Effect of some fractions of alveolar surfactant (phospholipids and SP-A) on the bactericidal activity of different antimicrobials against some respiratory pathogens

Objectives   To investigate the effects of physiologic concentrations, at alveolar level, of some fractions of pulmonary surfactant (phospholipids and SP-A) on the bactericidal activity of different antimicrobials against some respiratory pathogens.
Methods   The antimicrobial agents cefdinir, sparfloxacin, clarithromycin, teicoplanin, cefepime, ciprofloxacin, netilmicin and tobramycin, depending on their specific activity, were investigated against Staphylococcus aureus , Streptococcus pneumoniae , Haemophilus influenzae , Moraxella catarrhalis , Klebsiella pneumoniae and Pseudomonas aeruginosa . Killing curves were carried out with antimicrobials at 0.5 and 2 MIC, SP-A at 1 and 5 mg/L and phospholipids at 50 mg/L.
Results   Time-kill experiments showed that while SP-A never modified the activity of antimicrobials, phospholipids exerted, in some cases, a weak antagonistic effect. Among antibacterials and pathogens investigated, phospholipids were able to decrease the rate of killing of cefepime and ciprofloxacin only on P. aeruginosa , both at 0.5 and at 2 MIC, with an increase of about 1 log in CFU. The combination of SP-A and phospholipids never modified the effect observed in the presence of lipids alone.
Conclusions   The paucity of data only allow us to observe that the examined antibiotics do not have substantially reduced activity against respiratory pathogens studied in the presence of physiologic concentrations of some fractions of surfactant. Cefepime alone already exerted a small effect, and ciprofloxacin at 2 MIC, even in the presence of phospholipids, retained its bactericidal activity.