Characterization of Lactic Acid Bacteria Isolated from Idli Batter and their Susceptibility to Antibiotics

Idli is a common flour based fermented food prepared using lactic acid bacteria which bear probiotic properties, consumed in Sri Lanka and some parts of India. The objective of the present study was to characterize the lactic acid bacteria from idli batter, identify the changes of acidity during fermentation and to determine the antibiotic sensitivity of isolates. Lactic acid bacteria were isolated and characterized up to genus level. Subsequently, antibiotic susceptibility of isolates against four antibiotics was studied. Changes of pH, lactic acid bacterial count and titratable acidity with fermentation were determined. The pH value dropped steadily from 6.28 to 3.72 while titratable acidity increased from 0.24 to 0.92% during the fermentation period of 0 to 32 h. With fermentation, the lactic acid bacterial count was increased up to 9.88 log10cfu/g after 12 hours of fermentation and the count reduced with increasing acidity. A bacterial count of 5.91 log10cfu/g was recorded at the end of 32 hours of fermentation. Ten lactic acid bacteria isolates were identified from idli batter, of which six isolates were rod shaped and other four were cocci. All isolates were Gram positive, non-motile, no n-spore formers and catalase negative. According to the above tests, it was confirmed up to the genus level that all strains be longed to Lactic acid bacteria. All isolates were susceptible to more than two antibiotics. The diameter of the zone of inhibition ranged from 1-23 mm. The highest zone of inhibition was observed in isolates I-6 against chloromphenicol (23 mm) while the lowest zone of inhibition was observed in isolates I-2 against erythromycin (1 mm). With fermentation the biochemic al and sensory qualities of idli batter were changed. Lactic Acid Bacteria isolates showed different sensitivity towards antibiotics tested.