Two-step approach for cleaning and disinfection of Bacillus cereus biofilmAmanda Deal, Rebecca Hostettler, Dan Klein, and Paul Lopolito
STERIS Corporation, 7501 Page Avenue, Saint Louis, MO 63133
Paul Lopolito
STERIS Corporation
Email: [email protected]
Website: www.sterislifesciences.com
Phone: 314-290-4795
Contact1. Deal, A., Klein, D, Lopolito, P., and Schwarz, J.S., Cleaning and Disinfection of Bacillus cereus Biofilm. PDA J Pharm Sci and Tech 2016, 70 208-217.
2. McDonnell, G. (2007) Antisepsis, Disinfection and Sterilization: Types, Action and Resistance. ASM Press, Washington, DC.
3. Karunakaran, E. and Biggs, C.A., Mechanisms of Bacillus cereus biofilm formation: an investigation of the physicochemical characteristics of cell surfaces and extracellular proteins. Applied
Microbial and Cell Physiology. Published online: 09 October 2010.
4. Wijman, J.G.E. et al. (2007), Air-Liquid Interface Biofilms of Bacillus cereus: Formation, Sporulation, and Dispersion. Applied and Environmental Microbiology. Vol. 73, No. 5, pp. 1481-1488.
5. ASTM E2562-12, Standard Test Method for Quantification of P. aeruginosa Biofilm Grown with High Shear and Continuous Flow using CDC Biofilm Reactor, Approved April 1, 2012.
6. ASTM E2871-13, Standard Test Method for Evaluating Disinfectant Efficacy Against
P. aeruginosa Biofilm Grown in CDC Biofilm Reactor Using Single Tube Method, Approved Oct. 1, 2013.
References
Methodology has been evolving for the testing of disinfectants against bacterial
single-species biofilms, as the difficulty of biofilm remediation continues to gain
much needed attention. Bacterial single-species biofilm contamination
presents a real risk to GMP regulated industries. However, mixed-species
biofilms and biofilms containing bacterial spores remain an even greater
challenge for cleaning and disinfection. Among spore-forming microorganisms
frequently encountered in pharmaceutical manufacturing areas, the spores of
Bacillus cereus are often determined to be the hardest to disinfect and
eradicate. One of the reasons for the low degree of susceptibility to disinfection
is the ability of these spores to be encapsulated within an exopolysaccharide
biofilm matrix. In a series of experiments, we evaluated the disinfectant
susceptibility of B. cereus biofilms relative to disassociated B. cereus spores
and biofilm from a non-spore-forming species. Further, we assessed the impact
that pre-cleaning has on increasing that susceptibility.
Abstract
Methods and Materials
Liquid suspension testing for assessment of biocide activity
A liquid suspension study was used to assess the ability of treatments to
reduce the viability of spore cell suspensions. Aliquots of a sporicide,
containing hydrogen peroxide and peroxyacetic acid, were diluted with DI
water to 3% and 12% (v/v). The biocide activity was neutralized by adding an
aliquot of the organism/product mixture to chilled lecithin and tween (LAT)
broth (with 1% v/v catalase when testing oxidizers) and vortexed. Each
neutralized reaction was assayed for viable colony forming units via pour-
plating with LAT agar and incubated for 1 or 2 days at 37°C.
Assessment of surface cleaning
Testing occurred at room temperature. B. cereus ATCC 14579 biofilm on
polycarbonate coupons were cleaned by submersion in a stirred, pre-heated
volume of an alkaline detergent or a stirred volume of room temperature
sporicide (previously described 12% v/v in DI water). The alkaline detergent
contains sodium hydroxide, chelants and other components to improve surface
wetting, soil emulsification and dispersion of residues. Treated coupons were
then rinsed with DI water and either allowed to dry (single treatment), or placed
into an additional volume of stirred, room temperature sporicide (previously
described 12% v/v in DI water). Coupons that were cleaned with the second
solution (two-step treatment) were then rinsed with DI water and allowed to dry.
The dry, treated coupons were then swabbed and those swabs were analyzed
for adenosine triphosphate content (ATP) (Ultrasnap ATP swabs and
SystemSure Plus Lumonometer Hygenia/SS3).
Methods and Materials (continued)
The B. cereus biofilm grown under continuous flow and high shear conditions greatly
increased the cells’ resistance to inactivation with the sporicide compared to an
unassociated spore population. The data highlights the increased resistance associated
with biofilm, and even more so the challenges faced when dealing with spore-forming
bacteria. The two-step approach presented here incorporates an effective cleaning step
with an alkaline detergent followed by a sporicide to significantly reduce the
population of the B. cereus biofilm population. Combining an effective alkaline
cleaning detergent to remove the organic residue associated with the biofilm followed
by a sporicide is an effective means to address highly resistant biofilm cell populations,
such as B. cereus biofilm. The data shows that increasing the temperature and contact
time of the alkaline detergent can lead to a full kill of this resistant biofilm.
Conclusions
Preparation of B. cereus ATCC 14579 spore suspension
A broth suspension of B. cereus ATCC 14579 was passed onto nutrient agar
supplemented with manganese sulfate monohydrate and incubated for 12-14
days at 36±1°C. After incubation, bacterial spores were separated from
vegetative cells and cellular debris by repeated centrifugation, decanting, and
re-suspension in de-ionized (DI) water. After processing, the suspension was
checked for high spore titer using phase microscopy. The spore suspension
was stored at 2-4°C.
Growth of B. cereus ATCC 14579 biofilm using the CDC biofilm reactor
B. cereus ATCC 14579 biofilm was prepared following ASTM E2562-12, with
modification. B. cereus ATCC 14579 spores suspended in DI water were
passed to tryptic soy broth (TSB) (0.3 g/L) in a CDC biofilm reactor assembled
following ASTM E2562-12 using polycarbonate coupons (RD 128-PC,
Biosurface Technologies Corporation). The culture was stirred at 125 rpm for
24 hours at ambient temperature. After 24 hours, the culture was stirred for an
additional 24 hours, at ambient temperature, as fresh media (TSB 0.3 g/L) was
introduced at a constant rate of 11.7 mL/min. The reactor maintained a
constant volume of media by slowly discarding extra media through wash-out.
ASTM Single Tube Method for assessment of biocide activity against
biofilm
ASTM E2871-13 'Standard Test Method for Evaluating Disinfectant Efficacy
Against P. aeruginosa Biofilm Grown in CDC Biofilm Reactor Using Single
Tube Method' (ASTM E2871-13, 2013) was used to assess the effectiveness
of treatments in reducing biofilm viability.
Results
Figure 2. B. cereus spore suspension under 40X magnification using
phase contrast microscopy.
Figure 3. Micrograph of B. cereus biofilm stained with Live/Dead metabolic stain. Composite
image of FITC ex/em and Texas Red ex/em illumination. Green coloration: FITC signal. Red
coloration: Texas Red signal. ‘Spore’ arrow: bacterial spore morphology. ‘vege.’ Arrow:
vegetative cell morphology. 1000x optical magnification.
9.03
8.21
8.78
7.89
6.97
3.47
9.03
7.687.39
6.56
5.00
0.00
9.03
7.28 7.16
5.19
3.41
0.00 0.80
9.03
7.37
4.45
3.68
1.57
0.00 0.000.00
1.00
2.00
3.00
4.00
5.00
6.00
7.00
8.00
9.00
10.00
0 1 3 7 18 52.5 120
LO
G10 D
EN
SIT
Y/C
OU
PO
N
TIME (MINUTES)
Sporicide Inactivation of P. aeruginosa ATCC 15442 Biofilm
3% Sporicide 6% Sporicide 9 % Sporicide 12% Sporicide
Results (continued)
Figure 4. Inactivation of P. aeruginosa ATCC 15442 biofilm prepared following ASTM E2565-12 by the sporicide as assessed by ASTM E281-13. Each data point
represents the geometric mean of two determinations. (L-R bars) 3%; 6%; 9%; and 12% sporicide (v/v in DI water).
5.926.09
5.53 5.545.74
5.07
5.43 5.515.22
4.91
5.37
5.044.77
5.925.67
5.335.54
5.105.31 5.37
4.98
4.604.91
4.73 4.684.52
0.00
1.00
2.00
3.00
4.00
5.00
6.00
7.00
0.0 0.5 0.8 1.4 2.2 3.7 6.8 10.3 16.6 27.3 45.0 74.2 122.3
LO
G10 D
EN
SIT
Y/C
OU
PO
N
TIME (MINUTES)
Sporicide Inactivation of B. cereus ATCC 14579 Biofilm
3% Sporicide 12% Sporicide
Figure 5. Inactivation of B. cereus ATCC 14579 biofilm by the sporicide. Each data point represents the geometric mean of two determinations. (L-R bars) 3% and 12%
sporicide (v/v in DI water).
4.89 4.92 4.93 4.87 4.91 4.89 4.84 4.80 4.77 4.66 4.56
4.194.00
4.89 4.95 4.884.75
4.964.84
4.644.52
4.23 4.13
3.80
3.13
1.28
0.00
1.00
2.00
3.00
4.00
5.00
6.00
0.0 0.5 0.8 1.4 2.2 3.7 7.0 10.7 17.1 27.3 46.2 72.0 122.3
LO
G C
FU
VIA
BL
E C
OL
ON
IES
/ 1
.5 M
L
TIME (MINUTES)
Sporicide Inactivation of B. cereus ATCC 14579 spores in suspension
3% Sporicide 12% Sporicide
Figure 6. Inactivation of B. cereus ATCC 14579 spores in suspension by the sporicide. Each data point represents the geometric mean of two determinations. (L-R bars) 3% and 12% sporicide (v/v in DI water).
0.57
0.96
1.04
3.62
3.51
3.92
5.00
6.34
0 1 2 3 4 5 6 7
1% Formulated Alkaline Cleaner for 5 minutes at 30C followed by 12% Sporicide for 10 minutes at RT
1% Formulated Alkaline Cleaner for 5 minutes at 30C
12% Sporicide for 10 minutes at RT
No Treatment
VIABILITY: LOG CFU/COUPON RECOVEREDATP RECOVERY: LOG RFU/COUPON RECOVERED
Inactivation of B. cereus ATCC 14579 biofilm by a sporicide with and without pre-cleaning using an alkaline detergent
Viability ATP Recovery
Figure 7. Inactivation of B. cereus ATCC 14759 biofilm by the sporicide with and without pre-cleaning using an alkaline detergent. Each bar represents the geometric mean of six determinations. Light blue bars: Viable colony forming units recovered after treatment. Blue bars: Recovered ATP represented as relative fluorescence units.
0.00
0.23
0.56
3.81
0 1 2 3 4 5
1% Formulated Alkaline Detergent for 30 minutes at 60C followed by 12% Sporicide for 10 minutesat RT
1% Formulated Alkaline Detergent for 10 minutes at 60C followed by 12% Sporicide for 10 minutesat RT
1% Formulated Alkaline Detergent for 5 minutes at 60C followed by 12% Sporicide for 10 minutes atRT
No Treatment
VIABILITY: LOG CFU/COUPON RECOVERED
Inactivation of B. cereus ATCC 14579 biofilm by a sporicide and an alkaline detergent
Figure 8. Inactivation of B. cereus ATCC 14759 biofilm by the sporicide and using an alkaline detergent. Each bar represents the geometric mean of three determinations. Viable colony forming units recovered after treatment.
Figures 1. Photograph of CDC biofilm reactor Figure 2. CDC Biofilm Reactor disc