CLED MEDIUM Code: CM301
Recommended for diagnostic urinary bacteriology. The medium supports the growth of all urinary potential pathogens giving good colonial differentiation and clear diagnostic characteristics.
Formula gm/litre Peptone 4.0 `Lab-Lemco' powder 3.0 Tryptone 4.0 Lactose 10.0 L-cystine 0.128 Bromothymol blue 0.02 Agar 15.0 pH 7.3 + 0.2
Directions Suspend 36.2g in 1 litre of distilled water. Bring to the boil to dissolve completely. Sterilise by autoclaving at 121° C for 15 minutes. Mix well before pouring.
Description A dehydrated Cystine-Lactose-Electrolyte Deficient (CLED) medium made to the formula described by Mackey and Sandys
1. As a modification for urinary bacteriology of the Electrolyte Deficient Medium developed by Sandys.
2. This medium is recommended for urinary bacteriology, supporting the growth of all urinary pathogens and giving good colonial differentiations and clear diagnostic characteristics. The presence of important contaminants such as diphtheroids, lactobacilli and micrococci is also clearly elicited, giving an indication of the degree of contamination. In the laboratory CLED Medium provides a valuable non-inhibitory diagnostic agar for plate culture of urinary organisms. It is electrolyte deficient to prevent the swarming of Proteus species. The medium has been used successfully in the Dip-inoculum Transport Medium technique (Mackey and Sandys1,3). A variant of this technique has been described by Guttman and Naylor 4 who employed media-coated slides. These techniques overcome false bacteriological results associated with delay in the transport of the specimens of urine to the laboratory and permit a clinically accurate routine differential viable count. They are, therefore, suitable for both general practitioner and hospital work including the screening of ante-natal specimens for symptomless bacteriuria. For full details, the original papers should be consulted.
Growth Characteristics on CLED Agar (18 hours Incubation) E. coli - yellow, opaque colonies with a slightly deeper coloured centre about 1.25mm diam. (Non- lactose fermenting strains - blue colonies.)
Klebsiella species -extremely mucoid colonies varying in colour from yellow to whitish-blue.
Proteus species - translucent blue colonies usually smaller than E. coli. Salmonella species - flat blue colonies.
Ps. pyocyanea - green colonies with typical matt surface and rough periphery.
E. faecalis - Yellow colonies about 0.5mm diameter.
Staph. aureus - deep yellow colonies about 0.75mm diameter, uniform in colour. Coagulase negative Staphylococci - pale yellow or white, more opaque than E. faecalis, often with paler periphery.
Corynebacteria - very small grey colonies.
Lactobacilli - similar to corynebacteria but with a rougher surface.
Storage conditions and shelf life. Store the dehydrated medium below 25° C and use before the expiry date on the label. Store the prepared medium at 2-8° C. Quality Control Positive control: Proteus mirabilis ATCC1 10975 Staphylococcus aureus ATCC1 25923 Negative control: Uninoculated medium Precautions Shigella species may not grow on electrolyte-deficient medium.
References 1 Mackey J. P. and Sand G. H. (1966) B.M.J. 1. 1173. 2 Sandys G. H. (1960) J. Med. Lab. Techn. 17. 224. 3 Mackey J. P. and Sandys G. H. (1965) B.M.J. 2. 1286-1288. 4 Guttman D. and Naylor G. R. E. (1967) B.M.J. 2. 343-345. CLED MEDIUM (WITH ANDRADE INDICATOR) Code: CM423 A modification of the CLED Medium of Mackey and Sandys (B.M.J. 1966, 1, 1173) containing Andrade Indicator to enhance the differentiation of colony characteristics. Formula gm/litre Peptone 4.0 `Lab-Lemco' powder 3.0 Tryptone 4.0 Lactose 10.0 L-cystine 0.128 Bromothymol blue 0.02 Andrade Indicator 0.1 Agar 15.0 pH 7.5 + 0.2 Directions Suspend 36.2g in 1 litre of distilled water. Bring to the boil to dissolve completely. Sterilise by autoclaving at 121° C for 15 minutes. Mix well before pouring. Culture Media November 1998 2-77