How To Counting Bacteria in Milk

[ninive]

Hello and a happy new year,

I have a problem with a bacteria count because the agars got moldy because of unsterile drigalski applicator I suppose.

UHT-milk and fresh milk was testet.

Dilution series for both (with water) was
1:1
1:10
1:100
1:1000
1:10000

Both was testet on (german names) Chinablau-Lactose agar and
Bromthymolblau-lactose agar.
Free translation soluble blue agar and bromothymol blue agar. (not sure)

Could someone tell me what number of colonies are to estimate in each dilution and how the colors should change? Would be very nice if someone does know this, thanks.
The milk used was just milk from the supermarket, reasonable values are enough because they are just for a graph.

Even fantastic would be an explanation, so that I could desing a resoable curve.

Goodbye and thanks for helping,
ninive