Abstract
The best known physiologic function of secreted phospholipase A(2) (sPLA(2)) group IIA (sPLA(2)-IIA) is defense against bacterial infection through hydrolytic degradation of bacterial membrane phospholipids. In fact, sPLA(2)-IIA effectively kills Gram-positive bacteria and to a lesser extent Gram-negative bacteria and is considered a major component of the eye's innate immune defense system. The antibacterial properties of sPLA(2) have been demonstrated in rabbit and human tears. In this report, we have analyzed the bactericidal activity of dromedary tears and the subsequently purified sPLA(2) on several Gram-positive bacteria. Our results showed that the sPLA(2) displays a potent bactericidal activity against all the tested bacteria particularly against the Staphylococcus strains when tested in the ionic environment of tears. There is a synergic action of the sPLA(2) with lysozyme when added to the bacteria culture prior to sPLA(2). Interestingly, lysozyme purified from dromedary tears showed a significant bactericidal activity against Listeria monocytogene and Staphylococcus epidermidis, whereas the one purified from human tears displayed no activity against these two strains. We have also demonstrated that Ca2+ is crucial for the activity of dromedary tear sPLA(2) and to a less extent Mg2+ ions. Given the presence of sPLA(2) in tears and intestinal secretions, this enzyme may play a substantial role in innate mucosal and systemic bactericidal defenses against Gram-positive bacteria.