STUDY OF THE BACTERIAL LOAD OF BRUCELLA MELITENSIS 16M STRAIN IN THE SPLEEN OF LABORATORY MICE

Abstract

Brucellosis remains one of the most significant zoonotic infections in the Republic of Kazakhstan, which determines the need for standardized experimental models for the preclinical evaluation of specific prophylactic agents. The aim of this study was to assess the reproducibility of a bacteriological method for the quantitative determination of bacterial load in the spleen of laboratory mice experimentally infected with Brucella melitensis. The experiment was carried out in October 2025 at the Laboratory of Microbiology of the Research Institute for Biological Safety Problems on female white laboratory mice (n = 6) weighing 18-20 g, infected intraperitoneally with a suspension of B. melitensis 16M at a dose of 2 × 10⁵ CFU/0.1 ml. The control group (n

= 3) consisted of intact animals injected with sterile saline. Bacterial load was determined on day 15 post-infection by quantitative culture of spleen homogenate with subsequent CFU counting and conversion to CFU per gram of tissue. Differentiation of the isolates from the vaccine strain Rev-1 was performed on the basis of growth on media containing streptomycin and penicillin. Colonization of the organ by the pathogen was established in all cases. The mean bacterial load was 1.92 × 10⁵ ± 0.29 × 10⁵ CFU/ml, with individual values ranging from 1.5 × 10⁵ to 2.3 × 10⁵ CFU/ml (coefficient of variation 14.9 %); no microbial growth was detected in the control group. The morphological and cultural characteristics of the isolated colonies corresponded to the typical features of B. melitensis 16M. The obtained results confirm the reproducibility of the applied bacteriological method and the possibility of its use in preclinical studies.