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Lecture 6

Lecture 6.docx

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Health Sciences
William Yan

-this lecture deals with non-gram stainable bacteria Slide 2: Mycobacteria -all mycobacterium species share common features: -main diseases include tuberculosis and leprosy -are not gram stainable because there cell wall is different -it produces a thick layer of wax-like material on the cell wall, which prevents the stains from entering and binding to the cell wall -the wax material protects the bacteria from disinfectants and acids, heat, etc.; they are therefore hard to kill off -we use the Ziehl-Neelsen staining technique -also referred to as "acid-fast stains" -involves heating up the bacteria to soften the wax before the stain can penetrate the wax layer Slide 3: -involves the carbol fuchsin (red) stain -methylene blue is used to contrast the carbol fuchsin stain -look for red bacteria against a blue background to diagnose tuberculosis causes or other mycobacteria -the wax cell wall protects the bacteria from damage, but it also prevents nutrients from getting inside the cell -mycobacteria are therefore some of the slowest growing bacteria in the lab -e.g.: E.coli can multiply every 20 minutes and colonies will be visible after 15 hours; with mycobacteria, it could take 4 to 6 weeks for a colony to appear on the plate (thus, stains are used to make preliminary diagnoses because they are fast to do) Slide 4: Mycobacterium tuberculosis -causes tuberculosis -mainly found in developing countries -causes a respiratory tract / pulmonary infection -considered to be one of the most common bacterial pathogens around the world that causes death -prevalence is decreasing due to education -in some countries, there is a slow rise maybe due to more homeless, crowded living conditions because of the economy -some strains are become resistant -many people carry the organism but don't show symptoms -HIV patients infected with Mycobacteria tuberculosis are more likely to develop symptoms Primary Tuberculosis -when infected, the infection goes through multiple stages: -you have to breath in a small number of these bacteria; you can only pick up TB through person-to-person contact -bacteria start to multiply in the alveoli -immune system is triggered; macrophages, antibodies, etc. -if bacteria are not killed off, they form a primary complex and stay inside the lung as a small focal point of infection; they are dormant and may remain this way for life -in other cases, under certain conditions, the bacteria can multiply and spread to other parts of the body (i.e.: kidney, CNS, bones, etc.) and further multiply -in this case, the CMI is fully activated and the infection is stopped -with a small population, there may be reactivation -if it is reactivated in the lungs, it may be spread and cause a TB outbreak -when you screen the population, most people will test positive for TB because it is so common -the challenge is to identify people carrying live bacteria -the main test is the Mantoux Text -inject isolated protein from Mycobacterium tuberculosis under the skin -monitor reaction for 48-72 hours -chances are that most people will show redness -test positive = diameter of red zone is >10mm -doubtful test = 5-9 mm -negative test = <4 mm -testing positive does not mean there is currently an active infection -the Mantoux Test is only used as a screening test; a chest X-ray is used later to confirm Slide 11: Non-Tuberculosis (Atypical) Mycobacteria -many mycobacteria can cause TB-like symptoms -don't need to know names -these strains may also react with the antigen of the Mantoux test -in general, these infections are only involved with immunocompromised population Slide 12: Mycobacterium leprae -causes leprosy (tissue damage) -very rare Slide 13: Spirochetes Slide 14: 1) Treponema pallidum (Syphilis) -causative agent for syphilis -one of the most common STDs worldwide -classified as non-gram stainable, helical bacteria -not culturable in the lab; unculturable in vivo or in vitro -the only chance of seeing this bacteria is by using dark field microscopy -is non-stainable Primary Syphilis -when you first come into contact with the bacterium -3-4 weeks later, a canker may appear in the genital tract -people don't realize they are carrying the organism and allows for it to be so easily spread -lends to the bacteria's success -immune system will get rid of bacteria and there is a full recovery Secondary Syphilis -in some cases, if the infection is not stopped at the primary stage, the secondary stage occurs -infection spreads to other parts of the body -this stage is also self-limiting and the subject will recover in the end -characterized by generalized or local rash Latent Syphilis -no symptoms of infection -subject can still be contagious -tiny number of bacteria may still be present; neonatal / congenital infection is still possible -woman may opt for C-section Late Syphilis -in a small percentage of population, bacteria may reach different parts of the organ through the blood and can affect skin, nervous system, cardiovascular system, etc. Serology Testing -primary and secondary syphilis does not require treatment -uses the immune system to determine whether a person has been exposed to the bacteria -because it is so hard to culture the bacteria, it is difficult to obtain and purify proteins to use as an antigen to produce antibodies to test for the presence of these bacteria -serology tests are done in 2 steps: 1) Non-Treponemal Tests -using decoys (VDRL, RPR, Wassermann) / non-specific proteins that show similar antigenic
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