to ISO was between 6.6 and 77.4%, being higher in all cases than the percentage of biofilm eradication in cells treated with ciprofloxacin, which was between 4.3 and 67.5%. ISO has antibacterial and antibiofilm potential against nosocomial bacteria and could serve as an adjuvant in the control of these pathogens.

Keywords: Oxandra xylopioides; Pseudomonas aeruginosa; antibacterial activity; antibiofilms; isoespintanol; nosocomial infection.

Figure 1

Strong positive correlation between the concentration of ISO and the percentage of growth inhibition of clinical isolates. We observed that the higher the ISO concentration, the higher the inhibition of microbial growth. The hypothesis test on the correlation coefficient with a p-value < 0.05, indicates that there is a significant linear relationship, with 95% confidence.

Figure 2

Percentages of growth inhibition showing the MIC₅₀ of each group of species of clinical isolates at different ISO concentrations—(A): E. coli; (B): P. aeruginosa; (C): P. mirabilis; (D): S. epidermidis; (E): A. baumannii; (F): K. pneumoniae; (G): S. aureus; (H): Enterococcus (E. faecium, E. faecalis); (I): (C. koseri, S. marcescens, A. hydrophila, S. maltophilia, P. rettgeri).

Figure 2

Percentages of growth inhibition showing the MIC₅₀ of each group of species of clinical isolates at different ISO concentrations—(A): E. coli; (B): P. aeruginosa; (C): P. mirabilis; (D): S. epidermidis; (E): A. baumannii; (F): K. pneumoniae; (G): S. aureus; (H): Enterococcus (E. faecium, E. faecalis); (I): (C. koseri, S. marcescens, A. hydrophila, S. maltophilia, P. rettgeri).

Figure 3

ISO and CIP action on P. aeruginosa biofilms. (A) Biofilm formation at 37 °C for 24 h.The OD₅₉₀ between 1.1. and 3.0 indicates moderate biofilm production and OD₅₉₀ > 3 indicates strong biomass production in biofilms. (B) Biofilm production in the presence of ISO, CIP and without treatment (INO). (C) Percentage of biofilm eradication after 1 h of treatment with the MIC of ISO and CIP for each isolate. The results of the ANOVA have a value of p < 0.05 and Tukey’s test has a confidence level of 95%, indicating that there is a significant difference between the effect of ISO and the effect of CIP on the eradication of biofilms.