Dynamic aspects of airborne bacterial flora over an experimental area in a suburb and distribution of resistant strains to antibacterial agents among airborne staphylococci.

Abstract

Airborne bacterial floras were investigated at stations A to E and P on the UOEH campus located in a suburb of the city of Kitakyushu. Bacterial collections were carried out by a filtration method using a soluble gelatin foam filter at an altitude of 1 m from the ground and viable bacterial cells were enumerated on nutrient agar plates supplemented with 50 micrograms/ml cycloheximide. At station P, where airborne bacterial composition was evaluated as a mean value of 20 repeated experiments, there were 42% Gram-positive cocci, 37% Gram-positive rods, 3.5% Bacillus strains and 5.5% Gram-negative rods. Fluctuating values of cell amounts for Gram-positive cocci and rods during these experiments suggested that in the atmospheric layer near the ground, the former was a more transient group of airborne bacteria than the latter. When airborne bacterial flora over the experimental area was surveyed by observations at six stations, the dispersion profile of bacterial flora closely corresponded to vegetating states on the surface of the ground. Over vegetating areas, airborne bacterial flora appeared in about equal amounts of Gram-positive rods and cocci, while over bare ground, Gram-positive rods appeared more abundantly than Gram-positive cocci. To investigate the distribution of drug-resistant strains among airborne bacteria, sensitivity tests to six antibiotics were carried out with S. xylosus strains isolated at stations P and E. As a result, considerable amounts of single-drug-resistant strains for TC (DOX) and EM were recognized, but the distribution of multiple-drug-resistant S. xylosus was restricted to a few strains.