# alcohol in antibiotic solutions?

Dr. Hiranya S. Roychowdhury hroychow at nmsu.edu
Tue Oct 31 23:43:59 EST 2000

```Microbicidal conc. of etoh is 40-70%.
By your admission, the conc. of etoh in the medium would be 0.01%. At even
room temp, 25uL etoh should not take long to evaporate off the medium.

BTW, could you please illuminate me about the "molarity" of 200proof EtOH?
May be then I will get the "50mM" figure for etoh in the medium.

Also, I was wondering what would happen if I had just 100uL of the 20mg/mL
soln of Cm in EtOH? Should I still be adding 25uL to 10mL of LB? Should I
add 2.5uL to 1mL of LB? Should I make up 900uL of the 20mg/mL soln of Cm in
EtOH to bring the volume of the antibiotic stock solution to 1mL? It is
rather confusing ...

At 09:49 PM 10/30/00 -0600, Emir wrote:
>Let's just calculate. Say, you have 1 ml of 20mg/ml soln of Cm in EtOH. You
>add 25ul of that soln to 10ml of LB to make up to 50ug/ml Cm. Your finally
>EtOH concentration in the medium is ~50mM then. How miniscule it is? 2g/l of
>glucose for example is just about 10mM. The only good thing about it is that
>to my understanding E.coli cannot utilize EtOH when grown aerobically.
>Still, the presence of 50mM alcohol should have a certain effect on, say,
>the length of the lag phase when you re-inoculate your o/n culture into
>fresh LB-antibiotic medium.
>
>Emir
>

Dr. Hiranya Sankar Roychowdhury
College Asst. Prof.
Molecular Biology,
Dept. of Chemistry & Biochemistry
Box 30001 - 3MLS
New Mexico State University
Las Cruces, NM 88003

Lab: (505) 646 4722
Office: (505) 646 8256
hroychow at nmsu.edu

---

```