Optimal age at fostering for derivation of Helicobacter hepaticus-free mice.

Helicobacter hepaticus is well established as an unwanted variable in laboratory rodent colonies. Historically, cesarean section and embryo transfer have been used to derive Helicobacter-free mouse colonies. Neonatal transfer of newborn mice onto Helicobacter-free foster dams was recently reported as an alternative method of deriving Helicobacter-free mice, but until now, the age by which pups must be fostered to remain Helicobacter-free was unknown. The purpose of the study reported here was to determine the age by which mouse pups must be fostered to remain free of H. hepaticus. Beginning on the day of birth, 20 C57BL/6 mice were fostered from H. hepaticus-positive parents onto Helicobacter-free BALB/c dams each day for 14 days for a total of 280 pups fostered. Fecal specimens collected at weaning, and fecal, liver, and cecal specimens collected at euthanasia were analyzed by use of polymerase chain reaction (PCR) analysis. No pup fostered within 24 h of birth became infected with H. hepaticus; however, many of those fostered after 24 h became infected. These results were supported by those of a large field trial, in which 201 litters representing 71 strains of mice were fostered within 24 h of birth. Follow-up fecal PCR analysis was performed on 52 mice or their progeny that were randomly sampled from the 201 fostered litters. All mice tested remained free of H. hepaticus approximately 100 days after fostering. The results indicate that mouse pups must be fostered within 24 h of birth to remain free of H. hepaticus. In addition, cecal and fecal PCR analyses detected more infections, than did liver PCR analysis, thus indicating that those specimens are preferred for detection of H. hepaticus infection.