GERBAM — Deuxième Colloque International de Bactériologie marine — CNRS, Brest, 1-5 octobre 1984
IFREMER, Actes de Colloques, 3, 1986, pp. 617-619
74
RAPID METHOD FOR DETERMINING THE SENSITIVITY OF SULPHATEREDUCING BACTERIA TO BIOCIDES
A.P. SHARMA, N.S. BATTERSBY and D.J. STEWART
Department of Biological Sciences, Heriot-Watt University, Chambers street,
EDINGURGHEHI IHX - (UK)
ABSTRACT - The Minimal Inhibitory Concentration (MIC) of a biocide is usually determined by adding it in
various concentrations to a suitable growth medium which is then inoculated with the test bacterium. These
cultures are then observed for up to 28 days for growth of the organism as shown by its production of black
ferrous sulphide.
A method has been developed whereby the MIC of a biocide can be found within 4 days. Instead of noting
ferrous sulphide production, this new method measures changes in : 1) optical density and 2) sulphate reduction
of a logaritmic culture of the test strain exposed to the biocide.
Key words : Minimal Inhibitory Concentration, sulphate-reducing bacteria, glutaraldehyde.
RÉSUMÉ - La concentration minimale inhibitrice (MIC) d’un biocide est habituellement déterminée par
addition du biocide à différentes concentrations dans un milieu de croissance approprié qui est alors inoculé par
la bactérie testée. Ces cultures sont ensuite suivies pendant un maximum de 28 jours pour mettre en évidence la
production de sulfide ferreux noir. Une méthode permettant de déterminer le MIC d’un biocide en 4 jours a été
mise au point. Cette méthode n’étudie pas la production de sulfide ferreux mais mesure les variation de 1) la
densité optique et 2) de la réduction des sulfates dans une culture en phase logarithmique de croissance de la
souche testée, exposée à l’action du biocide.
Mots clés : Concentration Minimale Inhibitrice, bactérie sulfato-réductrice, glutaraldéhyde.
INTRODUCTION
One of the simplest ways to measure the effect of a biocide on an organism is by
determining the Minimal Inhibitory Concentration (MIC) which just prevents growth in a
suitable medium. The antibacterial agent is serially diluted in the medium and a standardised inoculum of the test strain added. After incubation for a predetermined period, at
the optimum temperature for growth, the cultures are examined and the MIC for the
biocide noted. This bacteriostatic test is only a measure of bacterial inhibition and gives
no information on the lethal effect of the agent under test. The bactericidal effect of a
biocide can be found by a time-kill test. Here, a culture of the test organism is exposed to
various concentrations of the biocide and the number of viable cells present at timed
intervals estimated.
API biocide tests :
The recommended American Petroleum Institute (API) method for testing the efficacy of
biocides against sulphate-reducing bacteria (SRB) is an MIC determination which
requires an incubation of inoculated bottles for 28 days (Anon, 1975). The API also
617
IFREMER, Actes de Colloques, 3, 1986, pp. 617-619
74
RAPID METHOD FOR DETERMINING THE SENSITIVITY OF SULPHATEREDUCING BACTERIA TO BIOCIDES
A.P. SHARMA, N.S. BATTERSBY and D.J. STEWART
Department of Biological Sciences, Heriot-Watt University, Chambers street,
EDINGURGHEHI IHX - (UK)
ABSTRACT - The Minimal Inhibitory Concentration (MIC) of a biocide is usually determined by adding it in
various concentrations to a suitable growth medium which is then inoculated with the test bacterium. These
cultures are then observed for up to 28 days for growth of the organism as shown by its production of black
ferrous sulphide.
A method has been developed whereby the MIC of a biocide can be found within 4 days. Instead of noting
ferrous sulphide production, this new method measures changes in : 1) optical density and 2) sulphate reduction
of a logaritmic culture of the test strain exposed to the biocide.
Key words : Minimal Inhibitory Concentration, sulphate-reducing bacteria, glutaraldehyde.
RÉSUMÉ - La concentration minimale inhibitrice (MIC) d’un biocide est habituellement déterminée par
addition du biocide à différentes concentrations dans un milieu de croissance approprié qui est alors inoculé par
la bactérie testée. Ces cultures sont ensuite suivies pendant un maximum de 28 jours pour mettre en évidence la
production de sulfide ferreux noir. Une méthode permettant de déterminer le MIC d’un biocide en 4 jours a été
mise au point. Cette méthode n’étudie pas la production de sulfide ferreux mais mesure les variation de 1) la
densité optique et 2) de la réduction des sulfates dans une culture en phase logarithmique de croissance de la
souche testée, exposée à l’action du biocide.
Mots clés : Concentration Minimale Inhibitrice, bactérie sulfato-réductrice, glutaraldéhyde.
INTRODUCTION
One of the simplest ways to measure the effect of a biocide on an organism is by
determining the Minimal Inhibitory Concentration (MIC) which just prevents growth in a
suitable medium. The antibacterial agent is serially diluted in the medium and a standardised inoculum of the test strain added. After incubation for a predetermined period, at
the optimum temperature for growth, the cultures are examined and the MIC for the
biocide noted. This bacteriostatic test is only a measure of bacterial inhibition and gives
no information on the lethal effect of the agent under test. The bactericidal effect of a
biocide can be found by a time-kill test. Here, a culture of the test organism is exposed to
various concentrations of the biocide and the number of viable cells present at timed
intervals estimated.
API biocide tests :
The recommended American Petroleum Institute (API) method for testing the efficacy of
biocides against sulphate-reducing bacteria (SRB) is an MIC determination which
requires an incubation of inoculated bottles for 28 days (Anon, 1975). The API also
617