From our experiences in overseas technical cooperations in South-East Asia, we keenly felt the necessity of development for easier and more reliable technique on the isolation culture of tubercle bacilli applicable in any rural area.
This paper presents the process of examinations on the dissolving for this problem.
I. Comparative studies between Ogawa original and WHO swab culture method
Ogawa's sputum culture method which is the standard method in Japan is very simple and unique technique that the specimen is directly inoculated by pipett into medium after alkali treatment without neutralization. On the other hand, the sputum swab culture method which is appeared in WHO/Tbc/Techn. Guide is the simplified technique that the specimen stucked on cotton swab is treated by acid and then neutralized by weak alkali. This swab culture method is widely employed in many countries of South-East Asia.
The comparative studies between both methods using the same sputum specimens were performed by two leading laboratories in Thailand.
The results are shown in tables 1, 2 and fig. 2. It is concluded that the Ogawa's method is fairly superior to WHO swab method, especially in contamination rate, though there are no significant differences statistically in the positivity.
The swab inoculation procedure was applied, furthermore, to Ogawa's method for convenience in rural areas, and this method was compared with both Ogawa original and WHO swab culture method. The results are presented in tables 3, 4 and figs. 3, 4.
There are no differences between Ogawa original and Ogawa swab method in both positivity and contamination rate, while Ogawa swab method is a little superior to WHO swab method.
The advantage of Ogawa swab method is its extreme simplicity and stability.
II. Studies on the medium for swab method without neutralization
For the purpose of investigating more adequate medium for the swab method without neutralization, several examinations were performed.
A provisional formula of medium was theoretically set up as follows; KH
2PO
42.0gr., Mg citrate 0.1gr., Na gultamate 0.5gr., distilled water 100m
l dissolve by heating, after cooling, glycerol 4m
l, 2% malachite green 4m
l, egg homoginate 200m
l mix and stire, dispense each 5 to 7m
l into McCartney bottle or test tube and coaggulate in slant by heating at 90°C for 1 hour. (2% modified medium)
1. H37Rv strain was suspended in both distilled water and 4% NaOH solution. These suspensions were inoculated onto Ogawa, Loewenstein-Jensen and 2% modified medium. The numbers of colony in each reading week are shown in fig. 5.
2. Table 5 indicates the most suitable combination of the dose of KH
2PO
4contained in the modified medium and the concentration of NaOH in pretreatment agent. The best result is obtained from the combination of KH
2PO
4 2gr. and 1.0m
lof 3% NaOH in sputum culture.
3. The comparison among several salts with Mg or citrate was made as a component of medium. The results suggest that Mg citrate in this medium can be substituted for Na citrate which dissolve more easily and more economical than Mg citrate.
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