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Volume 32, Number 8—August 2026

Emerging Infection Networks Letter

Detection of blaOXA-23–Positive Proteus mirabilis Isolate, United States, 2024

Giulia OraziComments to Author , Porscha Bumpus-White, Alyssa G. Kent, Erin Breaker, Matthew Doucette, Caryn Ivanof, Esther Fortes, Sanjib Bhattacharyya, Nicolas Epie, Susannah L. McKay, Stephen P. LaVoie, and Sarah Sabour
Author affiliation: Centers for Disease Control and Prevention, Atlanta, Georgia, USA (G. Orazi, P. Bumpus-White, A.G. Kent, E. Breaker, S.L. McKay, S.P. LaVoie, S. Sabour); Massachusetts State Public Health Laboratory, Department of Public Health, Jamaica Plain, Massachusetts, USA (M. Doucette, C. Ivanof, E. Fortes, S. Bhattacharyya, N. Epie)

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Table

Antimicrobial susceptibility testing profile of a blaOXA-23-positive Proteus mirabilis isolate (2024DK-00154) detected through the Centers for Disease Control and Prevention Antimicrobial Resistance Laboratory Network, Massachusetts, USA, 2024*

Antimicrobial class Antimicrobial Broth microdilution
 Disk diffusion
MIC, µg/mL Interpretation Zone size, mm Interpretation
Carbapenems Ertapenem <0.12 S 25 S
Meropenem 0.5 S 23 S
Imipenem† 4 R 22 I
Doripenem
 NT
 NA
22
 I
Cephems (Cephalosporins) Cefazolin NT NA 18 R
Cefepime <0.5 S 30 S
Cefotaxime <0.5 S NT NA
Cefoxitin <2 S NT NA
Ceftazidime <1 S 31 S
Ceftriaxone <1 S 35 S
Cefiderocol
 <0.03
 S
NT
 NA
Monobactams
 Aztreonam
 <1
 S
36
 S
β-lactam combination agents Ceftazidime/avibactam <0.5/4 S NT NA
Ceftolozane/tazobactam <0.5/4 S NT NA
Meropenem/vaborbactam <0.5/8 S NT NA
Piperacillin/tazobactam
 <4/4
 S
22
 SDD
Penicillins
 Ampicillin
 >32
 R
NT
 NA
Folate pathway antagonists
 Trimethoprim/sulfamethoxazole
 >8/152
 R
NT
 NA
Fluoroquinolones Ciprofloxacin <0.25 S NT NA
Levofloxacin
 <0.12
 S
NT
 NA
Aminoglycosides Amikacin <1 S NT NA
Gentamicin >16 R NT NA
Tobramycin 16 R NT NA

*MICs were obtained by reference broth microdilution performed at Centers for Disease Control and Prevention according to Clinical and Laboratory Standards Institute guidelines. Kirby-Bauer disk diffusion was performed by the Massachusetts public health laboratory. Results were interpreted according to Clinical and Laboratory Standards Institute guidelines (9). I, intermediate; NA, not applicable; NT, not tested; R, resistant; S, susceptible; SDD, susceptible–dose dependent. †P. mirabilis isolates commonly exhibit elevated MICs to imipenem by mechanisms other than carbapenemase production.

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References
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Page created: July 11, 2026
Page updated: July 25, 2026
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