Bacteriuria, or the presence of bacteria in urine, is associated with both asymptomatic, as well as symptomatic urinary tract infection (UTI) and underpins much of the dynamic of microbial colonization of the urinary tract. The prevalence of bacteriuria in dissimilar patient groups such as healthy adults, institutionalized elderly, pregnant women, and immune-compromised patients varies widely. In addition, assessing the importance of ‘significant bacteriuria’ in infected individuals represents a diagnostic challenge, partly due to various causal microbes, and requires careful consideration of the distinct etiologies of bacteriuria in different populations and circumstances. Recent molecular discoveries have revealed how some bacterial traits can enable organisms to grow in human urine, which, as a fitness adaptation, is likely to influence the progression of bacteriuria in some individuals. This study was designed as a comprehensive analysis of asymptomatic bacteriuria (ABU) causal organisms in dissimilar populations, and an in-depth microbiological analysis of the mechanisms used by one such causal organism, Streptococcus agalactiae. This organism causes UTI including ABU; however, growth of S. agalactiae in human urine has not been reported. In the first part of this study, we evaluate the prevalence and etiology of bacteruria, and discuss recent advances in the molecular detection of bacteriuria from a diagnostic viewpoint.