The differential effect of cigarette smoke on the growth of bacteria found in humans.

The effect of cigarette smoke on growth of those species of bacteria that are considered common potential human pathogens was examined in vitro. Smoke from both mentholated and nonmentholated cigarettes inhibited the growth of Gram-positive cocci to a greater degree than that of Gram-negative rods. Staphylococcus aureus, Streptococcus pneumoniae, and a variety of other streptococci were inhibited at a smoke solution dilution of 1:8. Enteric bacteria such as Klebsiella, Enterobacter, and Pseudomonas were not affected by a 1:1 dilution of the solution. As with the Gram-positive cocci, the Neisseria species and Branhamella were also inhibited at a dilution of 1:8. Culture results of the mouth of 15 smokers and 15 nonsmokers showed that the smokers have a propensity to develop heavy Gram-negative bacterial colonization.