Antimicrobial efficacy of Acacia nilotica, Murraya koenigii (L.) Sprengel, Eucalyptus hybrid, Psidium guajava extracts and their combination on Streptococcus mutans and Lactobacillus acidophilus

Abstract

Background: The aim of this in vitro study was to assess antimicrobial efficacy of Acacia nilotica,

Murraya koenigii (L.) Sprengel, Eucalyptus hybrid, Psidium guajava extracts, and their combination on

Streptococcus mutans and Lactobacillus acidophilus.

Materials and Methods: The branches of four plants were collected, identified, and authenticated

by a taxonomist. The plants were rinsed in water, healthy leaves were separated and shade dried over

a period of 3–4 weeks. Soxhlet apparatus using ethanol was employed for extraction procedure.

The combinations of plant extracts were prepared by mixing equal quantities of 10% solutions of

each of these extracts. 0.2% chlorhexidine and dimethyl sulfoxide were used as positive and negative

controls, respectively. The antimicrobial efficacy testing was done using agar well‑diffusion method

under anaerobic conditions. The mean diameter of inhibition zone was computed and compared

between different categories using one‑way analysis of variance and Tukey’s post‑hoc test. A qualitative

assay was carried out to identify the various phytochemical constituents in the plants. The data was

assessed by SPSS version 20. The statistical significance was fixed at 0.05.

Results: All the plants extracts and their combinations inhibited S. mutans and L. acidophilus. However,

the quadruple combination of A. nilotica + M. koenigii (L.) Sprengel + Eucalyptus hybrid + P. guajava

produced the maximum inhibition zone (23.5 ± 2.2 mm) against S. mutans. Although, 0.2%

chlorhexidine produced the highest inhibition zone against L. acidophilus (18.8 ± 1.2 mm),

A. nilotica extract produced maximum inhibition among the various plant extracts and their

combinations (14.1 ± 1.8 mm).

Conclusion: All the individual plant extracts and their combinations were effective against S. mutans

and L. acidophilus. These could be tried as herbal alternates to chlorhexidine. However, these in vitro

results have to be further evaluated for any toxicity of the polyherbal combinations in animal models

and effectiveness has to be assessed using in vivo studies on humans.

Key Words: Acacia, nilotica, Eucalyptus, hybrid, Lactobacillus acidophilus, Murraya, koenigii (L.) Sprengel anomaly, Psidium guajava, Streptococcus mutans