The antimicrobial activity of plants in the vicinity of a geothermal area in Perak, Malaysia

Introduction

Extreme environments provide a new scaffold for the study of natural products for drug discovery. These environments are a challenge to live in, therefore the plant species that are found there must have specific survival mechanisms. This increases the possibility of discovering unique biologically active compounds. The polar region is an example of an extreme environment that has been explored. In McMurdo Sound, Antarctica, benthic invertebrates are exposed to significant predation by sea stars and potentially infectious water-column microorganisms, which suggests that chemically-mediated defense strategies would be an advantage. For example, discorhabdin C (Figure 1), found in the sponge Lantrunculia apicalis, is alkaloid and possesses a unique structure with antitumor and antimicrobial activity, and plays a role in the sea star tube-foot retraction assay^1–3.

Figure 1. Discorhabdin C.

Alkaloid discorhabdin C found in the sponge Lantrunculia apicalis.

Malaysia, although the climate is tropical, is rich in various geography, including geothermal areas in the form of hot springs. The biodiversity of geothermal areas in Malaysia has yet to be fully studied, therefore, an opportunity to investigate the bioactivities of plants that grow near geothermal areas, has risen. Plants that survive here are unique because of their ability to adapt to extreme temperature. The most heat-tolerant plants are mosses and lichens, which can survive ground temperatures of 70°C. Prostrate kanuka (Kunzea ericoides var. microflorum) is a low, spreading variety of the kanuka shrub that only grows in geothermal areas. It can tolerate ground temperatures of up to 55°C⁴. Additionally, grasses such as Dichanthelium lanuginosum and Paspalum laeve Michx were also found in geothermally heated environments, namely in the Yellowstone National Park⁵ and Hot Springs National Park, Arkansas⁶, respectively. Locally, Hyptis suaveolens, located within the hot spring enclosure in the Tambun area of Perak is used to combat fever, and soothe headaches and skin rashes⁷.

Among the data presented in the 2nd edition of the National Antibiotic Guideline in conjunction with the Annual Scientific Meeting on Antimicrobial Resistance in 2015 in Putrajaya, Malaysia, was resistance of Escherichia coli to Ampicillin, which had risen to more than 50 percent. Streptococcus pneumoniae resistance towards Erythromycin had increased from 18.2 percent in 2013 to 28.1 percent in 2014, and Acinetobacter baumannii resistance against Meropenem had increased from 47.7 percent to 57.3 percent within seven years^8,9. Additionally, P.aeruginosa is generally resistant to a large range of antibiotics and may demonstrate additional resistance after unsuccessful treatment¹⁰. Hence, research for the discovery of new antibiotics and drugs against these bacteria is very much needed.

Methods

Plant material

Plants were collected by hand on the 26^th of April 2016 in the vicinity of Ulu Slim, Perak, Malaysia (Figure 2). It should be noted that these plants do not have flowers or any significant morphology that allows their identification, so identifying them was a challenge.

Figure 2. Geothermal area in Ulu Slim, Perak, Malaysia, where the plants were collected.

Results and discussion

Both plants were collected in the vicinity of the geothermal site at Ulu Slim, Perak, Malaysia. Water temperature was 90°C at the time of collection. Upon collection, plants were immediately identified by a botanist and then underwent methanol extraction. Both plants were identified to be C.icosandra (also called C.viscosa), locally known as Maman Pasir of the family Cleomaceae. In addition, Stachytarpheta species of the family Lamiaceae were also collected. Further species identification needs to be con-ducted for this particular plant; they are identified based on plant morphology and taxonomy. It should be noted that both plants are very small, subshrub-like and only consist of leaves that are absent of flowers. We believe that these plants may possess unique, biologically active compounds. We proceeded to evaluate their antimicrobial activity, but crude methanol extracts of both plants revealed no activity against the three tested bacteria E.coli, S.aureus and P.aeruginosa (Table 1, Figure 3)

Figure 3. Antimicrobial assay of crude methanol extracts of C.icosandra and Stachytarpheta sp.

The figure displays petri dishes containing filter paper discs with saturated crude methanol extracts of C.icosandra (C) and Stachytarpheta sp. (D), in (i) E.coli, (ii) S. aureus and (iii) P. aeruginosa. No inhibition halo was observed.

Conclusions

This is the first record taken of plants in the vicinity of the geothermal area in Ulu Slim, Perak, Malaysia. Plants near these unexploited environments of extreme condition should be further studied for their potential in drug discovery.

Data availability

All data required to re-analyse the study has been provided in the main body of text.