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Abstract
Summary
A total of 300 random samples including raw milk (90), soft cheeses (Kareish, Damietta and Mozzarella cheeses) 30 samples each, hard cheeses (Cheddar and Ras cheese) 30 samples each and ice cream (60) samples were collected from different localities in Assiut City. The samples were examined bacteriologically for the enumeration, isolation and identification of Staph. aureus.
Staph. aureus could be detected in 90, 60, 50, 50, 20, 43.3, 73.3, 83.3, 40 and 20% of the examined dairy farms raw milk, dairy shops raw milk , street distributors raw milk, Kareish cheese, Damietta cheese, Mozzarella cheese, Cheddar cheese, Ras cheese, small scale producers ice cream and street vendors ice cream samples, respectively, the average counts were 2.0x104, 1.6x104, 1.7x103, 2.3x105, 4.7x10, 0.3x10, 0.6x10, 4.6x103, 1.3x103 and 2.3x10 cfu/ml or g, respectively.
The incidences of Staph. aureus on Baird-Parker agar were 56.7, 26.7, 16.7, 46.7, 6.7, 40, 26.7, 56.7, 30 and 13.3% from the examined dairy farms raw milk, dairy shops raw milk , street distributors raw milk, Kareish cheese, Damietta cheese, Mozzarella cheese, Cheddar cheese, Ras cheese, small scale producers ice cream and street vendors ice cream samples, respectively, while, on Mannitol salt agar the incidences were 43.3, 40, 30, 3.3, 10, 33.3, 63.3, 46.7, 23.3 and 13.3%, respectively, on the other side, the incidences of Staph. aureus on Staphylococcus medium no. 110 were 73.3, 46.7, 20, 40, 16.7, 33.3, 60, 66.7, 20 and 16.7%, respectively.
Comparison between Baird-Parker agar, Mannitol salt agar and Staphylococcus medium no. 110 for isolation of Staph. aureus revealed that the superiority of Staphylococcus medium no. 110 and Baird-Parker agar, however, the use of one medium was not enough for isolation of Staph. aureus.
MRSA was isolated in the incidences of 46.7, 40, 13.3, 46.7, 10, 23.3, 16.7, 30, 33.3 and 10% from the examined dairy farms raw milk, dairy shops raw milk , street distributors raw milk, Kareish cheese, Damietta cheese, Mozzarella cheese, Cheddar cheese, Ras cheese, small scale producers ice cream and street vendors ice cream samples, respectively, while, VRSA was isolated in the incidences of 50, 53.3, 40, 30, 10, 16.7, 30, 36.7, 26.7 and 3.3% from the same examined samples, respectively.
Six out of twelve strains of MRSA and VRSA were isolated from raw milk (3 strains), Kareish cheese, Mozzarella cheese and ice cream samples (one strain each), and tested for enterotoxin production proved to be enteroxigenic and all the 6 strains produced enterotoxins A, while, 2 strains isolated from raw milk can also synthesis SEC and SED, in addition, the only strain isolated from Mozzarella cheese can produce SEA and SEB.
The effect of nisin on the survival of enterotoxins producing MRSA was evaluated using different concentrations of nisin (0.00, 100 and 200 IU/ml) in sterile milk which was laboratory prepared, inoculated with the previously isolated and identified MRSA to yield a concentration of 1x107 cfu/ml at room temperature (20±2ºC) and refrigerator temperature (4±2ºC). MRSA counts were demonstrated by using ORSAB and pH value were determined every twelve hours.
MRSA couldn’t be detected after 96 and 72 h in the samples of sterile milk containing nisin in concentrations of 100 and 200 IU/ml, while, the control sample MRSA still survive till the end of the 96 h of storage at room temperature. Moreover, MRSA failed to be detected after 48 and 24 h in the samples of sterile milk containing nisin in concentrations of 100 and 200 IU/ml in storage at refrigerator temperature, respectively.
Ice cream was prepared in our lab to study the effect of ground cinnamon on the survival of enterotoxins producing MRSA in addition to enterotoxin A production storage at freezing (0±2ºC) and deep freezing
(-18±2ºC) temperatures. The results showed that the advantage of using 0.6% is better than the using of 0.3% of ground cinnamon. Also, preserving ice cream in the deep freezing temperature has greater effect on the growth of MRSA.
The public health significance of the organism and the precautions, which should be taken to control this organism in dairy industry as well as the recommended sanitary measures, were also discussed.