Table 2. Efficiency of chemicals, gases, and radiation on the inactivation of Bacillus sporesa.
| Method | Concentration | Inoculum size | Time | Efficiency | Ref. | ||||
|---|---|---|---|---|---|---|---|---|---|
|
Chemical sterilization
| |||||||||
| Calcium hypochlorite |
20 ppm available; Cl2, pH 8.0, 20ºC |
3 x 105–4 x 105 spores of Bacillus subtilis in 5.0 mL sterile distilled H2O |
4.8 min |
99% killed |
8 |
||||
| 25 ppm available; Cl2, pH 6.0, 20ºC |
2 x 107 spores/mL of B. metiens in 10 mL of sterile distilled H2O |
2.5 min |
0.061 (log of average % survivors) 99% killed |
9 |
|||||
| Free available chlorine |
2.4–2.3 mg/L available; CL2, pH 7.2, 22ºC |
1.1 x 105 spore suspension of B. anthracis |
1 h |
>99.99% killed (1 spore/mL survived) |
10 |
||||
| Sodium hypochlorite (NaOCl) |
0.05%, pH 7.0, 20°C |
Spore suspension of B. subtilis
globigii, representing 1.6–2.2 x 109 CFU/mL |
30 min |
99.99% killed |
11 |
||||
| 0.05%, pH 11.0, 20°C |
50% spores survived |
||||||||
| Hydrogen peroxide (H2O2) |
25.8%, 24°C |
B. subtilis globigii spore suspension
(no concentration) |
15 min |
0.001% survived |
12 |
||||
| 25.8%, 76°C |
<1 min |
<0.0001% survived |
|||||||
| 0.88 mol/L, pH 5.0 |
106 CFU/mL B. subtilis spore suspension |
3 h |
100% killed |
13 |
|||||
| 0.88 mol/L, pH 4.3 |
10 mL B. subtilis spore suspension coated onto stainless steel carriers |
6 h |
100% killed |
||||||
| Peracetic acid (CH3COOOH) |
0.13 mol/L, pH 5.0, 6.5, 8.0 |
106 CFU/mL B. subtilis |
<30 min |
100% killed |
13 |
||||
| 0.39 mol/L, pH 4.0, 7.0, 9.0 |
10 mL B. subtilis spore suspension coated on stainless steel carriers |
24 h |
100% killed |
||||||
| Formaldehyde (CH2O) |
4% in water |
108/mL B. anthracis |
2 h |
104 inactivation factor |
14 |
||||
| 400 mg/m3, 30% RH |
102–3 x 108
B. globigii NCTC 10073 dried on disks |
22 min |
1 log10 reduction, at 23.5°C–25°C |
15 |
|||||
| 280 mg/m3, 50%RH |
31 min |
||||||||
| 250 mg/m3, 80% RH |
16 min |
||||||||
| 400 mg/m3, 98% RH |
9 min |
||||||||
| Glutaraldehyde (C5H8O2) |
2% in water, pH 8.0 |
108/mL spores B. anthracis |
15 min |
104 inactivation factor |
14 |
||||
| Sodium hydroxide
(NaOH) |
5%, 27.8ºC |
7 x 109 spores/mL
B. subtilis |
1.5 h |
99% killed |
16 |
||||
| 5%, 21.1ºC |
3.6 h |
99% killed |
|||||||
|
Gaseous sterilization
| |||||||||
| Ethylene oxide
(C2H4O) |
Exposed to constant boiling HCL at 20°C for 30 min before exposure to ethylene oxide at room temperature |
B. globigii and B. anthracis dried onto suture loop carriers (no concentration) |
1 h |
100% killed |
17 |
||||
| 500 mg/L, 30%–50% RH, 54.4°C |
~106 spores B. globigii on nonhygroscopic surfaces |
30 min |
4-log reduction |
18 |
|||||
| ~106 spores B. globigii on hygroscopic surfaces |
6-log reduction |
||||||||
| Chlorine dioxide
(ClO2) |
40 mg/L, 60%–80% RH,
25°C–27ºC |
1.4 x 106/0.2 mL
B. subtilis subsp. Niger dried on paper and aluminum foil strips |
1 h |
100% killed |
19 |
||||
| 30 mg/L, 80%–85% RH, 30ºC |
106 spores/biologic indicator; B. subtilis subsp. Niger |
30 min |
100% killed (estimated time to kill 90%, 4.4 min) |
20 |
|||||
| 6–7 mg/L, 20%–40% RH, 23ºC |
106 spores/biologic indicator; B. subtilis subsp. Niger |
30 min |
101 CFU/biologic indicator (estimated time to kill 90%, 4.2 min) |
21 |
|||||
| 70%–75% RH for 0.5 before exposure, 23ºC |
15 min |
0 CFU/biologic indicator (estimated time to kill 90%, 1.6 min) |
|||||||
| Hydrogen peroxide (H2O2) plasma |
0.208 mg/L, 1.5 Torr pretreatment for 10 min;
2.49 MHz, 150 W of pulsed plasma in a cycle of 0.5 ms plasma on, 1.0 ms plasma off |
3.4 x 105
B. subtilis subsp. globgii spores on paper disks and packaged in spun-bonded polyethylene |
15 min |
100% killed |
22 |
||||
| Methylene bromide (CH3Br) |
3.4–3.9 g/L, room temperature in the presence of moisture |
1 x 105–5 x 107 spores of B. anthracis dried on sterile filter paper strips |
24 h |
100% killed |
23 |
||||
| Peracetic acid vapor (CH3COOOH) |
1 mg/L, 80% RH |
6 x 105 – 8x 105
B. subtilis
niger dried on filter-paper disks and glass squares |
10 min |
<1 spore remained on paper and glass |
24 |
||||
| 1 mg/L, 60% RH |
2 spores remained on paper; 38 spores remained on glass |
||||||||
| 1 mg/L, 40% RH |
24 spores remained on paper; 1,530 spores remained on glass |
||||||||
| Propylene oxide
(C3H6O) |
1250 mg/L, 86% RH, 36°C–38ºC |
9.5 x 105–1.1 x 106 spores B. subtilis
niger dried on filter paper |
1.05 h |
90% killed |
25 |
||||
| 1000 mg/L, 37°C |
2.5 x 107 spores B. subtilis
niger in cereal flakes |
3 h |
3.7% survived |
||||||
| Ozone (O3) |
1.0 mg/L generated in water pH 3 |
1.8 x 105 spores/mL B. cerus |
5 min |
<101 CFU/mL survived |
26 |
||||
| 3.0 mg/L,
preconditioned at 54% RH |
108–2 x 108
B. subtilis dried on filter paper |
1.5 h 95% RH |
<0.001% survived |
27 |
|||||
| 108–2 x 108
B. cerus dried on filter paper |
1.5 h 95% RH |
<0.001% survived |
|||||||
| 900 ppm, preconditioned at 65%–70% RH for 15 h |
5 x 107 spores/glass coupon |
30 min 80% RH |
100 survived |
28 |
|||||
| 60 min 70% RH |
100 survived |
||||||||
|
Radiation
| |||||||||
| UV |
85% 2537A |
B. anthracis (mixed spores and vegetative forms) in beef extract agar pH 7.4
(no concentration) |
452 ergs/mm2 |
90% killed |
29 |
||||
| 4,800 μWs/cm2 |
0.1 mL of 108
B. anthracis spore suspension dried on aluminum carriers |
<96h |
2.4 log reduction, unreliable results |
30 |
|||||
| 450,000 μWs/cm2 |
0.1 mL of 108
B. anthracis spore suspension dried on ceramic carriers |
<96h |
2.03 log reduction, unreliable results |
||||||
| 52.8 x 106 μWs/cm2 |
0.1 mL of 108
B. anthracis spore suspension dried on wood carriers |
30h |
0.67 log reduction |
||||||
| Gamma irradiation | 106 spores/mL B. anthracis | Dose of 1 x 106 rad | 100% killed | 31 | |||||
aRH, relative humidity; conversions: 1 ppm = 1 mg/L; mol/L = gram molecular weight/L; 1 rad = 100 ergs/g; and 1 watt = 107 ergs/s.