A total of 256 coliform strains (132 from central, 124 from decentralized water supplies) as defined by the German drinking water regulation were characterized by the API 20E-system and by their susceptibility to 15 antimicrobial agents. Alltogether 22 different species from 10 genera could be differentiated, whereas 14 strains were unidentifiable by the applied system. The frequency distribution of the strains isolated from central water supplies yielded 48.5 % for Citrobacter freundii, 17.4 % for Klebsiella pneumoniae, 6.8 % for Buttiauxella agrestis and 6.1 % for C. diversus. In decentralized water supplies C. freundii was found in 33.9 %, K. pneumoniae in 14.5 %, Serratia fonticola in 8.9 % and K. oxytoca in 6.5 %.
About one third (73 strains) were fully susceptible to all used antibiotics. 42 strains, however, revealed complete or moderate resistance against three or more agents (multiresistant strains). Within this group a seasonal variation was evident. The proportion of multiresistant isolates was found to be relatively high in the first half of the year (21.4 % in January- March and 29.4 % in April-June) and relatively low in the second half-year (7.9 % in July-September and 11.3 % in October-December). This different distribution may indicate a conservation of R-factor bearing bacteria in the environment.
Adoption of a microbial health-based target for Australian drinking water regulation