Nontypeable Haemophilus influenzae (NTHi) is an opportunistic pathogen associated with exacerbations of COPD, community acquired pneumonia and otitis media. A number of studies have shown that NTHi can invade respiratory epithelial cells in vitro, although the clinical significance is unclear. It has also been shown that strains with altered penicillin binding protein 3 (PBP3) – which is associated with ampicillin resistance – are more invasive of BEAS-2B cells than strains with normal PBP3.
The aim of this study was to compare the invasion rate of NTHi with different respiratory cell types. A total of 16 clinical isolates were used, comprised of 7 isolates with normal PBP3 and 9 with altered PBP3. The gentamicin survival assay was used to measure the invasion rate of each NTHi with each cell type. The overall median invasion for BEAS-2B, NHBE, A549 and NCI-H292 cells were 3.17, 2.31, 0.11 and 1.52 respectively. Median invasion with BEAS-2B cells was significantly higher compared to A549 (P= 0.013), however, there were no significant difference in comparison to NHBE and NCI-H292 cells. Median invasion with A549 cells was significantly lower than the NCI-H292 (P= 0.013) cells but did not exhibit any statistical difference with NHBE cells. The normal PBP3 strains median invasion for BEAS-2B, NHBE, A549 and NCI-H292 cells were 0.07, 1.92, 0.02, and 1.1 respectively whereas it was 9.9, 2.7, 1.68 and 3.66 respectively for the strains with altered PBP3. Median invasion of altered PBP3 strains was significantly higher with BEAS-2B (P = 0.031) and A549 (P = 0.037) cells compared to normal PBP3 strains, although it was not statistically different with NHBE (P = 0.351) and NCI-H292 (P = 0.090) cells. This study shows that NTHi invasion rates vary depending on the cell type used, and that the association between altered PBP3 and increased invasion extends to A549 cells.