The antibacterial activity of plant extracts was investigated against wood degrading microbes including one strain of Gram positive bacteria B. cereus (14, 15) two strains of Gram negative bacteria E.coli (15–18) and P. aeruginosa (16, 17). Paudel and Qin (32) also reported the isolation of E. coli, Bacillus sp. and Pseudomonas sp. from decaying wood samples. Kumar, Pandey (33) regarded A. niger, E. coli and B. cereus as wood degrading microbes.
The study revealed that by using well diffusion method all selected plants exhibited antimicrobial activity but different solvents varied in antimicrobial activity against tested wood degrading microbes. Among plants S. chirata was evaluated to possess strongest biocidal potential followed by C. procera then C. zedoaria. In case of S. chirata, methanol extract showed prominent bactericidal potential against B. cereus although ethanolic extract of S. chirata exhibited extensive bactericidal and fungicidal action against E.coli, P. aeruginosa and wood soft-rot fungus A. flavus. Phoboo, Pinto (34) reported that the ethanolic extract of S. chirata possess mangiferin, amarogentin and swertiamarin as active phytochemicals that are responsible for antimicrobial activity. Wazir (35) also amplified the antibacterial activity of methanolic exract of S. chirata. Our findings are also close to the results of Sekar (36) study that Mangefrin derived from S. chirata exhibited antibacterial activity against E. coli, B. cereus and P. aeruginosa and antifungal activity against A. flavus. The bactericidal potential of ethanol extract was also mentioned by Rehman, Latif (37) against E. coli and P. aeruginosa. BEHERA, BARIK (38) also revealed the antibacterial activity of S. chirata against gram positive and gram negative bacteria and E.coli was particularly mentioned. The phytochemical screening of S. chirata depicted the presence of terpenoids, coumarins, flavonioids, tannins, glucosides and alkaloids as active secondary metabolites. The results of phytochemical screening are in accordance to results of Khanal, Shakya (39). C. procera also showed antimicrobial activity against all tested microbes but its methanol and chloroform extract exhibited stronger fungicidal potential against wood soft-rot fungi A. niger (40) and A. flavus (41) respectively, while only methanol extract was evaluated to possess high bactericidal potential only against E.coli (42), it was reported by Agoramoorthy, Chandrasekaran (43) that C. procera possessed strongest fungicidal potential but less bactericidal potential. The study was also supported by suggestions of Yesmin, Uddin (44) and Waheed, Jabeen (40) that the leaves of C. procera exhibited good antimicrobial potential. Our result that methanol extract of C. procera exhibited broad spectrum of antimicrobial activity is the close in agreement with KAR, PATTNAIK (45) and SRangaiah, Lakshmi (46). The phytochemical screening exhibited the presence of terpenoids, tannins, flavonoids, and alkaloids and glycosides as active secondary metabolites, their presence was also reported by Akbani, Chavan (26), Tabassum, Ali (47). Thus these secondary metabolites are responsible for antimicrobial potential of C. procera (48).
C. zedaira was assessed to exhibit only bactericidal potential but no antifungal activity observed by its extracts. The study is supported by the results of Wilson, Abraham (49) that methanol, ethanol and chloroform extracts of C. zedoaria exhibited stronger antibacterial potential as compared to its activity against fungi. Ethanol extract of C. zedoaria exhibited strongest bactericidal activity against P. aeruginosa and B. cereus. Islam, Hoshen (50) examined the antibacterial activity of ethanol extract of C. zedoaria against P. aeruginosa and B. cereus and the study concluded the plausible application of this extract to control infections by these bacteria (P. aeruginosa and B. cereus). The ethanol extract of C. zedoaria possess antimicrobial activity due to the presence of flavonoids and glycosides as active secondary metabolites as phytochemical screening revealed by Chachad, Talpade (27). The ethanol extract of S. chirata, methanol and chloroform extract of C. procera and ethanol extract of C. zedaira showed biocidal potential equal to antimicrobial drugs used as positive control against particular tested microbes. The statistical analysis showed that the means of control and these extracts are non-significant at p-value 0.05 shown in table 4. Thus these plants extracts can be used as alternative to the drugs applied to cease the growth wood degrading microbes. The phytochemical screening showed that they have flavonoids, terpenoids, alkaloids and tannins that are responsible for exhibiting biocidal potential. The results of MIC and MBC of the effective plant extracts suggested that ethanol extracts of S. chirata and C. zedaira as well as methanol extracts of S. chirata and C. procera can be used to control and prevent wood deterioration. A great variation in MIC of all extracts demonstrated in several investigations may be due to considerable variation in their method of extraction, constituents as well as microbial strains used. Also, variation in MIC of different plant extracts may arise from variation in their chemical constituents and volatile nature of their constituents. These results are in accordance with the results of Islam et al.50.
The plants extract that showed broadest spectrum of bactericidal and fungicidal action was applied to treat S. cumini wood and laminated veneer lumber soaked with extracts. However S. cumini wood showed relatively mild response to bactericidal and fungicidal potential of extracts against wood degrading microbes as compare to laminated veneer. The reason is that laminated veneer is manufactured in compact form, polished and adhesives have been added. But the study showed that these extracts can be used as alternative of chemical adhesives which are used in manufacturing of laminated veneer. As natural products are inexpensive, thus their use for veneer adhesives, lamination of veneers and polishing of crude wood can save wood industry expenditures for importing wood preservative chemicals and crude wood preservative materials. It has been reported that copper in wood preservatives does not inhibit bacterial growth on wood; it only inhibits fungal growth (22). In fact commonly wood preservatives are antifungal they do not have bactericidal potential but bacteria also degrade wood by consuming lignin. Aviat, Gerhards (51) reported that microbes associated with wooden utensils are the major cause of food poisoning. However treatment of wooden utensils with chemicals is health hazardous thus the use of natural preservative may sort out this issue. The studied plant extracts have both fungicidal and bactericidal potential, in application their use as natural wood preservative may enhance the durability of S. cumini and laminated veneer wood, and of course other wood samples too. It has been reported that tannins and phenolic compounds are used to make wood adhesives (52). Thus it was evaluated that above selected plant extracts exhibited biocidal potential against wood degrading microbes so, reported extracts can be exploited as potential safe wood preserving agent and a better alternative to chemical preservatives.