Microbiology: Spring 2010

PacoUSA, BSN, RN · Apr 2, 2010

can someone help me with bacterial counts of food? i'm not getting it. here's my example: ten grams of ground beef are added to 90 ml of sterile water. after blending, 0.1 ml is used to inoculate a plate of gen purpose media. after 24hrs incubation, a total of 73 colonies are present on the plate.
how many cfu's were present on the plate? and how many cfu's are present in 1 g of the ground beef?
what is considered a "best plate"? or how do you arrive at that?
i am clueless and my professor yells at everyone in lab if they ask questions. we literally have to teach ourselves the entire course.
thanks!

suse, i hope i am not too late to help you ... just learned this cfu concept in lab last night. i don't know if i have a grasp on it but i will try:

cfu stands for colony forming units. for convenience the results are expressed as cfu/ml (colony-forming units per milliliter) for liquids, and cfu/g (colony-forming units per gram) for solids. in your original question, "how many cfu's were present on the plate?", i would have to assume that the answer is 73 because it asks how many on the plate. the answers for cfu's are usually expressed in terms of ml or g as stated above.

now, your question "how many cfu's are present in 1 g of the ground beef?" ...

i understand 1 gram = 1 ml, so if we add 10 grams of ground beef to 90 ml of sterile water we would then get 100 ml of blended ground beef (sounds gross i know, but bear with me ) ...

since you blended the beef in sterile water, we can assume the only bacteria present are from the beef. question says that 73 colonies are present on the plate, which came from 0.1 ml of the blended solution placed on the plate, so by conversion we can also say that for every 1 ml there are 730 colonies (move decimal one place to the right on both the 0.1 and the 73). but we have 100 ml of blended ground beef:

100 ml x 730 colonies = 73,000 cfu's

10 grams of ground beef were blended but the question asks for cfu's in 1 gram, so divide everything by 10 or just move decimal one place to the left:

10 grams becomes 1 gram

73,000 becomes 7,300

therefore in 1 g of ground beef the are 7,300 cfu's or 7,300 cfu/g or 7.3 x 10^3 cfu/g

the number seems kind of low but this is how i would have figured it out. anyone else???

as far as best plate is concerned, this just basically means the number of bacterial colonies that are best to have on a plate to count. in other words, to calculate cfu/ml or cfu/g it's best to have between 30 and 300 colonies to count (in your problem, 73 was perfect). anything above that range is too many to feasibly count and below that would be too little for calculation and might result in error.

ladyoj69 · Apr 2, 2010

Paco,

Yeah, a lot of people are doing poorly in my class too. I heard it is worse in AP 2 though, this semester, 1/2 of the class is failing with D's and F's. Sad to say, but it is the truth. There are only about 4 A's in my Micro class, and I nailed an A in AP 2 last semester. A lot of the people doing poorly are just not trying very hard. I know Micro is a very notoriously tough class, but you have to put in the time and effort to succeed. How are you ever going to be a nurse if you can't get the skills to pass a prereq class? I don't mean to bark or be mean, but I have put so much time and effort in my classes and school, I only deserve the best. I wish everyone the best of luck, but luck has only a little part in our big journey to be nurses.

Love,

Kelli

PacoUSA, BSN, RN · Apr 3, 2010

Paco,
Yeah, a lot of people are doing poorly in my class too. I heard it is worse in AP 2 though, this semester, 1/2 of the class is failing with D's and F's. Sad to say, but it is the truth. There are only about 4 A's in my Micro class, and I nailed an A in AP 2 last semester. A lot of the people doing poorly are just not trying very hard. I know Micro is a very notoriously tough class, but you have to put in the time and effort to succeed. How are you ever going to be a nurse if you can't get the skills to pass a prereq class? I don't mean to bark or be mean, but I have put so much time and effort in my classes and school, I only deserve the best. I wish everyone the best of luck, but luck has only a little part in our big journey to be nurses.
Love,
Kelli

I could not agree with you more. I don't believe for a minute that earning a good grade in any of these classes is beyond anyone's realm. Lots of people are quick to blame professors for poor teaching and they refuse to believe that the problem might just be on the other end. That's not to say that there are bad professors out there because I myself have had them! But I manage to make sure I find out what I need to have to do well. If there are people in the class able to get A's, then it's possible for YOU to get one too. It behooves me how some of my fellow students have gotten upset just because I am doing well. They ask what I got on the last test, I tell them and they are like "You bum" or "You suck" ... WTH? :confused: ... but I don't let that deter me. I am quick to argue why they are getting mad with me because a good grade is just as attainable for them as it is for me. If it's a priority for you, you will make the time for success. And I am not one of those people who is like "you're on your own" but I do offer to help them get it. I actually study with 2 classmates before every test and one of them is always whining about something nonsensical and related to poor time management. I try my best to help them understand concepts and help her use stupidity to remember things (e.g., "induce labor and feed your baby milk" = way to remember that the Lac operon is an example of an enzyme induction). But, in the long run I can't spoonfeed everything, they also have to do their part.

I work more than 40 hours a week and I manage to fit lecture, lab and study time on top of that. If something is not sinking in I make the time to seek out additional help. I was having trouble understanding DNA replication, transcription and translation so I read websites that "dummied" up the explanation for me and I watched YouTube videos until I could understand what was going on. This is what you have to do if you want something bad enough. I don't go out as much as I would like to but this all part of the sacrifices we must make for our priorities. There's always time later for that, and what a reward it always is.

Gosh, it bears repeating that if one can't get through these prereqs in one piece how is one going to manage in a nursing program (especially if it's an accelerated one)? Prereqs are nothing compared to that. The time to cultivate those strong study skills is now!

ladyoj69 · Apr 4, 2010

Paco,

I can tell you do have a passion about being a good student. You will be a successful nurse no doubt about it! Keep up the good work~ladyoj69

Suse · Apr 4, 2010

suse, i hope i am not too late to help you ... just learned this cfu concept in lab last night. i don't know if i have a grasp on it but i will try:
cfu stands for colony forming units. for convenience the results are expressed as cfu/ml (colony-forming units per milliliter) for liquids, and cfu/g (colony-forming units per gram) for solids. in your original question, "how many cfu's were present on the plate?", i would have to assume that the answer is 73 because it asks how many on the plate. the answers for cfu's are usually expressed in terms of ml or g as stated above.
now, your question "how many cfu's are present in 1 g of the ground beef?" ...
i understand 1 gram = 1 ml, so if we add 10 grams of ground beef to 90 ml of sterile water we would then get 100 ml of blended ground beef (sounds gross i know, but bear with me ) ...
since you blended the beef in sterile water, we can assume the only bacteria present are from the beef. question says that 73 colonies are present on the plate, which came from 0.1 ml of the blended solution placed on the plate, so by conversion we can also say that for every 1 ml there are 730 colonies (move decimal one place to the right on both the 0.1 and the 73). but we have 100 ml of blended ground beef:
100 ml x 730 colonies = 73,000 cfu's
10 grams of ground beef were blended but the question asks for cfu's in 1 gram, so divide everything by 10 or just move decimal one place to the left:
10 grams becomes 1 gram
73,000 becomes 7,300
therefore in 1 g of ground beef the are 7,300 cfu's or 7,300 cfu/g or 7.3 x 10^3 cfu/g
the number seems kind of low but this is how i would have figured it out. anyone else???
as far as best plate is concerned, this just basically means the number of bacterial colonies that are best to have on a plate to count. in other words, to calculate cfu/ml or cfu/g it's best to have between 30 and 300 colonies to count (in your problem, 73 was perfect). anything above that range is too many to feasibly count and below that would be too little for calculation and might result in error.

thank you so much!!!

PacoUSA, BSN, RN · Apr 10, 2010

Paco,
I can tell you do have a passion about being a good student. You will be a successful nurse no doubt about it! Keep up the good work~ladyoj69

Thanks so much ladyoj69, means a lot to hear that :yeah: When you're passionate about something, you know it's something that you need to incorporate in your life because it makes it all worthwhile. 6 months ago I was literally terrified at the idea of taking microbiology this semester, the prospect of remembering all those Latin terms was scaring me but in the long run it turns out it was not as bad as it seems. No doubt, I am studying more than I did for A&P but turns out it's DO-ABLE! I mentioned once before that I got a D in general biology when I was a college freshman and too quickly lost hope in ever entering the medical field and from there I followed a winding career path that led me back to this. Here I am 20 or so years later a very different person with a very different focus. The right time for me was not then, but it definitely is now.

I hope people will remember that doing well in micro is NOT impossible, and if they are having trouble they should never be ashamed of looking for help.

blueyesue · Apr 20, 2010

3 weeks left of class. It's been tough, but I am still doing decent (B) I really like this last half of the semester as we are learning about all those pathogens! :coollook:

I can't believe it is almost over. How much longer do all of you have?

Congrats to all those who are finishing this class with a passing grade. :yeah:

PacoUSA, BSN, RN · Apr 21, 2010

3 weeks left of class. It's been tough, but I am still doing decent (B) I really like this last half of the semester as we are learning about all those pathogens!
I can't believe it is almost over. How much longer do all of you have?
Congrats to all those who are finishing this class with a passing grade.

I also have 3 weeks left! One more lecture exam, 3 more lecture online quizzes, one more lab quiz and the lab practical and THAT'S IT! I just had a lecture test earlier today and got 102! (there were extra credit questions worth 4 points total) .... can you freaking believe that? I am still in shock. It was on viruses, epidemiology and pathogens. Seriously, and that is with a professor that is apparently pretty bad (according to ratemyprofessors.com). But what I THINK is that if you study what she gives you, you're going to do well! No osmosis learning here!

PacoUSA, BSN, RN · Apr 23, 2010

I'm wondering how many people who posted here ended up withdrawing from micro and how many are still sticking it out. My class I think has @ 40 students now, originally full at 60. We are in the running stretch towards finals! Good luck all! :up:

butterfly135 · Apr 23, 2010

I am still in with an 95% in lab and 95.8 in lecture, we have 3 weeks left, turn in our unknown lab report next monday. I am ready to be done we have only lost about 5 in my class had 30 to begin with but i know alot of people have asked about extra credit to get their grades up. I will say this class has been way harder than any other class, but i am really liking the last half of the class. Good luck to everyone, with the closing stretch!

jazziphat · Apr 23, 2010

:yeah:I got an A!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

rholman · Apr 23, 2010

I have a final exam next Thursday. I am hoping to end with a B.. I am just soooo happy its over.