When Catheter Salvage Fails: Rapid Carbapenem Resistance and Recurrent Herbaspirillum huttiense Bacteremia in a Child With Severe Combined Immunodeficiency

To the Editors: We read with great interest the recent report by Ozen et al1 describing catheter-related bloodstream infections caused by Herbaspirillum huttiense in pediatric patients and their experience with antibiotic lock therapy (ALT). Their study, representing the largest pediatric series to date, provides valuable insight into catheter salvage strategies. We would like to contribute a complementary case highlighting a critical limitation of this approach, namely the rapid in vivo emergence of antimicrobial resistance and recurrence in a profoundly immunocompromised infant. Our patient was a 13-month-old boy with severe combined immunodeficiency who had undergone hematopoietic stem cell transplantation and developed 2 episodes of H. huttiense bacteremia 4 months apart. During the first episode, the isolate was broadly susceptible, with a meropenem minimum inhibitory concentration (MIC) of 0.047 μg/mL and an ertapenem MIC of 0.19 μg/mL. The central catheter was preserved using 10 days of amikacin-based alanine aminotransferase (ALT). However, during the second episode, the same pathogen exhibited marked resistance, with meropenem and ertapenem MIC values exceeding 32 μg/mL, corresponding to a >680-fold increase in meropenem MIC. Additionally, resistance to ceftazidime and piperacillin–tazobactam emerged de novo. This finding contrasts with the high meropenem susceptibility reported by Ozen et al.1 Although recurrence after ALT was observed in 2 patients in their series—both developing amikacin resistance and ultimately requiring catheter removal—their isolates retained carbapenem susceptibility. In contrast, other pediatric reports have described recurrent H. huttiense bacteremia in which carbapenem susceptibility was retained.2 Our case demonstrates the rapid emergence of high-level carbapenem resistance together with de novo resistance to additional beta-lactams, reflecting a more severe trajectory of treatment failure in a profoundly immunocompromised host. This observation raises concern that catheter salvage strategies may facilitate resistance selection in biofilm-associated infections. This may be explained by prolonged biofilm persistence and repeated antimicrobial exposure, promoting selection of resistant subpopulations in immunocompromised hosts. Supporting this, H. huttiense has been shown to harbor multiple resistance-associated genes, including those encoding efflux pumps and beta-lactamases.3 Notably, our patient experienced recurrence despite prior ALT and subsequently developed septic shock requiring pediatric intensive care. A second bloodstream infection with Stenotrophomonas maltophilia further complicated the clinical course, underscoring the vulnerability of this population to polymicrobial infections. Following catheter removal, the patient was treated with a combination regimen of extended-infusion meropenem (MIC >32 μg/mL), amikacin (MIC 6 μg/mL) and levofloxacin (MIC 0.5 μg/mL). Despite high carbapenem MIC values, combination therapy was employed to maximize pharmacodynamic exposure and potential synergistic effects. Levofloxacin remained the only fully active agent based on MIC values. Due to the absence of established breakpoints for Herbaspirillum spp., MIC values were interpreted cautiously. The patient achieved full clinical recovery with negative follow-up cultures. Reports of recurrent H. huttiense bacteremia in pediatric patients are limited, and rapid emergence of high-level carbapenem resistance between episodes has rarely been described. Our case highlights this clinically significant phenomenon in a profoundly immunocompromised host. Additionally, the use of a levofloxacin-containing combination regimen in this setting has been rarely reported. In conclusion, while ALT may be effective in selected patients, our findings emphasize its limitations in profoundly immunocompromised children. Early catheter removal and close microbiological monitoring, including repeated susceptibility testing, should be strongly considered in this high-risk population.