Gram Negative Bacilli I Flashcards
Lipopolysacchride
- AKA Endotoxin
- the major virulence factor of Gram-negatives
- a major component of the outer membrane
- very powerful immune stimulant
- much released into host as bacteria die
- “blebs” of LPS may be released at other times
Enterobacteriaceae reservoirs
- ubiquitous
- reservoir: normal flora of humans and animals intestines
- common in water, soil and vegetation
- an indicator of faecal contamination of water
Enterobacteriaceae transmission
•faecal contamination –water –food –hands –abdominal surgery •endogenous (self) •exogenous (other humans or animals)
Enterobacteriaceae common infection sites
CNS (Escherichia, Citrobacter)
Lower respiratory tract (Klebsiella, Enterobacter, Escherichia)
Blood stream (Escherichia, Klebsiella, Enterobacter)
Gastrointestinal tract (Salmonella, Shigella, Escherichia, Yesinia)
Urinary tract (Escherichia, Proteus, Klebsiella, Morganella)
What are the laboratory features of enterics?
Gram-negative, short-medium rods
Straight sides, rounded ends
Non-sporulating
Facultative anaerobes
Non-motile/motile with peritrichous flagella
Oxidase (catalysis of O2 to H20 or H2O2) negative
Ferments glucose with +/- produce gas production
Reduces nitrate to nitrite
Enterbacterial common antigen: part of LPS
How to differentiate between enterics?
•fermentation of lactose and other sugars •biochemical tests: –urease production –indole production –H2S production –Voges-Proskauer test
MacConkey agar
Selective to bacteria tolerant of bile salts - enteric bacteria.
Fermentation of lactose results in pink colonies such as Escherichia coli.
Enterics that do not ferment lactose, such as Salmonella are not pink.
Enterobacteriaeceae pathogenesis
Some are:
•strict pathogens
–never commensals
–e.g Yersinia pestis, Salmonella Typhi
•opportunistic pathogens
–commensals causing sterile site infections
–e.g. E. coli UTIs.
•commensals until virulence genes acquired
–from plasmids or bacteriophages e.g. EHEC
Enterobacteriaceae strain typing
•serological testing of antigens
–O polysaccharides in LPS
–K polysaccharides in capsules
–H proteins in flagella
Escherichia coli
- the most common facultative anaerobe in human GIT
- huge variability: > 700 O:H:K serotypes
- the most common enteric pathogen
- identify pathogenic strains by O:H:K serotyping
- serotypes linked to particular diseases and severity
Escherichia coli diseases
- gastroenteritis
- urinary tract infections (UTIs)
- septicaemia
- neonatal meningitis
- infected ulcers
- intra-abdominal infections
- pneumonia
- intravascular catheter infections
E. coli gastroenteritis
•watery, +/- bloody diarrhoea, vomiting, abdominal pain, cramps, fever
•Haemolytic Uremic Syndrome (HUS)
–a severe, sometimes fatal complication in children
–renal impairment, hypertension, CNS problems
•from exogenous strains with extra virulence genes
•mostly effects children in developing countries
EHEC gastroenteritis
•most common E. coli gastro. in developed countries
•USA 73, 000 cases, 60 deaths per annum
•bloody diarrhoea, severe abdominal pain, HUS
•from eating food contaminated with animal faeces
•often undercooked mince meat: “hamburger disease”
•O157:H7
–most common strain
–has acquired “Shiga toxin” from bacteriophage
E. coli UTIs
- > 80% of UTIs from E. coli
- endogenous origin – faeces
- anus to urethra to bladder to kidney
- from any E.coli (opportunistic pathogens)
- ‘uropathogenic’ E. coli strains are worse
E. coli septicaemia
•medical emergency •25-40% mortality •usually secondary to: –UTI –intraabdominal infection after intestinal leakage
E. coli neonatal meningitis
- a common aetiological agent of neonatal meningitis
* E. coli and GBS together cause the majority of infections
Klebsiella
•Most common pathogens: –K. pneumoniae –K. oxytoca •normal flora of GIT •opportunistic pathogens
Klebsiella diseases
•pneumonia •necrosis of lungs •other infections (less common): –wounds –soft tissue –urinary tract
Klebsiella diagnosis
•at risk groups: –men –middle-aged and older –alcoholism –diabetes –chronic bronchopulmonary disease •thick, bloody, mucoid “currant jelly” sputum •capsules and mucoid colonies
Salmonella enterica
- > 2500 O serotypes
- naming: Salmonella Serotype
- reservoir is the intestines of any animals
- Salmonella Typhi in humans only
- facultative intracellular parasite
- can pass through intestine wall
- survives in macrophages
Salmonella gastroenteritis
•from consumption of faecally contaminated
–(undercooked) eggs
–(undercooked) poultry
–(undercooked) dairy products
–water
–other foods from contaminated surfaces
•nausea, vomiting, nonbloody diarrhoea
•abdominal cramps, myalagias, headache common also
•very unpleasant then spontaneous resolution
Salmonella enteric fever
- from Salmonella Typhi – infects only humans only
- serious clinical disease – many epidemics with 1000s of deaths
- AKA typhoid fever or typhoid
- faecally contaminated water, food or surfaces
- most prevalent in children and elderly in developing countries
- vaccines available now, recommended for travellers
- consumed bacteria pass through cells lining the intestine
- engulfed by macrophages
- transported to liver, spleen, bone marrow then replicates
- gastroenteritis, fever, bacteraemia
Salmonella bacteraemia
•possible with all strains
•most frequently associated with infections due to:
–S. Typi
–S. Paratypi
–S. Cholerasuis
•similar (serious) symptoms to other Gram-negative bacteraemias
Shigella
- S. dysenteriae, S. flexneri, S. boydii, S. sonnei
- historical naming only - genetically all E.coli!
- infects intestines humans only
- causes “Shigellosis”
- 150 million cases worldwide annually
