Survival of upper respiratory tract bacteria on cotton-wool swabs

Abstract

Plain, buffered cotton-wool swabs and albumen-coated cotton-wool swabs were prepared with known numbers of the following: Haemophilus influenzae, Streptococcus pneumoniae, Staphylococcus aureus, corynebacteria and Escherichia coli. Swabs were plated immediately (0 hours) after loading with a 0.1 ml standardised inoculum; each swab was plated out four times by streaking on both halves of two plates. At 0 hours recovery rates from first platings on solid media ranged from 3.3%-8.9%; from platings 1-4 ranges were 2.5%-5.7%. Both types of swabs gave similar results. The greater the delay in plating swabs at room temperature and 4°C the lower was the recovery rate of H. influenzae and Strep. pneumoniae, though both species survived better on either kind of swab when these were held at 4°C. There was a very small reduction in numbers of Staph. aureus from 24 to 48 hours but the recovery rate of corynebacteria was similar over the 48-hour period, at both room temperature and 4° C. Twenty-four hour counts of E. coli at room temperature were approximately five times greater than at 0 hours, and at 48 hours colonies were too numerous to count. At 4°C, however, counts of E. coli fell during the 48-hour period.