Evaluation of Low-Colony-Number Counts of Mycobacterium tuberculosis on Solid Media as a Microbiological Marker of Cross-Contamination

Low-colony-number counts on solid media are considered characteristic of cross-contamination, although they are normally observed in true-positive cultures from some groups of patients. the aim of this study was to evaluate low-yield growth cultures as a microbiological marker for cross-contamination. We evaluated 106 cultures with < 15 colonies from 94 patients, and the proportions of false-positive cultures were 0.9% per sample and 1.1% per patient, which indicates that low-yield growth is not a reliable marker of cross-contamination.Tuberculosis Research Unit at Case Western Reserve UniversityU. S. National Institutes of Allergy and Infectious DiseasesNational Institutes of Health and Human ServicesFundacao de Apoio a Ciencia e Tecnologia do Espirito SantoUniv Fed Espirito Santo, Ctr Ciencias Saude, Nucleo Doencas Infecciosas, Vitoria, ES, BrazilUniversidade Federal de São Paulo, Escola Paulista Med, Dept Microbiol Imunol & Parasitol, São Paulo, BrazilCase Western Reserve Univ, Sch Med, Dept Med, TB Res Unit, Cleveland, OH 44106 USAUniv Hosp Case Med Ctr, Cleveland, OH USAUniv Arkansas Med Sci, Dept Pathol, Little Rock, AR 72205 USAUniversidade Federal de São Paulo, Escola Paulista Med, Dept Microbiol Imunol & Parasitol, São Paulo, BrazilNational Institutes of Health and Human Services: NO1-AI95383National Institutes of Health and Human Services: HHSN266200700022C/NO1-AI-70022Fundacao de Apoio a Ciencia e Tecnologia do Espirito Santo: 37396285/2007Web of Scienc