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 g enerating oxidative species, such as superoxide anion, hydrogen peroxi de, and oxidized halogen species. The oxyR gene of Salmonella typhimur ium controls a regulon induced by oxidative stress, such as exposure t o hydrogen peroxide. Some researchers have suggested that oxyR may pla y a key role in bacterial survival following phagocytosis. We have tes ted 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 bacteria l resistance to neutrophils. The katG gene, encoding the oxyR-regulate d enzyme hydroperoxidase I, was also without effect on survival follow ing exposure to neutrophils. We conclude that the oxyR response does n ot play a significant role in the resistance of S. typhimurium to phag ocytic killing in vitro.