Bacterial behaviour in middle ear effusion material: an in vitro study.

Known numbers (CFU/ml) of middle ear pathogens (S. pneumoniae, H. influenzae, M. catarrhalis, S. aureus and beta-haemolytic streptococci group A) and non-pathogens (alpha-haemolytic S. mitis) were inoculated into one end of a micropipet containing a 35 mm long pillar of culture-negative middle ear effusion. The micropipets with the effusion/bacterial suspension were incubated at 37 degrees C and kept at various inclinations to the horizontal plane (15 degrees, 30 degrees and -75 degrees). All S. aureus, M. catarrhalis, alpha- and beta-haemolytic streptococci isolates examined survived in this medium for 18 h. The majority of alpha- and beta-haemolytic streptococci isolates penetrated the MEE, irrespective of the inclination of the micropipet, whereas the number of S. pneumoniae (p<0.01) and H. influenzae (p = NS) isolates penetrating the substrate increased when the micropipets were inclined at -75 degrees to the horizontal. None of the S. aureus and M. catarrhalis isolates penetrated the MEE pillar during the incubation. The present in vitro study demonstrated that MEE possesses an antibacterial property and is able to selectively hinder bacterial penetration.