good morning all um so this lecture is on microbial growth microbial nutrition um for my ccp students this is chapter six of your textbook for my camden county students this is chapter seven of your textbook um so this is a pretty easy chapter and i don't want you guys to spend a whole lot of time on this chapter you know this would be a chapter that you sort of read through and kind of move on there's not a whole lot of wheat per se to really study in this chapter um but we're going to go over what conditions are required for microbial growth now before we talk about microbial growth growth is actually uh one cell dividing into more cells okay dividing into two sister cells daughter cells sorry uh and then continuing the division process it's not the cells getting bigger per se it's more than dividing so there are several physical requirements that are required for growth temperature ph osmotic pressure we'll talk about each of those in a second there are also various chemical requirements because all microbes are carbon based material they do need to have a carbon source nitrogen sulfur phosphorus are also important trace elements oxygen and various organic growth factors uh other important things would be like trace elements these would be things that trace element means that it's not in a high enough percentage or value to be listed but it is still required oxygen to play a role we just got done talking about metabolism or you will be getting into metabolism talking about aerobic versus anaerobic growth you know oxygen does play a role and then organic growth factors will be things like vitamins so looking at temperature you know most microorganisms are going to be what we call mesophiles mesophiles means that they are moderate temperature loving and this is anywhere from about 20 degrees celsius to about 40 degrees celsius most bacteria are going to love 37 degrees celsius most fungi will actually love 35 degrees celsius um psychophiles these are called loving bacteria so anything lower than 20 degrees celsius thermophiles these are heat loving organisms this would be anything greater than 42 43 degrees celsius you know if we sort of look at temperatures um if you've ever worked in the food industry uh you know that the temperature of what food is kept at is critical uh and the reason for this is that if you do have food being kept in that 20 to 40 degree range it is considered a danger zone and the reason why it's considered danger zone is because bacteria can replicate very quickly uh or duplicate very quickly you know when we get to infections of the gi tract one of the biggest causes of food poisoning in the u.s is actually contamination of cooked food meaning you touched cooked food maybe transferred some stuff to that cooked food and as a result um the bacteria was growing because that food was kept either at room temperature which is 27 degrees or maybe even a more lukewarm temperature of maybe 30 to 35 degrees and you got rapid growth of the bacteria so it is very important that you know if you're in the food service industry or you're cooking food that food is either kept above or below you know those danger zone temperatures for ph most bacteria will grow between six and a half and seven and a half uh molds and yeast are more acidic uh they like a ph of four to six and an acidophile would be an organism that really grows in an acidic environment um one area in the body that we'll talk about that's very acidic is the stomach and there's actually an organism called helibacter pylori which we'll get to when we get to gi infections h pylori uh can live and reside in the stomach which can have a ph of anywhere from zero to three uh and also um as a result um you know uh is able to withstand that very low ph uh the vaginal tract would be another area typically the vaginal tract has a ph of about four to four and a half so a lot of bacteria that live there are slightly acidific osmotic pressure this is when you have hypertonic environments hypertonic would mean like a salt rich environment this will cause plasmalysis due to the high osmotic pressure uh so this is one of the reasons why we do not find a lot of different bacteria on the surface of the skin despite most bacteria having cell walls they cannot take these hypertonic environments and what happens with plasmalysis is if you look in the picture here and you look at the right hand side what you'll notice is that you're still getting shriveling up of the cell within the cell wall uh so the plasma membrane tripling up the cell is shriveling up with the cell wall still maintaining the shape of the cell this does not allow for the bacteria to grow and it may even kill the bacteria again the surface of the skin very salty environment we are starting infections of the skin this week as well so you'll see a little bit more about that and when you look at the surface of the skin for example um you know because of that very high salt environments the bacteria are not able to grow but there is an orgasm that is which is called staph uh staph aureus chemical requirements these are things that have to because most bacteria are going to be heterotrophs which means they have to eat food they need a carbon source carbon is important because it's a structural backbone backbone of all organic molecules autotrophs are able to take co2 out of the atmosphere most heterotrophs cannot do that they have to have uh they have to bring in some type of carbon source autotrophs are able to take co2 undergo a process called photosynthesis and use that to make carbohydrate or carbon sources but most bacteria cannot do that process nitrogen is very important for cells because it's component of proteins amino acids the amine group dna and atp most bacteria will decompose protein material from nitrogen source some bacteria will use ammonia or nitrate from organic materials and despite the atmosphere being approximately 72 nitrogen uh it cannot take nitrogen from the atmosphere again it has to ingest or bring in a nitrogen source most likely from protein sources sulfur is important because it's used in amino acids thiamine and biotin most bacteria will decompose protein for their sulfur source um phosphorus this is another important molecule it's used in dna rna and atp it's also found in the membranes especially the phospholipid bilayer hence the name phospholipid bilayer the phosphorus referring to the phosphorus layer phosphate sources are pretty ubiquitous in the environment and many many many sources are available for that uh trace elements as i mentioned these are inorganic elements that are required in small amounts uh usually they will act as enzyme cofactors and they can include things such as iron copy copper and zinc oxygen state we have uh pretty much four major types of states with oxygen they're defined here but i'm going to go to the picture we have what's called an obligate arrow obligate means it's absolute so an obligate arrow what you have here is it's able to grow at the surface only because that's where the oxygen is facultative anaerobe is both aerobic and anaerobic growth but you get greater growth in the presence of oxygen okay so that's why you see more growth towards the surface here obligate anaerobic can only grow without the presence of oxygen and that's why you see the growth down here and then aero tolerant anaerobes they are anaerobic they only grow in anaerobic conditions but oxygen will not harm them and that's why you can see some growth up towards the surface as well because oxygen won't harm them but it's not required for them organic compounds these are obtained from the environment and these include vitamins amino acids purines and pyrimidines purines and pyrimidines are the monomers that we find in nucleic acids so looking at culture medium um this is how most microbes are going to get their nutritional sources when we are actually culturing them is it has to be placed into the medium and i'm not going to spend a whole lot of time on this because this is something that was defined in chapter three of your book when you looked at tools of microbiology um but you know we have chemically defined media complex media we've defined both of these terms already you should be familiar with them again this was chapter three if you forgot them already make sure that you you know relearn them okay of reducing media this is a media that's typically used for the cultivation of anaerobic bacteria reducing media will actually contain chemicals such as sodium chloride that will combine oxygen to deplete it it's heated to drive off the oxygen sometimes if you're growing up anaerobic cultures you can also set up an environment that is strictly anaerobic such as putting the petri dishes as you can see here in a sealed canister the sealed canister will actually also contain a gas bag that will release say co2 and hydrogen the hydrogen will bind up any oxygen you'll get some you know water formation but the co2 is going to fill the canister essentially creating an anaerobic environment within the canister capnophiles these are microbes that require high co2 conditions and you can either use a co2 packet or what they call a candle jar i don't picture that one thing you want to think about is there are areas of your body where you actually have higher co2 concentrations than the atmosphere and one major area would be the blood blood on average has about four percent co2 on the red blood cells um and if you think about that the atmospheric co2 is like point two to point three percent um so you have a much higher concentration of co2 uh available in blood than you do you know say in the atmosphere so sometimes some bacteria actually prefer that and that's why they are suited very well say for bloodstream infections but you know if you were to culture it in atmospheric air it wouldn't culture very well because there's just not enough co2 there so sometimes you have to mimic the appropriate conditions bio safety levels um you may have seen a lot of this especially with um what's been going on in the world but when we grow cultures we do take into account their biosafety levels the bio safety levels are just the levels of precautions that should be taken when you're handling microorganisms so something is classified as bsl1 no special precautions are taken basic teaching labs use bsl1 organisms and you know when we are actually in a physical lab doing these exercises it is considered bsl1 bsl2 you need to wear a lab coat gloves and eye protection bsl3 you need a biosafety cabinet to prevent airborne transmission so now the difference between bsl2 and bsl3 is bsl-2 can be transmitted by direct contact and by wearing gloves you are actually protecting yourself bsl3 this is something that can be transmitted airborne so you want to be operating with this underneath a cabinet that has negative pressure you want to make sure you have protective ppe on especially to sort of block any uh airborne transmission that's something that we're definitely seeing with uh coronavirus chronovirus would definitely be classified as a psl3 bsl4 these are really the nasty ones not only can they be aerosolized or transmitted in the air but they also have very high mortality rates associated with them uh and this culturing of these things needs to be handled in a bsl4 lab which is a completely sealed environment uh you're wearing sort of the spacesuits with your own air supply picture that's uh you know working in a cabinet which is that structure they're working under in any way and there's always somebody there with you you're never by yourself uh there are very few bsl4 labs in the country most are actually run by the federal government because of the high level of regulations uh and most of the sl4 labs are actually kept out of cities for example city of philadelphia actually has a law on the books that states no institution or company can actually have a bsl4 lab within the city limits uh different types of media again we kind of went over this in chapter three selective media uh this will suppress unwanted microbes and encourage desired microbes to grow uh it can contain inhibitors to suppress growth differential media this allows you to distinguish between one organism versus another some media have both selected and differential characteristics okay and this is just a little summary slide that goes over the different types of media again most of these were covered in chapter three this should just be for you to sort of refresh a little bit obtaining a pure culture last week you guys did lab exercise four which was the street plate method this is how you would actually obtain a pure culture and the goal with this is you know you initially will inoculate then you drag out some from that initial inoculation then you drag out some from that second inoculation and the goal here is you know you're initially putting down lots of bacteria then you're dragging out a small subset and then eventually you're dragging out even further small subset where you can get individual colonies that is the goal of speaking for isolation using the street plate method to get individual colonies okay okay bacterial growth um you will have one open-ended question on the exam that really comes from this chapter six for my ccp students or chapter 7 for my camden county students and the question is to describe list to describe the four step phases of growth okay bacterial growth is primarily done by binary fission but you can also get some budding and essentially what binary fission is is the cell will grow uh it will increase in size you need to make a copy of the single chromosome and then eventually the cell will just split into two it's a very simple process it occurs very rapidly for example e coli can actually replicate about every 20 minutes and here we can see that again when we talk about bacterial growth um it is exponential what that means is when you start off with one cell it's going to divide you have two cells when those two cell divide you have four cells when those four cells divide you have eight and those eight divide you of 16 and this is continues so that's what we mean by exponential growth as i mentioned you will have one open-ended question and the question will be and it's this is a question that's also on your lecture assignment it's the list to describe the four phases of growth here are the four phases of growth and we're going to go through each of those there's actually a little description here for each of the four phases of growth the first phase is lag phase during lag phase this is when the cell is introduced to a nutrient-rich environment because growth is a metabolic process and will occur when there's plenty of nutrients around when the cell senses that there's plenty of nutrients what will happen is it will actually turn on metabolic pathways to actually initiate growth uh and that takes some time so the lag phase is just sort of the quote-unquote cell waking up the log phase is exponential logarithmic log the rhythmic growth okay this is when the cell is doubling in numbers with each division and you'll see numbers increase during the log phase stationary phase is a period of equilibrium this is when microbial deaths balance production of new cells so essentially what you have during stationary phase is new cells are growing but equal numbers of cells that are dying so you're maintaining the cell number uh this is smart because you don't want to over populate your area because if you end up overpopulating you might not have enough food then to you know meet the demands of the cells and then finally we will enter into what's referred to as the death phase the death phase is when nutrients have started to decline as nutrients have started to decline what happens then is you start to lose cells and unfortunately the cells that end up dying also now become food for the remaining cells and those are the four phases of growth and a little description on each one this is a great slide if you're sort of preparing your answer there okay and that's it for um chapter six for my ccp students or chapter seven for my camden county students microbial growth as i mentioned this is a pretty uh easy chapter uh you know take it for what it is and please don't spend a whole lot of time on this my camden county students you guys will then be moving into metabolism which is a very difficult topic and will take most of the week for you to prepare for uh for my ccp students you had your metabolism chapter last week um but you're going to start getting into some infections this week um both of my schools have exams this week so please make sure you look for the start and end date for those exams and complete your exams during those times okay um have a good one guys