Notes for Exam 3 Lecture 17 Host Microbe Interactions Commensal vs Pathogenic 1 Pathogens can be transmitted in many ways a Ex Listeria monocytogenes Gram positive bacterium i Listeriosis usually caused by eating contaminated food fever muscle aches sometimes diarrhea miscarriage convulsions fatal to newborns ii Affects older adults pregnant women newborns rarely affects immunocompetent iii Common in soil and water animals carry and transmit to food for consumption iv Can grow in 4 C so remains viable even under refrigeration b Ex Neisseria meningitides Gram negative bacterium i Rare but close contact of dorms schools increases spread by contact ii Meningococcemia severe leads to brain damage hearing loss death iii Other symptoms are nausea vomiting sensitivity light confusion iv 3 vaccines antibiotics c Some microbes cause disease but most microbes do not many are beneficial to humans 2 Microflora Microbiota a Normal Resident Flora or Microbiota i Population of organisms normally found on or in the body of a healthy individual Live on skin in gut colon 1 2 Determined by origin birth exposure to environment and changes stress starvations infections antibiotics probiotics 3 Dynamic population composition is always changing ii Commensal they benefit while we are unaffected iii Diverse 500 different bacteria Aerobes facultative anaerobes anaerobes iv Benefits of Normal Flora 1 Gnotobiotic Germ free animals have no normal flora and have the following characteristics Increased susceptibility to pathogens a Poorly developed lymphoid system b c Requirement for vitamins K and B d Higher food intake less obese e Could be a source of pathogens 2 If recolonize gnotobiotic mice via fecal flora reconstitution so feed them poop and the bacteria from the poop will colonize the gut the following happens Intestinal flora produce vitamin B and k a b Block attachment sites on animal tissues pathogens must compete to attach Stimulate Development of Immune System c d Create antagonistic environment production of chemicals that inhibit the growth of other microbes competitive exclusion i Basis for Probiotics yogurt 3 We use fecal flora reconstitution in people a Transplanted feces to provide patient with good bacteria to fight diseases such as Clostridium difficile infections severe diarrhea b Feces are stripped of larger particles blended with saline and transferred by enema or put into pill form and swallowed v Commensal bacteria makeup depends on location mouth throat urethra Streptococcus nose skin Staphylococcus vagina Lactobacillus large intestine E coli Bacteroides b Transient Flora microbes we pick up from the environment but they do not colonize the skin or gut transient not permanent could potentially be pathogenic remember the thumbprint blood plate from lab c Virulence factors contribute to pathogenicity which contributes to disease development i Host pathogen interactions determine if one is in a state of good health asymptomatic or disease symptomatic 1 Host side commensal bacteria specific and nonspecific defenses treatments such as antibiotics prevention such as vaccines 2 Pathogen side virulence factors rapid growth large numbers synergies effects can combine with other factors to make disease worse for example HIV and HSV 2 are synergistic Having herpes makes you more prone to contracting HIV through sexual contact due to HIV susceptible immune cells presence at genital sores Having HIV makes you less able to control HSV 2 due to lowered cell immunity so you have more long lasting lesions more frequently 3 Virulence Factors characteristics that can make a microbe pathogenic a Transmission to susceptible host b Entry and adherence to target tissue c Colonization and invasion of tissues d Damage to host cells e Exit from host f Survival in environment aids in transmission 4 Opportunistic pathogens microbes that only cause disease in particular conditions HIV AIDS patients are susceptible to a number of opportunistic pathogens like Candida and P carinii due to being immunocompromised So these pathogens wouldn t cause disease in healthy people but will cause disease in immunocompromised people because their immune system isn t able to keep them in check 5 Transient pathogens not part of normal flora and was picked up from the environment through an exposure for example C tetani causes tetanus or lockjaw and is not found in your resident flora However you expose yourself to C tetani when you step on a rusty nail Now C tetani is on your skin and in your wound so now it is considered part of your transient flora d Koch s Postulates how we determine what microbe causes a disease i Microbe is present in every case of disease and absent in all healthy hosts ii Microbe must be isolated from diseased host and grown in pure culture iii Organism infected into new host and this host exhibits same symptoms iv Microbe must be isolated from second disease host grown in pure culture and shown to be identical to the agent used to infect the host v Molecular postulates same four rules above but for genes e To cause disease microbes have to do a number of steps i Establish an Infection adhere to a tissue and colonize grow on that tissue 1 First microbes need to enter through an acceptable portal of entry cut or insect bite on skin mouth ear nose eye conjunctiva anus vagina penis placenta 2 Not all microbes can enter through all different portals so how and where the transmission occurred determines whether an infection can be successfully established For example influenza cannot infect a person through a cut on the skin because it is designed to infect cells in the respiratory tract not the bloodstream 3 Microbes have many ways of adherence a Viral spikes b Bacterial Adhesins c Pili d Glycocalyx e Biofilms ex the plaque on your teeth 4 Adherence alone does NOT cause disease 5 Colonization of tissue means that the microbe must compete with normal resident flora acquire nutrients and grow and escape local immunity to survive 6 Colonization can be planktonic free swimming bacteria or biofilms surface community of bacteria Biofilms are tough to remove and can insulate bacteria from the immune system and drugs Invade Tissues breach anatomical barriers like the skin or mucosa ii iii Evade Host Defenses 1 Hiding within host cells 2 Avoiding killing by host proteins 3 Avoiding phagocytosis capsule prevents phagocytosis incomplete phagocytosis when the pathogen is ingested but not degraded so can still replicate