hello and welcome to the microbiology section of first aid express my name is Rainey woo and I'll be your guide through this section we'll start off with some general information about bacteria first before diving into specific information about bacteria fungi parasites viruses and finally antimicrobial therapy bacteria are single celled procario organisms with several structural elements that distinguish them from UK carots the table here lists these structural elements of bacteria and their functions we will highlight how these structures vary between gr positive and gram negative organisms in the next fact there are some key differences between the cell wall structures of gr positive and gram negative organisms gr positive organisms have thicker cell walls composed of a high amount of peptidoglycan and lipoic acids a combination of lipids and teic acids these characteristics are useful in distinguishing bacterial stereotypes promoting bacterial interaction with human cell receptors and initiating host immune responses gram negative organisms contain much thinner peptidoglycan layers outer membranes and periplasmic spaces the periplasmic space contains enzymes necessary for bacterial virence such as proteases phosphatases lipases and beta lactamases important Inhibitors of penicillin drugs only gram negatives contain lipopolysaccharide endotoxins within their outer membranes which is a potent activator of host immune cells and causes macras to release tnf Alpha which causes septic shock this table classifies bacteria by structural and morphologic characteristics it may be overwhelming now but will make more sense to you as you become more familiar with the bacteria in this chapter refer to this table as you move through the chapter to help you keep the various bacteria straight two bacteria are important in mentioning because of the unique properties of their cell walls micoplasma is a bacteria which does not have a cell wall microbacterium on the other hand has a cell wall but it contains molic acid in addition to polysaccharides peptidoglycans and lipids these unusual cell wall properties pose challenges to graming and identifying micoplasma and micro iium in addition to micoplasma and micro bacteria there are several other bacteria that do not Gram stain well but first what is a Gram stain it is an important staining technique that allows for differentiating bacterial strains based on the physical and chemical properties of their cell walls the primary stain is Crystal Violet CV die with subsequent application of iodine that complexes with the CV and becomes entrapped within the thick pep glycin cell walls of gr positive organisms thus gr positive bacteria stain purple or blue decolorizer washes away Unbound CV iodine complexes from Gram negative organisms that have thin peptidoglycan cell walls and could not effectively trap CV iodine complexes therefore gram negative bacteria lose their purple color finally application of a counter stain saffrin stains gram negative bacteria pink the organisms listed here are those that cannot be identified via grham stain but can be differentiated using other techniques we already mentioned micro bacterium and micoplasma micoplasma cannot be stained because it has no cell wall myobacterium cannot be gram stained but it can be stained with the acid fast method which takes advantage of the high lipid cell wall content of myobacterium myobacterium will be bright red after staining with carbal Fusion because its lipid Rich cell wall prevents acid from washing out or decolorizing the stain Trona is too thin to be visualized so one must use the dark field microscopy or fluorescent antibody staining to see it Ria Legionella and chlamidia are intracellular parasites and difficult to see therefore you must use imuno florescent staining to visualize these organisms Legionella can also be visualized by silver stain you should associate these specific stains with certain organisms for example a gima stain can be used to identify bellia plasmodium tranes and chlamidia the periodic acid shift stain can stain glycogen and mucopolysaccharides making it useful in identifying the bacterium Cheri wheli which is the cause of Whipples disease the Zeal Neilon stain is used to detect acid fast organisms keep in mind that Zeal Neilon is synonymous with acid fast the India ink stain can stain for cryptococcus neoformans and lastly the silver stain is useful to visualize fungi and Legionella here is an image showing how cryptococcus Neo formans would appear using the India ink stain bacterial culture is the process of growing bacteria on agar plates with medium and an additional nutrient Source it is another albeit slower method for identifying microorganisms media can be selective meaning it contains antibiotics to prevent growth of contaminating microorganisms such as the the Martin or VPN media which contains Venoy polymixin and nistatin to inhibit growth of organisms other than neria ganaria media can also be differential meaning it induces only the bacteria you are interested in to change color so that you can distinguish them from everything else an examp example of this is meoni's agar which will only turn pink in the presence of lactose fermenting bugs such as ecoli obligate aerobes are simply organisms that require oxygen in order to survive as you can imagine these organisms seek to infect areas such as the respiratory tract where there is plenty of oxygen to be found you can use this pneumonic to help you remember them nagging pest must breathe stands for nocardia pomonis microbacterium and bacillus the opposite are organisms that survive only in the absence of oxygen put another way these bacteria are incapable of growing in the presence of oxygen this is because they lack the enzyme super oxide dismutase and or catalase which are important antioxidant neutralizing mechanisms against the toxic compound super oxide super oxide forms when organisms are exposed to oxygen and without the enzyme superoxide dismutase it cannot be converted into benign molecules that are safe to the bacteria catalase is an enzyme that breaks down hydrogen peroxide into water and oxygen it is necessary when bacteria are exposed to oxygen to prevent the conversion of hydrogen peroxide into free radicals oblate Anor robes include claustrum bacteroides and actinomyces it is important to know if you are dealing with these bugs because they are resistant to aminoglycosides since these these drugs require oxygen in order to enter cells here are some bacteria which live within cells some because they must in order to survive the obligate intracellular organisms and others which can live within cells if they want to but have mechanisms for surviving extracellularly if they have to the facultative intracellular organisms the obligate intracellular organisms are Ria and chyia you can remember them with the pneumonic that they stay inside when it is really cold the facultative intracellular ones are in this pneumonic some nasty bugs may live facultatively this stands for the bacteria salmonella neria brucella myobacterium leria francisella Legionella and ursinia these are simply bacteria which are covered by an outer capsule made of polysaccharides these BAC IIA can be highly violent because the capsule protects them from phagocytosis and t- cell mediated immune responses people who lack a spleen anatomically or functionally as inle cell disease are highly susceptible to sepsis by encapsulated bacteria as a spleen is an important barrier against these organisms asplenic patients should be sure to receive vaccination against these organisms those with B cell deficiencies are also at increased risk of disease by encapsulated bacteria as B cell immunity is the main line of defense against these organisms use the pneumonic Shin skis to help you remember which are the encapsulated bacteria streptococus pneumonia hemophilus influenza type B neria menius salmonella kiella pneumonia and Group B strap some organisms contain cataly an enzyme which degrades hydrogen peroxide into water and oxygen you will learn more about chronic granny luminous disease cgd in the biochemistry section but just know that patients with cgd rely on hydrogen peroxide formation to fight off infections because hydrogen peroxide is an oxidative product that can kill bacteria however when cgd patients are infected by cataly positive species like stafilococ these bacteria have the ability to break down hydrogen peroxide and prolong their survival organisms which are cataly positive include staff orus seraia pomonis actinomyces Canada and eoli