Case presentation: Using a case series of four adult CF patients with varying baselines of health, one of whom was asymptomatic, this report attempts correlation of B. petrii colonization, by one common strain, with incidence of acute exacerbation of symptoms. As definitive guidelines for antimicrobial sensitivity/resistance do not exist for B. petrii, we completed a systematic review of available literature to collate evidence of antimicrobial efficacy against B. petrii. Comparison with the isolates in this study indicated B. petrii sensitivity to piperacillin/ tazobactam and minocycline but resistance to antimicrobials in the macrolide, other b-lactam and fluoroquinolone groups.