From the Research
No, there are currently no Clinical and Laboratory Standards Institute (CLSI) breakpoints specifically for Streptococcus anginosus against trimethoprim-sulfamethoxazole (Septra) or ciprofloxacin (Cipro). This absence of specific breakpoints makes it challenging to reliably interpret susceptibility testing results for these antibiotics against S. anginosus. When treating S. anginosus infections, clinicians typically rely on other antibiotics with established activity and breakpoints against this organism, such as penicillins (particularly penicillin G or amoxicillin), cephalosporins, or clindamycin. Beta-lactam antibiotics remain the first-line therapy for S. anginosus group infections due to their proven efficacy and the organism's consistent susceptibility pattern, as supported by studies such as 1. If alternative agents are needed due to allergies or other contraindications, susceptibility testing should be performed, but results for Septra and ciprofloxacin should be interpreted with caution given the lack of established breakpoints for this specific organism.
Some studies have investigated the antimicrobial susceptibility of S. anginosus, including a 1999 study that found the organism to be susceptible to clindamycin, chloramphenicol, vancomycin, and all beta-lactam antibiotics, except ceftazidime, to which 54.5% of the strains showed intermediate susceptibility 2. Another study from 2022 highlighted the effectiveness of levofloxacin-based oral regimens in treating S. anginosus intracranial infections, but this does not provide direct evidence for the use of ciprofloxacin or Septra in treating these infections 3.
Key points to consider when treating S. anginosus infections include:
- The lack of established CLSI breakpoints for Septra and Cipro
- The reliance on beta-lactam antibiotics as first-line therapy
- The importance of susceptibility testing for alternative agents
- The need for caution when interpreting results for Septra and Cipro due to the lack of established breakpoints.
In clinical practice, the choice of antibiotic should be guided by the severity of the infection, the presence of any underlying conditions, and the potential for resistance, as highlighted in studies such as 4 and 1.