Journal of Clinical Microbiology, October 2000, p. 3912-3912, Vol. 38, No. 10
0095-1137/00/$04.00+0

LETTERS TO THE EDITOR

Survival of Gram-Positive Bacteria on Hospital Fabrics

	LETTER

The results of the study on the survival of gram-positive bacteria on hospital fabrics (2) are certainly not to be taken lightly. However, the manner in which the materials were prepared for testing warrant clarification.

First is the chemical formulation used in laundering the fabrics. In addition to their having been subjected to a cycle with a proven disinfectant of sodium hypochlorite (chlorine bleach) (1), an Environmental Protection Agency (EPA)-registered quaternary ammonium bacteriostat should have been included in the final rinse. The effectiveness of this antimicrobial agent as a growth inhibitor of bacteria, fungi, and other microorganisms is known to remain with the textile until it is laundered again (4).

Second, it is noted that the fabrics were sterilized by ETO prior to being inoculated. Historically, reusable fabrics have been steam sterilized if need be (3). As a result, there is no way of knowing what effect, if any, the ETO could have had on the additive's antimicrobial effectiveness.

Assuming that both chlorine bleach and a "stat" were an integral part of the laundry process, the question that logically arises is whether the results would have proven to be the same if the materials would have been preconditioned by steam sterilization.

	REFERENCES

	AUTHOR'S REPLY

We thank Dr. Belkin for his attention to our article, and we welcome the opportunity to respond to his concerns. First, the article addressed the survival of gram-positive bacteria on plastic, as well as on fabrics. Since the plastic tested was polypropylene in the form of disposable plastic aprons used in our and other hospitals, any question of laundering is not pertinent to the part of the study relating to the disposable plastic.

Second, as to the chemical formulations used in laundering, our hospital uses a commercial laundry. The laundering process does include a cycle with sodium hypochloride and a final rinse with an EPA-registered quaternary compound.

Third, as to the ETO sterilization, this mode of sterilization was used rather than steam sterilization because the heat in the steam process affected the plastic that we were testing in the study. Therefore, to be consistent, both the plastic and the fabrics were sterilized using ETO. All samples were properly aerated following the ETO sterilization, so there would be no residual ETO effect.

Fourth, to address the question of whether ETO sterilization may have affected the laundering chemicals differently than steam sterilization, we have performed the following experiment. Two sets of swatches of terry cotton and of cotton-polyester blend were sterilized: one set by ETO, the other by steam. Equal amounts of a sampling of five test microorganisms were pipetted onto swatches sterilized by the two different methods. The bacteria were allowed to dry on the swatches for 0.5 h, and each swatch was placed in a tube of medium. To determine if the two different sterilization processes might have affected the number of viable bacteria, the tubes were vortexed, serially diluted, and plated onto agar, so that actual colony counts were obtained. For the five sets of terry cloth swatches, the average number of bacteria per swatch sterilized with steam was 5.84 log₁₀ versus 5.79 log₁₀ for the swatches sterilized with ETO (P = 0.944 by Student's t test). For the five sets of blend swatches, the average number of bacteria per swatch sterilized with steam was 6.36 log₁₀ versus 6.32 log₁₀ for swatches sterilized with ETO (P = 0.963). Although these were not large experiments, the results certainly suggest that the method of sterilization did not make a difference.

Finally, it should be pointed out that a bacteriostatic agent retards or prevents the growth of bacteria, it does not kill the bacteria. Hence, even if static agents are present, for example, in or on the fabric of a lab coat, that lab coat can still be a vector for carrying live bacteria from one patient to another. One of the major points of the original paper was to determine how long bacteria could survive on various fabrics and plastic so that we could see if the potential for the fabric or plastic to serve as a vector existed. No determinations were made of whether the bacteria could grow on these materials. Hence, the presence or absence of a static agent, which by definition affects growth and not survival, is perhaps a moot point in the context of this particular study.