[Examinations on the behaviour of grampositive and gramnegative bacteria on aluminium foil (author's transl)]

Abstract

The survival times of Staph. aureus, Strept. faecalis, E. coli, Klebs. pneumoniae, Ser. marcescens and P. aeruginosa were found out on aluminium foil. It was examined whether there exists a dependence on the initial colony count and in mixed cultures a mutual influence of the several species of bacteria. The longest survival times were found among the grampositive cocci. Ser. marcescens and Klebs. pneumoniae could no more be indicated after 19 days in case of initial colony count of log 7.0/cm2; E. coli could no more be shown after 14 days. P. aeruginosa had the shortest survival time. The dependence on the initial colony count was ascertained in 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. Ser. marcescens was more resistant to drying than Klebs. pneumoniae. The quickest dying rates showed P. aeruginosa without any dependence on initial colony count. In mixed cultures with Staph. aureus or Strept. faecalis survival times of Enterobacteriaceae were longer; the same result gave Klebs. pneumoniae in culture together with Ser. marcescens. The following explanation might be possible: because of the drying resistance of grampositive cocci the total bacteria number in these mixed cultures after several days is higher than in monocultures of E. coli, Klebs. pneumoniae or Ser. marcescens. This protects the Enterobacteriaceae against external influences for a longer time. Therefore it is understandable that the effect increases with the length of duration. The same interpretation could apply to the mixed cultures of Klebs. pneumoniae/Ser. marcescens.