Comparison of the sensitivities of Salmonella typhimurium oxyR and katG mutants to killing by human neutrophils.

The respiratory burst of neutrophils is believed to kill bacteria by generating oxidative species, such as superoxide anion, hydrogen peroxide, and oxidized halogen species. The oxyR gene of Salmonella typhimurium controls a regulon induced by oxidative stress, such as exposure to hydrogen peroxide. Some researchers have suggested that oxyR may play a key role in bacterial survival following phagocytosis. We have tested this possibility by comparing the survival, following exposure to human neutrophils, of isogenic strains bearing different oxyR alleles. Neither inactivation of the oxyR gene nor constitutive overexpression of the oxyR-regulated proteins (oxyR1 allele) greatly alters bacterial resistance to neutrophils. The katG gene, encoding the oxyR-regulated enzyme hydroperoxidase I, was also without effect on survival following exposure to neutrophils. We conclude that the oxyR response does not play a significant role in the resistance of S. typhimurium to phagocytic killing in vitro.