Is Enterococcus susceptible to Cipro (ciprofloxacin)?

From the Guidelines

Enterococcus species are generally not reliably susceptible to ciprofloxacin (Cipro) and it is not recommended as a first-line treatment for Enterococcus infections. While some strains of Enterococcus may show susceptibility to ciprofloxacin in laboratory testing, the use of ciprofloxacin is not ideal due to intrinsic resistance mechanisms against fluoroquinolones, including altered DNA gyrase targets and efflux pumps that remove the drug from bacterial cells 1. Additionally, Enterococcus can rapidly develop resistance during ciprofloxacin therapy, even if initially reported as susceptible 1.

Key Considerations

• Enterococci are relatively resistant to penicillin, ampicillin, and vancomycin, and are often inhibited but not killed by these antimicrobials 1
• The combination of a cell wall–active agent, such as penicillin or ampicillin, with an aminoglycoside, such as gentamicin, is often used to achieve a bactericidal effect against Enterococcus 1
• For serious infections, combination therapy with ampicillin plus an aminoglycoside is often used for synergistic effect, while vancomycin is the alternative for ampicillin-resistant strains 1
• Treatment decisions should always be guided by antimicrobial susceptibility testing for the specific isolate 1

Alternative Treatment Options

• Ampicillin or amoxicillin are typically the preferred antibiotics for susceptible Enterococcus infections, with doses of 500-1000 mg orally every 8 hours for uncomplicated infections
• Vancomycin (1000 mg IV every 12 hours) is the alternative for ampicillin-resistant strains
• Linezolid and daptomycin are the only two antimicrobial agents currently available in the United States that may be useful for the treatment of multidrug-resistant Enterococcus infections 1

From the FDA Drug Label

For testing Enterobacteriaceae, Enterococcus faecalis, methicillin-susceptible Staphylococcus species, penicillin-susceptible Streptococcus pneumoniae, Streptococcus pyogenes, and Pseudomonas aeruginosaa: Zone Diameter (mm)Interpretation ≥ 21 Susceptible (S) 16 – 20 Intermediate (I) ≤ 15 Resistant (R)

The Enterococcus species, specifically Enterococcus faecalis, is included in the list of microorganisms for which the zone diameter interpretive standards apply.

• The standards indicate that a zone diameter of ≥ 21 mm is considered Susceptible (S).
• The standards also provide a range for Intermediate (I) susceptibility, which is a zone diameter of 16 – 20 mm.
• A zone diameter of ≤ 15 mm is considered Resistant (R). Based on the provided information, Enterococcus can be considered susceptible to Cipro (ciprofloxacin) if the zone diameter is ≥ 21 mm 2.

From the Research

Susceptibility of Enterococcus to Ciprofloxacin

• The susceptibility of Enterococcus to ciprofloxacin is variable, with some studies indicating that a significant proportion of strains are resistant to this antibiotic 3.
• A study analyzing the antibiotic susceptibility of Enterococcus spp. isolated from urine found that 43% of E. faecalis strains and 14% of E. faecium strains were sensitive to ciprofloxacin 3.
• Another study discussed the treatment options for vancomycin-resistant enterococcal infections, but did not specifically address the susceptibility of Enterococcus to ciprofloxacin 4.
• The other studies reviewed did not provide information on the susceptibility of Enterococcus to ciprofloxacin 5, 6, 7.

Factors Affecting Susceptibility

• The susceptibility of Enterococcus to ciprofloxacin can be affected by various factors, including the species of Enterococcus, the source of the isolate, and the presence of resistance genes 3.
• High-level resistance to aminoglycosides (HLAR) has been observed in some strains of Enterococcus, and these strains may also be resistant to other antibiotics, including ciprofloxacin 3.

Clinical Implications

• The variable susceptibility of Enterococcus to ciprofloxacin highlights the importance of antimicrobial susceptibility testing to guide treatment decisions 6.
• The use of ciprofloxacin to treat Enterococcus infections should be based on the results of susceptibility testing and should take into account the potential for resistance and the presence of other treatment options 4, 3.