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[Changes in the antibacterial activity of nitrofurantoin preparations induced by peptone and hydrolysates]
Abstract:
The determination of the activity of the product nitrofurantoin (10 and 100 mcg) versus 324 strains of Gram-negative bacteria showed that the diameter of the inhibition zones and the MIC values on a medium with a definite composition (7SG) are considerably larger than on the Mueller-Hinton (MH) medium, in the bacto-tryptose (BT) medium. An increase with 8-12 mm phi or with 2-4 binary dilutions changes the interpretation from resistant, on the MH and BT media into sensitive on the 7SG medium. The low results recorded on the conventional media reveal the existence of an antagonism between peptone and nitrofurantoin, similar to that known for sulfamides. The authors believe that the peptone antagonism has hindered the knowledge of the activity of the nitrofurfural derivatives and the correct assessment of the bacteria sensitivity. They also consider questionable the elimination tendency of the small dosage of microtablets of nitrofurantoin (10 mcg) and sulfamide (30 mcg), since their apparent insufficiency might be due less to the inadequate contraction of substances and more to the inadequate testing media. The results plead for the use of the media with definite chemical composition sulfamide and nitrofuran antagonists free and for reconsideration of several methodologic problems: use of the media with definite chemical composition; introduction of an intermediary dosage of maximum 100 mcg/microtablet; reassessment of the sensitivity categories for sulphafurazole and nitrofurantoin.
Insights
Bacterial susceptibility testing for nitrofurantoin is significantly affected by culture media composition. Peptone in conventional media antagonizes nitrofurantoin, leading to inaccurate resistance interpretations.
Area of Science:
- Microbiology
- Pharmacology
- Clinical Chemistry
Background:
- Conventional microbiological media, such as Mueller-Hinton (MH) and Bacto-Tryptose (BT), are widely used for determining antibiotic susceptibility.
- The accuracy of antibiotic susceptibility testing is crucial for effective treatment and understanding antimicrobial resistance patterns.
Purpose of the Study:
- To investigate the impact of different culture media on the determined activity of nitrofurantoin against Gram-negative bacteria.
- To identify potential antagonisms between culture media components and nitrofurantoin, affecting susceptibility interpretations.
Main Methods:
- Testing nitrofurantoin (10 and 100 mcg) activity against 324 Gram-negative bacterial strains.
- Comparing results obtained on a chemically defined medium (7SG) versus conventional media (MH and BT).
- Evaluating inhibition zone diameters and Minimum Inhibitory Concentration (MIC) values.
Main Results:
- Significantly larger inhibition zones and lower MIC values were observed on the 7SG medium compared to MH and BT media.
- A shift in interpretation from resistant to sensitive was noted for several strains when using the 7SG medium.
- Evidence suggests an antagonism between peptone (a component of conventional media) and nitrofurantoin.
Conclusions:
- The presence of peptone in conventional media antagonizes nitrofurantoin, potentially hindering accurate assessment of bacterial sensitivity.
- The study advocates for the use of chemically defined media, free from peptone-related antagonists, for nitrofurantoin susceptibility testing.
- Reconsideration of current susceptibility categories and dosage recommendations for nitrofurantoin and related compounds is warranted.