Reducing bacteria in household sponges.
Each year in the United States, an estimated 5.5 million to 6.5 million cases of food poisoning food poisoning, acute illness following the eating of foods contaminated by bacteria, bacterial toxins, natural poisons, or harmful chemical substances. It was once customary to classify all such illnesses as "ptomaine poisoning," but it was later discovered that occur (1). In Europe, studies have shown that many foodborne-disease outbreaks occur in the household environment as a result of improper food preparation (2). Implicated im·pli·cate
tr.v. im·pli·cat·ed, im·pli·cat·ing, im·pli·cates
1. To involve or connect intimately or incriminatingly: evidence that implicates others in the plot.
2. in many instances is cross-contamination or direct contamination of food contact surfaces resulting from improper food handling, preparation, or storage (2).
Vehicles for spreading food pathogens include wet dishcloths and sponges (3-6). Many investigators have recognized the potential for dishcloths or sponges to spread micro-organisms and have noted that bacteria persist in these media (7,8). Bacteriological bac·te·ri·ol·o·gy
The study of bacteria, especially in relation to medicine and agriculture.
bac·te surveys conducted for kitchen dishcloths or sponges have revealed the presence of many enteric enteric /en·ter·ic/ (en-ter´ik) within or pertaining to the small intestine.
1. Of, relating to, or within the intestine.
2. pathogens, such as Escherichia coli Escherichia coli (ĕsh'ərĭk`ēə kō`lī), common bacterium that normally inhabits the intestinal tracts of humans and animals, but can cause infection in other parts of the body, especially the urinary tract. , Klebsiella pneumoniae Klebsiella pneu·mo·ni·ae
Friedlander's bacillus. , and Enterobacter cloacae (3,4,6). These enteric pathogens survive and multiply in wet environments like dishcloths and sponges. Other types of pathogens, such as Staphylococcus aureus Staphylococcus au·re·us
A bacterium that causes furunculosis, pyemia, osteomyelitis, suppuration of wounds, and food poisoning.
Staphylococcus aureus Staphylococcus pyogenes and Salmonella sp., as well as opportunistic pathogens such as Pseudomonas Pseudomonas
A genus of gram-negative, nonsporeforming, rod-shaped bacteria. Motile species possess polar flagella. They are strictly aerobic, but some members do respire anaerobically in the presence of nitrate. sp., also have been isolated. Thus, dishcloths or sponges containing high concentrations of pathogens may be reservoirs and disseminators of bacterial contamination in the kitchen (3).
Adequate cleaning and decontamination decontamination /de·con·tam·i·na·tion/ (de?kon-tam-i-na´shun) the freeing of a person or object of some contaminating substance, e.g., war gas, radioactive material, etc.
n. of food contact surfaces, dishcloths, and sponges may minimize the spread of micro-organisms in the kitchen. Sponges are commonly used to clean food contact surfaces such as cutting boards, pots and pans, dishes, countertops, sinks, refrigerator and faucet handles, and stovetops. Simple, effective methods for reducing micro-organisms in sponges have not been evaluated, except for disinfection disinfection,
n the process of destroying pathogenic organisms or rendering them inert.
disinfection, full oral cavity,
n a procedure used to reduce active periodontal disease, usually completed within a certain short time frame. of sponges and dishcloths in the microwave oven (9). This study evaluated different types of chemical and physical treatments for decontaminating scrubber sponges (greater than 99.9 percent reduction of bacteria). (Scrubber sponges incorporate scrim scrim
1. A durable, loosely woven cotton or linen fabric used for curtains or upholstery lining or in industry.
2. A transparent fabric used as a drop in the theater to create special effects of lights or atmosphere. material that cleans by abrasion.) The treatments were initially applied to laboratory-inoculated sponges and then verified to be effective with testing on consumer-used sponges.
Experimental Test Organisms for Laboratory-Inoculated Sponges
The following species of bacteria were used in this study: Escherichia coli ATCC ATCC American Type Culture Collection, see there 11229, Salmonella choleraesuis ATCC 10708, Psendomonas aeruginosa ATCC 15442, Staphylococcus aureus ATCC 6538, and Shewanella putrefaciens Shewanella putrefaciens Bacteriology A bacterium of environment and foods–ie, not part of normal human flora Clinical Found in mixed cultures, respiratory tract, urine, feces, pleural fluid; implicated in cellulitis, otitis media, septicemia ATCC 8071.
The bacteria were grown in trypticase soy broth incubated at 35 [degrees] [TABULAR DATA FOR TABLE 1 OMITTED] C. After at least three consecutive daily transfers, the final culture was grown in trypticase soy broth at 35 [degrees] C for 24 hours Adv. 1. for 24 hours - without stopping; "she worked around the clock"
around the clock, round the clock . The organisms were harvested by centrifugation Centrifugation
A mechanical method of separating immiscible liquids or solids from liquids by the application of centrifugal force. This force can be very great, and separations which proceed slowly by gravity can be speeded up enormously in centrifugal , and concentration was adjusted according to optical density with a spectrophotometer spectrophotometer, instrument for measuring and comparing the intensities of common spectral lines in the spectra of two different sources of light. See photometry; spectroscope; spectrum. . Single species of bacteria at equivalent concentrations were combined to prepare a composite inoculum inoculum /in·oc·u·lum/ (-ok´u-lum) pl. inoc´ula material used in inoculation.
n. pl. . The composite concentration was verified by enumeration 1. (mathematics) enumeration - A bijection with the natural numbers; a counted set.
2. (programming) enumeration - enumerated type. on letheen agar incubated at 35 [degrees] C for two days.
Laboratory Sponge Preparation
Household scrubber sponges were thoroughly rinsed by hand to wash out the magnesium chloride (humectant humectant /hu·mec·tant/ (hu-mek´tant)
2. a moistening or diluent medicine.
humectant ) and quaternary ammonium compound quaternary ammonium compound
Any of a group of compounds in which a central nitrogen atom is joined to four organic radicals and one acid radical, used as antiseptics, solvents, and emulsifying agents.
Noun 1. (mildew-static compound). These compounds were washed out to simulate a "used" condition. Sponges were dried at room temperature for several days and stored in bags.
The pour plate technique with letheen agar was used for determining bacterial concentrations. Prior to inoculation, no counts (fewer than 10 CFU CFU
see colony-forming units. per sponge) were detected in the scrubber sponges to be inoculated. For inoculation, each sponge was wetted with 54 milliliters (mL) of sterile distilled water and contaminated with 1.0 x [10.sup.5] to 2.0 x [10.sup.6] total bacteria (4 mL). To mix the bacteria, researchers squeezed each sponge several times and allowed the liquid to resaturate into the sponge, held in a storage bag. The sponges were stored at 25 [degrees] C for two days to allow the bacteria to acclimatize to the sponge environment. After two days, counts from contaminated sponges were 1.0 x [10.sup.5] to 1.0 x [10.sup.6] CFU per sponge (pretreatment pretreatment,
n the protocols required before beginning therapy, usually of a diagnostic nature; before treatment.
n See predetermination. counts). For each treatment, the number of sponges tested varied from two to 12. After treatment, each sponge was rinsed with water and the effluent was diluted to
neutralize the treatment. Plating with letheen agar followed immediately.
Different brands of household scrubber sponges were collected from consumers who had used the sponges as they normally would in the kitchen area (one- to two-week usage). Pretreatment and posttreatment plating was conducted with letheen agar on the consumer-used sponges. The number of sponges tested varied from two to 10, depending on availability. The chemical and physical treatments are described below.
Six chemical treatments were tested:
1. Regular Clorox[R] Bleach diluted with tap water at a ratio of 1:21.3 (3/4 cup per gallon);
2. Sav-On Solution of three percent hydrogen peroxide, undiluted;
3. Sav-On 70 Percent Isopropyl isopropyl
denotes the 1-methylethyl group, -CH(CH3)2.
rubbing alcohol, used as a solvent and rubefacient. Formed naturally in the rumen of the cow in nervous acetonemia. Rubbing Alcohol, undiluted;
4. Formula 409[R] (All Purpose Cleaner, Now Kills Bacteria!) both undiluted and diluted with tap water at a ratio of 1:2;
5. Parson's[R] Lemon Fresh Ammonia, diluted with tap water at a ratio of 1:32; and
6. Lady Lee[R] White Distilled Vinegar, undiluted.
The average wet weight of a sponge was 70 grams (g) [+ or -] 5 g. Before the sponge effluent was diluted for counts, the total weight of the sponge was adjusted with water to 70 g. The purpose of this step was to standardize the starting dilution. Sponges were soaked in 100 mL volume of undiluted or diluted test solution. Activity of the chemical treatment was then neutralized by thorough rinsing with tap water after five minutes of exposure. A 1 mL aliquot aliquot (al-ee-kwoh) adj. a definite fractional share, usually applied when dividing and distributing a dead person's estate or trust assets. (See: share) of rinse water squeezed from the sponge was transferred into 9 mL of letheen broth supplemented with 0.1 percent sodium thiosulfate. Further 10-fold dilutions were prepared with letheen broth supplemented with 0.1 percent sodium thiosulfate as diluent diluent /dil·u·ent/ (dil´oo-int)
1. causing dilution.
2. an agent that dilutes or renders less potent or irritant.
Serving to dilute.
n. . The pour plate technique was used for plating dilutions from [10.sup.-1] to [10.sup.-4] for laboratory-inoculated sponges and dilutions from [10.sup.-2] to [10.sup.-7] for consumer-used sponges.
Neutralization neutralization, chemical reaction, according to the Arrhenius theory of acids and bases, in which a water solution of acid is mixed with a water solution of base to form a salt and water; this reaction is complete only if the resulting solution has neither acidic nor Verification
An uninoculated sponge was exposed to the same chemical treatment conditions as the inoculated sponges. Triplicate 1 mL aliquots of liquid squeezed from the treated, uninoculated sponge were combined with 9 mL of letheen broth supplemented with 0.1 percent sodium thiosulfate. Approximately 200 total composite bacteria were inoculated into triplicate broth tubes containing treatment liquid. The broth cultures were incubated at 35 [degrees] C for two days. Growth in all culture tubes verified neutralization.
Physical-and-Chemical Combination Treatments
Two treatment methods were tested.
1. A Whirlpool washer and Whirlpool dryer were tested as follows: Each load consisted of a sponge, 61 pounds of poly-cotton ballast, and a soiled pillow case. All loads were agitated ag·i·tate
v. ag·i·tat·ed, ag·i·tat·ing, ag·i·tates
1. To cause to move with violence or sudden force.
2. for 12 minutes at 34 [degrees] C and dried for 60 minutes. On certain trials (for consumer-used sponges only), Tide[R] (1/4 cup) and Regular Clorox Bleach (1.5 cups) were added to the wash load.
2. A Kenmore dishwasher was tested as follows: One load consisted of one to three sponges on the top rack, soiled dishes, utensils, and glass cups washed with or without detergent for consumer-used sponges and without detergent for laboratory-inoculated sponges. Tests were conducted both with and without the hot dry cycle.
Two physical treatments were tested:
1. boiling - sponges were boiled in tap water for five minutes - and
2. Sharp microwave oven - a wet sponge in a storage bag was heated in the microwave oven for one minute on the highest power. (Sponges need to be wet before being heated in the microwave. Also, care was taken to avoid heating the sponges to dryness to preclude the possibility of a sponge catching fire.)
The treated sponges were analyzed for bacteria counts immediately after they had cooled to room temperature. To normalize normalize
to convert a set of data by, for example, converting them to logarithms or reciprocals so that their previous non-normal distribution is converted to a normal one. the starting dilution, researchers [TABULAR DATA FOR TABLE 2 OMITTED] adjusted the total wet weight of each sponge with water to about 70 g [+ or -] 5 g. Liquid (1 mL) squeezed from the treated sponge was combined with 9 mL letheen broth for diluting. Plating was conducted using letheen agar.
Table 1 and Table 2 summarize results for laboratory-inoculated sponges. Table 3 and Table 4 summarize results for consumer-used sponges. For the purposes of this study, an effective treatment is defined as 99.9 or greater reduction in the number of bacteria. This definition is similar to the U.S. Environmental Protection Agency Environmental Protection Agency (EPA), independent agency of the U.S. government, with headquarters in Washington, D.C. It was established in 1970 to reduce and control air and water pollution, noise pollution, and radiation and to ensure the safe handling and (U.S. EPA EPA eicosapentaenoic acid.
n.pr See acid, eicosapentaenoic.
n. ) requirement for a non-food-contact sanitizer sanitizer
a sanitizing product capable of cleaning and disinfecting; usually a formulation containing a disinfectant and a detergent. (10). For the purpose of this paper, a scrubber sponge used for cleaning is considered to be a non-food-contact surface since the sponge does not come in direct contact with food.
For laboratory-inoculated sponges, all chemical and physical treatments were effective in producing a greater than 99.9 percent reduction of bacteria (Table 1 and Table 2). For consumer-used sponges, physical treatments (boiling, heating in the microwave oven) and the combination of physical and chemical treatments (dishwashing with detergent or laundering with detergent and bleach) were effective in reducing the bacterial load more than 99.9 percent (Table 3). Laundering without detergent and bleach reduced the total number of bacteria by 90 percent in consumer-used sponges. Dishwashing without detergent resulted in adequate reduction of bacteria (99.9 percent) in consumer-used sponges.
Bleach and Formula 409 were the only chemical treatments that were effective on consumer-used sponges (Table 4). The other chemical treatments (vinegar, ammonia, alcohol, hydrogen peroxide) resulted in less bacteria reduction (about 56 percent to 98 percent) (Table 4).
Heating sponges in a microwave oven has been previously investigated as a means of reducing bacteria counts (9). Park and Cliver inoculated the sponges with single bacterial strains, with an initial concentration of 1.0 x [10.sup.9] CFU per sponge. Heating cellulose sponges for 30 seconds gave a reduction of more than 99.9 percent (eight logs) of E. coli O157:H7, or Staphylococcus aureus. Our study also demonstrated a greater than 99.9 percent reduction in one minute for composite test organisms initially inoculated at about 2.0 x [10.sup.6] (five logs reduction or 99.999 percent reduction) (Table 1). Heating consumer-used sponges in a microwave oven for one minute verified the effectiveness of this procedure in reducing the bacteria load by five logs (Table 3). Boiling cellulose sponges for five minutes gave similar results. For both laboratory-inoculated and consumer-used sponges, there was about a five-log reduction (Table 1 and Table 3).
Laundering without bleach and detergent and dishwashing without detergent reduced the bacterial load by more than 99.9 percent in laboratory-inoculated sponges (Table 1). For consumer-used sponges, the dishwashing treatment without detergent (but with the heat cycle) and the dishwashing treatment with detergent (but without the heat cycle) were similarly effective (99.9 percent), even though the dishwasher contained soiled dishes, utensils, and glassware (Table 3). The use of both detergent and heat cycle improved bacteria reduction 1,000-fold (99.9999 percent reduction). Laundering consumer sponges without detergent and bleach did not significantly reduce bacteria (Table 3). Similarly, Scott and Bloomfield have found that washing and rinsing dishcloths gives limited reduction in microbial microbial
pertaining to or emanating from a microbe.
the breakdown of organic material, especially feedstuffs, by microbial organisms. contamination - 63.8 percent reduction in CFU per square centimeter (CFU/[cm.sup.2]) (11). In that study, detergent washing, rinsing, and drying at 80 [degrees] C for two hours resulted in effective decontamination - 99.99 percent reduction in CFU/[cm.sup.2]. In the present study, the one-hour dry cycle at approximately 77 [degrees] C was ineffective, perhaps because of the shorter drying time or because the presence of ballast material in the drying load resulted in insufficient heating of the sponge. For laundering to be an effective method, detergent with bleach or some other disinfectant should be added to the wash load.
Several investigators have shown the effectiveness of adding disinfectants and detergent to a wash load. The use of 160 parts per million parts per million
mg/kg or ml/l; see ppm. (ppm) or 320 ppm available chlorine with an anionic detergent in wash water resulted in a 99.8 percent reduction of bacteria [TABULAR DATA FOR TABLE 3 OMITTED] [TABULAR DATA FOR TABLE 4 OMITTED] in the wash water and a 99.4 percent reduction in CFU/[cm.sup.2] for a cotton swatch (12). Diapers laundered at 54 [degrees] C with 200 ppm available chlorine inactivated inactivated
rendered inactive; the activity is destroyed.
treated so that they are no longer able to produce evidence of growth or damaging effect on tissue. poliovirus poliovirus /po·lio·vi·rus/ (pol´-e-o-vi?rus) the causative agent of poliomyelitis, separable, on the basis of specificity of neutralizing antibody, into three serotypes designated types 1, 2, and 3. in two minutes (13). Quaternary ammonium compound at 150 ppm resulted in 97 percent microbial kill in wash water (14). In our study, the effectiveness of the laundering treatment improved significantly with the combination of detergent and bleach to greater than four logs of bacterial reduction (more than 99.99 percent) (Table 3).
Just as disinfectants can be effective with laundering, soaking the sponge in a disinfectant solution was highly effective in reducing the total number of bacteria. In this study, two U.S. EPA-registered disinfectants (Clorox Bleach and Formula 409) significantly reduced the bacterial load in laboratory-inoculated sponges (99.998 percent reduction) (Table 2). Other products (hydrogen peroxide, isopropyl alcohol, ammonia, and vinegar) were also effective on laboratory-inoculated sponges (Table 2).
Consumer-used sponges treated with bleach and Formula 409 showed at least a three-log reduction (99.9 percent) in bacteria, as expected because of the known level of active ingredients in these products (Table 4). Other studies have shown that greater than 300 ppm sodium hydrochloride hydrochloride /hy·dro·chlo·ride/ (-klor´id) a salt of hydrochloric acid.
A compound resulting from the reaction of hydrochloric acid with an organic base. was needed to show antimicrobial effects against Listeria Listeria /Lis·te·ria/ (lis-ter´e-ah) a genus of gram-negative bacteria (family Corynebacterium); L. monocyto´genes causes listeriosis.
n. monocytogenes when a bacterial suspension was combined with disinfectant rinse solution from a sponge (15). Scott and Bloomfield have demonstrated that for dishcloths, 4,000 ppm available chlorine was sufficient to decrease the bacterial load by 99.9 percent in two minutes (10). For consumer-used sponges, the present study produced a similar level of reduction with 2,400 ppm of available chlorine (1:21.3 dilution) in five minutes (Table 4).
Lee showed the antimicrobial activity of commercial benzalkonium chloride against L. monocytogenes at levels of greater than 0.1 percent when a bacterial culture was treated with disinfectant solution squeezed from sponges (15). In a study by Roessler and Hoyt, the quaternary-based disinfectant cleaner reduced the total bacteria and total and fecal coliforms from two to three logs (a 99 percent to 99.9 percent reduction) within 30 minutes (16). In the present study, however, Formula 409 (a quaternary-based disinfectant) produced a 99.9 percent reduction within a shorter time of five minutes.
Parnes has reported that other products such as ammonia and vinegar were ineffective in killing bacteria on a sponge used to wipe a ceramic or formica surface contaminated with S. aureus The aureus (pl. aurei) was a gold coin of ancient Rome valued at 25 silver denarii. The aureus was regularly issued from the 1st century BC to the beginning of the 4th century AD, when it was replaced by the solidus. (17). The results of this study were similar: Applied to consumer-used sponges, products such as hydrogen peroxide, vinegar, ammonia, and alcohol were ineffective (Table 4). Use of these products for sponge decontamination is not advisable, because laboratory-inoculated sponges do not adequately represent domestic conditions. This study demonstrates that to determine the efficacy of a sponge treatment on sponges used in a realistic consumer environment, consumer-used sponges must be included in the testing.
This study found that several types of chemical and physical treatments were effective in reducing bacteria in sponges. Boiling yielded greater than 99.9 percent reduction of bacteria for consumer-used sponges, as did heating in a microwave oven. Disinfectant products were consistently more effective than the other chemical treatment products. Combinations of physical and chemical treatments also significantly reduced the bacterial populations.
Testing of consumer-used sponges, which were more difficult to sanitize To remove sensitive data from an information system, a database or an extract from a database. See sensitive. than laboratory-inoculated sponges, validated these treatments. Under the test conditions, the population of bacteria in sponges subjected to kitchen usage was verified to be heartier than laboratory-grown bacteria. The treatments determined to be effective in this study can be used to decrease the bacterial load in sponges and can reduce the cross-contamination associated with unsanitary un·san·i·tar·y
Not sanitary. kitchen practices.
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Corresponding Author: Judy Ikawa, Senior Microbiologist, Clorox Services Company, 7200 Johnson Drive, Pleasanton, California 94588-8004.