Occurrence of Heterotrophic and Coliform Bacteria in Liquid Hand Soaps from Bulk Refillable Dispensers in Public Facilities

By Chattman, Marisa; Maxwell, Sheri L. et al. | Journal of Environmental Health, March 2011 | Go to article overview

Occurrence of Heterotrophic and Coliform Bacteria in Liquid Hand Soaps from Bulk Refillable Dispensers in Public Facilities


Chattman, Marisa, Maxwell, Sheri L., Gerba, Charles P., Journal of Environmental Health


Introduction

Liquid hand soap is used daily by millions of people worldwide. Some public restrooms have soap dispensers that require bagged or cartridge-sealed soap replacements and others have containers that are refillable using stock soap solutions that are often diluted with tap water. Although liquid hand soaps are not required to be sterile, the microbial burden is to be kept to a minimum and free of objectionable microorganisms. They must also be adequately preserved to prevent contamination once in the hands of the consumer.

A study conducted in Japan in the early 1990s by Amemiya and Taguchi (1992) revealed significant contamination in soap from public restrooms. They found that as many as 4 x 107 bacteria per mL could be recovered from liquid hand soaps and that 71% contained 1,000 or more bacteria per mL. Until now, no large survey studies of this kind have been done in the U.S. The purpose of our study was to assess the frequency and extent of bacterial contamination in soaps from open refillable dispensers commonly used by patrons of public restrooms across the U.S. We also identified organisms that were found in order to determine whether the use of soap from public restrooms poses a potential health hazard.

Materials and Methods

Liquid soap samples were collected from public restrooms in five cities (Boston; Atlanta; Columbus, Ohio; Los Angeles; and Dallas). Sample locations were organized into four categories: offices, health clubs, restaurants, and retail stores. Soap was collected from refillable soap dispensers (N = 541) into sterile 50 mL centrifuge tubes through the soap dispenser mechanism. The soap samples were shipped on ice to the University of Arizona and processed the same day they were received. Approximately 20% of the individual sampling sites were independently audited within 30 days after initial collection. The auditors were not the same persons who collected the initial soap samples. The auditors verified the accuracy of the information recorded by the original collector and that all of the samples had been obtained from bulk through-the-counter or wall-mounted refillable dispensers.

One mL of Dey-Enger (DE) neutralizing broth was added to each sample tube and shaken for 30 seconds. Heterotrophic plate counts (HPC) were obtained by spread plating 0.1 mL of sample onto duplicate petri dishes containing R2A media. Plates were incubated at 30[degrees]C for five days. After incubation, the colonies were counted and the mean values were recorded for each set of duplicates. Plates containing colonies that were too numerous to count (>300 CFU/plate) were reassayed the next day by performing 10-fold dilutions of the soap in sterile buffered saline (0.85% NaCl). The dilutions were then plated onto duplicate petri dishes containing R2A agar and incubated at 30[degrees]C for five days. Plates were counted and the HPC for each soap sample was calculated. Any soap sample that contained more than 500 CFU/mL was also assayed for the presence of coliform bacteria and Staphylococcus aureus bacteria. The cutoff of 500 CFU/mL was chosen because it represents the maximum microbial burden in cosmetic products as recommended by the Personal Care Products Council (PCPC).

Coliform enumeration was performed by spread plating the appropriate dilution of each of the contaminated soap samples on mEndo agar plates and incubated at 37[degrees]C for 24 hours. Representatives of each colony type were streaked for isolation on petri dishes containing tryptic soy agar (TSA) in order to perform oxidase tests and identification. TSA plates were incubated at 35[degrees]C for 24 hours. Oxidase tests were performed on all isolates by applying Kovacs reagent. A positive control (Pseudomonas aeruginosa, American Type Culture Collection [ATCC] #27313) and a negative control (E. coli, ATCC #25597) ensured the quality of the Kovacs reagent.

S. aureus analysis was performed by spread plating the appropriate dilution of the original sample on TSA amended with 5% sheep blood (blood agar) to check for hemolysis. …

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