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Cefepime resistance with preserved ceftriaxone susceptibility in Proteus mirabilis osteomyelitis associated with bla OXA-1 gene amplification: Two case reports with genomic analysis.
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Lima Amorce, Collins Mackenzie, Jaramillo Mario, Gonzalez-Ferrer Shekina, Sircar Anita, Allyn Paul R, Yang Shangxin
Аннотация
OBJECTIVE: Retrospective case series to describe an unusual cefepime-resistant, ceftriaxone-susceptible phenotype in Proteus mirabilis osteomyelitis associated with bla OXA-1 gene amplification.
PATIENTS: Two adult patients with diabetes mellitus and chronic osteomyelitis, one with diabetic foot ulcer and one with infected hip prosthesis, both with prolonged antibiotic treatment.
METHODS: Clinical data and antimicrobial susceptibility results were reviewed. Whole-genome sequencing was performed using short-read and long-read platforms with hybrid assembly. Resistance gene identification, phylogenetic analysis, and gene copy number estimation were conducted.
RESULTS: Three isolates of P. mirabilis from two patients demonstrated an unusual phenotype of cefepime resistance (MIC 16-32 μg/mL) with susceptibility to ceftriaxone. Hybrid assembly and coverage analysis demonstrated amplification of the bla OXA-1-containing cassette, with approximately 16- and 24-fold duplication in patient 1 and 6-fold duplication in patient 2. Increased copy number correlated with cefepime resistance. All isolates harbored the multidrug resistance cassette containing bla OXA-1 within an IS6-family (IS26-like) transposon, which are found to widely circulate in plasmids or chromosomes of P. mirabilis and many other Enterobacterales species.
CONCLUSIONS: This study showed that duplication of a transposon-associated bla OXA-1-containting cassette in P. mirabilis can confer cefepime resistance while preserving ceftriaxone susceptibility. In the outpatient setting, recurrent infection during prolonged therapy may select for gene amplification-mediated resistance with atypical susceptibility patterns, complicating antibiotic selection. This highlights the need to monitor resistance and reassess treatment strategies in cases of chronic osteomyelitis that are not improving or worsening on therapy.
PATIENTS: Two adult patients with diabetes mellitus and chronic osteomyelitis, one with diabetic foot ulcer and one with infected hip prosthesis, both with prolonged antibiotic treatment.
METHODS: Clinical data and antimicrobial susceptibility results were reviewed. Whole-genome sequencing was performed using short-read and long-read platforms with hybrid assembly. Resistance gene identification, phylogenetic analysis, and gene copy number estimation were conducted.
RESULTS: Three isolates of P. mirabilis from two patients demonstrated an unusual phenotype of cefepime resistance (MIC 16-32 μg/mL) with susceptibility to ceftriaxone. Hybrid assembly and coverage analysis demonstrated amplification of the bla OXA-1-containing cassette, with approximately 16- and 24-fold duplication in patient 1 and 6-fold duplication in patient 2. Increased copy number correlated with cefepime resistance. All isolates harbored the multidrug resistance cassette containing bla OXA-1 within an IS6-family (IS26-like) transposon, which are found to widely circulate in plasmids or chromosomes of P. mirabilis and many other Enterobacterales species.
CONCLUSIONS: This study showed that duplication of a transposon-associated bla OXA-1-containting cassette in P. mirabilis can confer cefepime resistance while preserving ceftriaxone susceptibility. In the outpatient setting, recurrent infection during prolonged therapy may select for gene amplification-mediated resistance with atypical susceptibility patterns, complicating antibiotic selection. This highlights the need to monitor resistance and reassess treatment strategies in cases of chronic osteomyelitis that are not improving or worsening on therapy.