Endotoxin, coliform, and dust levels in various types of rodent bedding

Abstract

Endotoxins in grain dust, household dust, and animal bedding may induce respiratory symptoms in rodents and humans. We assayed the endotoxin, coliform, and dust levels in 20 types of rodent bedding. Endotoxin concentrations were measured by using a commercial test kit, coliform counts were determined by using conventional microbiologic procedures, and dust content was evaluated by using a rotating-tapping shaker. Paper bedding types contained significantly less endotoxin than did other bedding types; the highest levels of endotoxin were detected in hardwood and corncob beddings. The range of endotoxin content for each bedding type was: corncob bedding, 1913 to 4504 endotoxin units per gram (EU/g); hardwood bedding, 3121 to 5401 EU/g; corncob-paper mixed bedding, 1586 to 2416 EU/g; and paper bedding, less than 5 to 105 EU/g. Coliform counts varied from less than 10 to 7591 cfu/g in corncob beddings, 90 to 4010 cfu/g in corncob-paper mixed beddings, less than 10 to 137 cfu/g in hardwood beddings, and less than 10 cfu/g in paper beddings. Average dust content was less than 0.15% in all commercial bedding types. We conclude that paper bedding is the optimal bedding type for conducting LPS inhalation studies and that rodent bedding containing high levels of endotoxin may alter the results of respiratory and immunologic studies in rodents.

Figure 1.

Endotoxin levels (mean ± SE) in rodent bedding. Corncob bedding, n = 62 bags; corncob–paper mixed bedding, n = 21 bags; paper bedding, n = 40 bags; hardwood bedding, n = 23 bags. Paper bedding contained significantly (P < 0.0001, ANOVA and Fisher least significant difference test) less endotoxin than did other types of bedding.

Figure 2.

Endotoxin levels from individual samples with and without blocking of β-(1,3)-glucans. (A) Corncob bedding. (B) Corncob–paper mixed bedding. (C) Hardwood bedding. (D) Paper bedding. Endotoxin levels with and without blocking did not differ, according to paired t tests within each bedding type.

Figure 3.

Coliform counts (mean ± SE) by bedding type. (A) Corncob bedding. (B) Corncob/Paper Mix bedding. (C) Hardwood bedding. All paper beddings were culture-negative for coliforms.