Detection of bacteria contained in a sample and determination of the type of bacteria are often performed in clinical examinations and food sanitation examinations. The types of bacteria are typically classified by Gram stainability of the bacteria (e.g., Gram positive or Gram negative), and by shape (e.g., bacillus or coccus). Gram-negative bacillus and Gram-positive coccus frequently produce adverse effects on the human body.
The agar culture method is the most common method for classifying bacteria. This method involves culturing a sample in an agar medium for a predetermined time, either staining or not staining colonies formed in the culture, and having an observer classify the bacteria using a microscope. However, the agar culture method is a difficult process inasmuch as it is essentially a manual method. Furthermore, considerable time must elapse before the type of bacterium can be determined since culturing is required.
In recent years, methods have been tried which automatically measure bacteria using a particle analyzer, such as a flow cytometer or the like. This technology involves the following aspects: (1) a method and apparatus for measuring microorganisms, which respectively measure pre-culture and post-culture samples to prevent measurement errors due to impurities in the sample by determining the difference between the two measurement results (e.g., see: U.S. Pat. No. 6,165,740); and (2) a method for counting bacteria in samples containing impurities, which separates the bacteria from the impurities, counts the bacteria by adding a cationic surfactant to a sample containing bacteria so as to increase the colorant transmission of the bacteria and stains the bacteria through the action of the colorant (e.g., see: European Patent Publication No. 1136563 A2).
Measurement can be accomplished in a relatively short time when the method automatically measures the bacteria by a particle measuring apparatus such as a flow cytometer or the like. However, among such methods, no technique has yet been proposed for differentiating bacillus and coccus with greater accuracy.