Aeromonas hydrophila bacteria, coloured scanning electron micrograph (SEM). Aeromonas hydrophila is a toxic heterotrophic, Gram-negative, rod-shaped bacterium mainly found in areas with a warm climate in in fresh or brackish water. It can survive in aerobic and anaerobic environments and can digest materials such as gelatine and haemoglobin. It is resistant to most common antibiotics and cold temperatures. Those infected by A. hydrophila may get rice-water diarrhoea or dysenteric gastroenteritis, which causes loose stools filled with blood and mucous. Magnification: x16,000, when printed 15cm wide.