Pseudomonas aeruginosa is a gram-negative, rod-shaped bacterial pathogen that, rising incidents of antibiotic resistance, poses a serious threat to patients in hospital care. It’s large repertoire of virulence factors combined with its metabolic versatility enables P. aeruginosa to quickly establish infections and disseminate throughout the host. Proteins secreted by the type 5 secretion system (T5SS) are often found to be virulence factors which play a role in pathogenicity of other gram-negative infections. One of the lesser studied members of this secretion system is PlpD; the first discovered protein of a new T5SS subfamily. PlpD is a patatin-like phospholipase with affinity towards phospholipids commonly found in eukaryotic membranes, pulmonary surfactant, and lipids involved in eukaryotic signalling pathways. Despite initial interest in its biochemistry, the exact function of PlpD and its potential role in P. aeruginosa infections remains unknown.
In this study, a cohort of 164 P. aeruginosa isolates from chronic and acute infections along with matched serum was collected in Brisbane, Australia. Genomic analysis found the plpD gene was present in 83.9% of acute strains and 96.5% of chronic strains. To determine possible expression of PlpD during infections, titres of anti-PlpD antibodies were measured via ELISA and found that patient sera extracted from chronic infections contained significantly higher titres of anti-PlpD antibodies than sera from acute infections. 7.4% of patients with acute and 20% of patients with chronic P. aeruginosa infections produced high titres of antibody against PlpD, indicating that this protein is expressed in some infections. In future, the impact of PlpD expression during infections will be investigated further and its impact on infections in vivo will be determined.