Bactericidal properties of group IIa secreted phospholipase A2 against Pseudomonas aeruginosa clinical isolates

It has been shown that human group IIa secreted phospholipase A(2) (sPLA(2)), found at high levels in inflammatory fluids, displays direct bactericidal properties against Gram-positive bacteria, while activity against Gram-negative bacteria requires the complement system or additional co-factors produced by neutrophils. Pseudomonas aeruginosa, an increasingly prevalent opportunistic human pathogen, is the most common Gram-negative rod found in cystic fibrosis lung infections, where it is associated with an inflammatory environment. Because murine intestinal group II sPLA(2) produced by Paneth cells has been shown to be directly bactericidal against Gram-negative bacteria, IIa sPLA(2) activity against P. aeruginosa clinical isolates was evaluated and provides the first evidence that the enzyme can be fully bactericidal in a concentration- and time-dependent manner against Gram-negative rods. Furthermore, it was demonstrated that these bactericidal properties were unaffected by high protein and salt concentrations, as observed in cystic fibrosis secretions, and that bacterial killing paralleled phospholipid hydrolysis. Finally, no cytotoxicity was observed when IIa sPLA(2) was incubated with human pulmonary cells, highlighting its potential use to synergize bactericidal antibiotics by promoting sublethal alterations of the bacterial cell wall.