A tour of the Microbiology Lab – Section one

A tour of the Microbiology Lab - Section one



hi my name is George I'm a medical lab technologist who works in a hospital microbiology department I've been asked to give you a short overview of what we do here with the specimens that you'd send down for culture we've been described as healthcare detectives and our mission is to detect to isolate to identify and to help eradicate those organisms that are causing infections in your patients to do that we have to see those organisms and we can see them in two ways one way is microscopically like the microscope that I have behind me and using a 1,000 power magnification the other way is to grow those organisms and bacteria don't grow in size they grow in number one bacteria divides into 2 2 into 4 4 into 16 and they grow exponentially over a period of 6 to 8 hours and after that 6 to 8 hour period they start to produce byproducts and they begin to die off in order to grow bacteria there are four criteria that we have to look out for or take care of one is the nutritional nutritional requirements of bacteria the second is a time requirement for growth the third is a temperature requirement and the fourth is the atmospheric requirement to satisfy the nutritional requirements of bacteria we use agar and the most common agar plate we use is sheep blood agar agar is very soft and its consistency it's something like yellow you can see my finger prints on there and it's very moist to the touch and this agar has all the amino acids and nutritional requirements that bacteria need so normally when we get a swab that you sent down to from the floors we would take that swab inoculate the agar rolling the swab to get all the bacteria off it and then we would take a wire sterilize it and we would spread all that inoculum over the whole plate now you may wonder why we do this streaking technique it's to spread the bacteria out to find the specific pathogens if I had a bag of say white marbles but I was looking for one specific black one the way to find it would be to take that bag open it up and spread those marbles out well that's basically what we do when we streak the plate we're spreading out the inoculum to find the specific pathogens that might be there and as you can see the material has been spread out and what we have here is individual colonies and now we can work with each individual colony and do testing on it we have a whole variety of agar plates they come in all kinds of colors white black pink orange green yellow and they all serve a different purpose what we set swabs or specimens on depends on the sight that the specimen is taken on for instance an eye swab will just get a chocolate plate and a blood agar plate the reason being is everything that we're looking for in an eye swab that can cause infection which can be isolated on these two plates if we just used the blood agar plate we might get something like this no growth at all but by incorporating the chocolate plate which is an enriched plate it's more nutritious we will find something like this the same organism grew on the chocolate but did not grow on the blood agar and this organism is home office it's very fastidious and requires chocolate plates in order to grow some plates our differential if you look at this plate you can't see much difference between the colonies but because we use the McConkey plate the difference is a lot clearer the mikake plate is a differential plate it utilizes lactose to differentiate one bacteria from another so here you see the pink colonies that are lactose fermenters as opposed to the non pink colonies that are non lactose fermenters and this is a good help in helping us identify bacteria other plates we use are selective and an example is CNA if you look at this plate is just a broad growth of organism really just a big mess because the gram negative organisms has grown over the whole plate but there's something else in there that you can't really see these hemolytic colonies right there because we also set it up on a CNA plate those colonies are clearly visible and clearly accessible this plate is is differential because we use antibiotics coalesced in and neljä toxic acid that inhibits the Proteus and allows the gram positive organism to grow and then finally we have plates that are selective and differential an example is mannitol mannitol uses salt to make it selective and it uses mannitol to make it differential this is used to isolate and identify staph aureus staph aureus is tolerant to salt so it grows and it utilizes mannitol and and it so it turns yellow so if you compare these two plates we know this plate has staph aureus on it and this plate does not because this one is yellow the second requirement of bacteria is time you have to get in sufficient time to grow there's no such thing as a stat culture we get requests sometimes for a stat throat culture for instance now we can't make that stat bacteria and need at least 24 hours to grow most bacteria grow in 24 hours anaerobes take 48 and some bacteria are slow growing so we will keep most cultures up to 96 hours up to 4 days to ensure that that time requirement is met the third requirement of bacteria is to provide them with the proper temperature by far most bacteria grow at body temperature well that range is between 35 and 37 degrees this is a 37 degree incubator we monitor the temperature with a thermometer to make sure it's always maintained at 37 and most bacteria grow at body temperature there are a few exceptions though we do have a 42 degree incubator for a specific organism called Campylobacter you've probably heard of that it's an enteric pathogen and it's grown at 42 degrees because number one Campylobacter prefers it a little bit warmer and also 42 degrees inhibits all the normal flora that normally we found in the stool and we also have a 30 degree incubator and this is used specifically for yeasts it's a little bit cooler and it seems some yeasts prefer 3 degrees to grow so with this 3 degree incubator the 42 and the 37 we can meet all the temperature requirements of any bacteria that might cause infection in your patients

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