3059/04/89
Journal of Applied Bacteriology 1990,68,279-283
Investigations of the effectiveness of detergent washing, drying and chemical disinfection on contamination of cleaning cloths E L I Z A B E T SCOTT H & S A L L YF . B L O O M F I E LChelsea D Department of Pharmacy, King’s College, University of London, Manresa R d , London SW3 6 L X , U K Accepted 5 July 1989
SCOTT,E . & B L O O M F I E L DS.F. , 1990. Investigations of the effectiveness ofdetergent washing, drying and chemical disinfection on contamination of cleaning cloths. Journal of Applied Bacteriology 68,279-283.
Detergent washing, drying and chemical disinfection for decontamination of cleaning cloths was investigated with cloths contaminated by use in the domestic environment. Detergent washing produced only limited reductions in microbial contamination and cloths then stored at room temperature for 24 h showed increases in contamination due to multiplication of residual survivors. For effective and consistent decontamination of cloths, detergent washing followed by drying at 80°C for 2 h was required. Hypochlorite and phenolic disinfectants produced significant reductions in contamination, but chemical disinfection may be. unreliable where cloths are heavily contaminated.
Heavy contamination of wet mops and cleaning utensils and the potential for spread of such contamination has been recognized by several workers. In domestic dishcloths, Davis el al. (1968) reported total counts of up to lo8organisms/cloth with up to lo7 Escherichia coli. Heavy contamination of wet cloths and cleaning utensils in hospitals with enterobacteria and Pseudomonas aeruginosa was reported by Westwood et al. (1971), Whitby & Rampling (1972) and Baird et al. (1976). Although reusable wet cleaning cloths are now discouraged in UK hospitals, these items are still in use. Most particularly, cloths are used in domestic and other food preparation environments. A survey of domestic dishcloths and cleaning cloths by Scott et al. (1982) showed that about 50% had counts of greater than 100 cfu/25 cm’. Organisms included E . coli, Citrobacter freundii, Klebsiella pneumoniae, Enterobacter spp., Pseudomonas spp., Staphylococcus aureus and streptococci. Similar results were reported by Finch et al. (1978).
Only limited data have been published which can be used to formulate effective policies for decontamination and maintenance of re-usable cleaning utensils (Westwood et al. 1971; Walter & Schillinger 1975; Scott et al. 1984). Recent laboratory investigations (Scott 8c Bloomfield 1989) showed that although drying at room temperature produces substantial reductions in recoverable organisms from artificially contaminated cloths, Gram-negative and Gram-positive species may survive for up to 4 h and in some cases up to 24 h. Although there may be an initial decline in numbers for Gram-negative species this is followed by an increase on cloths which may be relatively dry. Experiments confirmed that where contaminated cloths come into contact with the fingers or a clean surface organisms may be transferred in sufficient numbers to represent an infection hazard if in contact with food. Transfer by contact with contaminated cloths has also been reported by Babb et al. (1981) and Mackintosh & Hoffman (1984). These studies emphasize the
280
Elizabeth Scott and Sally F . Bloomjield
importance of decontamination procedures for reusable cloths in kitchens or environments where cross-contamination represents a hazard. In this paper, washing, drying and disinfection procedures for decontamination of cloths contaminated by use in the domestic environment are investigated.
units (cfu) determined on tryptone soya agar by the method of Miles et a!. (1938). Results are expressed as the total count/cm2 of cloth. D E T E R G E N T W A S H A N D D R Y I N G OF CLOTHS
Cloths were of the dry-woven ‘J-cloth’ type (Paynes Scientific, Slough). Volunteers used the cloths as ‘washing up’ cloths etc in the domestic kitchen for 3 d and then returned them to the laboratory for immediate investigation. Cloths were not to be used in combination with chemical disinfectants.
Cloths were divided into four portions (approx. 325 cm’). One portion was immediately transferred to quarter-strength Ringer solution to determine the total count. The remaining portions were washed in anionic detergent (diluted to 1.2% v/v) and rinsed in tap water. One portion was transferred to quarter-strength Ringer solution for determination of total count, whilst the remaining two portions were stored in glass Petri dishes for 24 h before performing total counts. For one cloth, the Petri dish was maintained with the lid closed at room temperature, 30% r.h., whilst the other was maintained with the lid ajar at S O T , 50% r.h. To examine the effect of drying at elevated temperature, cloths were divided into five portions (approx. 200cm’). One portion was used to determine the initial viable count whilst the remaining portions were washed in anionic detergent, rinsed in tap water and stored in glass Petri dishes (lid ajar) at 80”C, 3.2 x 1.7 x 1.9
103
1.6
103
Detergent wash and rinse, stored 24 h at room temperature
2.3 x 103 2.2 x 103
x lo2
~
2.6
x 10' x 10' x 103 x 10'
103
8.8 x lo2 2.3 103 2.0 x 103
for 24 h were immersed in neutralizing medium for 10min. They were then wrung out and folded before transfer to Petri dishes for storage at room temperature and sampling as described above.
Results
Detergent wash and rinse, stored 24 h at 50°C
3 3 2 7.0 x 10' 0
2.6 x 10' 1.7 x 10'
reductions in total counts but contaminants were recoverable from four of six cloths and the highest count was 70cfu/cm2. The results of detergent wash and drying at 80°C (Table 2) indicate that whereas drying at 80°C for 1 h produced total elimination of contamination from all but one cloth, drying at 80°C for 2 h or more was effective for all cloths.
DETERGENT WASH A N D D R Y I N G OF CLOTHS
CHEMICAL DISINFECTION OF CLOTHS
Results given in Table 1 indicate that following detergent wash and rinse treatment, the mean total count was reduced from 1600 to 580cfu/ cm2. This reduction was significant at the P < 0.2 level although in one sample, the washing process produced some increase in contamination. Cloth portions stored at room temperature for 24 h showed some increase in average total count to 2000cfu/cm2 but this increase was not significant compared with counts determined prior to treatment. Drying cloths at 50°C for 24 h produced significant
Effects of chemical disinfection on contamination of cloths are shown in Table 3. There were no detectable survivors in five of 13 cloths after treatment with 2% (v/v) Stericol (2 min contact period). For the remaining eight cloths, although reductions were achieved, total counts in excess of 103/cm2 were recorded. The emciency of the disinfection procedure was related to initial contamination levels; for the five cloths which were satisfactorily disinfected, initial counts were 102-103/cm2 compared with 104-106 for cloths where satisfactory disinfection was not observed. For all nine cloths stored without neutralization of residual Stericol, the initial reduction was maintained over 24 h, indicating some further activity. For two of these cloths, a further reduction t o give no detectable survivors was achieved. Where Stericol was neutralized before storage, regrowth of residual survivors occurred in all four cloths even though a zero count had been previously recorded in two cloths. Sodium hypochlorite solution, 4000 ppm AvCI, , achieved somewhat better results, with no detectable survivors in 10 of 13 cloths immediately after disinfection. For the remaining three cloths, although reductions occurred,
Table 2. Total counts recovered from contaminated cloths after detergent wash and rinse and drying at 80°C Total count wr cm2 cloth ~~
Detergent wash and rinse followed by drying at 80°C for Cloth sample I 2 3 4 5
Initial count 1.0 x 8.8 3.5 x 5.5 x 2.5 x
105 104 lo4 104 104
lh
2h
3h
4h
0
Journal of Applied Bacteriology 1990,68,279-283
Investigations of the effectiveness of detergent washing, drying and chemical disinfection on contamination of cleaning cloths E L I Z A B E T SCOTT H & S A L L YF . B L O O M F I E LChelsea D Department of Pharmacy, King’s College, University of London, Manresa R d , London SW3 6 L X , U K Accepted 5 July 1989
SCOTT,E . & B L O O M F I E L DS.F. , 1990. Investigations of the effectiveness ofdetergent washing, drying and chemical disinfection on contamination of cleaning cloths. Journal of Applied Bacteriology 68,279-283.
Detergent washing, drying and chemical disinfection for decontamination of cleaning cloths was investigated with cloths contaminated by use in the domestic environment. Detergent washing produced only limited reductions in microbial contamination and cloths then stored at room temperature for 24 h showed increases in contamination due to multiplication of residual survivors. For effective and consistent decontamination of cloths, detergent washing followed by drying at 80°C for 2 h was required. Hypochlorite and phenolic disinfectants produced significant reductions in contamination, but chemical disinfection may be. unreliable where cloths are heavily contaminated.
Heavy contamination of wet mops and cleaning utensils and the potential for spread of such contamination has been recognized by several workers. In domestic dishcloths, Davis el al. (1968) reported total counts of up to lo8organisms/cloth with up to lo7 Escherichia coli. Heavy contamination of wet cloths and cleaning utensils in hospitals with enterobacteria and Pseudomonas aeruginosa was reported by Westwood et al. (1971), Whitby & Rampling (1972) and Baird et al. (1976). Although reusable wet cleaning cloths are now discouraged in UK hospitals, these items are still in use. Most particularly, cloths are used in domestic and other food preparation environments. A survey of domestic dishcloths and cleaning cloths by Scott et al. (1982) showed that about 50% had counts of greater than 100 cfu/25 cm’. Organisms included E . coli, Citrobacter freundii, Klebsiella pneumoniae, Enterobacter spp., Pseudomonas spp., Staphylococcus aureus and streptococci. Similar results were reported by Finch et al. (1978).
Only limited data have been published which can be used to formulate effective policies for decontamination and maintenance of re-usable cleaning utensils (Westwood et al. 1971; Walter & Schillinger 1975; Scott et al. 1984). Recent laboratory investigations (Scott 8c Bloomfield 1989) showed that although drying at room temperature produces substantial reductions in recoverable organisms from artificially contaminated cloths, Gram-negative and Gram-positive species may survive for up to 4 h and in some cases up to 24 h. Although there may be an initial decline in numbers for Gram-negative species this is followed by an increase on cloths which may be relatively dry. Experiments confirmed that where contaminated cloths come into contact with the fingers or a clean surface organisms may be transferred in sufficient numbers to represent an infection hazard if in contact with food. Transfer by contact with contaminated cloths has also been reported by Babb et al. (1981) and Mackintosh & Hoffman (1984). These studies emphasize the
280
Elizabeth Scott and Sally F . Bloomjield
importance of decontamination procedures for reusable cloths in kitchens or environments where cross-contamination represents a hazard. In this paper, washing, drying and disinfection procedures for decontamination of cloths contaminated by use in the domestic environment are investigated.
units (cfu) determined on tryptone soya agar by the method of Miles et a!. (1938). Results are expressed as the total count/cm2 of cloth. D E T E R G E N T W A S H A N D D R Y I N G OF CLOTHS
Cloths were of the dry-woven ‘J-cloth’ type (Paynes Scientific, Slough). Volunteers used the cloths as ‘washing up’ cloths etc in the domestic kitchen for 3 d and then returned them to the laboratory for immediate investigation. Cloths were not to be used in combination with chemical disinfectants.
Cloths were divided into four portions (approx. 325 cm’). One portion was immediately transferred to quarter-strength Ringer solution to determine the total count. The remaining portions were washed in anionic detergent (diluted to 1.2% v/v) and rinsed in tap water. One portion was transferred to quarter-strength Ringer solution for determination of total count, whilst the remaining two portions were stored in glass Petri dishes for 24 h before performing total counts. For one cloth, the Petri dish was maintained with the lid closed at room temperature, 30% r.h., whilst the other was maintained with the lid ajar at S O T , 50% r.h. To examine the effect of drying at elevated temperature, cloths were divided into five portions (approx. 200cm’). One portion was used to determine the initial viable count whilst the remaining portions were washed in anionic detergent, rinsed in tap water and stored in glass Petri dishes (lid ajar) at 80”C, 3.2 x 1.7 x 1.9
103
1.6
103
Detergent wash and rinse, stored 24 h at room temperature
2.3 x 103 2.2 x 103
x lo2
~
2.6
x 10' x 10' x 103 x 10'
103
8.8 x lo2 2.3 103 2.0 x 103
for 24 h were immersed in neutralizing medium for 10min. They were then wrung out and folded before transfer to Petri dishes for storage at room temperature and sampling as described above.
Results
Detergent wash and rinse, stored 24 h at 50°C
3 3 2 7.0 x 10' 0
2.6 x 10' 1.7 x 10'
reductions in total counts but contaminants were recoverable from four of six cloths and the highest count was 70cfu/cm2. The results of detergent wash and drying at 80°C (Table 2) indicate that whereas drying at 80°C for 1 h produced total elimination of contamination from all but one cloth, drying at 80°C for 2 h or more was effective for all cloths.
DETERGENT WASH A N D D R Y I N G OF CLOTHS
CHEMICAL DISINFECTION OF CLOTHS
Results given in Table 1 indicate that following detergent wash and rinse treatment, the mean total count was reduced from 1600 to 580cfu/ cm2. This reduction was significant at the P < 0.2 level although in one sample, the washing process produced some increase in contamination. Cloth portions stored at room temperature for 24 h showed some increase in average total count to 2000cfu/cm2 but this increase was not significant compared with counts determined prior to treatment. Drying cloths at 50°C for 24 h produced significant
Effects of chemical disinfection on contamination of cloths are shown in Table 3. There were no detectable survivors in five of 13 cloths after treatment with 2% (v/v) Stericol (2 min contact period). For the remaining eight cloths, although reductions were achieved, total counts in excess of 103/cm2 were recorded. The emciency of the disinfection procedure was related to initial contamination levels; for the five cloths which were satisfactorily disinfected, initial counts were 102-103/cm2 compared with 104-106 for cloths where satisfactory disinfection was not observed. For all nine cloths stored without neutralization of residual Stericol, the initial reduction was maintained over 24 h, indicating some further activity. For two of these cloths, a further reduction t o give no detectable survivors was achieved. Where Stericol was neutralized before storage, regrowth of residual survivors occurred in all four cloths even though a zero count had been previously recorded in two cloths. Sodium hypochlorite solution, 4000 ppm AvCI, , achieved somewhat better results, with no detectable survivors in 10 of 13 cloths immediately after disinfection. For the remaining three cloths, although reductions occurred,
Table 2. Total counts recovered from contaminated cloths after detergent wash and rinse and drying at 80°C Total count wr cm2 cloth ~~
Detergent wash and rinse followed by drying at 80°C for Cloth sample I 2 3 4 5
Initial count 1.0 x 8.8 3.5 x 5.5 x 2.5 x
105 104 lo4 104 104
lh
2h
3h
4h
0
