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Effect of pH of medium and size of inoculum on activity of antibiotics against group D Streptococcus (Enterococcus)
Abstract:
Seventy-one clinical isolates of 5 species of group D Streptococcus (Enterococcus) were tested for susceptibility to 15 antibiotics at pH 5.0, 7.4, and 8.5. Penicillin G, ampicillin, cephalothin, cephaloridine, and novobiocin were considerably more active against all strains at pH 5.0 than in the more alkaline media. On the other hand, lincomycin, clindimycin, erythromycin, and gentamicin were moderately to markedly more active at pH 8.5. No important differences were noted in the susceptibility of the strains to kanamycin and streptomycin, at the pH levels tested, but the organisms were quite resistant to them in these tests. The various species differed quantitatively in their susceptibility to the individual drugs and in the effects of pH. The size of the inoculum also had a variable effect on susceptibility, depending on the species of Enterococcus, the antibiotics, and the pH of the test medium. The data suggest that, in the antibiotic treatment of urinary tract infections caused by Enterococcus, attempts should be made to achieve the optimum pH in the urine, particularly in view of the fact that organisms of this group are often resistant to several antibiotics in the usual tests.
Insights
Urinary tract infections caused by Enterococcus bacteria are often resistant to antibiotics. Optimizing urine pH can significantly improve antibiotic effectiveness against these challenging infections.
Area of Science:
- Microbiology
- Pharmacology
- Clinical Medicine
Background:
- Group D Streptococcus, now classified as Enterococcus, are significant pathogens.
- Urinary tract infections (UTIs) are commonly caused by Enterococcus species.
- Antibiotic resistance in Enterococcus complicates treatment strategies.
Purpose of the Study:
- To investigate the in vitro susceptibility of Enterococcus to various antibiotics.
- To determine the impact of different pH levels (5.0, 7.4, 8.5) on antibiotic activity.
- To assess the influence of inoculum size on Enterococcus susceptibility.
Main Methods:
- Tested 71 clinical isolates of 5 Enterococcus species.
- Evaluated susceptibility to 15 different antibiotics.
- Incubated cultures at three distinct pH values: 5.0, 7.4, and 8.5.
Main Results:
- Penicillin G, ampicillin, cephalothin, cephaloridine, and novobiocin showed increased activity at acidic pH (5.0).
- Lincomycin, clindimycin, erythromycin, and gentamicin were more effective at alkaline pH (8.5).
- Kanamycin and streptomycin showed consistent resistance across tested pH levels.
Conclusions:
- Urine pH significantly influences the efficacy of certain antibiotics against Enterococcus.
- Tailoring urine pH may enhance antibiotic treatment outcomes for Enterococcus UTIs.
- Enterococcus species exhibit variable susceptibility patterns influenced by pH and antibiotic choice.