Is the Providencia rettgeri isolate susceptible to ertapenem?

Providencia rettgeri and Ertapenem Susceptibility

Providencia rettgeri isolates are typically resistant to ertapenem, and ertapenem should not be relied upon for treatment of P. rettgeri infections.

Evidence from FDA Drug Label

The FDA label for ertapenem explicitly lists Providencia rettgeri among organisms that exhibit in vitro susceptibility (at least 90% with MIC ≤ susceptible breakpoint), but critically notes that "the efficacy of ertapenem in treating clinical infections due to these bacteria has not been established in adequate and well-controlled clinical trials" 1. This means while some P. rettgeri isolates may appear susceptible on laboratory testing, clinical effectiveness is unproven.

Clinical Reality: Carbapenem Resistance is Common

Multiple outbreak reports demonstrate that carbapenem-resistant P. rettgeri is an emerging clinical problem:

• All isolates in a Korean outbreak showed high-level resistance to ertapenem (along with meropenem and imipenem), with strains co-producing NDM-1 carbapenemase and PER-1 extended-spectrum β-lactamase 2

• A South African outbreak documented resistance to imipenem, ertapenem, and meropenem in all four cases 3

• A Chinese study found all six carbapenem-resistant P. rettgeri strains carried the blaNDM-1 carbapenem resistance gene and demonstrated resistance to ertapenem 4

• Recent surveillance from Mexico identified P. rettgeri with resistance to all tested antibiotics, highlighting extreme drug resistance patterns 5

Practical Implications

You must perform susceptibility testing before considering any carbapenem for P. rettgeri. Even if an isolate tests susceptible to ertapenem in vitro, the lack of clinical trial data supporting efficacy means you should:

1. Prioritize other carbapenems (meropenem, imipenem) if carbapenem therapy is necessary, as these have broader clinical validation
2. Consider alternative agents based on susceptibility results
3. Assume carbapenem resistance is likely in healthcare-associated infections, particularly in patients with prior antibiotic exposure or invasive procedures 4, 2

The gepotidacin data shows P. rettgeri MIC90 of 16 µg/mL, suggesting this novel agent may have future utility, though it's not yet clinically available 6.