The Fate of Mycobacterium Tuberculosis in Mouse Tissues as Determined by the Microbial Enumeration Technique

Abstract

Populations of tubercle bacilli of human origin exposed in vivo to pyrazinamide and a companion drug, vanished from the tissues of the mouse in so far as could be determined by microscopy, culture, or guinea pig subinoculation. The vanishing did not represent a complete elimination of the tubercle bacilli from all the animals. 90 days after the completion of treatment, tubercle bacilli could be cultured from approximately one-third of the animals examined at that time. This complete disappearance of the tubercle bacilli thus meets the definition of a truly latent infection in that the infection is present but is hidden beyond the limits of diagnostic reach. All but one of the strains of tubercle bacilli which survived in the animals and were detectable in the posttreatment period, were susceptible to pyrazinamide when tested under appropriate conditions in vitro. Only two factors could be identified which were essential for the uniform occurrence of the disappearance of tubercle bacilli: the administration of the pyrazinamide in a high daily dosage for at least eight of a total of 12 weeks of antimicrobial therapy; and the concurrent or prior exposure of the microbial populations to isoniazid or in some cases to other antituberculous drugs. The observations suggest that the ability of pyrazinamide-containing chemotherapies to bring about the disappearance of a tubercle bacillus is closely related to the occurrence of some alteration in the bacillus, essential for maximal pyrazinamide action, in response to environmental influences, including other antituberculous drugs present in the environment.

Rifamycin action on RNA polymerase in antibiotic-tolerant Mycobacterium tuberculosis results in differentially detectable populations

“…The first reported experimental generation of VBNC Mtb was in Mtb-infected mice that after combination chemotherapy with INH and PZA yielded no cfus in culture of their organs or even the whole carcass (45)(46)(47). This apparent microbiologic cure was proven false when about a third of identically treated mice that were reserved for observation eventually relapsed, and nearly all did so when immunosuppressed with corticosteroids (45)(46)(47) or when deficient in inducible nitric oxide synthase (48). Mtb colonies recovered from relapsed mice remained susceptible to INH and PZA (45).…”

“…This apparent microbiologic cure was proven false when about a third of identically treated mice that were reserved for observation eventually relapsed, and nearly all did so when immunosuppressed with corticosteroids (45)(46)(47) or when deficient in inducible nitric oxide synthase (48). Mtb colonies recovered from relapsed mice remained susceptible to INH and PZA (45). Thus, noncolony-forming Mtb were phenotypically tolerant to combination chemotherapy, and their viability was demonstrated by their ability to cause relapse.…”

Microbial Persistence

“…Nor does either drug administered alone, produce it, when the population is predominantly resistant to the other drug (3,5).…”

“…The basic model used in these experiments has been described in the preceding report (1) and in previous publications (2,3). In its essentials, it consists of: infecting large numbers of * This study was supported in part by Public Health Service Research Grant AI00635 from the National Institute of Allergy and Infectious Diseases; by grants from the National Tuberculosis Association-American Thoracic Society, the New York Tuberculosis and Health Association, and the Philip Hanson Hiss, Jr., Memorial Fund.…”

Experimental Study on the Relapse of Tuberculosis after the Termination of Antituberculous Chemotherapy Using Immunodeficient Nude Mice

“…Though the precise mechanism by which corticosteroid effects the relapse of tubercle bacilli is not fully elucidated yet, the present experiment suggests that acquired immunity might be slightly reduced with the use of corticosteroid in dd mice. Reports on the experimental efficacy of PZA on relapse are rare (16), although there are some experimental studies on PZA (7,(12)(13)(14). It is interesting to note that the addition of PZA to the chemotherapy regimen seems to prevent relapse to some extent even in nude mice.…”