Do your cultures grow in quantity going from 24 to 48 hours? Have any of you seen preliminaries where you've gotton more growth going from 24 to 48 hrs? If so, was it that they were always there to begin with and were not seen or was it external factors like you didn't cool them off by using freeze pack?
We incubate our bacteria samples in house and yes I've seen more growth in the 24-48 hours period compared to the first 24. Sometimes a single cfu just gets bigger and sometimes there is just more there the next day. I think they are always there and just are not visible until they have had time to grow on the paddle.
The organisms that are common in water have a slow metabolism. That makes them slow growing and hard to identify sometimes. Many of these organisms will not show any growth at 24 hours.
Chuck If I had to guess I would say that on the second day it was obvious to the lab that there was a contaminant. I think that most labs use an agar plates not paddles. When samples are plated they can be contaminated if the lab tech talks while plating. What looked worth reporting on day 1 looked entirely different on day 2. Oral flora contaminates are easlily spotted by a qualified lab tech. More rarely when using the paddles, the bacteria can grow in a clear layer all over the surface with no individual colonies.
For reasons like this I have always thought that reading plates at 24 hour was a waste of time unless troubleshooting a problem.
Bacteria can show up between 24 and 48 hours. This can be normal for some bacteria. The bacteria count will not go down. Once a colony forms, it will not go away....although, a few colonies close together may grow together to look like one colony.
Keep in mind that the rest of the world cooks the sample for 5 days. When using TSA, most bacteria will show up within 48 hours. But, some bacteria can show up after 48 hours. The lab actually will count the bacteria AFTER 48 hours but before 72 hours.
The Water Guy - Florian Services
Posts: 488 | Location: Chicago | Registered: 24 January 2005
MicroM (or anyone else ..) Could you share your thoughts on how you respond to culture paddles with a "clear layer all over the surface with no individual colonies"? I was told by Millipore that if multiple spots combine, that you count that as one colony. But if the whole paddle is covered, that would have to be considered TNTC (too numerous to count). That raises red flags because it could be over-limit. Then there is a "gray area" when maybe 1/2 or 3/4 of the paddle is covered. We have had several instances of this this past year, especially with our Millenium PRO's. We seem to have it under control now, but for a while we were doing weekly lo/hi pH cleanings and 2x/week renalin disinfections. Thanks!
<Steve>
Posted
Hey do you mind emailing me. I had the exact problem with my F-801's. Never saw this till this year also. Our last sent out cultures were ok but just took repeats with the paddles.
Hilotech2 Colony sizes can vary a lot but I am sure that I would not call that 1 colony. This is just my opinion but I have been counting colonies from dialysis for 15 years. Repeating culture with a diluted sample is your next step but I would repeat the undiluted sample as well. I am not a big fan of the millipore samplers; I think they can be hard to read. The CDC recommends at least a magnifying glass and at most a disecting microscope. When reading the sampler, use good light both direct and indirect. Colonies can be very tiny as well as covering the grid completely.
