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Antimicrobial susceptibility of Legionella pneumophila Serogroups I--IV
Abstract:
Strains of Legionella pneumophila from 10 geographic areas were evaluated for their in vitro susceptibility to 14 antimicrobial agents. Included in this study were clinical and environmental isolates as well as strains from all 4 known serogroups. The minimal inhibitory concentration was established by agar dilution with a Steers replicator. The inhibitory index was then calculated considering the mean peak serum level for the associated antibiotic. Rifampicin, cefoxitin, chloramphenicol, ticarcillin, and parenteral erythromycin had the highest inhibitory indices. The only difference among serogroups was the increased susceptibility among serogroup II isolates to the penicillins and the increased susceptibility of serogroups III and IV to sulfamethoxazole-trimethoprim. Though there have been recent reports of the inadequacy of oral erythromycin in clinical cases of Legionnaires' disease, there was no erythromycin resistance noted among the 14 isolates tested.
Insights
This study evaluated Legionella pneumophila susceptibility to 14 antimicrobial agents. Rifampicin, cefoxitin, chloramphenicol, ticarcillin, and parenteral erythromycin showed the highest effectiveness against these bacteria.
Area of Science:
- Microbiology
- Infectious Diseases
- Pharmacology
Background:
- Legionella pneumophila is a significant cause of bacterial pneumonia.
- Understanding antimicrobial susceptibility is crucial for effective treatment of Legionnaires' disease.
- Previous reports suggested potential oral erythromycin inadequacy.
Purpose of the Study:
- To assess the in vitro antimicrobial susceptibility of diverse Legionella pneumophila strains.
- To compare the efficacy of 14 different antimicrobial agents.
- To identify potential differences in susceptibility among Legionella serogroups.
Main Methods:
- Agar dilution method with a Steers replicator was used to determine minimal inhibitory concentrations.
- Inhibitory indices were calculated using mean peak serum levels of antibiotics.
- Clinical and environmental isolates from 10 geographic areas, including all 4 serogroups, were tested.
Main Results:
- Rifampicin, cefoxitin, chloramphenicol, ticarcillin, and parenteral erythromycin demonstrated the highest inhibitory indices.
- Serogroup II isolates showed increased susceptibility to penicillins.
- Serogroups III and IV isolates were more susceptible to sulfamethoxazole-trimethoprim.
- No erythromycin resistance was observed in the tested isolates, despite reports of clinical inadequacy.
Conclusions:
- Several antimicrobial agents, including rifampicin, cefoxitin, chloramphenicol, ticarcillin, and parenteral erythromycin, are highly effective in vitro against Legionella pneumophila.
- Specific serogroups exhibit differential susceptibility patterns to certain antibiotics.
- In vitro testing did not reveal erythromycin resistance, suggesting its potential utility in parenteral forms for Legionnaires' disease.