Should a patient with a urine culture showing Enterococcus greater than 100,000 colony-forming units per milliliter (CFU/mL) and Pseudomonas less than 100,000 CFU/mL be treated for both organisms?

From the Guidelines

Treatment decisions for a urine culture showing Enterococcus >100,000 CFU/mL and Pseudomonas <100,000 CFU/mL should focus primarily on the Enterococcus. Treat the predominant organism (Enterococcus) with appropriate antibiotics such as ampicillin (1-2g IV every 6 hours or 500mg PO four times daily) or amoxicillin (500mg PO three times daily) for uncomplicated cases, as suggested by guidelines for treating enterococcal infections 1. For complicated infections or penicillin allergies, consider vancomycin (15-20mg/kg IV every 8-12 hours) or nitrofurantoin (100mg PO twice daily for 5-7 days) for lower UTIs. The lower-count Pseudomonas likely represents contamination or colonization rather than true infection, but if the patient has risk factors (immunocompromise, structural abnormalities, recent instrumentation) or is clinically unstable, broader coverage including both organisms may be warranted with a fluoroquinolone (ciprofloxacin 500mg PO twice daily) or piperacillin-tazobactam (3.375g IV every 6 hours), as recommended for infections due to multidrug-resistant organisms 1. Treatment duration should be 7 days for uncomplicated UTIs and 10-14 days for complicated infections, following the principle of treating the predominant pathogen while avoiding unnecessary broad-spectrum antibiotics that could promote resistance. Key considerations include the patient's clinical status, risk factors, and the potential for antibiotic resistance, guiding the choice between targeted therapy for Enterococcus and broader coverage that includes Pseudomonas, with the most recent guidelines providing a framework for decision-making 1.

Some key points to consider:

• The choice of antibiotic should be guided by susceptibility testing when possible.
• The treatment of Enterococcus infections may involve combination therapy in certain cases, such as with ampicillin and an aminoglycoside for endocarditis, as suggested by 1.
• For Pseudomonas infections, particularly those that are multidrug-resistant, options like ceftolozane/tazobactam or ceftazidime/avibactam may be considered, as outlined in 1.
• The duration of treatment should be tailored to the specific infection site and the patient's response to therapy, with guidelines suggesting 5-14 days for various infections due to multidrug-resistant organisms 1.

From the FDA Drug Label

To reduce the development of drug-resistant bacteria and maintain the effectiveness of AZACTAM (aztreonam for injection, USP) and other antibacterial drugs, AZACTAM should be used only to treat or prevent infections that are proven or strongly suspected to be caused by susceptible bacteria When culture and susceptibility information are available, they should be considered in selecting or modifying antibacterial therapy. AZACTAM is indicated for the treatment of the following infections caused by susceptible Gram-negative microorganisms: Urinary Tract Infections (complicated and uncomplicated), including pyelonephritis and cystitis (initial and recurrent) caused by Escherichia coli, Klebsiella pneumoniae, Proteus mirabilis, Pseudomonas aeruginosa, Enterobacter cloacae, Klebsiella oxytoca*, Citrobacter species*, and Serratia marcescens* Following identification and susceptibility testing of the causative organism(s), appropriate antibiotic therapy should be continued.

The patient has a urine culture with Enterococcus greater than 100,000, which is a Gram-positive organism, and Pseudomonas less than 100,000, which is a Gram-negative organism.

• Aztreonam is effective against Gram-negative organisms, including Pseudomonas aeruginosa.
• However, Aztreonam is not effective against Gram-positive organisms, including Enterococcus.
• The FDA label recommends concurrent initial therapy with other antimicrobial agents when the causative organism is not known, especially in seriously ill patients who are also at risk of having an infection due to Gram-positive aerobic pathogens.
• The label also states that following identification and susceptibility testing of the causative organism(s), appropriate antibiotic therapy should be continued. Based on this information, it is recommended to treat for both Enterococcus and Pseudomonas with appropriate antibiotics, considering the susceptibility of each organism 2.
• For Pseudomonas, Aztreonam can be considered as a treatment option.
• For Enterococcus, a different antibiotic that is effective against Gram-positive organisms should be used.

From the Research

Treatment of Urinary Tract Infections with Enterococcus and Pseudomonas

• The presence of Enterococcus greater than 100,000 CFU/mL in a urine culture indicates a significant infection that requires treatment 3.
• For Enterococcus infections, treatment options include ampicillin, nitrofurantoin, or fosfomycin for uncomplicated cystitis 3.
• In cases where the Enterococcus infection is complicated or resistant, combination therapy with ampicillin and ceftaroline, cefepime, or ceftriaxone may be effective 4.
• The presence of Pseudomonas less than 100,000 CFU/mL in a urine culture may not necessarily require treatment, but it is essential to consider the patient's overall clinical presentation and risk factors 5, 6.
• Treatment options for Pseudomonas infections include fluoroquinolones, ceftazidime, cefepime, piperacillin-tazobactam, and carbapenems, among others 5, 6.
• Combination therapy with a beta-lactam and an aminoglycoside or a fluoroquinolone may be effective against Pseudomonas infections, but the choice of treatment should be guided by antimicrobial susceptibility testing and clinical judgment 7.

Considerations for Treatment

• The decision to treat both Enterococcus and Pseudomonas infections simultaneously should be based on the patient's clinical presentation, the severity of the infections, and the potential risks and benefits of treatment 3, 5, 6.
• Antimicrobial stewardship is essential to preserve the effectiveness of available antibiotics and prevent the development of resistance 5, 6.
• Treatment should be guided by local susceptibility patterns, and antimicrobial susceptibility testing should be performed to inform treatment decisions 5, 6.