Pathogenic Bacteria from Diseased Silkworm (Bombyx mori L.)

 Isolation and Characterization of Pathogenic Bacteria from Diseased Silkworm (Bombyx mori L.) and Antibacterial Activities of Different Plant Extracts


About 34 to 40 percent of total crop in a year has been reported to be loss due to diseases because of the occurrence of four major diseases namely pebrine (Protozoan disease), flacherie (bacterial disease), grasserie (Viral disease) and muscardine (Fungal disease). Flacherie is known to be caused the assembly of various pathogenic bacteria in silkworms and are commonly known as bacterial flacherie.

The art of silk production is called sericulture that comprises cultivation of mulberry, silkworm rearing and post cocoon activities leading to production of silk yarn. Sericulture provides gainful employment, economic development and improvement in the quality of life to the people in rural area and therefore it plays an important role in anti poverty programme and prevents migration of rural people to urban area in search of employment. Sericulture or silk farming is the rearing of silkworms for the production of raw silk. During the silkworm rearing, the silk worm comes in contact with pathogenic agent viz, protozoa, virus, fungi and bacteria. Silkworm rearing free from diseases is a major constraint in sericulture industry.


Bacteria isolated from different tissues of diseased silkworm were studied. Samples of different tissues were suspended in physiological saline and one loopful of each suspensions were separately inoculated into nutrient agar medium at 370oC for 2 days and bacterial strains were isolated from the samples. The isolated bacteria were examined microscopically for their morphological and physiological characteristics. Morpho-physiological characteristics and biochemical properties as well as DNA sequencing of 16S rRNA gene indicated that the bacterium was Kiebsiella pneumoniae and Staphylococcus species. The biochemical properties were also compared based on the instruction of Bergey’s Manual of determinative bacteriology to identify the bacterial type. The optimum culture condition of Kiebsiella pneumoniae and Staphylococcus species for good growth in PH 7.0 and temperature 37°C were also studied. The antibiotic resistance pattern is generally used for strain identification in ecological studies. It is evident from the present investigation that isolated bacteria were resistance to cephardine, penicillin, nalidixic acid, cefuroxime sodium, and ceftazidime and utilize different carbohydrates viz. xylose, glucose, fructose, lactose, sucrose, mannose, galactose and maltose.


Growth of bacterial species were observed in the presence of various plant extracts such as Cannamomum zeylenica (cinnamon), Azadirachta indica (neem), Curcuma domestica (turmeric) and Zingiber offIcinale (zinger). Various concentrations of the plant extracts have been determined and its application towards control of the flacherie causing bacteria Klebsiellapneumoniae species has been assessed. It was found that antibacterial activity of the ethanol extracts of Cinnamomum zeylenica (22mm), Curcuma domestica (2 1mm), Zingiber officinale (20mm) showed the sensitive zone against Kiebsiella pneumoniae respectively.

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