Zosyn Coverage Against Proteus Species
Yes, Zosyn (piperacillin-tazobactam) provides effective coverage against Proteus species, including both Proteus mirabilis and Proteus vulgaris, with demonstrated clinical efficacy in urinary tract infections. 1, 2
Microbiological Activity
Piperacillin-tazobactam demonstrates robust in vitro activity against Proteus mirabilis with an MIC90 of 1.56 mcg/mL and against Proteus vulgaris with an MIC90 of 3.13 mcg/mL, showing 4- to 64-fold greater potency than piperacillin alone or other beta-lactam/beta-lactamase inhibitor combinations. 2
The FDA-approved drug label specifically lists Proteus mirabilis and Proteus vulgaris among organisms for which at least 90% of isolates exhibit MICs at or below the susceptible breakpoint, though it notes these are not beta-lactamase producing bacteria and are therefore susceptible to piperacillin alone. 1
Clinical Evidence in Urinary Tract Infections
In a clinical trial of 217 patients with complicated UTIs treated with piperacillin-tazobactam 4g/500mg every 8 hours, the overall pathogen eradication rate was 82%, with 86% of clinically evaluable patients cured or improved. 3
Piperacillin-tazobactam has demonstrated effectiveness across multiple clinical trials for complicated urinary tract infections, with clinical and bacteriological response rates of 85% and 73% respectively at study endpoint. 3, 4
Guideline Recommendations
For healthcare-associated complicated UTIs where Proteus species are commonly encountered, guidelines recommend piperacillin-tazobactam as part of empirical therapy regimens, particularly for postoperative infections caused by more resistant flora. 5
The European Association of Urology guidelines identify Proteus spp. among the most common species found in complicated UTI cultures, and piperacillin-tazobactam is included in recommended empirical treatment algorithms for these infections. 5
Important Clinical Considerations
Proteus species are frequently involved in healthcare-associated infections and can develop multidrug resistance, including ESBL production, which may compromise piperacillin-tazobactam efficacy in some isolates. 5, 6
For ESBL-producing Proteus isolates specifically, piperacillin-tazobactam may retain activity against ESBL-producing E. coli but effectiveness varies, and carbapenem therapy should be considered for severe infections or confirmed ESBL producers. 7, 6
Local susceptibility patterns should guide empirical therapy selection, as resistance mechanisms in Proteus can include loss of porins, reduced PBP expression, or acquisition of resistance genes affecting multiple antibiotic classes. 6