SLE334 Practical Exam Questions And
Accurate Answers
Clostridium perfringens - ANSWER Gram positive anaerobe, endospore forming causing
necrotic enteritis. Forms green colony colour on CP chromoselect agar. Causes gas
gangrene and produces lecithinase alpha toxin which hydrolyses lipids in cell
membranes.
Salmonella enterica - ANSWER Gram negative rod shaped bacillus of
enterobacteriaceae
Helicobacter pylori - ANSWER Gram negative spiral bacterium associated with
duodenal and gastric ulcers. Produces cytotoxin, acid-inhibiting protein, adhesins and
urease allowing for buffering of acidic environment and virulence factors allow adhesion
to gastric mucosa and cause tissue damage via inflammatory mediators.
Escherichia coli - ANSWER Gram negative rod shaped, facultative anaerobe commonly
found in gut. ß-galactosidase cleaves Red-gal in chromogenic UTI plate forming pink
colonies & positive control in indole test.
Streptococcus salivarius - ANSWER Gram-positive, spherical, facultative anaerobe
producing lactic acid bacteria. Catalase and oxidase negative. Grows as blue colonies
on Salivarius/Mitis plate. Respiratory pathogen and requires biosafety cabinet handling.
Streptococcus pyogenes - ANSWER Gram positive, aerotolerant, spherical, non-motile
and non-spore forming cocci that tend to link. Catalase negative and does not growth on
MAC, produces hemolysin causing beta-hemolysis. Common cause of pharyngitis in
children and strep throat. Respiratory pathogen and requires biosafety cabinet
handling.
Neisseria gonorrhoeae - ANSWER Gram-negative, diplococci and intracellular
monococci bacteria causing gonorrhoea through infection of the epithelium, can cause
discharge, lesions but often asymptomatic. Non-motile, oxidase positive, non-spore
forming. Pilus to attach to mucosal regions with a constant and hypervariable region
analogus to human antibody variation. Opa proteins to assist in epithelial cell adhesion
and anti-phagocytic capsule to resist antibodies, complement and phagocytosis.
Transcytose through sub-epithelial space and induces cytokine, matrix metalloprotease
and nitric oxide production which disassemble host cell junctions. Can systemically
spread to cause skin papules, arthritis, inflammation and meningitis, latter especially in
patients deficient in complement. Cultured well on CHA, not on HBA, treated with
Ceftriaxone, Fluroquinolones and Azithromycin.
Vibrio cholerae - ANSWER Gram-negative, facultative anaerobic bacteria, comma
, shaped. Causes cholera via infection of intestines via strong adhesion to mucosal
surfaces and exotoxin production that causes upregulation of cAMP leading to chlorine,
sodium loss and water excretion causing potentially fatal diarrhoea.
Bacilus anthracis - ANSWER gram positive, aerobic, rod shaped endospore forming
bacteria causing anthrax. PXO2 - Protein capsule and PXO1 - anthrax toxin with
protective antigen, lethal factor and odema factor. Sensitive to Penicilin G.
Klebsiella pneumoniae - ANSWER Gram-negative, lactose fermenting, non-motile,
facultative anaerobic rod shaped bacterium causing pneumonia, bloodstream
infections. Respiratory pathogen requiring biosafety cabinet handling.
Staphylococcus prophyticus - ANSWER Commonly found gra positive cocci bacteria
causing urinary tract infections. Catalase positive, DNAse and Coagulase negative and
novobiocin resistant. ß-galactosidase + and ß-Glucosidase and Tryptophan deanimase -
on the chromogenic UTI plate causing formation of pink and white colonies.
Candida albicans - ANSWER Common diploid oval gram positive opportunistic yeast
infection but is often harmless - facultative anaerobe. Can switch between phenotypes
between unicellular or multicellular by forming hyphae or gram tubes. Forms circular,
convex white colonies on HBA, CHA and green colonies on chromogenic candida plate
due to hexosaminidase production that cleaves X-NAG.
Treponema pallidum - ANSWER Spirochaete; gram negative, spiral bacterium with high
motility. Causes syphilis with sore/ulcer around entry point, and after months can cause
rash, fever, swollen glands and fatigue. After years can cause mental illness, blindness,
deafness, neurological issues and heart disease in 30%.
ELIZA - ANSWER enzyme-linked immunosorbent assay: In an Elisa is enzyme that can
catalyse reaction that leads to colour change of chromogenic chemical thats covalently
attached to an antibody. Competitive Eliza used to detect Treponema pallidum, purified
source of substance bound to plate and reacted with known concentration of
enzyme-antibody conjugate. If substance present it will compete with bound antigen for
antigen binding sites of antibody, causing reduced colour change, as antigen-antibody
complex is removed during wash. Amount of test substance in serum estimated by
comparing reduction in colour change to standard curve from known concentrations.
AN-IDENT Discs - ANSWER Rapid and simple method to presumptive identification of
anaerobic gram negative bacteria, designed for Bacteroides fragilis, consists of
Erythromycin (E), Rifampicin (RD), Colistin (CT), Penicillin (P), Kanamycin (K) and
Vancomycin (VA).
MacFarland Standard - ANSWER Turbidity standard (0.5) to compare a bacterial
suspension against, which should result in a suspension of 1-2x10^8 CFU/mL, using
black lines to contrast each tube turbidity. Often used in antibiotic testing.
Gram-positive Antibiotic Tests - ANSWER Oxacillin (OX 1µg), Vancomycin (VA30µg),
Erythromycin (E 15µg), Penicilin (P 10U), Tetracycline (TE 30µg)
Accurate Answers
Clostridium perfringens - ANSWER Gram positive anaerobe, endospore forming causing
necrotic enteritis. Forms green colony colour on CP chromoselect agar. Causes gas
gangrene and produces lecithinase alpha toxin which hydrolyses lipids in cell
membranes.
Salmonella enterica - ANSWER Gram negative rod shaped bacillus of
enterobacteriaceae
Helicobacter pylori - ANSWER Gram negative spiral bacterium associated with
duodenal and gastric ulcers. Produces cytotoxin, acid-inhibiting protein, adhesins and
urease allowing for buffering of acidic environment and virulence factors allow adhesion
to gastric mucosa and cause tissue damage via inflammatory mediators.
Escherichia coli - ANSWER Gram negative rod shaped, facultative anaerobe commonly
found in gut. ß-galactosidase cleaves Red-gal in chromogenic UTI plate forming pink
colonies & positive control in indole test.
Streptococcus salivarius - ANSWER Gram-positive, spherical, facultative anaerobe
producing lactic acid bacteria. Catalase and oxidase negative. Grows as blue colonies
on Salivarius/Mitis plate. Respiratory pathogen and requires biosafety cabinet handling.
Streptococcus pyogenes - ANSWER Gram positive, aerotolerant, spherical, non-motile
and non-spore forming cocci that tend to link. Catalase negative and does not growth on
MAC, produces hemolysin causing beta-hemolysis. Common cause of pharyngitis in
children and strep throat. Respiratory pathogen and requires biosafety cabinet
handling.
Neisseria gonorrhoeae - ANSWER Gram-negative, diplococci and intracellular
monococci bacteria causing gonorrhoea through infection of the epithelium, can cause
discharge, lesions but often asymptomatic. Non-motile, oxidase positive, non-spore
forming. Pilus to attach to mucosal regions with a constant and hypervariable region
analogus to human antibody variation. Opa proteins to assist in epithelial cell adhesion
and anti-phagocytic capsule to resist antibodies, complement and phagocytosis.
Transcytose through sub-epithelial space and induces cytokine, matrix metalloprotease
and nitric oxide production which disassemble host cell junctions. Can systemically
spread to cause skin papules, arthritis, inflammation and meningitis, latter especially in
patients deficient in complement. Cultured well on CHA, not on HBA, treated with
Ceftriaxone, Fluroquinolones and Azithromycin.
Vibrio cholerae - ANSWER Gram-negative, facultative anaerobic bacteria, comma
, shaped. Causes cholera via infection of intestines via strong adhesion to mucosal
surfaces and exotoxin production that causes upregulation of cAMP leading to chlorine,
sodium loss and water excretion causing potentially fatal diarrhoea.
Bacilus anthracis - ANSWER gram positive, aerobic, rod shaped endospore forming
bacteria causing anthrax. PXO2 - Protein capsule and PXO1 - anthrax toxin with
protective antigen, lethal factor and odema factor. Sensitive to Penicilin G.
Klebsiella pneumoniae - ANSWER Gram-negative, lactose fermenting, non-motile,
facultative anaerobic rod shaped bacterium causing pneumonia, bloodstream
infections. Respiratory pathogen requiring biosafety cabinet handling.
Staphylococcus prophyticus - ANSWER Commonly found gra positive cocci bacteria
causing urinary tract infections. Catalase positive, DNAse and Coagulase negative and
novobiocin resistant. ß-galactosidase + and ß-Glucosidase and Tryptophan deanimase -
on the chromogenic UTI plate causing formation of pink and white colonies.
Candida albicans - ANSWER Common diploid oval gram positive opportunistic yeast
infection but is often harmless - facultative anaerobe. Can switch between phenotypes
between unicellular or multicellular by forming hyphae or gram tubes. Forms circular,
convex white colonies on HBA, CHA and green colonies on chromogenic candida plate
due to hexosaminidase production that cleaves X-NAG.
Treponema pallidum - ANSWER Spirochaete; gram negative, spiral bacterium with high
motility. Causes syphilis with sore/ulcer around entry point, and after months can cause
rash, fever, swollen glands and fatigue. After years can cause mental illness, blindness,
deafness, neurological issues and heart disease in 30%.
ELIZA - ANSWER enzyme-linked immunosorbent assay: In an Elisa is enzyme that can
catalyse reaction that leads to colour change of chromogenic chemical thats covalently
attached to an antibody. Competitive Eliza used to detect Treponema pallidum, purified
source of substance bound to plate and reacted with known concentration of
enzyme-antibody conjugate. If substance present it will compete with bound antigen for
antigen binding sites of antibody, causing reduced colour change, as antigen-antibody
complex is removed during wash. Amount of test substance in serum estimated by
comparing reduction in colour change to standard curve from known concentrations.
AN-IDENT Discs - ANSWER Rapid and simple method to presumptive identification of
anaerobic gram negative bacteria, designed for Bacteroides fragilis, consists of
Erythromycin (E), Rifampicin (RD), Colistin (CT), Penicillin (P), Kanamycin (K) and
Vancomycin (VA).
MacFarland Standard - ANSWER Turbidity standard (0.5) to compare a bacterial
suspension against, which should result in a suspension of 1-2x10^8 CFU/mL, using
black lines to contrast each tube turbidity. Often used in antibiotic testing.
Gram-positive Antibiotic Tests - ANSWER Oxacillin (OX 1µg), Vancomycin (VA30µg),
Erythromycin (E 15µg), Penicilin (P 10U), Tetracycline (TE 30µg)
