Further studies on the falsification of the steam resistance of bioindicators by superheating
Spicher, G.; Peters, J.; Borchers, U.
Zentralblatt für Hygiene und Umweltmedizin 196(2): 181-196
1994
ISSN/ISBN: 0934-8859 PMID: 7802906 Document Number: 426476
As a supplement to a preceding paper (Zbl. Hyg., 194 (1993). 369-279) the resistance of bioindicators has been investigated which differed only in the material of which the carriers are made (filter paper and glass fibre fleece, respectively). The conditions of the tests were such that further evidence could be expected for the fact that the characteristic values of bioindicators can be falsified by superheating of the carrier and its envelope. As a test organism Enterococcus faecium has been used. To avoid side effects, the bacteria have been dried on to the carriers from a suspension in water distillators. The exposition basket of the resistometer has been loaded with 3 rows of 15 indicators (disc shaped; diameter: 6 mm), arranged parallel. At a temperature of 68 degrees C the dependency of (relative) frequency of indicators having surviving test organisms capable of multiplying on exposure time to saturated steam has been determined. Free exposed indicators made of filter paper required considerably longer exposure periods than indicators made of glass fibre fleece to change from "(nearly) all the indicators have test organisms capable of multiplying" to "(nearly) all the indicators are free from test organisms capable of multiplying". The exposure time to free 50% of carriers made of filter paper from test organisms capable of multiplying (t50%) amounted to 44.1 minutes. The frequency of indicators free from test organisms was higher at the ends than in the middle of the exposed rows. When such indicators had been wetted before exposure, they showed a t50% value of 2.3 minutes, and the frequency of indicators free from surviving test organisms was distributed over the exposed indicators evenly. Free exposed indicators made of glass fibre fleece showed a t50% value of 4.4 minutes. The frequency of indicators free from test organisms was evenly distributed. Wetting of the indicators before exposure changed t50% value only slightly. When indicators made of glass fibre fleece had been exposed between two layers of filter paper they showed a very high t50% value (47.5 minutes), and the frequency of indicators free from test organisms was unevenly distributed. Indicators being sterile could be found mainly at the ends of the exposed rows. In an envelope of parchment paper bioindicators made of glass fibre fleece showed considerably higher characteristic values than when free exposed. Superheating of the carriers amounted to about 3 Kelvin.