Week 7 - Gram Negative Bacilli Flashcards
Enterobacteriaceae
Most common GNB Causes 50% of septicaemias, 60-70% GIT infections and 70% UTIs Opportunistic pathogens Many endogenous in gut and LUT NF at large intestines
Enterobacteriaceae Characteristics
Catalase Pos Oxidase Neg Fermentative Facultative anaerobes Non-fastidious Grey, moist, shiny colonies on BA Slightly opaque centre than edge Usually non-haemolytic
Enterobacteriaceae Overt Pathogens
Salmonella
Shigella
Yersinia
E.coli
Gram Negative Antigenic Properties
Major antigens: - H flagellar protein - K capsular polysaccharide - O somatic lipopolysaccharide (cell wall) Other antigens - F fimbrial (adherence)
What are the two non-motile Enterobacteriaceae?
Klebsiella
Shigella
Escherichia Species
Colonise GIT
Usually very biochemically active and motile
E.coli most common human bacterial pathogen
E.coli
Lactose fermenter - bright pink on MAC/ yellow on CLED
Motile
Indole Pos
Indole Production
Tests if an organism produces the enzyme tryptophanase
Tryptophanase breaks down amino acid tryptophan into indole
Diseases that E.coli causes
Septicaemia Wound infection Peritonitis UTI Diarrhoael diseases
Indole Test Methods
Method 1
- bottle/tube and in API strips
- incubate inoculated peptone broth overnight
- add 5-10 drops of Kovacs reagent
- positive = pink ring on surface
Method 2
- few drops of Kovac’s reagent to piece of filter paper
- transfer a quantity onto filter paper
- positive = pink/red colour
Use BA as it has tryptophan unlike MAC or CLED
Klebsiella
NF in gut
Opportunistic invaders especially in moist conditions
Found in environment and plants
2 species
K.pneumoniae - causes pneumonia, septicaemia, UTI, nosocomial
K.oxytoca
Klebsiella Characteristics
Lactose Fermenters - pale pink on MAC/pale yellow CLED Non-motile Capsulated - mucoid and sticky K.oxytoca indole pos K.pneumoniae indole neg
Enterobacter Characteristics
Lactose variable
Motile
Indole neg
Proteus, Providencia and Morganella Characteristics
NF in GIT UTI Wound infections Non lactose fermenters - blue on CLED/very pale pink on MAC Phenylalanine deaminase/trytophan deaminase pos Urea positive Non-capsulated Motile
How to prevent swarming of Proteus on MAC
Use a no salt or low salt formula
Zoonoses
Diseases of animals which may be transmitted to humans
Diseases caused by Salmonella
Gastroenteritis
Enteric fever
Extra-intestinal infections
Carrier status
Bacillary Dysentry
Caused by Shigellae Associated with humans only Low infectious dose (10-100 organisms) Invasion of wall of large intestine Inflammatory response Blood, mucous and pus
Yersinia disease caused
Yersinia enterocolitica main GIT pathogen of genus Causes: - Enterocolitis - Fever - Diarrhoea
Pseudomonas
Soil, plants and water supplies
Opportunistic
- UTI
- Otitis externa
Pseudomonas aeruginosa
Non-fastidious Obligate anaerobe Motile Oxidase pos Oxidative Flat, matt colonies Shield shaped
Haemophilus Characteristics
NF at URT
Small GNB or coccobacillus
Capnophilic
Fastidious
Grey/translucent, circular shiny colonies on CHOC
No growth on selective/differential media
Neisseria gonorrhoeae
Strict human pathogen - not NF
Causes gonorrhoea
- pyogenic (pus producing) infection of urethra
Neisseria meningitidis
NF of URT
Humans only reservoir
Spread by droplets
Causes meningococcal meningitis
