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Lecture 4

Lecture 4.docx

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Health Sciences
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William Yan

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Lecture 4 Slide 1: -organized by structural morphology Gram Positive Cocci -bacteria that stain gram positive and are round (cocci) Slide 2: Staphylococcus aureus (genus species name) -most important gram positive cocci pathogen we will cover -gram positive bacteria -the cellular arrangement of the round cells resemble a cluster of grapes ("staphule") -dairy products (creamy sauces) are most vulnerable to S.aureus -considered a 'prototype' for successful pathogens; one of the most successful pathogens -makes many toxic substances that allows it to overcome many barriers when it encounters the body -cytotoxin (cellular toxin) affects / kills certain cells in the body -hemolysins break down RBCs that release nutrients / iron that bacteria can use to thrive -enterotoxins (entero refers to the enteric system or the gut) causes troubles in the digestive system -are heat sensitive -exfoliative toxins affect skin and cause severe rashes -common in infants -toxic shock syndrome toxin 1 can lead to toxic shock syndrome -more rare than other toxins Slide 3: Enzymes -coagulase -coagulates blood and forms localized blood clots -blood clots helps protect the bacteria long enough so that it can survive and multiply -important virulence factor for S.aureus -among the many species of Staph, only S.aureus produces coagulase -coaguluse can be used as a test / screen to detect this bacteria -beta-lactamase (penicillinase) -is an inactivating enzyme that can break down the anti-biotic -destroys penicillin -allows for resistance against penicillin by S.aureus Slide 4: -S.aureus is a very common infectious agents due to its characteristics -treated by anti-biotic therapy -penicillin was the perfect drug for treating S.aureus infection -overuse has selected for a highly resistant population -95% of the time, the strain is resistant -penicillin is rarely used now -vancomycin was used for resistant strains; there are now vancomycin-resistant S.aureus -after using both penicillin and vancomycin together, there are strains that are resistant to both -methacilin was also used in combination; MRSA (multiple resistant / methacillin resistant S.aureus) -must rely on the body's immune system to kill of strains that are resistant to all these anti-biotics -hospitals cannot afford to let MRSA spread so patients are isolated immediately -causes localized infections (lesions, boils) -can infect the eye (conjunctivitis) -can progress into pneumonia, heart infections, etc. but these are rare -can cause food poisoning, toxic shock syndrome, scalded skin syndrome depending on the toxin that the strain produces Slide 5: -the hospital is the most likely place to get S.aureus infection because it is so widespread -cannot rely on anti-biotics -prevention is key to minimize infection -using proper aseptic techniques in the ER and OR where wound infections are common -education -handwashing -resistance may be decreasing now because of the minimized use of anti-biotics -there is no advantage for resistant strains if anti-biotics aren't used; the selective pressure for resistant strains is decreased Slide 6: Staphylococcus epidermidis -same genus as S.aureus -main difference between the 2 are that S.epidermidis is not considered a true pathogen; considered an opportunistic pathogen -most common bacteria in the normal flora of the skin Slide 7: Streptococci -gram positive cocci -same cellular structure as Staphylococcus (gram positive) -arranged in chains or pairs; "streptos" = twisted -there are many species of streptococci that are true pathogens to humans -there are 3 separate schemes to separate the large number of strains of Streptococci 1) Hemolytic Properties -some strains of streptococci can make hemolysins a) beta hemolytic strain (complete hemolysis) -produces a very large amount of hemolysins -beta hemolytic strains grown on a blood agar plate results in lysed RBCs by toxins -the colony has a distinct halo that is completely transparent -all the RBCs around the colony are lysed, producing the transparent halo b) alpha hemolytic strain (partial hemolysis) -only breaks down some of the RBCs -creates a faint halo around the colony; less distinct c) non-hemolytic strain (gamma hemolytic) -no halos can be seen -no hemolysins are present in strains; no hemolysis of RBCs 2) Carbohydrate C Antigen Typing (Lancefield Classification) -used frequently for many bacteria -system is based on antibody-antigen reaction -in the cell wall of Streptococci, there is a carbohydrate antigen which is used to differentiate it from different bacteria -the most common is carbohydrate A antigen and so on 3) M-Protein -involves antibody-antigen reactions -the antigen is an M-protein -M-protein is a specific pilli -used to separate the large number of beta hemolytic streptococci -used to divide group A classified streptococci Slide 8: Streptococcus pyogenes -most common streptococci pathogen -group A (most common) Lancefield typing -beta hemolytic -respiratory tract infection -causes acute tonsillitis (strep throat) which is probably the most common infection cause by S.pyogenes -persisting infection may cause rheumatic heart disease, but this is rare -can cause skin infections -i.e.: impetigo, cellulitis -if it enters the blood stream, it may cause fever and septicemia -S.pyogenes can make toxins -streptolysin (O and S) -functions to kill off neutrophils and macrophages -helps the bacteria overcome the immune system -Spes (streptococcal pyrogenic exotoxins) -causes scarlet fever rash -common in younger children Slide 9: Streptococcus pyogenes -certain strains can also make hyaluronidase (an enzyme that helps the spread of bacteria into tissues) -most strains are highly sensitive to penicillin G -is still the drug of choice to treat infection -prevention is important Slide 10: -the most serious consequence from an S.pyogenes infection is necrotizing fasciitis (flesh eatin
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