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Maria Carolina Sisco,1,2 Marlei Gomes da Silva,1 Luciana Distasio de Carvalho,3 Carlos Eduardo Dias Campos,3 Paulo Cesar De Souza Caldas,3 Beatriz Lopez,4 Claudia Argüelles,5 Ana Carolina Carvalho,6 Jacobus de Waard,7,8 Philip Suffys,2 Rafael Silva Duarte1 1Laboratório de Micobactérias, Departamento de Microbiologia Médica, Instituto de Microbiologia Paulo de Góes, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil; 2Laboratório de Biologia Molecular Aplicada às Micobactérias, Instituto Oswaldo Cruz, Rio de Janeiro, Brazil; 3Laboratório de Referência Nacional Para Tuberculose e Micobacterioses, Centro de Referência Professor Hélio Fraga, Escola Nacional de Saúde Pública, Rio de Janeiro, Brazil; 4Instituto Nacional de Enfermedades Infecciosas, Buenos Aires, Argentina; 5Instituto Nacional de Producción de Biológicos – ANLIS Carlos G Malbrán, Buenos Aires, Argentina; 6Faculdade de Farmácia, Universidade Federal do Rio de Janeiro, Campus Macaé, Rio de Janeiro, Brazil; 7Departamento de Tuberculosis, Instituto Autónomo de Biomedicina Dr. Jacinto Convit, Caracas, Venezuela; 8One Health Research Group, Facultad de Ciencias de La Salud, Universidad de Las Américas, Quito, EcuadorCorrespondence: Philip Suffys Email psuffys@gmail.comPurpose: Mycobacterium bovis Bacillus Calmette-Guérin (BCG) is the only vaccine licensed against tuberculosis. Despite the protection offered by the vaccine, in some circumstances children and immunocompromised individuals can develop associated infections, known as BCGitis. Drug susceptibility patterns of BCG clinical strains have rarely been described. We aimed to describe the susceptibility pattern of BCG clinical strains isolated in two different countries.Methods: We performed culture-based drug susceptibility testing of thirty one BCG strains isolated from patients in Brazil (n=5, 16%) and Argentina (n=26, 84%) using the broth micro-dilution method (phenotypic method). Final antibiotic concentrations for susceptibility testing ranged from 0.5 to 16 mg/L for amikacin, 0.3125 to 10 mg/L for ethambutol, 0.05 to 1.6 mg/L for isoniazid and 0.25 to 8 mg/L for rifampicin, streptomycin and ofloxacin. Additionally, we compared the results with genetic data obtained by whole genome sequencing.Results: By using the phenotypic method we detected one strain resistant to ethambutol, three strains resistant to rifampicin and one resistant to isoniazid. Additionally, two strains that were phenotypically resistant to both isoniazid and rifampicin carried mutations in the katG and rpoB genes simultaneously.Conclusion: There is evidence of the emergence of BCG-resistant strains isolated from vaccine-related complications. We recommend drug susceptibility testing of the BCG strain causing the infection in order to prevent treatment failure.Keywords: BCG, mycobacteria, resistance, vaccine