The flagella may be single or multiple. Upon division, they are found at both ends of the bacterium. For certain bacteria such as H. felis, they are extensions of fibrillar structures surrounding the bacterial body, in the same way as is observed in Spirochaetes. It has been shown that reduced-mobility strains of both C. jejuni and H. pylori could not colonise their hosts. Microaerophily The atmosphere at the mucus level covering the cells is microaerobic.
Oxygen diffuses from the underlying tissues.
Nearly all bacteria colonising the mucus have the property of growing at low oxygen pressures and, equally, many microaerophilic bacteria are mucosal bacteria. The optimum oxygen concentration depends on the species and even the strain in question. Certain microaerophilic bacteria can however grow anaerobically by using a different electron acceptor to oxygen such as fumarate, for example. The cause could be insufficient catalase or superoxide dismutase production or activity. The stomach is a special part of the digestive tract because of the acid production that goes on.