Are Escherichia coli and Group A Beta-Hemolytic Streptococcus (Streptococcus pyogenes) sensitive to doxycycline (doxy)?

From the Guidelines

Doxycycline is generally effective against Escherichia coli but may not be the optimal choice for Group A Beta Hemolytic Streptococcus (Streptococcus pyogenes). For E. coli urinary tract infections, doxycycline can be used at a dose of 100 mg twice daily for 5-7 days, though local resistance patterns should be considered 1. However, for Strep pyogenes infections, penicillin remains the first-line treatment due to universal susceptibility and better clinical outcomes, as stated in the guidelines for the diagnosis and management of group A streptococcal pharyngitis 1. Doxycycline is not recommended as first-line therapy for Strep pyogenes infections because of increasing resistance rates and poorer clinical efficacy. If treatment is needed for both organisms simultaneously, or if penicillin allergy exists, alternative antibiotics like fluoroquinolones or trimethoprim-sulfamethoxazole might be more appropriate based on susceptibility testing 1. Some key points to consider when choosing an antibiotic include:

• Local resistance patterns
• Specific infection site
• Patient allergy history
• Potential for increased resistance with certain antibiotics It's also important to note that doxycycline works by inhibiting bacterial protein synthesis by binding to the 30S ribosomal subunit, but its effectiveness varies significantly depending on local resistance patterns and the specific infection site 1. In the case of skin and soft tissue infections, the guidelines recommend considering the severity of the infection, the presence of systemic toxicity, and the potential for resistant organisms when selecting an antibiotic 1. Ultimately, the choice of antibiotic should be based on the most recent and highest quality evidence available, as well as consideration of individual patient factors and local resistance patterns.

From the FDA Drug Label

Doxycycline is indicated for treatment of infections caused by the following gram-negative microorganisms, when bacteriologic testing indicates appropriate susceptibility to the drug: Escherichia coli. Because many strains of the following groups of gram-negative microorganisms have been shown to be resistant to tetracyclines, culture and susceptibility testing are recommended: Escherichia coli Doxycycline is indicated for treatment of infections caused by the following gram-positive microorganisms when bacteriologic testing indicates appropriate susceptibility to the drug: Upper respiratory infections caused by Streptococcus pneumoniae Up to 44 percent of strains of Streptococcus pyogenes and 74 percent of Streptococcus faecalis have been found to be resistant to tetracycline drugs.

The bacteria Escherichia coli may be sensitive to doxycycline, but culture and susceptibility testing are recommended due to potential resistance. The bacteria Streptococcus pyogenes (Group A Beta Hemolytic Strep) has a high resistance rate to tetracycline drugs, with up to 44 percent of strains found to be resistant. Therefore, doxycycline should not be used for Streptococcus pyogenes infections unless the organism has been demonstrated to be susceptible 2 2.

From the Research

Antibiotic Sensitivity of Escherichia coli and Group A Beta Hemolytic Strep

• Escherichia coli susceptibility to various antibiotics was studied in 3, which found high susceptibility to levofloxacin and gatifloxacin, but low susceptibility to amoxicillin/clavulanic acid.
• The study 3 did not specifically test doxycycline, so its effectiveness against Escherichia coli is not clear from this study.
• Group A Beta Hemolytic Strep (Strep pyogenes) susceptibility to antibiotics was studied in 4 and 5, which found that these bacteria are sensitive to penicillin, cephalosporins, and other antibiotics.
• The study 5 found that Group A streptococci were resistant to tetracyclines, including doxycycline, with a resistance rate of 23.8% and an intermediate susceptibility rate of 15.9%.
• Doxycycline's antimicrobial activity and pharmacokinetics were reviewed in 6, which found that doxycycline has excellent activity against gram-positive and gram-negative aerobic and anaerobic pathogens.
• However, the effectiveness of doxycycline against Escherichia coli and Group A Beta Hemolytic Strep is not clear from these studies, as the resistance rates and susceptibility patterns vary.

Doxycycline's Use in Treating Bacterial Infections

• Doxycycline is commonly used to treat various bacterial infections, including respiratory tract infections, skin and soft tissue infections, and genitourinary infections 6.
• The study 7 discussed the use of doxycycline in dermatology, where it is used to treat various noninfectious conditions, including hair follicle diseases and granulomatous diseases.
• However, the use of doxycycline to treat Escherichia coli and Group A Beta Hemolytic Strep infections is not well-established, and its effectiveness against these bacteria is not clear from the available studies.