Microbial activity in natural rubber latex with currently existing preservative systems

Abstract

Natural rubber latex is sterile within the tree and destabilizes within a few hours after tapping due to heavy microbial contamination. The main sources of contamination are the tree laces, tapping panel barks and cup which receives the latex. The work described is a systematic study on the behavior of microflora in Hevea latex with different preservative systems in order to investigate the reasons for latex quality deterioration even after the preservation with currently used preservative systems.

Observations were made on microbes present in natural rubber (NR) latex without adding any preservatives, latex preserved with LATZ (low ammonia, TMTD/ZnO and latex preserved with high ammonia (0.7%) (w/w). These samples were cultured in modified Klingers Iron Agar (KIA) at room temperature for 36 hours. The morphology of colonies was observed visually. Gram staining was done after preparation of heat fixed smear. Above colonies were further purified by streak plate technique and subjected to biochemical tests like acid fast, catalase and glucose fermentative activity.

According to Bergey’s manual of determinative bacteriology and results obtained from biochemical tests, the main types of bacterial species identified are Bacillus polymixa, Bacillus subtilis, Bacillus coagulans, Lactobacillus casei, Lactobacillus fermenti and Cocci species.

The media used to culture the bacteria consist of Bromocresol purple which turns yellow with acid producing bacteria and turn pink with non-acid producing bacteria. Observing the colour around the colonies revealed that only some bacteria produce acids even with high concentration of ammonia (i.e. 0.7% (w/w)), but they do not produce acids when the latex is preserved with LATZ. These results showed that ammonia resistant bacteria can be controlled using secondary preservatives.

The results permit to understand the microbial activity in sterile and preserved natural rubber latex and can be used to select effective preservative system instead of currently used systems.