Sticky microbes and dust on objects in historic houses

Amber L. Tarnowski, Christopher J. McNamara, Kristen A. Bearce, and Ralph Mitchell

Abstract

This research investigated the role microorganisms play in bonding dust to surfaces. Nonbiological mechanisms of dust adhesion include molecular dispersive forces, electrostatic interactions, and capillary condensation. In addition, dust adhesion may result from contact with sticky exopolymers produced by microbial biofilms. Biofilms are communities of microorganisms, which are present on all surfaces. Biofilms are held together by exopolymers, which are created as products of microbial metabolism. Layers of dust, microorganisms, exopolymers, and substratum form a complex system that makes it difficult to clean delicate surfaces in historic interiors. Dust samples were collected from Knole House at Sevenoaks in Kent, and from Blickling Hall in Norfolk, England. Plate counting and nuclear staining were performed to qualify and quantify the microbes. Dust samples plated onto nutrient agar culture plates yielded high numbers of bacteria. Investigation of microbial metabolism revealed that in controlled humid environments, microorganisms utilized dust components as the sole source of nutrition. Exopolymers visible under the microscope were produced within days. Solvent extractions of dust samples were analyzed with gas chromatography-mass spectroscopy (GCMS) to identify the hydrocarbon and fatty acid components in the dust that serve as nutrition for microbes. While these English country estate homes are relatively removed from the typical sources of hydrocarbon nutrients that can support microbial growth, such as smog and heavy traffic pollution, sufficient nutrients remain in the dust. To illustrate the interaction of microbial activity on textiles, thin biofilm samples were examined with electron microscopy. Bacterial isolates displayed preferences for breaks and ends of wool or silk fibers. The analytical techniques used in this study are standard in the field of microbiology, and can be used to analyze housekeeping practices of historic house interiors and their contents.

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