[Significance of antibiotic-forming microorganisms in biological waste water clarification]

Streptomyces spec. producing antibiotics were detected very seldom in the wastewater pretreatment plant of Braunschweig. However, Bacillus spec. producing antibiotics are common. There are about one permille of the total population of bacteria in wastewater (Fig. 1). Reflecting the total number of bacteria, the psychrophilic microorganisms growing at 20 degrees C increase more during the oxidation step of wastewater treatment than the mesophilic bacteria growing at 30 or 37 degrees C. But reflecting the bacilli the strains producing antibiotics growing at 30 or 37 degrees C propagate stronger than the psychrophilic group (Fig. 2). About 90% or more of a total of 194 isolated Bacillus strains producing antibiotics showed antibiotic activity against the tested grampositive bacteria Listeria monocytogenes and Staphylococcus aureus. Only few strains were active against Candida albicans, E. coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, and Salmonella typhimurium (Fig. 3, 4, and Table 1). During the summer (July) the percentage of strains producing antibiotics against grampositive bacteria was higher than in the winter (January) (Fig. 4). Also the deep freezing of samples increased the percentage of antibiotic producers (Fig. 2). Some species were isolated even only from freezed and again thawed samples (Table 1).