A shift from acute to chronic spontaneous pyelonephritis in male MM mice associated with a change in the causal micro-organisms

Abstract

27Summary Proteus mirabilis was the predominant cause of acute diabetes-associated pyelonephritis occurring spontaneously in male MM mice until they were segregated in a new environment. Thereafter Pasteurella pneumotropica and Streptococcus faecalis emerged collectively as the most common causal organisms, the pyelonephritis became more chronic and Proteus mirabilis iso· lates from faeces and urine produced atypical non-swarming colonies on blood agar plates. This did not account for the reduced pathogenicity of Proteus mirabilisj when MM males were returned to the original environment the pyelonephritis again became acute but was associated with the atypical type of Proteus mirabilis although the normal type was abundant in the environment.The MM mice were Caesarian-derived and cross-fostered shortly before their transfer to the second environment, which probably accounts for their changed microbial status, but the reason for the emergence of the atypical type of Proteus mirabilis is not understood. The acute nature of the male MM pyelonephritis when caused by Proteus mirabilis parallels the situation described in other animals and humans.

Altered clinical and histological features of male MM mouse pyelonephritis associated with a change in its microbiology

“…As the role of Proteus diminished in EB, the male MM pyelonephritis became more chronic (Taylor, 1988). Renal scarring, for example, which was more common in EB, is recognized as a common consequence of chronic pyelonephritis resulting in the typical 'shrunken' kidney; the reduced role of Proteus was consistent with the knowledge that Proteus causes particularly acute pyelonephritis (Braude, Siemienski & Shapiro, 1960).…”

“…The increased longevity of the EB pyelonephritics was associated with changes in the histological picture, and the concomitant microbiological changes between EA and EB are described elsewhere (Taylor, 1988). Although the various renal changes associated with the acute phase were still present, a new more chronic form of the disease was regularly seen.…”

“…Details of the many mouse strains maintained and the husbandry regimes for the conventional (Taylor & Fraser, 1973) and germfree (Taylor, 1975;1978) mice have been published previously. The differences between the original environment (environment A (EA)) and the second environment (environment B (EB)) have been described elsewhere (Taylor, 1988); the periods of study in each environment were approximately 30 months and 40 months respectively.…”

“…Other notable changes were that protrusion of crystalline material from the meatus was rare and cage odour was sufficiently reduced to allow a return to the normal weekly frequency of cleaning. Large groups of MM mice from both environments were subjected to detailed autopsy; the mortality and microbiological data from these and control C57BL mice are presented elsewhere (Taylor, 1988). The average age at death of female MMs in EB compared with EA was significantly increased from 388 to 504 days (P < 0.001); this was due to the absence of mammary tumours which were eliminated towards the end of the EA study by Caesarian derivation and cross fostering.…”

“…The disease also became more chronic, and affected animals survived to a greater age. At the same time it was found that all isolates of Proteus mirabilis from the new environment were atypical strains; it was demonstrated that they were still potentially pathogenic and it is not known why they were outranked by the other organisms causing UTI in this environment (Taylor, 1988). It is assumed that crossfostering following Caesarian derivation permitted the establishment of a nonrepresentative gut microflora which became fixed in the new environment.…”