Table 2. Formaldehyde fixation of infected spleen, liver, and lung tissue from guinea pigs in study of inactivation of bacterial Tier I Select Agents*.

Infectious agent, tissue type	Maximum tissue weight, g	Maximum tissue size, mm	Maximum CFU/g	Fixation time, d	Sample inactivation	Positive control
Bacillus anthracis Ames (inhalational and intramuscular), n = 3
Spleen	1.04	20 × 20 × 6	1.1 × 109	13	–/–†	+
Liver	1.78	20 × 10 × 10	9.8 × 107	13	–/–†	+
Lung	1.14	20 × 20 × 10	2.1 × 108; 5.5 × 104 (heat resistant)	13	–/–†	+
Burkholderia pseudomallei 1026b, n = 4
Spleen	0.81	20 × 15 × 10	7.5 × 108	13	–/–‡	+
Liver	2.15	20 × 15 × 10	1.4 × 107	13	–/–‡	+
Lung	1.56	20 × 15 × 10	4.0 × 107	17–18	–/–‡	+
Francisella tularensis Schu S4, n = 3
Spleen	1.50	15 × 15 × 10	9.3 × 109	13	–/–§	+
Liver	2.29	25 × 13 × 11	9.5 × 107	13	–/–¶	+
Lung	1.30	15 × 13 × 11	4.3 × 108	13	–/–¶	+
Yersina pestis CO92, n = 3
Spleen	0.96	15 × 10 × 8	1.4 × 1010	13	–/–§	+
Liver	2.09	30 × 15 × 10	1.1 × 109	13	–/–¶	+
Lung	1.81	25 × 20 × 15	7.0 × 108	13	–/–¶	+

*<4 guinea pigs were infected with 1 Select Agent. Tissues were excised and then measured, weighed, and plated for CFU. Tissues were fixed in 10% neutral buffered formalin for the indicated time, rinsed for 30 min in phosphate-buffered saline, and then homogenized. +/– indicates presence or absence of growth in broth/on plates.
†100% of sample tested.
‡50% of sample tested.
§90% of 1 sample tested, 10% of others tested.
¶10% of sample tested.