Bacteria tests Flashcards
Corneybacterium
Obligate aerobes
Gram positive rods
Curved/ club shaped. ‘Kanji’ writing
Smooth, round, dove grey colonies.
Dark blue/ green polyphosphate granules seen with Alberts stain
Diptheria toxin production can be detected with ELEK plate. Non-toxigenic found as commensals in throat, toxigenic cause diptheria.
Clostridium
Gram positive rods.
Obligate anaerobes.
Hot malachite green to stain for spores.
Can be beta-haemolytic
Widely present as saphrocytes in soil.
Clostridium perfringens
Perfringens: rough-edged, volcano shaped colonies. Haemolytic, 2 zones of lysis. Oval, central spores. Nagler reaction to detect alpha toxin.
Gas gangrene when spores infect severely damaged skeletal muscle.
Clostridium sporogenes
Small opaque, irregular colonies often with wispy edges- medusae.
Oval bulging sub-terminal spores.
Non-pathogenic by itself? Can be involved in gas gangrene?
Clostridium tetani
Produces wispy colonies/ swarms over plate.
Round bulging, terminal spores.
No common sugars metabolised.
E. coli
Gram negative bacilli Facultative anaerobe Large colonies Ferments lactose -> Red MacConkey's, yellow CLED. May be haemolytic.
Commensal in gut. Pathogenic strains usually toxigenic, present in greatly increased numbers. Capsulated serotypes may cause meningitis in children. Common cause of UTIs. Recovery from wound indicated fecal contamination.
Salmonella
Gram negative bacilli
Facultative anaerobes
Non-fermenter of lactose -> pale MacConkey, blue CLED.
Species identified by antisera against surface O (carbohydrate) and flagellar H antigens. Clumping = positive.
Gastroenteriris, enteric fever, septicaemia.
Pseudomonas aeriginosa
Gram negative bacilli
Obligate aerobe
Green, diffusible pigment on nutrient agar. V large, amorphous colonies.
Fewer porins in outer membrane than most gram negative to inherently more resistant to antibiotics.
Found especially in infections of burns.
Bacteriodes fragilis
Gram negative rod
Obligate anaerobe
Metronidazole inhibits growth.
Normal flora of large intestine. May cause wound infections/ septicaemia after injury/ surgery/ appendicitis.
Staphylococcus aureus
Gram positive cocci
Grape like clusters
Catalase and coagulase positive.
Orange/yellow colonies.
Skin infections, food poisoning, dental abscesses, nonsocomial infections. Methicillin resistant = MRSA. Pyogenic- pus forming.
Staphylococcus epidermidis
Gram positive cocci
Grape like clusters.
Catalase positive, coagulase negative
Colonies usually off white.
Viridans streptococcus
Gram positive cocci,
Often diplococci, pairs/ chains.
Watery colonies
Catalase negative
Beta (incomplete) haemolysis.
No lancefield antigens.
Commensal in human throat, very serious in blood- may form septic foci or colonise heart valves, esp those already damaged by e.g rheumatic fever.
Streptococcus pneumoniae
Gram positive cocci, pairs or chains
Watery colonies
Catalase negative
Incomplete haemolysis.
Lancet-shaped, capsulated diplococci.
Commensal in human throat/ nasopharynx.
Very serious in blood- may form septic foci or colonise heart valves, esp those already damaged by e.g rheumatic fever.
Bacterial pneymonia, ear infections, meningitis.
Streptococcus pyogenes
Gram positive cocci
Pairs/ chains
Lancefield group A
Only grows on blood agar
Complete haemolysis
Titrate serum for antibody to streptolysin O.
Throat infections, rheumatic fever (type II) and glomerulonephritis (group III)
Enterococcus faecilis
Gram positive cocci Watery edged colonies Oval diplococci Catalase negative Non-haemolytic (usually) Lancefield group D. Red on MacConkey's, yellow on CLED.
Commensal of gut. UTIs.
