Chemistry: molecular biology and microbiology – Measuring or testing process involving enzymes or... – Involving viable micro-organism
Patent
1994-06-21
1996-02-27
Robinson, Douglas W.
Chemistry: molecular biology and microbiology
Measuring or testing process involving enzymes or...
Involving viable micro-organism
435 29, 435 34, 435 4, 435 36, 4352536, 4352525, 4352534, 435832, C12Q 118, C12Q 102, C12Q 114, C12N 120
Patent
active
054948053
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method for the detection of residues of antibacterial compounds in liquids. The invention also relates to a unit for the detection of residues of antibacterial compounds in liquids and the use of the unit.
Similar tests have been described in GB-A-1467439, EP-A-0005891 and DE 3613794. These documents all deal with "ready to use" tests that make use of a test organism and will give a result generally between 21/2 to 31/2 hours by the change of colour of an acid-base or redox indicator added to the test system. The principle is that when an antibacterial compound is present in the sample liquid in a sufficient concentration to inhibit the growth of the test organism the colour of the indicator will stay the same, whilst when no inhibition occurs, the growth of the test organism is accompanied by the formation of acid or reduced metabolites that will change the colour of the indicator. In all these tests a single indicator is used to detect the formation of acid or reduced metabolites.
According to this invention a marked reduction in test duration, up to one hour, can be achieved when a combination of two or more indicators is used. Such a shortened test duration is of importance to the user because the quality of the sample liquid is known more quickly thus allowing an earlier delivery or processing etc.
Therefore the invention provides a method for detecting antibacterials in a test sample which comprises medium, that antibacterials in the test sample inhibit the test organism in the agar medium.
The present invention also provides a unit for detecting antibacterials which comprises an agar medium comprising a test organism, optionally a separate nutrient source and two or more redox indicators which each can be present in the agar medium, in the test sample or in the separate nutrient source.
The unit of the present invention is useful for detecting residues of antibacterials such as sulpha compounds and antibiotics.
The unit may be used for detecting antibacterials in liquids, for example milk, water, meat juices, serum or urine.
The test organism is preferably a strain of Bacillus or Streptococcus. A preferred species of Streptococcus is Streptococcus thermophilus, more preferably Streptococcus thermophilus T101 (DSM 4022, deposited on Mar. 3, 1987). A strain of this species may be introduced into the agar medium, preferably in concentrations of 10.sup.5 to 10.sup.9 colony forming units (CFU) per ml agar medium.
A preferred species of Bacillus is Bacillus stearothermophilus, more preferably Bacillus stearothermophilus var. calidolactis C953. Bacillus stearothermophilus may be introduced into the agar medium preferably in concentrations of 10.sup.5 to 10.sup.9 CFU per ml of agar medium.
Examples of units useful for the purpose of the invention are transparent tubes, single or in a set or combined to a block of translucent material provided with a number of holes shaped therein.
A large variety of redox indicators may be used according to the process of the present invention. Such redox indicators are also known as redox mediators, redox catalysts and electron carriers. Examples of such compounds are Brilliant Black, Methylene Blue, Toluidine Blue, Safranine O, Indigo Carmin, Thionin, Gallocyanine, Nile Blue A, Brilliant Crocein MOO, Acid Yellow 38, Acid Orange 51, Acid Blue 120, Basic Blue 3, Azure A, Azure B, Congo Red, 1-10 Phenanthroline, Janus Green B, Brilliant Cresyl Blue. Other redox indicators (redox mediators, redox catalysts and electron carriers) may be used as well. Such compounds are commercially available see e.g. `Stains, Dyes and Indicators`, Catalogue of Aldrich Chemie. Preferably one of the indicators should give a colour change in the visible part of the spectrum. Preferred combinations are
Nutrients are added to enable the multiplication of the test organism.
The unit of the present invention optionally comprises at least part of the nutrients which are not incorporated in the agar medium and thus are added as a separate source, for example as a tabl
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Beukers Robert
Kerkhof Johannes
Van Rijn Ferdinand T.
Gist-Brocades N.V.
Leary Louise N.
Robinson Douglas W.
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