THE GROWTH RATE PHENOTYPIC PROPERTY OF MYCOBACTERIUM TUBERCULOSIS CLINICAL STRAINS: DEPENDENCE ON TUBERCULOSIS LOCALIZATION, TREATMENT, DRUG SUSCEPTIBILITY

Abstract

The phenotypic properties of the M. tuberculosis strains obtained from patients with pulmonary or extra-pulmonary tuberculosis are  determined by a complex set of factors: the genetic characteristics  of the pathogen, its ability to adapt in vivo and in vitro, the influence of the host’s immune system and chemotherapy. The growth rate as  the phenotypic property is the most accessible for the study of the  host-pathogen relationships at the level of host/strain population  interactions. The aim of the study is to assess in vitro of the growth  rate of M. tuberculosis strains isolated from patients with pulmonary  and extra-pulmonary tuberculosis: untreated and treated (with  surgical and non-surgical treatment) and also sensitive and resistant isolates in comparison with the reference strain H37Rv. To estimate  the growth rate of 116 clinical isolates we have used the modified  method originally developed by von Groll and co-authors: to get the  bacteria growth curve the fluorescence intensity of growing strains  (with indicator resazurin) has been measured daily for 8 days in 96- well plate. The growth rate is determined as the slope of the growth  curve. The mean values of the growth rate have been calculated in  the following groups of patients: 1 — untreated patients with  pulmonary tuberculosis (PT), respiratory material; 2 — non-surgical  treated PT patients, respiratory material; 3 — surgical treated PT  patients (mainly with chronic and hyperchronic process), respiratory  material; 4 — patients like in 3rd group, surgical material; 5 — bone  and joint tuberculosis (BJT), surgical material. In addition, groups of  sensitive and resistant strains have been examined, but there are no  significant differences in growth rates. It has been obtained that  the growth rate of strains isolated from the PT patients is higher than in BJT patients: it can be explained less favorable  conditions for the pathogen vegetation in the BJT. In the case of a  closed tuberculous lesion where the pathogen transmission to  another host is impossible, then the selection of strains with the  property to survive in the tissues of the osteoarticular system is  impossible too, therefor it should be observed only an adaptation of  the pathogen strain population to the individual host. The growth  rate of isolates from untreated PT patients is higher than that of the  treated ones. Comparison of the growth parameters of only MDR  strains 1–5 groups to eliminate the influence of the  sensitivity/resistance has resulted in the same conclusions. We  suggest that the decrease in the growth rate of strains from the  treated PT patients is in not only result of the treatment, but also is  conditioned by adaptation of the pathogen to its external  environment, which is the internal environment of the  macroorganism. To confirm this assumption, the bacterial load of  1,083 diagnostic specimens grouped in a similar manner has been  estimated, taking into account only MDR/XDR strains. In the group  of treated patients the frequency of high bacterial load (CFU ≥ 100)  reached 52.5–63.8% that shows the conserved fitness of bacteria in  such patients. The mean values of the growth rate of the strain  H37Rv non-adapted to the macroorganism (due to numerous  passages on artificial media) are higher than in all groups of clinical  strains. Thus, heterogeneity of phenotypic properties of M.  tuberculosis clinical strains on the basis of growth rate has been  obtained. The growth rate of M. tuberculosis clinical strains is  depended on the tuberculosis localization (PT, BJT) and on the joint  effect of patient treatment and pathogen adaptation to the host.