Isolation and Characterization of the Microbiota from the Left Ventricle in NIH Mice (Mus musculus): An In Vitro Study

Aim: The aim of this study was to characterize the hematic microbiota of the left ventricle of NIH strain mice via culture, Gram staining and catalase assays. Materials and Methods: An in vitro study was conducted in the Department of Pharmacology of the Faculty of Medicine at the Autonomous University of Chiapas and the Laboratory of Experimental Microbiology at the Technological Institute of Tuxtla Gutierrez, Mexico, between November 2019 and February 2020. Thirty NIH mice were used, distributed into groups and maintained under sterile conditions. Blood samples were obtained via puncture of the left ventricle and inoculated in different culture media (blood agar, Sabouraud agar and brain-heart agar) for isolation and characterization of the microbiota. Results: The results revealed the growth of the microorganisms on all the culture media. On blood agar, 22, 22 and 29 colony-forming units (CFUs) were recorded for the mice in groups A, B and C, respectively. On Sabouraud agar, 65, 44 and 78 CFUs were observed, and on brain-heart agar, 26, 131 and 10 CFUs were observed. Taxonomic characterization revealed the presence of gram-positive and gram-negative bacteria, as well as fungi, with a predominance of Streptococcus and Bacillus in different samples. Conclusion: This study revealed the existence of a native microbiota in the blood of NIH mice, which are predominantly gram-negative, with diverse fungi.