dune 30, LO4E,.

My. Norain Gross,

Paul~Lewis Laborator4Les, Inc.,
Milwaukee, isconsin.

Dear Xr. Gross,

Thank you very much for your shipment of tetrazolium which arrived a
few days ago. Having made some studies on effective concentrations, I see
now thet this wlll be a very large quantity, indeed, as there seems to be
no point in using more than 100 ag./l.

My first letter to Dr. Oesting contains all essential points of a
possible procedure, using TZ for the diagnosis of Salmonella. My first
results with the formula: Lactose 10 g., Bacto Casamino Acids 10 g., Yeast
Extract 1 g., Agar 16 g. and TZ 50 mg. were very encouraging, and it looked
as if a sharp different&ation between lactose-fermenters and non-fernenters
could be made on that basis. Since our conversation, however, I have observed
that this particular medium does not distinguish between slow and non-fermenters,
and it will have to be altered. Further experizents will bs needed to deter=

and nitrogen
mine what the optimal secohdary carbon sources and buffering capacity should
be to give the maximum contrast. In addition, some preliminary trials on
stool specimens point cut the need of adding an inhibitor, such as brilliant
green, that will suppress coliforms. A few preliminary trials suggest that
brilliant green will not be incompatible with the pH-sensitive TZ reaction,

I should point out that my first interest was to d-velop a medium that
would be useful in the selection of lactose-negative mtants, and that a pos-

sible application to stool analysis is entirely secondary. I am not going to
e

~2- N. Gross,Paul-Lewis. 6/30/48.

be able to devote my full time to this problem. Therefore, if your people
would like to out in some work on developing this preparation, I would cer
tainly be pleased. I would request only « suitable acknowkedgaent and prompt
publication, However, I will be continuing to try to find a suitable combi-~
nation for the detection of mutants, and I am yuite sure that this will be
directly appiicable to the mum less esoteric question of enteric diagnosis,
Please give Dr. Oesting my best regards, I indicated in our talk that
I would be very grateful for any hints on where I could get sertain compounds.
These include b-D-galactosides, §-l-srabinosides, b-D-fucosides and b-D~galacturon.-
sides. I'm not vary optimistic about it, but it's worth asking.

I am very sorry that the material is not in a more satisfactory state,
but I will be very happy to report to anyone who is interested on my progress,
er to consult with them on its further development.

Yours sincerely,

Joshua Lederberg
Assistant Professor of Genetics,