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The oxidation-reduction potential (ORP) in the cecal contents of conventional rats, germ-free mice, and mice with a Colonization Resistance Factor flora (CRF-mice) was investigated. By using animals that were anaesthetized for a longer period of time, we attempted to eliminate the disturbing influence of oxygen. In addition, measurements were made under anaerobic conditions. For the rats, the ORP values reached a more or less constant level after about 30 min following the insertion of the electrodes. The mean ORP at that time was -458 mV (SD = 45 mV). The mean ORP values for the mice showed a more gradual reduction than was found in the rats. The curves leveled off at about 100 min following the insertion of the electrodes. The mean ORP values 100 min after electrode insertion were: germ-free mice, + 3 mV (SD = 39 mV); CRF-mice, -554 mV (SD = 29 mV). In rats, the ORP value decreased after death; no decrease was observed in mice. No difference was found in the values obtained when measuring under anaerobic or aerobic conditions after death.

The use of combusted natural gas as atmosphere for cultivation of the anaerobic bacterial flora from the cecum of mice is described. The combusted gas (inert gas) continuously flushes a glove box in which it is possible to cultivate a number of strict anaerobes from the cecum of mice.

A survey was conducted in 1971 in healthy reptiles supplied to the Central Animal Laboratory of Nijmegen for experimental animal research. In order to determine which salmonella serotypes occur, and whether there are several serotypes per animal, several strains of each positive sample were typed.It was found that 160 of 169 samples contained salmonellas or lactose-negative Arizonas or both, and 95 different serotypes were isolated.Of 127 animals examined individually, 67 were carriers of more than one serotype, 42 animals having two types, 21 three types and 4 animals four types.Three enrichment methods were compared. These were tetrathionate broth incubated at 37 degrees C. (T37) and at 43 degrees C. (T43), and selenite broth incubated at 37 degrees C. (SB). All were incubated for 48 hr. before subculture on brilliant-green agar plates. The enrichment methods T37, T43 and SB produced 99, 125 and 123 positive samples respectively, when taken separately. The combinations of T37 and T43, T37 and SB, and T43 and SB produced 145, 142 and 150 positive samples respectively.The yield of serotypes in comparable samples showed no difference between the three enrichment methods. With the use of two methods the yield increased by about 38% compared with one method, and the combination of three methods showed an increase in serotype yield of about 64% compared with one method. A distinct preference by serotypes for definite enrichment methods was not proved.