EXAMINATIONS ON THE BEHAVIOR OF GRAM-POSITIVE AND GRAM-NEGATIVE BACTERIA ON ALUMINUM FOIL

Abstract

The survival times of Staphylococcus aureus, Streptococcus faecalis, Escherichia coli, Klebsiella pneumoniae, Serratia marcescens and Pseudomonas aeruginosa on aluminium foil were determined. The dependence on the initial colony count and, in mixed cultures, the mutual influence of the several species of bacteria were studied. The longest survival times were found among the gram-positive cocci. S. marcescens and K. pneumoniae disappeared after 19 days, when initial colony counts were log 7.0/cm2; E. coli disappeared after 14 days. P. aeruginosa had the shortest survival time. The dependence on the initial colony count was ascertained for 3 different concentrations of bacteria. The highest concentrations showed the smallest reduction of cocci and the longest survival times of Enterobacteriaceae, respectively. The middle and lowest initial colony counts showed quicker reduction or shorter survival times. S. marcescens was more resistant to drying than K. pneumoniae. P. aeruginosa had the quickest dying rates, with no dependence on initial colony count. In mixed cultures with S. aureus or S. faecalis, survival times of Enterobacteriaceae were longer; the same result was seen for K. pneumoniae in culture together with S. marcescens. The following explanation might be possible: because of the drying resistance of gram-positive cocci the total bacteria number in these mixed cultures after several days is higher than in monocultures of E. coli, K. pneumoniae or S. marcescens. This protects the Enterobacteriaceae against external influences for a longer time and the effect increases with the length of duration. The same interpretation could apply to the mixed cultures of K. pneumoniae/S. marcescens.