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| Summary |
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F10 Super Concentrate Disinfectant (F10SC) is a quaternary ammonium and biguanidine compound based disinfectant. Independent tests have shown it to be effective against bacteria, fungi, viruses and spores (bacterial and fungal spores). It had been reported that when using the sensitivity/resistance zone of inhibition test method on bacterial isolates that inconsistent results occur. A study1 was initiated to determine the most appropriate laboratory method to be used for evaluation of F10SC when using zone of inhibition test methods using commercially available susceptibility dics of 10µg Gentamicin and 5 µg Enrofloxacin as controls. |
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In 1036 readings all eight organisms tested were sensitive to F10SC disinfectant in a dilution of 1/250 in broth and complete visual inhibition was observed at this and much lower levels. The more resistant organisms, for example
Pseudomonas aeruginosa and Escherichia coli, produced small inhibition zones on agar at a concentration equal to a 1/250 dilution, but were still completely inhibited by 1/1000 and 1/4000 dilutions of F10SC in broth respectively. The more sensitive organisms, for example
Staphylococcus aureus, produced large inhibition zones on agar at a concentration equal to a 1/250 dilution of the product and were completely inhibited in broth by dilutions as low as 1/16 000. A total of 146 readings were taken of each of the Gentamicin and Enrofloxacin
controls. |
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However the study did show
that this type of test must be carried out
within strict parameters otherwise inconsistent
and misleading results would be obtained. |
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Introduction |
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The study was conducted with the following objectives: |
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To investigate an agar disc diffusion zone of inhibition test method for evaluating the susceptibility of aerobic and facultative anaerobic bacteria against F10SC. |
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To compare zone
inhibition results over a range of four
to six different concentrations of F10SC
on two different types of agar normally
used for susceptibility testing i.e.
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Mueller Hinton agar (supplier Merck) and Iso-Sensitest Agar (Oxoid) (supplier C. A. Milsch). |
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To compare the sensitivity or resistance of the eight test organisms to commercially available susceptibility discs gentamicin 10µg and Enrofloxacin 5µg on two different types of agar. |
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To establish the MIC values of the agent against a number of commonly occurring bacterial pathogens, these included known ATCC strains, local isolates and avian pathogens. |
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The Study |
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Test organisms
The following organisms were used: |
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| Preparation of bacterial suspensions |
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According to NCCLS guidelines4 the direct colony suspension method was selected. |
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The cultures were grown on non selective agar ( nutrient agar slopes) for 16 - 18 hours at 35°C (± 2°C) and growth was re-suspended with sterile 0,85 % saline. The concentrated suspensions obtained were diluted with sterile 0,85 % saline to match the turbidity of a 0,5 McFarland standard (approximately 70 - 75 %T at 600 nm). The resulting bacterial suspensions contained approximately 1,5 x 108 cfu/ml . |
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Macro-broth dilution MIC determination |
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Broth dilution MIC determination was performed in accordance with the guidelines as described by the NCCLS4. |
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Mueller-Hinton broth (pH 7,2 - 7,4) supplied by Merck. The broth was prepared and sterilized according to the manufacturer's instructions. The cation concentration of the broth was not adjusted and the broth was used “as is”. |
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