EFFECT OF CARBON DIOXIDE ON BACTERIA 



Z13 



EFFECT ON BACTERIA IN MILK 



Hoffmann's experiments with milk were 

 unique. No other work of a similar 

 nature has come under the writer's 

 observation. This author investigated 

 the effect of carbon dioxide on the bacteria 

 in milk, and on the milk itself. Under 

 50 atmospheres of carbon dioxide the 

 bacterial count could be materially 

 reduced in 48 hours, (from 1,011,930 at 

 the start to 7,176); but complete steriliza- 

 tion was evidently never obtained. The 

 results were no better when the milk was 

 heated to 5o°C for zo minutes. The 

 reduction was more marked, but a slow 

 curdling of milk took place. The obser- 

 vation was made that carbon dioxide 

 exerts considerable influence on sterile 

 milk. After allowing 50 atmospheres of 

 carbon dioxide to act at 5 6° for Z4 hours on 

 raw milk, the casein could easily be sepa- 

 rated from the whey. It was observed 

 that samples of raw milk under 10 atmos- 

 pheres of carbon dioxide pressure remained 

 in apparently good condition for at least 7Z 

 hours. The untreated samples curdled in 

 Z4 hours. The author concluded that the 

 question of milk sterilization by CO2 

 was far from satisfactory. 



Altana (1907) experimented with 75 

 different organisms, including higher 

 bacteria, moulds and yeasts, and according 

 to his results divided the organisms 

 studied into three different groups as 

 follows : (a) those which were completely 

 inhibited by carbon dioxide (high tension), 

 (z) those that were not affected at all by 

 this agent, and (3) an intermediate group 

 composed of species that were more or less 

 variable. 



Van Slyke and Bosworth (1907) investi- 

 gated the preserving action of C0 2 on 

 milk. Lactic fermentation was delayed 

 in C0 2 under pressure. No noticeable 

 effect was observed under ordinary atmos- 

 pheric pressure, however. 



Berghaus (1907) subjected thirteen 

 species of microorganisms to various 

 pressures, under carbon dioxide. His 

 list comprised the following: V. cholerae, 

 B. anthracis, Bact. typhosum, Bact. colt, 

 Bact. fecalis-alkaligenes, Bact. enteritidis 

 Gaertner, Bact. dysenteriae (Shiga-Kruse 

 and Flexner), Bact. paratyphoswn A and B, 

 Staph, aureus, Ps. pyocyanea and Proteus 

 vulgaris. These organisms were subjected 

 to carbon dioxide on freshly poured agar 

 plates for a period of Z4 hours, at 37°C. 

 The strains under investigation were 

 divided into three groups as follows: 

 (1) V. cholerae (killed in Z4 hours at one 

 atmosphere pressure), (z) B. anthracis and 

 Bact. fecalis-alkaligenes (growth inhibited 

 in Z4 hours, but no killing), and (3) Bact. 

 coli and Bact. enteritidis (able to develop 

 under two atmospheres of carbon dioxide 

 pressure). Variations in resistance were 

 shown by various strains of Bact. coli. 

 Four of the strains required 15 atmos- 

 pheres of carbon dioxide, while with two 

 other strains a pressure of 9 atmospheres 

 was sufficient to kill. 



During the period from 191 1 to 191 5 a 

 series of articles by the following investi- 

 gators appeared, dealing with various 

 phases of bacteriology in carbonated 

 beverages: Klein (191 1), Young and Sher- 

 wood (1911), Eldson (1912.), Allen, La- 

 Bach, Pinnell and Brown (191 5) and 

 Colin (191 5). Aside from variations in 

 experimental technic, different organisms 

 studied, and the objects or aims which 

 prompted the investigations, certain ob- 

 servations are common to all of these 

 works. According to them, carbonated 

 beverages found on the market may or may 

 not be free from living microorganisms. 

 Reduction could be obtained with the 

 pathogenic forms, but not complete 

 sterilization. The sources of microorgan- 

 isms in commercial products are evidently 

 unclean bottles and unsanitary conditions 





