Cat. no. Z53 RSU Broth, 15x145mm Tube, 0.5ml 10 tests/kit


Hardy Diagnostics RSU Broth is a minitube culture, used as a rapid sucrose and urea test for the presumptive identification of Corynebacterium jeikeium .


Clinical significance of Corynebacterium jeikeium has been well documented as the etiologic agent in several serious infections including sepsis, prosthetic valve endocarditis, meningitis and peritonitis; predominately in immunosuppressed patients. (4) Because skin colonization and superficial infections represent significant clinical concern in these patients, expeditious differentiation of this organism from morphologically similar commensal organisms is beneficial. (5) Several differentiating methods have been proposed for the presumptive identification of C . jeikeium including enhanced growth on lipid containing media and resistance to multiple antibiotics. However, not all isolates exhibit the typical resistance patterns and several less pathogenic organisms utilize lipids. Methods for identification including API ® 20S are available but costly, time consuming, and require a large inoculum. (3)

The use of the minitube RSU Broth culture incorporates two key biochemical tests; that of urease production and sucrose utilization. Using a minimal amount of inoculum, a presumptive identification of C. jeikeium from other aerobic, pleomorphic, catalase-positive, gram-positive bacilli (or non- C. jeikeium ) may be made in three hours or less. (3)


Ingredients per liter of deionized water:*

Sucrose 7.0gm
Urea 2.0gm
Proteose Peptone No. 3 1.0gm
Tween ® 80 0.4gm
Bromothymol Blue 44.0mg
Phenol Red 25.0mg

Final pH 7.0 +/- 0.2 at 25ºC.

* Adjusted and/or supplemented as required to meet performance criteria.


Upon receipt store at 2-8ºC. away from direct light. Media should not be used if there are any signs of deterioration (dehydration or discoloration), contamination, or if the expiration date has passed.



Specimen Collection: This product is not intended for primary isolation of patient specimens. This product is used in conjunction with other biochemical tests to identify cultures of isolated organism.

Method of Use: Using a visible, but relatively light inoculum, (2-3 colonies) from a 24 hour culture of well isolated organisms, inoculate the RSU Broth. Colonies must be obtained from a non-glucose containing media such as Tryptic Soy Agar with 5% Sheep Blood (Cat. no. A10). Incubate at 35ºC. for three hours, reading the color of the RSU Broth hourly.


A positive urease production test is indicated by the media turning a bright purple to violet color. A positive sucrose utilization test is indicated by the media turning bright yellow in color. Broth that shows no color change or a only slight yellowing in three hours is considered negative for both urease and sucrose.

A presumptive identification of C. jeikeium is indicated by a negative sucrose and urease reaction. If the isolate produces no color change in three hours, it is a presumptive identification for C. jeikeium . A color change to bright purple or yellow in three hours of incubation is evidence that the isolate is non- C. jeikeium .


Colonies of the isolated diphtheroid must be taken from a glucose-free, non-inhibitory media. The presence of this sugar may interfere with the sucrose utilization reaction.

Heavy inoculation of the media may result in false-positive reactions due to the slight acidification of the medium produced by the large inoculum.

Aerobic, small, gray, colonies identified as gram-positive, coccobacilli to short rods that are catalase-positive, sucrose-negative and urease-negative may be presumptively identified as Corynebacterium jeikeium . Other biochemical and susceptibility tests are recommended for complete identification.

Results of a recent study using this method reported 100% sensitivity and 90% specificity. (3)


Standard microbiological supplies and equipment such as loops, other culture media, swabs, applicator sticks, incinerators, and incubators, etc., as well as serological and biochemical reagents, are not provided.


Test Organisms Inoculation Method* Incubation Results
Time Temperature Atmosphere
Proteus mirabilis
ATCC ® 12453
E 3hr 35°C Aerobic Positive urease: Media turns bright purple/violet
Enterobacter cloacae
ATCC ® 23355
E 3hr 35°C Aerobic Positive sucrose: Media turns bright yellow
Corynebacterium jeikeium
ATCC ® 43734
E 3hr 35°C Aerobic Negative urease and sucrose: Yellowish-brown or no color change seen

User Quality Control


RSU Broth should appear clear, and yellowish-orange to yellowish-brown in color.

P. mirabilis growing in RSU Broth

Proteus mirabilis (ATCC ® 12453) growing in RSU Broth (Cat. no. Z53). Incubated aerobically for three hours at 35ºC. The purple color change was indicative as a positive for urease reaction.

E. cloacae growing in RSU Broth

Enterobcater cloacae (ATCC ® 23355) growing in RSU Broth (Cat. no. Z53). Incubated aerobically for three hours at 35ºC. The yellow color change was indicative as positive for sucrose utilization.

C. jeikeium growing in RSU Broth

Corynebacterium jeikeium (ATCC ® 43734) growing in RSU Broth (Cat. no. Z53). Incubated aerobically for three hours at 35ºC. The yellowish-brown color change was indicative as negative for urease activity and sucrose utilization. Growth with turbidity but without color change also indicates this reaction pattern.

RSU Broth

Uninoculated tube of RSU Broth (Cat. no. Z53).


1. Jorgensen., et al. Manual of Clinical Microbiology, American Society for Microbiology, Washington, D.C.

2. Anderson, N.L., et al. Cumitech 3B; Quality Systems in the Clinical Microbiology Laboratory, Coordinating ed., A.S. Weissfeld. American Society for Microbiology, Washington, D.C.

3. Cartwright, C.P. and F. Stock, et al. 1993. Rapid method for presumptive identification of Corynebacterium jeikeium. J. Clin. Microbiol.; 31: 3320-3322.

4. Coyle, M.B. and B.A. Lipsky. 1990. Coryneform bacteria is infectious diseases: clinical and laboratory aspects. Clin. Microbiol. Review.; 3:227-246.

5. Larson, E.L. and K.J. McGinley, et al. 1986. Skin colonization with antibiotic resistant (JK group) and antibiotic sensitive lipophilic diphtheroids in hospitalized and normal adults. J. Infect. Dis.; 153:701-706.

API is a registered trademark of bioMeriuex, France.
ATCC is a registered trademark of the American Type Culture Collection.
Tween is a registered trademark of ICI Americas, Inc.