campylobacter jejuna Flashcards
as a new disease
- campylobacter fetus was well established as a veterinary pathogen in cows/ sheeps and rarely humans
- in 1972 first report of C.jejuni isolated from faeces of patients with enteritis using a filter technique
- employed a microaerobic environment
what did Mark Skirrow demonstrate
- 1977
- demonstrated that campylobacters could be isolated from faeces of patients with diarrhoea using a new method
- involved a selective antibiotic containing medium and incubation in an atmosphere of 5% oxygen at 43 degrees
campylonacter jejuni - the organism
- gram negative, motile, spiral
- campylobacter derived from Grek for curved rod
- microaerophilic - similar to related bacterium helicbacter pylori
- grows best at 37-42 degrees
- higher temps are selective and represent higher body temperatures of avian species
- belongs to epsilon subdivision of the proteobacteria
the disease
- classic symptoms of infection are an acute self limiting gastroenteritis
- estimated 2-5 days incubation following ingestion
- sometimes fever
- typically, 3 -10 days of inflammatory diarrhoea follow with presence of leukocytes
- can contain blood, pus, mucus
- abdominal cramping common
- infection resolves generally without treatment
- bacteraemia is rare - immunocompromised
what can more serious cases be treated with
antibiotics e.g. erythromycin or fluoroquinolones
- resistance is now problematic
diagnosis
- direct microscopy of faecal samples - spiral bacteiral with a characteristic rapid darting motility
- latex agglutination with specific antisera coated on beads
- PCR
- typically based on culture of organism on antibiotic containing selective agar plates incubated at 42 degrees
- colony morphology, gram stain and phenotypic tests
treatment and resistance
- most of those infected will not seek medical support and infection will resolve
- staying hydrated is important
- antibiotics are used for more serious cases
- typically, macrolides erythromycin and azithromycin or fluoroquinolones typically ciprofloxacin
- floroquinolone resistance is increasingly problematic
- multi drug resistance is also emerging
campylobacter in the UK
- commonest cause of bacterial gastroenteritis in the UK
- estimated 500,000 cases in england and wales annually
- summer peak is consistent feature around June/ July
- in low and middle income countries constant exposure to campylobacter is thought to lead to immunity in adults
- there is significant infant mortality assicated with this endemic infection
campylobacter and chickens
- estimated 70% of campylobacter cases linked to chicken
- it is commensal in chickens
- colonise to very high numbers in the chicken caecum
- carriage is largely asymptomatic
- no effective strategy to reduce levels of campylobacter in this food product
virulence
- lack of classical virulence features
-no T3SS though does have flagella based system for injecting proteins - no enterotoxins though do produce cytolethal distending toxin
key properties of organism
- cell shape and flagella mediated motility
- ability to generate cell surface structural diversity for longer term colonisation in animal hosts
- mimicry of host gangliosides on cell surface by lipooligosaccharide
- secretion of proteins into host cells via. flagella based secretion system
generating strain diversity - natural transformation
- C.jejuni naturally competent for DNA up take and transformation
- specific uptake system to transport DNA across membrane barriers into cytoplasm
RecA recombinase for integration of homologous DNA into the chromosome - naturally transformable bacteria recognise closely related DNA through presence of short hyperabundant DNA uptake equences
- C. jejuni does not use this mechanism to recognise DNA from other campylobacters
- in contract a campopylobacter transformation system methyltransferase methylates RAATTY sites on C. jejuno DNA and only methylated DNA can transform in campylobacter strains
generating strain diversity - phase variation
- a number of campylobacter genes contain intragenic homopolymeric tracts
- typically, single nucleotide repeats of 8-12 G or C residues
- these are error prone during replication so that the number of repeats varies randomly
- this leads to reversible on-off switching of production of functional protein
- influence structure of LOS, CPS and flagellin glycan
- creates extensive surface diversity
C.jejuni lipo-oligosaccharide
the C.jejuni outer membrane contains LOS - truncated structure that lacks O antigen which is present in LPS
- terminates in a short oligosaccharide
- in many strains, this region contains unusual sugar sialic acid
- by coating the cell in human ganglioside - lipe epitopes C.jejuni will potentially reduce recognition by the host and consequent immune response
- this can lead to autoimmunity due to production of antibodies against C.jejuni LOS
how many cases can lead to giullain- barre or miller-fish syndrome
approx 1 in 1000 cases of C.jejuni infection
Guillan - barre syndrome and C.jejuni
- potenitally life threatening post infectious disease characterised by progressive, symmetrical weakness of the extremities
pathogenesis of GBS
molecular mimicry of pathogen - borne antigens, leading to generation of cross reactive antibodies that also target gangliosides, is part of the pathogenesis
treatments for GBS
intravenous immunoglobulin and plasma exchange are proven effective treatments but many patients have considerable residual deficits
why does GBS occur
GBS typically occurs after an infectious disease in which the immune response generates antibodies that cross react with gangliosides at nerve membranes
- campylobacter jejuni is the most common infection leading to the infection
capsular polysaccharide
C.jejuni strains produce an extracellular capsular polysaccharide and can be used to serotype strains
- mutants lacking CPS do not colonise chicks
- lack of CPS also reduces adherence to and invasion of intestinal epithelial cells and serum resistance
- CPS reduces activation of TLR and cytokine stimulation
what is CPS composed of
composed of a repeating backbone of 2 or more sugars
- this repeat structurally varies in different strains defining serotype
what is intrastrain structural variation of CPS due to
- variable modification of the backbone sugars with O-methyl phosphoramidate and O-methyl
- mediated by phase variable expresssion of MeOPN and O-Me transferase
- MeOPN can act as bacteriophage receptor and O-Me modification can disrupt bacteriophage docking
what systems does C.jejuni contain to glycosylate different proteins
- O- linked protein glycosylation system that specifically modifies flagellins forming the extracellular flagella filament
- N linked general protein glycosylation system that modifies many extra cytoplasmic proteins
O- linked protein glycosylation of C.jejuni flagellin
- as many as 19 serine and threonin residues on the flagellin subunit protein can be modified with unusual monosaccharides pseudaminic acidand legionaminic acid
- flagellin glycosylation is essential for flagellin to polymerise into the extracellular filament for motility
- genes involved in flagellin glycosylation vary between strains and phave vary within strains
- structural variation for flagella tropic phase/ immune system evasion
N linked general protein glycosylation system
- modifies over 100 periplasmic and inner/ outer membrane proteins with a conserved heptasaccharide glycan
- these proteins are modified at a specific asparagine residue within a consensus motif
- inactivation of glycosylation affects host cell adherence and invasion, colonisation of chicks and mice
- N linked glycosylation of surface proteins may protect against degradation by extracellular host proteases and enhance protein thermostability
