The estimation of small numbers of micro-organisms in opalescent non-alcoholic drinks by applying centrifugation
article
1. Experiments relating to direct massive plating of liquid foods containing only small numbers of organisms, but rich in insoluble material (e.g. fruit juices), showed that this procedure is unreliable due to the background infection which invaria bly occurs during the counting of foods in solid and liquid media.
2. The use of membrane filters for this purpose appeared also impossible, because the ordinary filtration of fruit juices which must be carried out before subjecting the product to membrane filtration removes > 90 % of the microorganisms present.
3. Centrifugation of such juices for 15 min. at 2.500 r.p.m. in 10 × 3 cm tubes at a radius of 20 cm, and subsequent plating of the pellet, appeared an effective procedure. This appeared also to be the case, when the pellet was too rich in insoluble material to be plated directly and the microbes had therefore subsequently to be separated from this insoluble material by resuspending the pellet and allowing 15 min. sedimentation of the suspension obtained.
2. The use of membrane filters for this purpose appeared also impossible, because the ordinary filtration of fruit juices which must be carried out before subjecting the product to membrane filtration removes > 90 % of the microorganisms present.
3. Centrifugation of such juices for 15 min. at 2.500 r.p.m. in 10 × 3 cm tubes at a radius of 20 cm, and subsequent plating of the pellet, appeared an effective procedure. This appeared also to be the case, when the pellet was too rich in insoluble material to be plated directly and the microbes had therefore subsequently to be separated from this insoluble material by resuspending the pellet and allowing 15 min. sedimentation of the suspension obtained.
TNO Identifier
49743
Source
Annales de l'Institut Pasteur de Lille, 11, pp. 193-202.
Pages
193-202
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