Unmatched Selectivity for
Salmonella Isolation with XLT-4 Agar
Eliminate Proteus Swarming and Reduce False-Positive Workups in High Microbial Load Food & Environmental Samples.
When safety standard compliance is on the line, background flora shouldn't stand in your way. Hardy Diagnostics' XLT-4 (Xylose-Lysine-Tergitol 4) Agar delivers superior suppression of non-Salmonella organisms such as Proteus, giving your QA/QC team clear, unambiguous target differentiation in half the confirmation time compared to HE or XLD agars.[1,2]
Prepared Culture Media
Pre-poured, reliable, and available in flexible formats, XLT-4 agar plates give you immediate
testing capability without the overhead of manual batch preparation.
Dehydrated Culture Media
Prepare exact batch volumes in-house with quick-dissolving dehydrated media built for
long shelf life and consistent performance. Available in four versatile size options:
XLT-4 Supplement (Tergitol 4), Cat. no. B0901, is required for this dehydrated culture medium.
How does XLT-4 Agar inhibit swarming organisms like Proteus?
XLT-4 Agar contains Tergitol 4 (Niaproof 4), an anionic surfactant that selectively inhibits Gram-positive bacteria and suppresses troublesome Gram-negative organisms—specifically preventing the swarming overgrowth of Proteus spp. that often obscures colonies on standard media like XLD.
What is the expected appearance of colonies on XLT-4 Agar?
After 18-24 hours incubation, Salmonella colonies appear as black or black-centered with a yellow periphery. If the plates are incubated further, the colonies will become entirely black, or pink to red with black centers.(1-2) Salmonella strains that do not produce H2S appear pink-yellow on XLT-4 Agar. Citrobacter colonies will appear yellow without evidence of blackening. Escherichia coli and Enterobacter aerogenes colonies that are not inhibited will be yellow with no blackening. Growth of Proteus, Providencia, Pseudomonas, Alteromonas putrefaciens, Yersinia enterocolitica, and Acinetobacter calcoaceticus are partially to completely inhibited on XLT-4 Agar.
Is XLT-4 Agar a direct replacement for XLD or HE Agar in regulated testing?
No. Standard regulatory methods (including FDA-BAM and USDA-FSIS MLG) do not currently list XLT-4 as a primary official medium. XLT-4 is designed to be used as a supplemental isolation medium in tandem with your current regulatory-mandated media to eliminate background interference and reduce false positives in high-risk, heavily contaminated matrices.
References:
1. Miller, R.G., Tate, C.R., Mallinson, E.T., & Scherrer, J.A. (1991). "Xylose-lysine-tergitol 4: an improved selective agar medium for the isolation of Salmonella." Journal of Food Protection, 54(11), 842-849.
2. Tate, C.R., Miller, R.G., & Mallinson, E.T. (1990). "Evaluation of xylose-lysine-tergitol 4 (XLT4) agar for the isolation of Salmonella enteritidis from poultry environmental samples." Poultry Science, 69(12), 2221-2226.