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M-enterococcus (ME) agar
524
Handbook of Culture Mediafor Food Microbiology, J.E.L. Corry et al. (Eds.) 9 2003 Elsevier Science B.V. All rights reserved
M-Enterococcus (ME) agar This monograph has been assessed by members of the IUMS-ICFMH Working Party on Culture Media and given 'Approved' status. Description and history In 1957 Slanetz and Bartley described this improved version of the original medium of Slanetz et al. (1955). The medium relies upon the selective inhibitory properties of sodium azide and the incorporation of tetrazolium which most organisms growing on this medium will reduce to some extent under the conditions provided. Although devised originally for use with membrane filters, the medium can also be used for direct plating. Selectivity is increased by incubation at 37~ for 4 h followed by 44 + 1~ for 44 h.
Composition (grams) Tryptose Yeast extract Glucose Di-sodium hydrogen orthophosphate .2H20 Sodium azide 2,3,5-Triphenyltetrazolium chloride Agar Distilled or deionized water
20.0 5.0 2.0 4.0 0.4 0.1 10.0 1000.0
Preparation The first five ingredients are dissolved in the water and the pH value adjusted to 7.2. The agar is then added and the solution heated sufficiently to dissolve the agar. When cooled to about 50~ add 1 ml of 1% filter-sterilized triphenyltetrazolium chloride solution per 100 ml of molten medium. Do not autoclave or overheat this medium.
Physical properties Appearance pH
Pale straw. 7.2 + 0.2
525
Shelf life Ready to use medium
7 days at 4 + 2~
Inoculation method for samples Surface spreading over whole plate using 0.1 ml per pre-dried 9 cm plate.
Incubation method At 37~ for 48 h or at 37~ for 4 h followed by 44 + 1~ for 44 h, in air.
Reading of results and interpretation Round, pink to dark maroon-coloured colonies, 0.5-3 mm diameter, are considered to be Lancefield Group D streptococci (including enterococci).
Quality assessment (i) Productivity Test strains
Inoculation method
(ii) Selectivity Test strains
Enterococcus faecalis NCIMB 50030 Enterococcusfaecium NCIMB 50032 Modified Miles-Misra, spiral plating or streaking/ ecometry.
Lactococcus lactis ssp. lactis NCIMB 50058 Escherichia coli NCIMB 50034
Supplementary strains
Bacillus cereus NCIMB 50014 Staphylococcus aureus NCIMB 50080
Inoculation method
Modified Miles-Misra, spiral plating or streaking/ ecometry.
(iii) Characteristic appearance of colonies Round, pink to dark maroon-coloured colonies, 0.5-3 mm in diameter.
References Burkwall, M.K. and Hartman, EA. (1964) Comparison of direct plating media for the isolation and enumeration of enterococci in certain frozen foods. Appl. Microbiol. 12, 18-23. Slanetz, L.W. and Bartley, C.H. (1957) Numbers of enterococci in water, sewage and faeces determined by the membrane filter technique with an improved medium. J. Bacteriol. 74,
526 591-595. Slanetz, L.W., Bent, D.E and Bartley, C.H. (1995) Use of membrane filter technique to enumerate enterococci in water. Publ. Hlth. Reports 70, 67-72. Taylor, E.W. and Burman, N.P. (1964) The application of membrane filtration techniques to the bacteriological examination of water. J. Appl. Bacteriol. 27, 294-303.
Handbook of Culture Mediafor Food Microbiology, J.E.L. Corry et al. (Eds.) 9 2003 Elsevier Science B.V. All rights reserved
M-Enterococcus (ME) agar This monograph has been assessed by members of the IUMS-ICFMH Working Party on Culture Media and given 'Approved' status. Description and history In 1957 Slanetz and Bartley described this improved version of the original medium of Slanetz et al. (1955). The medium relies upon the selective inhibitory properties of sodium azide and the incorporation of tetrazolium which most organisms growing on this medium will reduce to some extent under the conditions provided. Although devised originally for use with membrane filters, the medium can also be used for direct plating. Selectivity is increased by incubation at 37~ for 4 h followed by 44 + 1~ for 44 h.
Composition (grams) Tryptose Yeast extract Glucose Di-sodium hydrogen orthophosphate .2H20 Sodium azide 2,3,5-Triphenyltetrazolium chloride Agar Distilled or deionized water
20.0 5.0 2.0 4.0 0.4 0.1 10.0 1000.0
Preparation The first five ingredients are dissolved in the water and the pH value adjusted to 7.2. The agar is then added and the solution heated sufficiently to dissolve the agar. When cooled to about 50~ add 1 ml of 1% filter-sterilized triphenyltetrazolium chloride solution per 100 ml of molten medium. Do not autoclave or overheat this medium.
Physical properties Appearance pH
Pale straw. 7.2 + 0.2
525
Shelf life Ready to use medium
7 days at 4 + 2~
Inoculation method for samples Surface spreading over whole plate using 0.1 ml per pre-dried 9 cm plate.
Incubation method At 37~ for 48 h or at 37~ for 4 h followed by 44 + 1~ for 44 h, in air.
Reading of results and interpretation Round, pink to dark maroon-coloured colonies, 0.5-3 mm diameter, are considered to be Lancefield Group D streptococci (including enterococci).
Quality assessment (i) Productivity Test strains
Inoculation method
(ii) Selectivity Test strains
Enterococcus faecalis NCIMB 50030 Enterococcusfaecium NCIMB 50032 Modified Miles-Misra, spiral plating or streaking/ ecometry.
Lactococcus lactis ssp. lactis NCIMB 50058 Escherichia coli NCIMB 50034
Supplementary strains
Bacillus cereus NCIMB 50014 Staphylococcus aureus NCIMB 50080
Inoculation method
Modified Miles-Misra, spiral plating or streaking/ ecometry.
(iii) Characteristic appearance of colonies Round, pink to dark maroon-coloured colonies, 0.5-3 mm in diameter.
References Burkwall, M.K. and Hartman, EA. (1964) Comparison of direct plating media for the isolation and enumeration of enterococci in certain frozen foods. Appl. Microbiol. 12, 18-23. Slanetz, L.W. and Bartley, C.H. (1957) Numbers of enterococci in water, sewage and faeces determined by the membrane filter technique with an improved medium. J. Bacteriol. 74,
526 591-595. Slanetz, L.W., Bent, D.E and Bartley, C.H. (1995) Use of membrane filter technique to enumerate enterococci in water. Publ. Hlth. Reports 70, 67-72. Taylor, E.W. and Burman, N.P. (1964) The application of membrane filtration techniques to the bacteriological examination of water. J. Appl. Bacteriol. 27, 294-303.