Alright, on this video we're going to go ahead and do a series of four urines. Usually on my videos I just do one culture at a time, but I'm going to go ahead and do four of these. The first one is just going to be kind of a gram-negative urine, the next one is going to be a gram-positive urine, and the last two will be mixed cultures that have more than one colony type.
Okay, so generally when a urine is set up, It's set up on two plates. We have a just a regular 5% sheep blood plate and then we have a bi plate with McConkeys and CNA. And when this is set up it's used with a calibrated loop. So you can either have a calibrated loop that is 1 100th or 1 1000th of a milliliter.
And the reason why we do that is because... the doctor needs to know if, you know, just kind of get a general idea of how much bacteria is there. So if we're using a calibrated loop, meaning that it's delivering a fixed amount, a predictable amount, then if there's 10,000 colonies as opposed to 100,000 colonies, well, that's important information for the doctor to know as far as treating the patient. Okay, now just on that note of... what I said about using the calibrated loop, just to kind of give you some guidelines.
Urine cultures are usually reported out with a number. Now, on other of my videos, you'll hear me saying rare, few, moderate, many to describe the amount of bacteria, but with urines, we use a specific number. And, you know, we're not going to go ahead and count all the colonies on a plate so rather we use ranges like under 10,000, 10 to 20, 20 to 50, 50 to 100, greater than 100,000 and the label that we use with that number is greater than 100,000 colony forming units per milliliter or CFU per ml.
So you're going to see that those terms used with urine cultures. All right, let's go ahead and take a look at our plates here. And the reason why we have three different types is now we know that with my students, I insist that they have a clear understanding of media because media can give you a lot of information about what, excuse me, I'm recovering from the flu, a lot of information about what is growing.
So we have a CNA McConkie's plate. So we know that CNA is a selective differential plate. And selective means that it is selective for gram-positive organisms, including yeast. And it inhibits gram-negative organisms.
Now, it's differential because with a blood plate, one of the differential features of it is hemolysis. Okay. Now, let's go ahead and take a look at our McConkey's. Now, McConkey's is also a selective differential plate.
Now, selective, it's selective for gram-negative organisms. And when I say gram-negative, I'm talking about the very healthy Enterobacteriaceae and Pseudomonas, as opposed to the more fastidious Haemophilus. It's differential. because it's used, either a colony will be pink or it will be clear, and that's based on lactose fermentation. So whenever we look at colonies on maconkeys and there's growth, we should always be commenting on whether it's lactose positive or lactose negative.
Now in this particular urine culture, there's nothing growing on the CNA, so that tells me that we don't have any gram-positive organisms growing here. And it looks like we only have one colony type on the McConkeys and they're pink. So that means they're lactose fermenters, lactose positive. All right.
Now the other plate is just a sheep blood plate. And the reason that is here is that's the plate that we use to determine, to count, to make our count about how many different, the count of colonies. Now your calibrated loop is basically used. On this and the two other plates, but this is the one we use for count. Okay, now I am not going to count all these because there are just too many to count.
So this would be greater than 100 colonies, which you would report out as greater than 100,000 CFUs. per ml. Now another thing we have to take into consideration is how we're going to work this thing up. And bearing that in mind, because you know there are different ways that urines can be collected, they can be collected for example as a clean catch or a midstream.
Now that method tends, lends itself to being the most, the one that gets contaminated most often. But there are also other methods, for example indwelling catheter. or even a suprapubic aspirate. But generally speaking, if we have a urine that is from a catheterized or a suprapubic aspirate, we're going to use a much lower threshold as far as working up an organism.
Because basically when we're reading urines, what we're trying to tell the doctor when we're reading the numbers, if there is contamination, colonization, or infection. And, you know, in this particular patient, I would say it's obviously infection. It's greater than 100,000 of one particular organism. And that, actually, that particular organism looks like a classic organism that causes UTIs, urinary tract infections. All right.
Now, a catheterized specimen, if it's... you know, 10,000. Now that maybe that's significant. That's, it all depends on the guidelines or the standard operating practice or SOP in the facility that you're working in. You must follow the SOP and use the guidelines set out in there as far as like what you're going to work up.
So let's move on here. So what do we do with this plate? As I said, we have greater than a hundred thousand of a novel. This organism on here is the same one on here.
So, and this particular organism looks very much like E. coli, which is the number one cause of urinary tract infections, especially in women. All right. So whenever we have a gram-negative rod, the first test that we always do is an oxidase.
And remember, we don't do the oxidase test off a plate, off a McConkie's plate, because... It's a color-based test, and if you take it off here, the colonies are already colored, so it may affect how you read that test. So we'd go ahead and do that test off here. And guessing that it's going to be oxidase negative, this would go to the instrument for identification and susceptibility testing. All right, so we want to get this information to the doctors, so we want to send out a preliminary report.
So the preliminary report. Preliminary report for this particular culture is going to be greater than 100,000 CFUs per ml of probable E. coli. Identification and susceptibility testing to follow.
All right, let's go ahead and move on here to the next urine culture. Okay, that's our sheep blood. Here's our bi-plate and we have CNA and McConkeys.
Now, in contrast to the last culture type that we just did, this one has growth on the CNA and nothing on the McConkeys. So what does that tell us? Well, as I said in the previous, talking about the previous culture, is that CNA is selective. And it's selective for gram-positive organisms and yeast.
So. What we need to determine at this point, first of all, I'm going to have a little bit closer look just to make sure that we're dealing with a single colony type and it's not a mixed culture. So looking at this, it's probably kind of hard for you to see.
To me, it looks like it's just one colony type. So that's good. That means that we can go ahead and proceed with identifying this organism.
Okay. All right. Now, doing our count off the sheep blood, it looks like, again, Like the last culture, these are definitely smaller colonies, but I would say, again, we have greater than 100,000 colonies. So regardless of whether it's a clean catcher or it's a catheterized urine, we're going to go ahead and work up this organism.
So I don't want to go too much into the workups in these videos. It's more about just reading the plates. But I have to jump into this a little bit. So if we talk about gram-positive, you know, organisms that are pathogens in urine, basically the three most common are Staph saprophyticus, Enterococcus, and yeast, or Canada albicans. So at this point, now, For you looking at this, it's just kind of a creamy whitish colony.
Now, me, I can see this. These particular colonies have what are called feet. And this is what yeast tend to do, or Canada Albican specifically tends to do. It starts to just kind of send off these little kind of, here's the colony, and you just have these little feet around.
the perimeter of the colonies. And that's what I'm seeing on this, on these, uh, colonies here. So, uh, we could probably work it up as yeast.
If I, if it were my students, um, I would make them gram stain because, you know, it's really, especially when you're new in microbiology, you really shouldn't be making assumptions just because you see a white colony and staff saprophyticus is. one of the common pathogens, you shouldn't just assume that that colony is probably Staph saprophyticus. You really should be doing a gram stain. So at this point, I would make the student do a gram stain and then work it up from there. Now me as a microbiologist, I feel pretty confident that those are yeast.
I can see the feet. I've seen many, many urine cultures with this before. I feel very confident about it. So I'm going to go ahead and work it up as if it were yeast. But once again, we want to send a preliminary report out to the doctor.
And at this point, it's going to be greater than 100,000 yeast identification to follow.