Microbiology 3 Flashcards
What are the major phyla making up the gut flora?
- Firmicutes
- Bacteroides
- Proteobacteria
Describe Firmicutes
- Majority Gram +ve
- Some form endospores
- Mollicutes (Mycoplasmas) lack cell walls altogether
- Some sub groups have porous pseudo outer membrane casuign Gram -ve staining
- Found in various environments
- Commensals and pathogens
List the important Gram +ve Firmicutes
- Listeria
- Staphylococcus
- Enterococcus
- Lactobacillus
- Streptococcus
List the important Gram +ve endospore forming Firmicutes
- Clostridium
- Bacillus
Describe Bacteroides
- Composed of 3 large classes of bacteria
- Bacteroidales, Bacteroides, Porphyromonas
- Widely distributed in environment
- Rarely pathogenic
- Some evidence for opportunistic infection by Bacteroides (abundant in faeces)
- Bacteroides, Porphyromonas Gram -ve
Describe Proteobacteria
- All Gram -ve
- Includes commensals and pathogens
- Defined by rRNA sequences
- Diversity of forms
- Either facultative or obligate anaerobes
- Heterotrophic (numerous exceptions)
- Divided into 5 sections: alpha, beta, gamma, delta, epsilon
Give an example of alpha Proteobacteria
Rickettsia
Give examples of beta Proteobacteria
- Neissericeae
- Burkholderia
What are the families within gamma Proteobacteria?
- Psuedomonadaceae
- Enterobacteriaceae
- Vibrionaeceae
Give an example of Psuedomonadaceae
Pseudomonas
Give examples of Enterobacteriaceae
- Escherichia
- Salmonella
- Proteus
- Klebsiella
- Yersinia
- Enterobacter
- Shigella
- Citrobacter
Give an example of Vibrionaceae
Vibrio
Give an example of delta Proteobacteria
Myxobacteria
Give an example of epsilon proteobacteria
- Helicobacter
- Campylobacter
Describe Alphaproteobacteria
- Symbionts of plants and animals
- Important group, contains pathogens (Rickettsiaceae)
- Minute Gram -ve, obligate intracellular pathogens
- Not GI
- Rickettsia rickettsii = rocky mountain spotted fever in US, vector bourn (ticks)
- Rickettsia typhi - rodent vectors
Describe Betaproteobacteria
- Aerobic or facultative
- Several groups
- highly versatile in degradation capacities
- Range from plant pathogens, environmental organisms to pathogenic species
Describe Gammaproteobacteria
- 3 important groups
- Important pathogens
- Not all are GI importance
Describe Epsilonproteobacteria
- Contains Vibrio pathogens Helicobacter and Campylobacter
- Microaerophilic
Describe Actinobacteria
- Contains Mycobacteria (acid fast) and Bifidobacterium (Gram +ve)
- Corynebacterium
- Range of organisms, some cause disease, some healthy commensals
Describe the genus Bacteroides
- Gram -ve
- Rod
- Anaerobic
- Non-endospore
- Variable motility between species
- Novel membrane sphingolipids and mesodiaminopimelic acid in peptidoglycan layer
- Major component of GI flora
- Complex molecules to simpler ones in host intestine
- Simple sugars when available, main source of energy is polysaccharide from plant sources
Describe the genus Lactobacillus
- Gram +ve
- Facultative anaerobe/microaerophilic
- Firmicutes
- Lactose and other sugars to lactic acid
- Common and benign
- Mucosa of reproductive and GIT
- makes environment acidic, inhibitis growht of someharmful bacteria
Describe the genus Clostridia
- Gram +ve
- Rod
- Obligate anaerobes
- Can produce endospores
- Pathogenic
- Botulinum, dificile, perfringes, tetani all important species
Describe the genus Streptococci
- Gram +ve
- Coccoid
- Firmicutes phylum
- May be commensal or pathogenic
- Lots of species
- Distinguish by haemolysis, serology and biochemical testing
- Grow in chains or pairs
Describe Enterococcus faecalis
- Gram +ve
- Non-motile
- Commensal
- Facultatitve anaerobe
- Catalase -ve
- Gamma haemolytic
- Niche gastrointestinal tracts of mammals
- May be opportunistic pathogen
Describe the genus Bifidobacterium
- Gram +ve
- Non-motile
- May appear branched
- Anaerobe
- GIT of mammals
- Ferment carbohydrates/oligosaccharides
Describe how restriction enzymes function
- Sequence specific
- Recognise and bind to specific DNA sequences
- Once bound to recognition sequence, cut sugar-phosphate backbones of DNA strands
- Some leave overhanging sticky ends
- Sticky ends can be reattached by ligase enzyme
- Catalyses chemiccal reaction that rejoins sugar-phosphate bonds
Describe the process of DNA sequencing
- New DNA strand synthesis using existing strand as template
- Add nucleotides in 5’ to 3’ direction
- 5’ carbon of incoming deoxynucleotide (dNTP) joined to 3’ carbon at end of chain
- Hydroxyl groups in each position form ester linkages with central phosphate
- Nucleotide chain elongates
Describe Sanger’s method of DNA sequencing
- dideoxynucleotides (didNTP) incorporate into chain by forming phosphodiester linkage at 5’ end
- Lack 3’ hydroxyle group needed to form linkage with incoming nucleotide
- Addition of didNTP stops elongation
- To sequence DNA 4 reactions needed to give information about each nucleotide
- Each reaction contains template DNA, short primer, DNA polymerase, 4dNTPS (one radioactively labelled) and one type of didNTP (A, C, T, G)
- Same as normal process, but when didNTP added to chain by polymerase synthesis is terminated generating DNA strand of certain size
- Put through gel electrophoresis
- Read bottom to top, knowing the terminator lane give sequence of nucleotides in tempate DNA
Outline cycle sequencing
- Based on Sanger method
- Fragments produced in same way
- Each didNTP emits light of characteristic wavelength
- Record as coloured band on simulated gel image
What is point mutation?
A base replaced by a different base
What is a silent mutation?
ONe that does not change the peptide sequence i.e. has no effect
What is a mis-sense mutation?
One that changes a codon to code for a different amino acid
What is a non-sense mutation?
One that changes a codon to stop truncate peptides, usually negative
What is the effect of a mutation in the coding region?
- May have no effect if silent mutation
- May prevent synthesis of the protein (non-sense)
- May alter the protein in structure or ability to function (non-sense mutation)
What is the effect, on gene expressiong, of a mutation in the regulatory region of a sequence?
- Can impact on promotor or enhancer sequences, termination signals, splice donor and acceptor sites and ribosome binding sites
- Initiation of transcription controlled by short sequence elements called promotors
- Genes include information that tells RNA polymerase where to start and stop
- May prevent protein being expressed or may increase expression
What are somatic mutations?
- Those only affecting one cell and those created from the mutated cell
- Cannot be passed onto offspring as does not affect the cells that create gametes
What are germ line mutations?
Ones that affect every cell in an organism and are passed onto offspring
Give the key types of infections of the oral cavity
- Endogenous (usually bacterial and fungal)
- Exogenous (usually viral)
- Number of viral diseases
- Bacterial oral infection usually opportunistic and preceeded by trauma
- Mycotic oral infection uncommon
Outline the key types of infections in the oesophagus
- No defined flora or pathogens but viral infections occur
- Rapid passage of material through oesophagus
- Tough stratified epithelium, infection uncommon
- Some viral infections cause ulcers
- Most notable BVDB and mucosal disease
- Newcastle disease in poultry
Outline key infections of the stomach
- Hostile to organisms
- Helicobacter
Outline key features of small and large intestinal infections
- Affect all domestic animals
- Effective vaccinations against many viral pathogens
- Close confinement increases risk of contracting disease
- Stress can increase growth of pathogens in intestine
- Major clinical manifestation is vomiting or diarrhoea
Describe the group Enterobacteriaceae
- E. coli, Salmonella serotypes
- Inhabit intestinal tract of animals and man
- Gram -ve rods
- Growth on enriched media
- Oxidase negative
- Tolerate bile salts
- Mostly non-haemolytic
- Pathogens: E. coli (also commensal), Salmonella enterica, Yersinia species
- Opportunistic pathogens: Proteus spp, Enterobacter spp, Klebsiella spp.
- All look roughly the same on cultures
- Differentiation by growth characteristics and biochemistry
How can Proteus spp. be distinguished on media?
Unusual swarming pattern (ripples on a pond)
What tests can be used to distinguish between members of the Enterobacteriaceae group?
- Culture characteristics
- Motility at 30degreesC
- Lactose fermentation
- IMViC tests
- Hydrogen sulphide production
- Lysine decarboxylase
- Urease activity
- Can combine tests in XLD for example
Describe Escherichia coli
- Opportunistic infections
- Possess virulence factors which allow them to cause disease
- 3 main groups of pathogenic E coli
- ETEC, AEEC, EAggEC
- AEEC also has subgroups EPEC and STEC/EHEC
Describe ETEC (name, virulence factor, pathology, disease examples)
- Enterotoxigenic E coli
- Characteristic fimbrail adhesins
- LT and ST pig associated, Sta calves and pigs, STb pigs
- Cause secretory diarrhoea
- Increase Cl- and HCO3- secretion and inhibit Na+ absorption
- Less water absorption
- Mechanism of each toxin differs slightly
- Diarrhoea in neonatal piglets, calves, lambs, post-weaning diarrhoea in pigs, diarrhoea in pups
Describe EPEC in general
- Enteropathogenic
- Atypical and typical types
- No enterotoxins
- Different virulence factors for typical and atypical
- Both cause attaching and effacing lesions, determined by locus of enterocyte effacement (LEE)
- Intimate adherence to enterocytes and effacement of microvilli
Describe atypical EPEC (virulence factor, disease examples)
- Outer membrane protein intimin
- Wide range of diseases
- Slight changes or haemorrhagic diarrhoea in calves, pigs and dogs
- Lambs and kids occasionally affected
- Major cause of diarrhoea in neonatal and weanling rabbits
Describe typical EPEC (virulence factors, disease examples)
- Intimin (OMP) and EPEC adherence factor (EAF)
- Uncommon pathogens in intestinal tract of animals
- Causes human infantile diarrhoea in developing countries
What does STEC stand for and what are the 2 subgroups?
- Shiga Toxin producing E coli
- EHEC
- Strains of E coli producing oedema disease
Describe EHEC (virulence factors, pathology caused, diseases)
- Intimin adhesin, STx toxins (affect endothelial cells)
- Attaching and effacing lesions
- Intimate adherence to enterocytes and effacement of microvilli
- Rare cause of haemorrhagic diarrhoea in calves
- Cattle asymptomatic carriers
- Other domestic animals may be reservoirs
Describe strains of E coli producing oedema disease (virulence factors, pathology caused, disease)
- F18 fimbriae adhesin
- STx2e toxin
- Alpha haemolysin also present
- STx2e damages vascular endotehlium in target tissues = localised oedema
- Oedema disease in recently weaned pigs
Describe EAggEC
- Enteroaggregative
- Typical and atypical subgroups
- Both cause histopathological lesions charaterised by “stacked brick” formation of epithelial cells
Describe atypical EAggEC (virulence factors, pathology caused, disease)
- No adhesins or enterotoxins identified
- Histopathological lesions characterised by stacked brick appearance of epithelial cells
- Frequently subclinical, occasionally associated with diarrhoea in animals
Describe typical EAggEC (virulence factors, pathology caused, disease)
- Aggregative adherence fimbriae, EAST1 toxin, plasmid encoded toxin
- Histopathological lesions characterised by “stacked brick” formation of epithelial cells
- Diarrhoea in humans
Describe Salmonella
- 2 species
- S. bongori and S. enterica
- S. enterica has number of subspecies: Typhimurium, Enteritidis, Gallinarium, Pullorum
- Some host specific, others non-host specific
- Over 2400 serotypes
- O and H antigens
- Invades gut lining
List sources of Salmonella infection
- Water
- Soil
- Animal feed
- Raw meat
- Eggs
- Offal
- Plant material
Describe enteric Salmonellosis
- Acute disease, can affect most farm animals
- Restricted to intestine and its mucosa
- Fever
- Depression
- Anorexia
- Profuse foul smelling diarrhoea
- Severely affected animals may become recumbent
- When endemic, milder signs may occur due to acquired immunity
- Inflammatory disease
How does Salmonella cause its pathology?
- Attachment and invasion damages enterocyte
- Penetration of mucosal barrier leads to inflammation and fluid secretion
- Neutrophils attracted to site increasing inflammation
- Infection of macrophages
Explain how Salmonella is detected
- Enrichment in selenite broth
- Inoculation onto MacConkey or XLD
- Confirm suspect colonies with serotyping
Describe Campylobacter
- Many commensals in GIT of warm blooded animals
- Number of species in genus
- Most common jejuni, coli, lari
- C. fetus in abortion
- In humans jejuni and coli
- Commensal of poultry, cattle adn sheep
- Unclear in young pups
- Most common infection
- Not as severe as EHEC or Salmonella
- Contaminates meat and eggs of poultry
- Causes inflammation, tissue damage, secretion and fluid release, inflammatory diarrhoea
- Sporadic infection not outbreaks
Describe Campylobacter jejuni
- Gram -ve
- Vibrio (coccoid under stress)
- Flagellated, motile
- Non-fermentative, oxidase positive, variable catalase reaction
- Microaerophilic
- Optimum range 37-42degreesC
- Nutrient or isolation media using Campylobacter selective medium
- Adapted optimally in poultry, can grow in mammals
How is Campylobacter cultured or typed?
- Neck swabs from birds, caecal contents, faecal swabs
- Culture at 37-42degreesC
- Selective or enrichment medium
- Smear with dilute carbol fuchsin or Gram
- Look for vibrio shape
- Identification by specieation (biochem, specific PCR), subtyping, MLST, serotyping
What can be used to distinguish between Campylobacter species?
- Colonial morphology
- Biochemistry
- Growth temp
- Serology
What can be used for differentiation within Campylobacter species?
- Serology
- Molecular analysis (ribosome sequence analysis, MLST, whole genome based comparisons)
Describe Spirochetes
- Spiral motile bacteria
- Endoflagella
- Gram -ve
- many zoonoic
- 3 important genera: Leptospira, Borellia, Brachyspira
Describe the respiration of Leptospira, Borellia, Brachyspira
- Leptospira: anaerobic
- Borellia: microaerophilic
- Brachyspira: anaerobic
What are the important species of Brachyspira?
- Hyodysenteriae
- Innocens
- Pilosicoli
- Intermedia
- Alvinipulli
Describe the growth of Brachyspira
- Strict anaerobe
- Does not form discrete colonies
- 42degreesC for at least 3 days (slow)
- B. hyodysenteriae is haemolytic
What can be used to differentiation between Brachyspira
- Pattern of haemolysis
- Indole test
- Hippurate test
How is Brachyspira diagnosed?
- Sleective media (blood agar with selective antibiotics)
- Stained faecal smear for spirochaetes
- Silver stain faecal mear
- PCR tests
Describe the pathogenesis of Brachyspira
- Motility in gastric mucus essential
- Haemolytic activity correlates with virulence
- Proteases
- Mucosal disruption leas to cell shedding and oedema
What are the virus protein functions?
- Genome protection, delivery, replication and spread
- Host interaction
Explain the role of virus proteins in genome protection, delivery, replication and spread
- Structural (genome protection)
- Entry and uncoating
- replication of genome (polymerase and/or accessory factors)
- Reguation of virus gene expression
- Assembly, genome packaging, exit from cell
Explain the role of virus proteins in host interaction
- Determine type of host infected and tissues affected
- Persistence (in environment and host)
- Evasion of host immunity and intracellular defences
- Manipulation of intracellular environment to support virus replication (host shut off, cell cycling)
- Pathogenesis, tumorigenesis
What is the basic process of viral replication?
- Receptor binding
- Entry
- Uncoating of viral nucleic acid
- Genome transcription
- mRNA translation
- Replication of nucleic acid
- Assembly of new virus particles
- Release by cytolysis or budding
- Genome affects exact steps in replication
Explain the role of polymerase enzymes in viral replication
- Replicate viral genetic material to produce mRNA and genomic nucleic acid
- Can be provided by cell ro virus depending on genome type
- If not provided by cell, virus must supply polymerase (many RNA viruses)
- Most DNA viruses replicate in nucleus
- Most RNA viruses replicate in cytoplasm
Describe replication of +ssRNA
- Viruses encoved RNA polymerase translated directly from viral genome i.e. acts as mRNA
- Can act directly as mRNA, genome directly infectious
- RNA translated to produce single polyprotein
- Protein cleaved by viral proteases
- Genome replicated by viral polymerase
What is unusual about the replication of Coronavirus and Arterivirus?
- +ssRNA
- More complex
- Produce nested mRNAs via negative strand intermediate
DEscribe replication of -ssRNA
- RNA polymerase contained within adn encoded by virus
- Replication of genome via synthesis of complimentary RNA strand
- Transcription then translation
- Cannot act directly as mRNA
- Virions contain (and genome encodes for) RNA dependent RNA polymerase
- generates +ve mRNA
- Genome replicated by same RNA polymerase, via +ve sense intermediate
- Replicate in cytoplasm
What is unusual about the replication of Bunyaviridae and Orthomyxoviridae?
- -vessRNA
- Replicate in nucleus
Describe the replication of retroviruses
- Viral RNA reverse transcribed
- Uses reverse transcriptase (RNA-dependent DNA polymerase)
- Converts genome ot complimentary DNA (cDNA)
- Integrates into chromosome of host cell by viral integrase enzyme
- Integrated DNA termed proviral DNA
- Integrated DNA then produces RNA and protein using normal cell machinery
- Integration into host genoome permanent
- Can disrupt normal activity and lead to tumour formation
Describe the replication of dsDNA
- Replicate in host cell nucleus
- transcription of DNA viruses by cellular (DNA-dependent) RNA polymerase
- Encode own DNA polymerases so can control replication of genome independently of cellular DNA replication
Describe the replication of ssDNA
- Requires dsDNA intermediate
- Active host DNA polymrase needed to replicate genome (produce dsDNA)
- Use host RNA polymerases to produce mRNA
- Can infect only dividing cells where DNA polymerase is active
- E.g. intestinal, bone marrow, cardiac, neural cells
Describe viral gene expression
- Some regulate expression very tightly
- Can go for long periods with little viral gene expression
- latency important featuer of some viruses
- Helps explain patterns of disease
- Intermittent, delyaed
- Only expressed when conditions optimal for virus
Outline post-translational modification of viral proteins
- Viral proteins may also be modified by other host systems e.g. glycosylation
- Can prevent antibody binding to virus
Outline different ways in which viruses are adapted to compensate for limited genome size
- Larger viruses able to encode larger number of proteins
- Own polymerases, regulatory proteins etc
- Smaller can only code for limited number of proteins
- Can maximise encoding potential by number of strategies
- Overlapping genes (different reading frames), production of polyproteins, multiple splicing to produce RNAs
What are the methods of genetic variation in viruses?
- Spontaneous mutation
- Gene trasnfer between viruses or cell via recombination or reassortment
Describe spontaneous mutation in viruses
- Mistakes made during genome replication
- RNA viruses higher rate of mutation
- Enzymes cannot proof read
- Very high replication rate of some RNA viruses means very large numbers of mutant viruses
- Virus population exists as a quasispecies
Describe gene transfer between viruses or cell
- Transfer of genetic information between 2 usually related viruses which have infected the same cell
- Produces hybrid genomes
- Entire genes/gene sequences derived from another virus
- Via recombination or reassortment (segmented viruses)
Describe recombination in viral genetics
- Relatively uncommon
- Between viruses with related DNA/RNA sequence or between virus and host nucleic acid
- Can lead to viruses acquiring host sequences
Describe gene reassortment in viral genetics
- Occurs with segmented genomes
- Simple exchange of genes when 2 different viruses infect cell (influenza, rotavirus)
- Frequency of viable recombinants higher than for random mutations
- Emergence of successful variants
- Extends gene pool of virus
- Produces daughter strain with combination of parent genes
- Rapid mutation of virus circulation
Describe the consequences of viral mutation
- Lethal mutation
- Silent muation
- Growth advantage/disadvantage
- May be better at survival and spread
- Different antigens (vaccines!)
- Virulence altered (clinical consequences)
- Altered host range
- Drug resistance
Describe mycobacteria in terms of their Gram staining
- Do not stain with Gram stain
- Cytochemically Gram +ve
- Lipid and mycolic acid content of walls prevents uptake of Gram stain dyes
- Acid fast
What stain is used to visualise mycobacteria?
- Ziehl-Neelson
- Stain red
How does Ziehl-Neelson stain work?
- Cell wall lipids bind to carbol fuchsin
- Not removed by acid-alcohol decolouriser
Describe teh growth rate of pathogenic mycobacteria
- Most slow growing
- Colonies take a few weeks
- Saphrophytes grow quickly
Describe the general growth requirements of pathogenic species of Mycobacteria
- Complex
- Egg-enriched media
Describe the cultural and growth requirements of M. tuberculosis
- 3-8 weeks
- 37degreesC
- Aerobic
- Colonies rough, buff and difficult to break apart
- Enhanced growth with glycerol
- Pyruvate has no effect on growth rate
Describe the growth requirements of M. bovis
- 3-8 weeks
- 37degreesC
- Aerobic
- Colonies cream coloured, raised central roughness, break apart easily
- Growth inhibited with glycerol
- Enhanced growth with pyruvate
Describe the growth of M. avium
- 2-6 weeks
- 37-43degreesC
- Aerobic
- Colonies sticky, off-white, break apart easily
- Enhanced with glycerol
- No effect with pyruvate
Describe the pigments produced by some mycobacteria
- Some produce carotenoid pigments
- Non-chromogens produce colonies with no carotenoid pigments (M. avium)
- Photochormogens = non-pigmented colonies that become pigmented when exposed to light
- Scotochromogens produce pigments when cultured in dark/light
What disease is caused by M. tuberculosis?
TB in humans and captive primates
What disease is caused by M. bovis?
TB in cattle
What disease is caused by M. avium?
TB in most avian species excpet Psittacines
What are the clinical characteristics of Johne’s disease
- Diarrhoea (intermittent becoming permanent and profuse)
- Weight loss (without loss of appetite)
Where does M. avium reside during infection?
- In macrophages
- Granuloma formation
- Intracellular pathogen (more difficult for immune system)
What is the public health risk with Johne’s disease?
- Milk transmission
- Non-pasteurised can carry infection (also true for cheese)
What is the outcome of Johne’s disease in cattle?
- No treatment
- Slaughtered
Describe Clostridia
- Large
- Gram +ve
- Rods
- Endospores
- Anaerobic
- Catalase and oxidase negative
- Motile
- Enriched media required for growth
- Diverse forms of disease in many animal species
Where are clostridia normally found?
- Soil
- Alimetnary tracts of animals
- Faeces
What are the 4 pathogenic groups of clostridia?
- Neurotoxic
- Histotoxic
- Enteropathogenic
- Enterotoxaemic
What types of C. perfringens are most important in domestic animals?
- Have types A-E
- A, B, C and D most important
What does C. perfringens look like on blood agar?
- Surrounded by zones of double haemolysis
- Ring of complete haemolysis in centre around colony
- Aroudn first ring, second ring of incomplete haemolysis
What is the egg yolk antigen toxin media test with C. perfringens called?
Nagler reaction
Describe the Nagler reaction
- C. perfringens
- Identifies alpha toxin
- Antitoxin specific to alpha toxin applied to half of egg yolk plate
- C. perfringens streaked across place, incubated at 37degreesC for 24 hours
- Organisms grows on both halves, activity only on half of plate (where no antitoxin)
What divides the groups of C. perfringens and what are the types?
- The significant and minor toxins they use
- Types A-E
What are the major and minor toxins of type A C. perfringens?
- Major: alpha
- Minor: NetB toxin
What are the major and minor toxins of type B C. perfringens?
- Major: Alpha, beta
- Minor: epsilon (protoxin, needs to be activated by proteolytic enzymes)
What are the toxins of type C C. perfringens?
Alpha, beta and enterotoxin
What are the toxins of type D C. perfringens?
Alpha, epsilon (both major)
What are the toxins of type E C. perfringens?
Alpha and zeta (both major)
What do the enterotoxins beta, epsilon and zeta toxins do?
- Beta: lethal, necrotising
- Epsilon: increases intestinal and capillary permeability, lethal
- Zeta: dermonecrotic, lethal
What are teh virulence factors shared by all enteric strains of E. coli?
- Pili (fimbriae)
- TTSS (type three secretion systems)
Define adhesin
- Cell surface components or appendages of bacteria that facilitate adhesion or adherence to other cells or surfaces
- Type of virulence factor
Define toxin
- A poison of plant or animal origin, especially produced by or derived from microorganisms and acting as an antigen in the body
Describe intimins
- Type of adhesin
- EPEC, EHEC
- Formation of attaching and effacing lesions
- On bacterial cell surface
- Bind to receptor Tir (translocated intimin receptor)
How is Tir introduced into eukaryotic cells?
- Translocated intimin receptor
- By E. coli TSS with 25 other bacterial proteins
- Inserted into plasma membrane of host cell
Describe fimbrial adhesins
- ETEC
- Attachment to mucosal surfaces in SI and LUT
- Facilitates colonisation by diminishing expulsive effects of peristalsis and flushing effect of urine
- Formerly known as pili
- Significant: K88, K99, 987P, F41
- Pigs: K88, K99
- F41 in calves
- K99 in lambs
Describe LT enterotoxin
- Heat labile
- K88 adhesins
- Lead to hypersecretion of fluid into intestine
- Stimulate adenylate cyclase activity
Describe STa enterotoxin
- Pigs, sheep, humans, cattle
- ETEC
- Increases guanylate cyclase activity in enterocytes
- Intracellular guanosinemonophosphate stimualte fluid and electrolyte secretion into SI
- Inhibits fluid absorption from intestine
Describe STb enterotoxin
- Causes secretion of chloride and bicarbonate ions
- Inhibits absorption of sodium ions
- Differs from STa and LT1
Describe Shiga toxins
- STEC
- Letahl for cultured veo cells
- Heat labile
- STEC colonises intestinesand damages enterocytes
- Absorbed into blood stream, deleterious effect on endothelial cells (CNS in pigs)
- Inhibits protein synthesis in eukaryotic cells
- Vascular damage and ST2E is oedema disease of pigs
Describe cytotoxic necrotising factor 1
- CNF1
- Encoded chromosomally
- Exact role uncertain
- Extraintestinal E coli infections
Describe cytotoxic necrotising factor 1
- CNF2
- Extraintestinal E coli infections
- Encoded by transmissible plasmid known as Vir
- Exact role uncertain
Describe SEPEC (virulence factors, pathology, disease)
- Septicaemia
- Adhesins differnt for each host
- Fimbrial adhesins in many, CS31A surface antigen in calves
- Produce toxins CNF and CDT
- Hypogammaglobulinaemia
- Capsular antigens smooth LPS and other OMPs contribute to resistance to circulating antibody
- Septicaemia in some domestic animals
- Occasionally fatal pneumonia in horses, dogs and cats
Describe UPEC (virulence, pathology, disease)
- Uropathogenic
- Adhesins: type 1, P and S fimbriae
- Toxins: alpha haemolysin and CNF1
- Adhere to bladder epithelium, iron scavenging mechanisms
- UTI, pyometra in dogs
Describe opportunistic E coli infections (virulence, pathology, disease)
- Strains causing localised infection
- Adhesins not identified
- Endotoxin
- Opportunistic infection by environmental E. coli, host factors predispose to infection
- Mastitis, omphalitis, other localised infections
Explain how E. coli can be both a pathogen and a commensal
- Commensal does not carry TTSS (needed for invasion)
- Depends on which strain is where, may be commensal in one system and pathogenic in another
- Host species specificity
- Commensal in one species, pathogenic to another
