ABSTRACT
Spreading of antibiotic
resistant bacteria into environment is becoming a major public health problem,
implicating affair of the indirect transmission of antibiotic resistant
bacteria to human through drinking water, or vegetables, or daily products.
Until now, the risk of nosocomial infection of antibiotic resistant bacteria
has mainly been evaluated using clinical isolates by phenotypic method. To
evaluate a risk of community-acquired infection of antibiotic resistant
bacteria, a new method has been developed based on PCR-RFLP without isolation.
By comparing restriction fragment lengths of the 16S rDNA gene from bacterial
mixture grown under antibiotic treatment to those simulated from the DNA
sequence, bacterial taxonomies were elucidated using the method of Okuda and
Watanabe [1] [2]. In this study, taxonomies of polymyxin B resistant bacteria
group in field soils, paddy field with organic manure and upland field without
organic manure were estimated without isolation. In the both field soils, the
major bacteria grown under the antibiotic were B. cereus group, which
had natural resistance to this antibiotic. In field applied with organic
manure, Prevotella spp., and the
other Cytophagales, which were suggested to be of feces origin and to acquire
resistance to the antibiotic, were detected. When numbers of each bacterial group
were roughly estimated by the most probable number method, B. cereus group was enumerated
to be 3.30 × 106 MPN/g dry soil in paddy field soil and 1.32 × 106 MPN/g dry soil in upland filed. Prevotella spp. and the other Cytophagales in paddy field were enumerated to be 1.31 × 106 MPN, and 1.07 × 106 MPN·g-1 dry soil.