Coliforms Aerobic or facultatively anaerobic,gram-negative, non-endospore forming rods that ferment lactose to acid gas within 48 hr,at 35 C 。Indicator organisms Used to detect fecal contamination 。MPN Most probable number/100 ml of water • Aerobic or facultatively anaerobic, gram-negative, non–endospore forming rods that ferment lactose to acid + gas within 48 hr, at 35°C • Indicator organisms • Used to detect fecal contamination • MPN • Most probable number/100 ml of water Coliforms