E. coli is "lactose positive/purple/flat," Klebsiella is "lactose
positive/pink-purple/mucoid," Enterobacters are "pink/mucoid/yellowish
sometimes" etc. In other words, you just get used to how they look. I
probably would have a hard time at first distinguishing colonies on EMB
but I would adjust eventually.

If you hold Mac up to the light you can see subtle differences in shades
of purple and pink, and also see differences with non-lac fermenters.
EMB is a darker medium. I don't know if you'd get the same effect. In
mixed cultures this is a really helpful thing to do.

Even if E. coli has an iridescent sheen, you don't call it from that, do
you? Don't you run some sort of biochemical to prove it? We use GNI+
cards and get an ID in 3-5 hours. We set up positive urine ID/sensis
first thing on day shift AND second shift (we also read urines arriving
after 3 p.m. on second shift) so we sign out positives by the end of the
shift (if we're lucky and if they're pure). So, how does the sheen come
into play when reporting and identifying? I've been told the reason we
do full biochemicals is that one cannot charge an ID code unless one
does at least three tests to prove an organism is what it is. Indole and
sheen, indole and citrate (what we used to do at another employer)
doesn't cut it for charging a full ID any more. You can, I suppose, call
it presumptive EC on a report with a sheen.

So, it's just because of old habits? I'll admit, my old habit is using
Mac.

Judy Dilworth, M.T. (ASCP)
Microbiology