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Flashcards in Microbiology Deck (260)
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Examples of gram positive bacilli?

actinomyces, bacillus, clostridia, diptheria, listeria monocytogenes


Examples of gram negative bacilli?

E coli, campylobacter, pseudomonas, salmonella, shigella, proteus


What is the catalase test?

to see if the microbe has catalase which destroys H2O2 and produces O2, if O2 is produced it is positive and is staphlococcus and it has catalase, it no O2 it is negative and streptococcus


Purpose of catalase test?

distinguishes between staphylococcus and streptococcus


What test is used on gram positive cocci?

catalase test


What test is used on staphylococci?

coagulase test


What is the coagulase test?

coagulase converts fibrinogen to fibrin and differentiates between staphylococcus aureus and staphylococcus epidemidis (positive is s.aureus and appears cream/yellow, negative is white)


How does s.aureus appear?

pigmented clusters, coagulated (solid), had DNAase


How does s.aureus cause disease?

high disease potential, pore forming toxin proteases. toxic shock syndrome toxin, spread by aerosal and touch and can colonize skin wounds


Treatment of s.aureus?

flucloxacillin (MRSA is resistant to B lactams though so needs vancomycin)


How does s.epidemidis appear?

non pigmented clusters, non coagulated, no DNAase


How does s.epidimidis causes disease?

low disease potential and s opportunistic and forms persistent biofilms


What test is done to distinguish streptococci?

haemolysis on blood agar


What are the 3 outcomes of haemolysis on blood agar and how do they appear?

beta haemolytic strep - clearing of agar around colonies due to strepolysin O and S production
alpha haemolytic strep (viridans strep) - greening of agar around the colonies due to H2O2 production
gamma haemolysis - no lysis


What test is done on beta haemolytic strep and how does it work?

The Lancefield test - serogroups antigenic gorup, differentiates according to surface antigens and their properties and the non coagulated one is the one to classify properties, producing A, B, C G


What is the likely diagnosis of group A Lancefield test?

s.pyogenes - causes tonsillitis, impetigo, scarlet fever, cellulitis


What test is done on alpha haemolytic strep?

optochin test


What are the results of the optochin test?

Put the disc on the bacteria and if bacteria moves away from the disc then it is sensitive (s.pneumoniae) and if it doesn't it is resistant (s.viridans)


What does strep viridans cause and where does it occur?

in oral dental canes and deep organ abscess, caused infective endocarditis


Where does strep. pneumoniae act on and what does it cause?

in oropaharynx, it has capsule, inflammatory wall constituents and cytotoxins causing impaired mucus trapping, causes hypomnaglobinaemia and is dependent on antibody to capsule


What infections does step. pneumoniae cause?

pneumonia, sinusitis and meningitis


Where are the sterile parts of the body?

blood, peritoneal cavity, CSF, joint, pleural fluid, urinary tract, lower resp tract


Where can norma flora culture?

mouth, skin, urethra, large intestine, vagina


What test is used on gram negative bacillus?

the appearance on MacConkey or CLED or XLD


What are the outcomes of appearance on MacConkey agar?

white (non lactose fermenting - shigella, salmonella, pseudomonas, proteus)
pink (lactose fermenting - enterobacteriacae (coliforms)


What are the outcomes on XLD agar?

red with black dots (fermenting xylose)
red (non fermenting xylose)
yellow (salmonella)


What test is done on non lactose fermenting bacteria?

oxidase test using a redox indicator


What are the results of an oxidase test?

blue as produces cytochrome c oxidase from bacterial ECT (positive - pseudomonas aeruginosa)
no colour change (enterobacteriaceae - proteus and shigella)


What test is done on oxidase positive pseudomonas sp.?

anti pseudomonal sensitivity test


What is the treatment of pseudomonas sp?

beta lactams