Difficulty in removing biofilm from dry surfaces.

Cleaning is fundamental to infection control. This report demonstrates that a Staphylococcus aureus biofilm is significantly more difficult to remove than dried planktonic bacteria. A single wiping action removed >99.9% (>3 log10) of dried planktonic bacteria, whereas only 1.4 log10 of biofilm (96.66%) was removed by 50 wiping actions with a standardized wiping process.

Transfer of dry surface biofilm in the healthcare environment: the role of healthcare workers' hands as vehicles.

BACKGROUND: Dry surface biofilms (DSBs) persist for extended periods in hospital, and may play a significant role in transmission of healthcare-associated infections. AIM: To determine whether DSBs may be transferred from hospital surfaces to healthcare workers' hands. METHOD: Twelve-day Staphylococcus aureus DSB was grown on polycarbonate and glass coupons in a CDC Biofilm Reactor®. A total of 1.8 × 106 and 8.8 × 105 bacteria grew on the polycarbonate and glass coupons respectively. Transmission was tested by lifting the coupon with forefinger and thumb of ungloved hands to a height of 30 cm, then touching horse blood agar (HBA) plates 19 sequential times. Transferred bacterial number was determined by colony-forming units. The effect of DSB wetting on biofilm transfer was tested with 5% neutral detergent treatment for 5 s. FINDINGS: Between 5.5 and 6.6% of the DSB bacteria were transferred to hands with one touch and ∼20% were then transferred to HBA with one touch, giving an overall transfer rate of 1.26% and 1.04% for polycarbonate and glass coupons, respectively. Detergent treatment had little effect on bacterial removal from coupons, but, for biofilm grown on polycarbonate, significantly increased transferral to HBA (P < 0.001) to 5.2%. Large numbers of bacteria were transferred by bare hands to multiple fomites. One-third of polycarbonate coupons transferred >1000 colonies during the first five sequential touches. Sufficient bacteria to cause infection were transmitted up to 19 times following one touch of the DSB. CONCLUSION: DSB bacteria are transferred by hands from one fomite to multiple fomites, suggesting that DSB may serve as a persistent environmental source of pathogens.

Staphylococcus aureus dry-surface biofilms are more resistant to heat treatment than traditional hydrated biofilms.

BACKGROUND: The importance of biofilms to clinical practice is being increasingly realized. Biofilm tolerance to antibiotics is well described but limited work has been conducted on the efficacy of heat disinfection and sterilization against biofilms. AIM: To test the susceptibility of planktonic, hydrated biofilm and dry-surface biofilm forms of Staphylococcus aureus, to dry-heat and wet-heat treatments. METHODS: S. aureus was grown as both hydrated biofilm and dry-surface biofilm in the CDC biofilm generator. Biofilm was subjected to a range of temperatures in a hot-air oven (dry heat), water bath or autoclave (wet heat). FINDINGS: Dry-surface biofilms remained culture positive even when treated with the harshest dry-heat condition of 100°C for 60min. Following autoclaving samples were culture negative but 62-74% of bacteria in dry-surface biofilms remained alive as demonstrated by live/dead staining and confocal microscopy. Dry-surface biofilms subjected to autoclaving at 121°C for up to 30min recovered and released planktonic cells. Recovery did not occur following autoclaving for longer or at 134°C, at least during the time-period tested. Hydrated biofilm recovered following dry-heat treatment up to 100°C for 10min but failed to recover following autoclaving despite the presence of 43-60% live cells as demonstrated by live/dead staining. CONCLUSION: S. aureus dry-surface biofilms are less susceptible to killing by dry heat and steam autoclaving than hydrated biofilms, which are less susceptible to heat treatment than planktonic suspensions.

Staphylococcus aureus dry-surface biofilms are not killed by sodium hypochlorite: implications for infection control.

BACKGROUND: Dry hospital environments are contaminated with pathogenic bacteria in biofilms, which suggests that current cleaning practices and disinfectants are failing. AIM: To test the efficacy of sodium hypochlorite solution against Staphylococcus aureus dry-surface biofilms. METHODS: The Centers for Disease Control and Prevention Biofilm Reactor was adapted to create a dry-surface biofilm, containing 1.36 × 10(7)S. aureus/coupon, by alternating cycles of growth and dehydration over 12 days. Biofilm was detected qualitatively using live/dead stain confocal laser scanning microscopy (CLSM), and quantitatively with sonicated viable plate counts and crystal violet assay. Sodium hypochlorite (1000-20,000parts per million) was applied to the dry-surface biofilm for 10min, coupons were rinsed three times, and residual biofilm viability was determined by CLSM, plate counts and prolonged culture up to 16 days. Isolates before and after exposure underwent minimum inhibitory concentration (MIC) and minimum eradication concentration (MEC) testing, and one pair underwent whole-genome sequencing. FINDINGS: Hypochlorite exposure reduced plate counts by a factor of 7 log10, and reduced biofilm biomass by a factor of 100; however, staining of residual biofilm showed that live S. aureus cells remained. On prolonged incubation, S. aureus regrew and formed biofilms. Post-exposure S. aureus isolates had MICs and MECs that were not significantly different from the parent strains. Whole-genome sequencing of one pre- and post-exposure pair found that they were virtually identical. CONCLUSIONS: Hypochlorite exposure led to a 7-log kill but the organisms regrew. No resistance mutations occurred, implying that hypochlorite resistance is an intrinsic property of S. aureus biofilms. The clinical significance of this warrants further study.