One hundred twenty samples of fermented foods comprising 24 each of dosa premix, rice beer, idli, curd and soya sauce were collected randomly from different areas of Ranchi for possible contamination with heat resistant Bacillus cereus. Samples were collected aseptically in sterile polythene bags and brought immediately to the Laboratory for bacteriological examination. The differential and selective medium used was Mannitol Egg Yolk Polymyxin B sulphate (MEYP) agar (Mossel et al., 1967). |
Processing of samples For isolation of Bacillus cereus 7.0 ml of rice beer/7.0 grams of fermented foods was taken in flasks containing 63.0 ml of 0.1 percent peptone water to give a dilution of 1:10. Therefore ten fold dilutions were made for inoculation on MEYP agar plates and incubated at 37°C for 24 h. Characteristic B. cereus colonies (large light pink colonies, 3 to 7 mm diameter with irregular border, flat surrounded by a zone of opacity) were picked up and identified as B. cereus by biochemical tests as described by Cowan (1974), Gibson and Gordon (1974) and Norris et al. (1981). Biotyping The scheme proposed by Jha and Narayan (1995) was followed for typing the heat resistant B. cereus field isolates recovered from fermented foods on the basis of fermentation of three ammonium salt sugars viz xylose, salicin and cellobiose. Out of 120 samples examined 25 (20.83%) were found contaminated with B. cereus. Curd and soya sauce were least contaminated in comparison to dosa premix, rice beer and idli. The incidence of B. cereus in dosa premix, rice beer, idli, curd and soya sauce were 37.50, 33.33, 25.00, 4.16 and 4.16 percent, respectively (Table 1). The normal deviate test indicated significance difference between dosa premix and curd, dosa premix and soya source, rice beer and curd, rice beer and soya sauce. But no significant difference was found between idli and other fermented foods (Table 1). Area-wise distribution of B. cereus in different food items has also been studied. The incidence of B. cereus in dosa premix were 33.38, 33.33, 50.00 and 33.33 percent, rice beer 50.00, 33.33, 16.66 and 33.33 percent, idli 33.33, 16.66, 33.33 and 16.66 percent, curd 0.00, 16.66, 0.00 and 0.00 percent and soya sauce 0.00, 0.00, 16.66 and 0.00 percent from Dhurwa, Hinoo, Main Road, Ranchi, Kanke and Kanke Road, respectively.
In present study the principal constituent of all the fermented food is rice, which has been proved as one of the important sources of B. cereus (Gilbert and Parry, 1977, Kamat et al., 1989 and Willayat (1997). Willayat (1997) observed 7.29 percent heat resistant Bacillus strain's in rice which survived boiling at 100ºC for 20 minutes. It is evident from the above results that autoclaving of foods may not be safe though it reduces the counts drastically. Attempts were made to type the field isolates of B. cereus from fermented foods as per the biotyping scheme of Jha & Narayan (1995). Out of 25 isolates recovered from field samples 21 (84.00%) fermented xylose, 2 (8.00%) salicin and 2 (8.00%) cellobiose. In the present study, the isolates of B. cereus were grouped in 8 out of 9 theoretically possible biotypes. Eighteen of the 25 (72.00%) isolates were typed as biotype 4. The other biotypes present in the fermented foods were biotypes 1 (16.00%), 2 (4.00%), 5 (4.00%) and 8 (4.00%). Biotypes 2, 5 and 8 had lowest number of isolates (1, 1 and 1). The distribution of heat resistant B. cereus isolates according to biotypes is presented in Table 2. Majority of the isolates of dosa premix, rice beer, idli and curd fell in biotype 4. Some isolates of Dosa premix, rice beer and soya sauce also fell in biotypes 1, 2, 5 and 8 respectively. The percentage typeability of different biotypes and their distribution on the basis of source of isolates are summarized in Table 3. The percentage of biotypes 1,2,4,5 and 8 were 16.00, 4.00, 72.00, 4.00 and 4.00 percent, respectively agreement.
The present findings are in close to the findings of Singh (1990) who reported that most of the Indian strains fermented xylose contrary to the European strains which did not ferment xylose (Gilbert et al., 1981). Jha (1992) also reported 35.71 and 47.62 percent isolates as xylose and salicin positive. Motina (1997) reported that 29.62 percent isolates fermented xylose whereas 8.64% fermented salicin. Willayat (1997) observed 34.21% isolates fermented xylose whereas 51.31% fermented salicin. Jha (1992) while studying the distribution of 42 isolates of B. cereus according to source could find 3 isolates in biotype 7 and one in biotype 5. Motina (1997) reported biotypes 1, 2, 4, 5, 6, 7 and 8 from milk and milk products among which biotypes 1, 2 and 6 were most common. Willayat (1997) reported biotypes 7, 6, 5 and 2 from raw rice. Top Tables | Table 1: Contamination of fermented foods with heat resistant Bacillus cereus
| | Sl. No. | Types of samples | No. of samples | Positive | Percent positive |
| | 1 | Dosa premix | 24 | 9 | 37.50a | | 2 | Rice beer | 24 | 8 | 33.33a | | 3 | Idli | 24 | 6 | 25.00ab | | 4 | Curd | 24 | 1 | 4.16b | | 5 | Soya sauce | 24 | 1 | 4.16b | | Total | 120 | 25 | 20.83 |
| | ≥ 1.96*, ≥ 2.56** |
| | | Table 2: Distribution of heat resistant Bacillus cereus isolates according to biotypes
| | Biotypes | FERMENTED FOOD | Total |
| | Dosa premix | Rice beer | Idli | Curd | Soya sauce |
| | 1 | 3 (33.3) | 1 (12.5) | — | — | — | 4 | | 2 | — | 1 (12.5) | — | — | — | 1 | | 3 | — | — | — | — | — | — | | 4 | 6 (66.6) | 5 (62.5) | 6 (100) | 1 (100) | — | 18 | | 5 | — | — | — | — | 1 (100) | 1 | | 6 | — | — | — | — | — | — | | 7 | — | — | — | — | — | — | | 8 | — | 1 (12.5) | — | — | — | 1 | | Total | 9 | 8 | 6 | 1 | 1 | 25 |
| | Figures in parentheses indicate percentage. |
| | | Table 3: Distribution of biotypes on the basis of source of isolates
| | Sl. No. | Source of isolates | Biotypes | Total isolates |
| | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 |
| | 1 | Dosa premix | 3 | — | — | 6 | — | — | — | — | 9 (36.00) | | 2 | Rice beer | 1 | 1 | — | 5 | — | — | — | 1 | 8 (32.00) | | 3 | Idli | — | — | — | 6 | — | — | — | — | 6 (24.00) | | 4 | Curd | — | — | — | 1 | — | — | — | — | 1 (4.00) | | 5 | Soya sauce | — | — | — | — | 1 | — | — | — | 1 (4.00) | | Total | 4 (16.00) | 1 (4.00) | — | 18 (72.00) | — | — | — | 1 (4.00) | 25 |
| | Figures in parentheses indicate percentage. |
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