Effects of Bacterial Growth on the Environment 191 



organism— a favorable effect. For example, when aerobic bacteria 

 grow in the vicinity of anaerobic bacteria, the aerobes reduce the 

 oxygen tension and create conditions favorable for the growth of 

 the anaerobes. 



When bacteria exhibit antagonisms— the reverse of symbiosis— 

 the designation of antibiosis is applied to the condition. The 

 struggle for supremacy, even among such lowly forms of life as 

 microbes, is vital to our well-being, in fact, to our very survival. 

 Antibiosis partially accounts for the limitations of bacterial growth, 

 which, if left unchecked, might well force all other forms of life 

 from the face of the earth. The old law of survival of the fitter 

 operates even at this reduced level of life. 



Man in recent years has put this microbial competitive spirit 

 to work for human good bv the development of such medically 

 important antibiotics as penicillin, Chloromycetin, aureomycin, 

 BACITRACIN, STREPTOMYCIN, and Other substances. The development 

 of these agents represents one of the great milestones in medical 

 science. Many years have been added to the lives of untold thou- 

 sands of individuals who have been treated with the chemother- 

 apeutic agents, oftentimes called wonder drugs. 



Antibiotic means against life, and it refers to an anti-microbial 

 substance produced or derived from living organisms, and which 

 acts adversely on other forms of life, usually microscopic organisms. 

 Students vitally interested in the field of antibiotics are referred 

 to advanced texts and pamphlets in the field, since this discussion 

 will do little more than introduce the topic. 



The discovery of penicillin occurred in 1929 when Alexander 

 Fleming, an English bacteriologist, noted that a culture of Staphy- 

 lococcus aureus failed to grow around a mold contamination on one 

 of his culture plates. The mold proved to be PenicilUum notatum. 

 When this species was grown in nutrient broth, the filtrate of this 

 culture was found to exert a powerful effect against certain bacteria, 

 and when tested against laboratory animals, the filtrate was no 

 more toxic than the nutrient broth alone. Fleming named this 

 active principle penicillin and he advocated its possible use in the 

 treatment of infectious diseases. After a lapse of eight years, Florey 



