A Sticking Point in Assessing Bacterial Contamination: Adhesive Characters of Bacterial Specializations, Swab Features, and Fomite Surface Properties Skew Colony Counts

Relative bacterial load as assessed by swabbing of surfaces is used to make critical decisions about safety in medical, food and athletic venues, with little consideration of bacterial attachment features (capsules, pili, flagella), swab type, or adhesive properties of fomites. To consider the impact of these parameters, a known quantity of bacteria with different adhesive specializations was applied to fomites of varying topography and surface energy and retrieved using multiple types of swabs. Swab type affected the total number of bacteria retrieved but had little effect on proportion of bacterial species collected (p = 0.455, by paired t-test). Mutant strains were observed for E. coli to determine contribution of surface features to fomite adhesion. Pili and flagella had greatest impact on retrieval from fomites with varied topography (ANOVA [F..sub.(444)] = 6.099; p = 6.0 X [10.sup.-4]), whereas surface chemistry and capsule chemistry had greatest impact on retrieval of species from fomites of different surface energies (ANOVA [F.sub.(203)] = 52.08, p= 1.24 X [10.sup.-9]). Adhesive properties of additional surface structures may need to be assessed and a more quantifiable study of fomite topography needs to be explored. Ultimately, a paradigm needs to be devised to make accurate comparisons of CFUs retrieved by swabbing surfaces for microbial contaminants. Keywords: Bacterial Adhesion, Pili, Flagella, Swabbing, Fomites, CFUs.