Appl. Radiat. Isot. Vol. 37, No. 12, pp. 12351239, 1986 ht. J. Radiat. Appl. Instrum. Part A Printed in Great Britain. All rights reserved 0883-2889/86 $3.00 + 0.00 Copyright :LI 1986 Pergamon Journals Ltd Evaluation of a Radioisotope Labelling Technique for Measuring Bacterial Adherence on Fabrics YOU-LO HSIEH, DEBRA TIMM and JOANNE MERRY Division of Textiles and Clothing, College’of Agriculture and Environmental Sciences, University of California, Davis. CA 95616, U.S.A. zyxwvutsrqponmlkjihgfedcbaZYXWV (Receiw d 17 July 1985) A technique utilizing tritiated thymidine labelled bacteria to quantify bacteria on fabrics has been evaluated. Quenching or self-absorption of isotope solution and labelled bacteria suspension by some of the fabrics has been observed. The extents of self-absorption of both isotope and labelled bacteria solutions on various fabrics was found to be dependent upon the fiber contents, i.e. the chemical compositions, of the substrata. This observation confirms that reduction of scinitillation efficiency or self-absorption does occur when radio-labelled substances in suspensions were measured with the presence of some fabrics. Cautions should be taken when radio-labelling techniques are applied to detect isotope-labelled micro-organisms or other substances which are in contact with fabrics in the form of solutions. However, when there is no excess and nonattached labelled bacteria in the aqueous surrounding of the fabric, scintillation counting efficiency of the labelled bacteria on all fabrics studied remained constant over a period of 8 h. This indicates that the application of the described isotope labelling procedure is appropriate for quantifying adherent bacteria on fibrous substrate. Introduction Liquid scintillation counting of radioisotope labelled compounds on solid supports has been a well- practiced technique in biochemistry. However, cau- tion has to be used in applications of this approach on polymeric materials because of the possible “self-absorption” or “quenching” phenomenon. Self- absorption of isotope labelled substance on plastics has been observed as lowered counting efficiency of labelled substances in polyethylene vials than in glass vials. Self-absorption by plastic vials also increased as time increased between sample preparation and scin- tillation measurement.” ‘) The diffusion of either the solute and/or the solvent into the plastic vials has been suggested to be the cause of reduced counting efficiency.‘2) Quantification of adherent bacteria on sutures has been evaluated by labelling bacteria with radio- isotopes. (4~5’ With this approach, the in-t’itro adher- ence of bacteria to sutures was found to correlate well with the degree of infection in animals(4) and was related to both physical and chemical configurations of sutures.@) However, the information on whether or how self-absorption of labelled bacteria occurs in the presence of fibers is not available in the current literature. The purposes of this study are to evaluate the self-absorption of radioisotope labelled bacteria in presence of fabrics and to verify the validity of using radioisotope labelling in quantitative mea- surement of bacterial adherence on fabrics. Materials and Methods Bacteria The bacteria studied are the gram positive Staphy lococcus aureus (S. aureus) and Staphy lococcus epidermidis (S. epi) and the gram negative Escherichia coli (E. co/i). ATCC 1346 type E. coli was used. S. aureus and S. epi were isolated and cultured from hospital patients. Labelling of bacteria and calibration The bacteria were inoculated with a wire loop to a sterilized brain heart infusion (BHI) nutrient. A lOO/lCi of tritiated thymidine (methyl-‘H) with a specific activity of 50Ci/mmol (ICN Pharma- ceuticals, Inc., Ivrine, Calif.) was added to 5 mL aqueous suspension BHI and incubated for 18 h. The bacterial solution was then separated from the sus- pension by repeating centrifugation and washing four times, each time with 5 mL of phosphate buffered saline (PBS). The final suspension was made by diluting 1: 10 with PBS. A viable count was performed for each freshly prepared bacterial solution to determine the total 1235