Enterobacteriaceae 2

Enterobacteriaceae 2

1. Habitat, nutrients, energy and oxygen

   • Salmonella
     • Reservoir
       • Guts of humans, animals, birds, reptiles
     • Diagnosis
       • Biochemistry / Serotypes / Biotypes / Phage types
         • Precise identification only tends to be done in legal cases to prove the bacteria are the same
       • Many polymorphs in faeces
       • Fluorescent antibody staining (PM material)
       • Serology
         • ELISA / tube agglutination
         • Single sera NOT used
           • Presence alone is not enough to diagnose – many carriers
         • Acute & convalescent paired sera
           • Rising titre in paired titre indicates infection (+ clinical disease)
         • Use for a flock/herd
           • Wouldn't necessarily use for an individual
   • Shigella
     • ID
       • Serotyping and toxin assays for Shiga toxin
   • Yersinia
     • Y. Pseudotuberculosis
       • Reservoir (worldwide)
         • Soil
         • Gut - wild mammals (rodents); birds; domestic animals
       • ID → O and H serotyping
     • Y. Enterocolitica
       • Reservoir (worldwide)
         • Soil
         • Guts of wild and domestic animals
         • Pig tonsils
       • ID → O serotyping
         • O3 & O9 – pigs AND humans → ZOONOTIC
         • O9 also on Brucella abortus (another gram –ve)
           • LPS end up being similar to others
   • Proteus
     • ID → O & H serotyping
   • E. coli
     • ID
       • Fimbrial antigens & toxins
       • Fluorescent antibody tests & PCR
   • Organisms that live in the intestine, but primarily cause disease at other sites
     • Proteus
     • Klebsiella
     • Enterobacter
     • Citrobacter
     • Serratia
     • Morganella
     • Edwardsiella
   • Primary pathogens of the intestine
     • Salmonella
     • Shigella
     • Yersinia
   • Klebsiella
     • ID → 77-82 K types
       • K1:K2:K3– pneumonia (humans)
         • Capsule: K antigen
       • K1:K5:K7– metritis (mares)
       • Many K Ags – mastitis (cows)
         • Limited availability to split into groups – cannot be serotyped in same way

2. Diseases caused

   • Salmonella
     • Serotypes
       • Host adapted, e.g. S. Dublin, S. Pullorum
         • S. Dublin is from Dublin, causes disease in cattle. Rarely found in others, but can be found in people
         • S. Pullorum is found in chickens only
       • Non-host adapted, e.g. S. Typhimurium
         • S. Typhimurium causes typhoid in mice, commensal in cattle. Can also affect other species
       • N.B. Adaptation is not absolute
       • Almost all serotypes can affect humans. Poultry-adapted serovars like S. Pullorum non-pathogenic in man
   • Shigella
     • Bacillary dysentery
       • Humans and primates
       • ZOONOTIC
   • Yersinia
     • Y. Pseudotuberculosis
       • Infections
         • Captive rodents / birds
         • Zoo animals
         • Domestic animals
         • Humans
     • Y. Enterocolitica
       • Infections
         • Animals (captive deer): gastroenteritis ± invasion
         • Humans: non-invasive gastroenteritis
           • Causes diarrhoea
   • Proteus
     • Found in soil/water (faecally contaminated)
     • Human/ animal gut commensal
     • Important diseases
       • Otitis externa – dogs and cats
         • ‘Fishy’ smell → likely to be proteus
       • Urinary tract infections – dogs and horses
       • Diarrhoea – young of most species
         • In adult – can remain in the gut without causing disease – into open wound/abrasion in gut
       • Surgical problems – e.g. gut surgery
         • Post surgery will cause diarrhoea if in large numbers (will be dealt with by immune system in small numbers)
       • Wound infections - common in humans
   • Klebsiella
     • Human/animal gut commensal; soil/water/hands/instruments
     • Important diseases:-
       • Wound infections
         • Joint (navel) ill in foals/lambs
         • Wound infection in humans
       • Mastitis – post-parturition (cows/sows)
       • Urinary tract infections – dogs
       • Pneumonia – foals
       • Genital tract infections – horses
   • E. coli
     • Can be an intestinal pathogen but also causes other diseases depending on which serotype we are dealing with
     • Commensals & opportunistic pathogens & Obligate pathogens
       • Wound infections
       • Surgical problems
       • UGT infections
       • Udder infections
     • Bovine mastitis
       • Very common and serious
       • Most common gram –ve cause

3. Process of disease

   • Salmonella
     • Enteritis
       • Motility to wall of intestine → contact
       • Fimbrial mediated adherence – sticks to wall of intestine
       • Parasite induced endocytosis – inject proteins into cell to cause endocytosis
       • Survival in endosome (e.g. catalase activity) – can therefore cause diarrhoea and not be washed out
       • Endotoxin + cell damage
       • → Adenylate cyclase activation + inflammation
         • More salmonella can get in, and the cycle continues
     • Sepicaemia
       • Adherence/PIE/ic survival
         • PIE = parasite induced endocytosis
       • Deeper invasion → blood stream
         • Toxins are shed into the blood stream
       • → Endotoxic shock +/- deposition
         • Deposition causes repeated waves of infection (chronic infection of the gall bladder)
         • Intestine is reseeded with infection – need to identify the organ and remove it
         • Antibiotics are unlikely to work
       • Joints – arthritis/osteomyelitis
       • Brain – meningitis
       • Placenta/foetus – abortion
       • Lungs – pneumonia
       • Endotoxaemia induced ischaemia of hind limbs/ears/tail in calves = terminal dry gangrene
         • NB: If an endotoxin is being produced, then it is time to start using antibiotics
     • Spread of Salmonella
       • Animals
         • Sources
           • Environment
           • Milk from carriers
             • Pasteurisation of milk should overcome this as an issue
           • Infected hosts / convalescent hosts / carriers
           • Vertical transmission from infected breeding stock
         • Outbreaks
           • Individual animal - susceptible herd/flock
           • Contaminated food / water
           • Shedding from rodents / birds
           • Protein supplements
       • Reptiles and birds
         • Source of infection
           • Faecal-oral spread
           • Vertical transmission
       • Humans
         • Source of infection
           • Food bourne
             • Infected source animal/bird
               • Birds tend to be carriers
             • Infected food handler/utensils
       • S. Typhimurium – in all species
       • S. Enteritidis – in poultry
       • Issue in imported eggs and poultry
   • E. coli
     • Factors affecting disease type
       • Enteritis &/or septicaemia
       • Serotype
         • Enteritis/septicaemia/both
       • Host species
       • Predisposing factors
         • Poor husbandry
         • Age – neonates / newly weaned (maternal Abs)
     • Categories of obligately pathogenic E. coli serotypes
       • Enterotoxigenic E. coli (ETEC)
         • Fimbrial adhesins
           • e.g. F4 (K88) – piglets, horses
           • F5 (K99) – piglets, calves, lambs
           • Different types found in different species
         • Specific enterotoxins
           • LT (heat labile toxin) and/or ST (heat stable toxin)
         • Cause liquid release from cells, so bacteria need to hold on tight to the epithelium → diarrhoea
       • Verotoxigenic E. coli (VTEC)
         • Fimbrial (+ other) adhesins
         • Verotoxins (Shiga-like toxins) – cause bloody diarrhoea
           • VT1, VT2 and VT2e
         • Bloody diarrhoea, toxin affects blood vessels – kidney, lung
           • Caused by O157
           • Breaks down walls of blood vessels in capillary beds
         • Young animals more susceptible
         • Not common – good hand-washing and hygiene will get rid of it
       • Attaching and Effacing E. coli (AEEC)
         • Also known as Enteropathogenic E. coli (EPEC)
         • Attachment via the intimin protein
           • Attach to intestine wall and multiply as a group
         • Toxins produced locally, water loss, mucosal loss
         • Brush border destroyed, toxins alter host cell cytoskeleton
         • Bacteria are internalised
         • Localised lesions
       • Unclassified and new types of E. coli
         • Mushy chick disease
         • Yolk sac infection
         • Septicaemia in poultry
         • Zoonotic infection
         • Necrotoxigenic E. coli
           • Toxins, which result in necrosis of the body
           • Not too common
       • Enteroinvasive E. coli (EIEC)
         • Doesn’t produce toxins/diarrhoea
         • Adhesins – intimin and fimbriae
         • Surface proteins mediate endocytosis
         • Bacteria escape by destroying the cell
           • Spread around host
         • Causes mechanical damage to the mucosa
   • Yersinia
     • Invades intestine, tracks to lymph nodes, walled off by immune system
     • Virulence determinants
       • As for Y. pseudotuberculosis + heat-stable enterotoxin
       • Not simple diarrhoea
   • Proteus
     • Virulence determinants
       • Adhesins ??
       • Endotoxin ??
       • Urease
   • Klebsiella
     • Virulence determinants
       • Fimbrial adhesins (produces fimbriae)
       • Capsule - Steric hindrance of complement
       • Endotoxin
       • Looks 'wet' on a plate
     • Is it capsular? Is there alot of it?
       • YES - commensal
       • NO - pathogen

4. Control measures

   • Shigella
     • Treatment/prevention
       • Antibiotics not used in simple disease as they can cause prolonged infection and the disease is self-limiting
         • Need to keep up fluids
         • Tend not to give antibiotics
       • Fluid replacement – supportive therapy
       • Vaccines (to adhesins / shiga toxin / invasion genes)
       • Improve conditions – better sanitation, decreased stress, decreased overcrowding
         • Antibiotics would wipe out bacteria in lumen, not cells – are therefore less effective
         • Will make bacteria virulent, prolonging infection
         • Therefore supportive therapy is better and a more common solution
   • Yersinia
     • Y. Pseudotuberculosis
       • Treatment / Prevention
         • Antibiotics
         • No commercial vaccines
       • No antibiotics if an immunocompromised patient – monitor fever and dehydration
     • Y. Enterocolitica
       • Antibiotics
         • Need to be used due to toxin being produced – attacking the lumen wall, breaking down cells
       • No commercial vaccines
   • Salmonella
     • Treatment
       • Enteritis
         • Good nursing
         • Fluid/electrolyte replacement
         • NOT antibiotics
           • Kills commensals
           • Selects for R salmonella
           • Selects for high virulence
           • Enteritis + Antibiotics = Septicaemia
       • Septicaemia
         • Good nursing
         • Fluid/electrolyte replacement
         • Antibiotics
           • Parenteral admin
     • Control
       • Animals
         • Good husbandry
         • Vaccines – inactivated & live attenuated
         • Competitive exclusion
       • Humans
         • Break chain of infection
         • Clean water/food hygiene/sewage disposal
           • Poor sewage disposal is often the cause of outbreaks in less developed areas
   • E. coli
     • Treatment
       • Antibiotics + fluid/electrolyte replacement
       • Tend to use early, aggressive antibiotic treatment where possible
     • Prevention
       • Good husbandry (susceptible to uv, drying and disinfectants)
       • Vaccines (fimbrial proteins / toxins) – neutralise the toxins
         • Neonate : passive immunisation
         • Neonate : active immunisation
   • Proteus
     • Antibiotics
       • Will start to colonise the rest of the body, hence need to use antibiotics
     • No commercial vaccines
     • Hygiene / aseptic technique
   • Klebsiella
     • Antibiotics. No commercial vaccines
     • Hygiene / aseptic technique

5. Factors affecting disease type

   • Virulence determinants
   • Innate and adaptive host defences
   • Interaction of these factors affects
   • In a chronic subclinical infection, an immune response has been mounted, but the animal continues shedding the disease
   • If the infected organ can be identified, then surgery is possible to remove it

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