Rearing rats in a germ-free environment eliminates their odors of individuality.

In order to test the hypothesis that commensal bacteria influence the urinary odors of individuality, we collected urine from PVG and PVG.R1 male rats born by cesarian section and reared in a germ-free environment. Using the habituation-dishabituation test with PVG.RT1 (u) and Lister hooded rats as subjects, we found that urine from the germ-free rats was not discriminated, while urine from conventionally housed rats of the same strains could be discriminated (experiment 1). When the germ-free rats were moved to a conventional animal house after recolonization with commensural flora and their urine collected, it was discriminated, indicating an essential role of bacteria in determining the unique urinary odors of MHC-congenic rats (experiment 2). The conventionally housed and germ-free rats did not differ in the amount of class I antigen in their urine (experiment 3). Finally, urines of PVG and PVG.R1 donors inoculated with a defined and highly restricted flora to render them specific-pathogen-free (SPF) could not be discriminated. Urine from SPF donors moved to a conventional animal house could be discriminated (experiment 4). These results indicate that commensal bacteria are essential for the production of the unique individual odor of the urine of MHC-congenic strains of rats.

A germ-free status does not protect from the lethal effects of acute lung damage caused by O,S,S,-trimethyl phosphorodithioate.

To investigate whether a normal resident microbiological flora of conventional rats influences the lethality of chemical-induced lung damage, the pneumotoxin O,S,S-trimethyl phosphorodithioate (OSSMe, 75 or 100 mg/kg, s.c.) was administered to age-matched conventional and germ-free male F344 rats. Microbiological and serological examinations confirmed the germ-free state of the germ-free rats and showed that no specific lung pathogens were present in the conventional rats. As in conventional rats, clinical symptoms and death of OSSMe-treated germ-free rats resulted from respiratory failure. The germ-free rats were not more resistant, but rather more susceptible to OSSMe than conventional rats. Increases in lung weight and histological examination of lung tissue 3 days after dosing with OSSMe (75 mg/kg, s.c.) showed no differences between germ-free and conventional rats. Despite alterations in their nasopharyngeal flora, death in the conventional rats was probably not caused by bacterial superinfection. The higher susceptibility of germ-free rats to OSSMe can be partly attributed to pharmacokinetic differences, since plasma levels of OSSMe decreased more slowly in germ-free than in conventional rats. It is concluded that germ-free rats are not protected from the lethal consequences of acute chemical-induced lung damage.