antimicrobial efficacy of acacia nilotica, murraya koenigii (l.) sprengel, eucalyptus hybrid, psidium guajava extracts and their combination on streptococcus mutans and lactobacillus acidophilus

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