Microbial Behaviour ‘In Vivo’ and ‘In Vitro.’

Biochemical challenge of microbial pathogenicity.

“…Thus, virulence is determined by small genetic differences which may be fully expressed only under the conditions of the test for virulence; i.e., during growth in vivo. The decisive nutritional condi-tions, those of host tissues under microbial attack, are not physiological but pathological and continually changing (110,116); at present, they are not reproducible in vitro. Changes in metabolism would therefore be expected when bacteria from infected animals are cultured in vitro (116), and such changes have been demonstrated (see below).…”

“…In turn, these changes in metabolism could affect virulence. Bacterial virulence is usually reduced by subculture in vitro, because bacteria lose the capacity to form one or more of the full complement of virulence attributes manifested in infected animals (110,116). Also, apparent virulence factors might be produced in vitro which are not formed, and therefore not relevant, in vivo (116).…”

“…Bacterial virulence is usually reduced by subculture in vitro, because bacteria lose the capacity to form one or more of the full complement of virulence attributes manifested in infected animals (110,116). Also, apparent virulence factors might be produced in vitro which are not formed, and therefore not relevant, in vivo (116). Thus, bacteria grown in vitro can be incomplete or misleading with regard to the possession of virulence attributes; this, coupled with the fact that bacterial behavior in vivo is not easily examined (see below), forms the essence of the difficulties encountered in studies of pathogenicity.…”

“…Finally, tests in vitro can be made more relevant to behavior in vivo. These methods for gaining knowledge of bacterial behavior in vivo have been described elsewhere (116); several examples are included in the sections below.…”

“…Together with other factors (33), a differential ability of bacterial species to accomplish these early stages of infection might explain why some diseases (e.g., brucellosis) are more communicable than others (e.g., anthrax). Furthermore, interactions between different pathogenic species on the mucous surfaces might explain some of the marked effects one infection can have on another in mixed infections (116).…”