Comparative study of antibacterial activity bet- ween Cynodon dactylon crude and solid phase extraction extracts against selected bacterial pathogens Sir, Cynodon dactylon is a type of perennial grass that possesses great medicinal values. Due to numerous reports on usage of C. dactylon as traditional anti- infection agent, this grass has been intensively studied for its antibacterial properties. Previous studies shown C. dactylon killed some common bacterial pathogens including common nosocomial-caused infection patho- gens such as Escherichia coli, Staphylococcus aureus, Kleb- siella pneumonia and Pseudomonas aeruginosa (Abdullah et al., 2012; Abdullah et al., 2013). Although the antibacterial activity reported is consider- ably strong, however, the activity is much depending on the extraction protocols. Our present study compared the antibacterial activity of C. dactylon crude and Solid Phase Extraction (SPE) flush fraction extracts against Bacillus cereus, Bacillus subtilis, E. coli, Klebsiella spp., P. aeruginosa, S. aureus, Streptococcus pyogenes and Streptococcus pneumonia using disc diffusion and broth micro-dilution bioassays. Disc diffusion bioassays of the C. dactylon crude and SPE extracts showed different extent of antibacterial activity against the selected bacterial pathogens (Table I). In general, C. dactylon SPE extracts showed stronger antibacterial activity against the bacterial pathogens compared to plant crude extracts. It is observed that the size of inhibition for the crude extracts is between 7.0 ± 0.0 mm to 10.0 ± 1.0 mm for ethanol extract and 7.0 ± 0.0 to 12.0 ± 1.0 mm for ethyl acetate extract. Meanwhile, size of inhibition for the flush fraction of SPE extract is ranging from 8.0 ± 0.0 mm to 15.7 ± 0.6 mm for ethyl acetate and 8.0 ± 0.0 mm to 13.0 ± 0.0 mm for ethanol SPE extracts. The minimum inhibitory concentration (MIC) expressed as the lowest extract concentration at which no visible growth was observed and measured via turbidity in broth. The MIC values for the crude extracts are ranging from 50-60 mg/mL for ethanol crude extract while 40-60 mg/mL for ethyl acetate crude extract. The MIC study revealed remarkable antibacterial properties from the SPE extracts. The SPE flush fraction from both ethanol and ethyl acetate showed lower MIC values compared to the crude extracts with the values for ethyl acetate SPE extract range from 15-30 mg/mL while 10-20 mg/mL for ethanol SPE extract, two fold from crude extracts MIC values implies that the SPE extracts possess stronger antibacterial activity. The phytochemical constituents of A Journal of the Bangladesh Pharmacological Society (BDPS); www.bdps.info Bangladesh J Pharmacol 2014; 9: 527-28 Journal homepage: www.banglajol.info Abstracted/indexed in Academic Search Complete, Agroforestry Abstracts, Asia Journals Online, Bangladesh Journals Online, Biological Abstracts, BIOSIS Previews, CAB Abstracts, Current Abstracts, Directory of Open Access Journals, EMBASE/Excerpta Medica, Google Scholar, HINARI (WHO), International Pharmaceutical Abstracts, Open J-gate, Science Citation Index Expanded, SCOPUS and Social Sciences Citation Index ISSN: 1991-0088; DOI: 10.3329/bjp.v9i4.20616 Letter to Editor Table I: Comparison of antibacterial activity (measured by diameter of inhibition in mm and Minimum Inhibitory Concentration, MIC values) between C. dactylon ethanol and ethyl acetate crude and Solid Phase Extraction (SPE) extracts Tested microbial pathogens C. dactylon Ethanol crude extract Ethanol SPE extract (flush fraction) Ethyl acetate crude extract Ethyl acetate SPE extract (flush fraction) Inhibition* (mm) MIC# (mg/mL) Inhibition* (mm) MIC# (mg/mL) Inhibition* (mm) MIC# (mg/mL) Inhibition* (mm) MIC# (mg/mL) Bacillus cereus 9.0 ± 0.0 50 13.0 ± 0.0 10 12.0 ± 1.0 40 15.7 ± 0.6 15 Bacillus subtilis 7.0 ± 0.0 50 8.0 ± 0.0a 10 8.0 ± 0.0a 50 11.0 ± 0.0 20 Escherichia coli 8.3 ± 0.6a 60 8.0 ± 0.0a 20 8.0 ± 0.0a 60 9.0 ± 0.0 30 Klebsiella spp. 8.3 ± 0.6a 60 7.0 ± 0.0 20 8.0 ± 0.0a 60 8.0 ± 0.0a 30 Pseudomonas aeruginosa 8.0 ± 0.0 60 7.0 ± 0.0 20 9.3 ± 0.6a 50 10.0 ± 0.0a 30 Staphylococcus aureus 9.0 ± 1.0a 50 9.0 ± 0.0a 10 10.0 ± 0.0a 40 10.0 ± 0.0a 15 Streptococcus pyogenes 10.0 ± 1.0 60 11.0 ± 1.0 15 8.0 ± 0.0a 60 8.0 ± 0.0a 25 Streptococcus pneumonia 7.3 ± 0.6a 60 8.0 ± 0.0a 20 7.0 ± 0.0a 60 10.0 ± 0.0 20 *Values presented are means of three replicates ± SD; each disc loaded with approximately 60 µL or 6 mg per disc of plant extract; n.d = antibacterial activity not detected during the bioassay; CHL= Chloramphenicol (1 mg/mL, 30 µg per disc). All values of inhibition of different extracts on respective bacterial pathogens are significantly different at p=0.05 based on Tukey-test except superscripted with same lettera; #MIC was recorded as the concentration (mg/mL) that resulted in total inhibition of all replicates after 24 hours at 37 ºC C dactylon had been comprehensively discussed in some previous work (Abdullah et al., 2012; Abdullah et al., 2014). The use of SPE in this study is aiming to further purify the active compounds of C. dactylon from ethanol and ethyl acetate crude extracts by the mean of removing most of the impurities through the selective SPE column sorbent. In this SPE system, the sorbent matrix is designed to retain polar compounds based on three mechanisms; 1) π-π bonding, 2) hydrogen bonding and dipole-dipole interactions and 3) hyrophobic interaction (Żwir-Ferenc and Biziuk, 2006). Previously, SPE was used for plant extracts for further purifying and concentrating the bioactive components by selectively separating the plant compounds from the crude mixture through the SPE sorbent; which ultimately enhance the antimicrobial effect (Escuredo et al., 2012). Through SPE, the bioactive compounds from C. dactylon are further concentrated and purified which gives better antibacterial effect. The authors acknowledge their profound gratitude to Ministry of Education Malaysia for financially supporting the research through Fundamental Research Grant Scheme (FRGS0288), Sustainable Palm Oil Research Unit (SPOR) and Faculty of Science and Natural Resources, Universiti Malaysia Sabah for providing the facilities for research work. We also would like to thanks Dr. Katirna and the team of Queen Elizabeth Hospital (QEH) for providing biological materials. Syahriel Abdullah1, Januarius Gobilik2 and Khim-Phin Chong1 1Sustainable Palm Oil Research Unit (SPOR), Faculty of Science and Natural Resources, Universiti Malaysia Sabah, Jalan UMS, 88400, Kota Kinabalu, Sabah, Malaysia; 2Faculty of Sustainable Agriculture, Universiti Malaysia Sabah, Sandakan Campus, Mile 10, Sg. Batang, 90000, Sandakan, Sabah, Malaysia Corresponding author: chongkp@ums.edu.my; Tel: +6088- 320000 Ext: 5571; Fax: +6088-43532 References Abdullah S, Gobilik J, Chong KP. Preliminary phytochemical study and antimicrobial activity from various extract of Cynodon dactylon (L.) Pers. (Bermuda) against selected pathogens. Int J Pharm Pharm Sci. 2012; 4: 227-30. Abdullah S, Gobilik J, Chong KP. In vitro antimicrobial activity of Cynodon dactylon (L.) Pers. (bermuda) against selected pathogens. In: Developments in sustainable chemical and bioprocess technology. Pogaku R, Bono A, Chu C (eds). USA, Springer, 2013, pp 227-37. Abdullah S, Gobilik J, Chong KP. 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