The microbiological and parasitological colonisation of specified-pathogen-free mice maintained in a conventional animal house

2 groups of 44 specified-pathogen-free (SPF) mice, caged in groups of 4, were housed at weaning either in isolation in a building housing conventionally-reared animals, or in contact with those animals. 4 mice from each group were examined for microbiological flora and 4 for parasites at intervals for up to 90 days after transfer. Proscribed bacteria were isolated from the 'in contact' group after 42 days and endoparasites were observed by 16 days and thereafter. No proscribed bacteria were isolated from the other group, although some endoparasites were observed by 16 days. Proscribed bacteria were shown to be present in the conventionally-reared animals at weaning and ecto- and endoparasites by day 16 and thereafter. It is suggested that it may be possible to maintain SPF animals outside a SPF Unit for short periods of time, and that with great care the animals remain free of proscribed microflora.