| Popis: |
ABSTRACT Contact-dependent hemolysins are virulence factors in a number of human pathogens, including Helicobacter pylori, Rickettsia typhi, Bartonella bacilliformis, Mycobacterium tuberculosis, entero-invasive Escherichia coli, and Shigella. Here we demonstrate that Neisseria gonorrhoeae produces an outer membrane protein, phospholipase A, that exhibits contact-dependent lytic activity on host cell membranes. This enzyme can lyse human erythrocytes over a 3-day period, whereas a phospholipase A mutant cannot. We demonstrated phospholipase A activity in the parent strain but not in two, independent phospholipase A mutants. A gene for phospholipase A, pldA (hereafter referred to as pla to avoid confusion with the gene for phospholipase D, pld), is present in all sequenced gonococcal strains. Fluid phase, hemolytic activity assays showed that 25 of 29 gonococcal strains tested had hemolytic activity greater than 50% of the positive control. In support of PLA as a gonococcal outer membrane protein, supernatants from 24-, 48-, and 72-h cultures of N. gonorrhoeae strain 1291 did not contain hemolysin activity, and a monoclonal antibody specific for gonococcal phospholipase A failed to detect the enzyme in these supernatants. The organism must be viable for lysis to occur, and the inclusion of EDTA in the media removes all activity. Our studies have shown that a phospholipase A mutant has significantly reduced survival in human neutrophils and primary human cervical epithelial cells compared to the parent gonococcal strain after 3 h of incubation. Collectively, our data demonstrate that gonococcal PLA lyses host cell membranes, which is important for intracellular survival.IMPORTANCEIntracellular survival is crucial to the success of Neisseria gonorrhoeae as a human pathogen. Multiple factors contribute to the intracellular survival of gonococci, including the ability to prohibit apoptosis of the epithelial cell the organism invades and mechanisms to evade host innate defense systems. The role of phospholipase A (PLA), an outer membrane protein, is important as it disrupts the host vacuolar and phagolysosomal membranes, preventing the effective delivery of innate immune factors that normally restrict organism growth within human cells. After cell entry, PLA disrupts the integrity of these host cell membranes, allowing the gonococcus to live free within disrupted vacuoles where it pilfers host cell nutrients that enable its survival and replication. A vaccine or drug that could neutralize PLA activity would disrupt the intracellular survival of the gonococcus. |
