Antibiotic-mediated bacterial filamentation: A potentially important laboratory phenomenon

Abstract

0196-4399/00 (see frontmatter) © 2007 Elsevier Clinical Microbiology Newsletter 29:3,2007 Introduction We describe the case of a 9-year-old male burn patient who developed Serratia marcescens bacteremia during his hospital course. Two days after empiric antibiotic therapy with piperacillin/ tazobactam, amikacin, and vancomycin was initiated, a blood isolate was identified as S. marcescens susceptible to both the piperacillin/tazobactam and amikacin. Several days later, the patient had not improved clinically, and repeat Gram stain of the organism growing in the liquid medium of a new blood culture bottle revealed long, filamentous, gram-negative rods with hyphal-like features. On subculture, the long filamentous organisms were confirmed as S. marcescens, likely a result of exposure to the β-lactam piperacillin. The initial confusion, due to the filamentous appearance of the organism, could have resulted in inappropriate empiric therapy with a systemic antifungal agent. Microbiology personnel and clinicians should be aware of this potentially important laboratory phenomenon which may occur during initial workup and have an impact on appropriate antimicrobial management.