15 – E. Coli Flashcards
Microbial characteristics
- Gram-negative fermentative rods
- Biocontainment level 1-3
- Commonly divided based on ability to FERMENT LACTOSE
- Blood agar: colonies are typically grey (small round colonies to swarming plate)
E.coli on blood agar and MacConkey
- Pink colouration reflects LACTOSE FERMENTATION
Proteus mirabilis on blood aga
- Swarm entire plate!
Natural host or habitat
- Widely disseminated and ubiquitous (environment, intestinal and respiratory tract)
- Some occupy specialized niches (Salmonella typhi=only humans reservoir)
- Some ‘generalist nature’ in their name
Taxonomy
- Differential agar plates useful
- Biochemical tests
- Tube motility tests
- Triple Sugar Iron (TSI)
E. coli genes
- Many core genes
- Accessory genes continues to grow!
- *tremendous diversity
Virulence factors: 2 broad organizations
- Diarrheagenic E. coli (DEC)
- Extraintestinal pathogenic E. col (ExPEC)
Virulence factors: diarrheagenic E. coli (DEC)
- Shiga toxin producing (STEC)
- Enterotexigenic (ETEC)
- Enteropathogenic (EPEC)
Virulence factors: extraintestinal pathogenic E. coli (ExPEC)
- Uropathogenic (UPEC)
- Sepsis-causing (SEPEC)
- Avian pathogenic (APEC)
E. coli STEC: virulence factors
*Shiga toxin family
- Stx: multiple variants, act by interfering with protein synthesis
o Causes edema and hemorrhage
- Phage mediated:
o Fluoroquinolones and TMS may increase expression
*intimin: eae
E. coli ETEC cause of
- Neonatal colibacillosis in ruminants and pigs
o ‘weanling diarrhea’ and ‘travellers diarrhea in people
E. coli ETEC species and age specific pathogenicity
*presence of receptors in host
- F4 fimbriae: receptors found in piglets up to 8 weeks old
- F5 fimbriae: receptors found in calves in first few days of life
E. coli ETEC toxins include
- Heat labile toxin (LT)
- Heat stable toxin (ST)
E. coli ETEC: heat labile toxin (LT)
- Increase cAMP levels leading to increased fluid and electrolyte excretion
- Similar to toxin produced by Vibrio cholerae
E. coli ETEC: heat stable toxin (ST)
- Interferes with enteric nervous system
E. coli EPEC: histologically see attaching and effacing lesions
- bacteria seen closely attached to enterocytes
- heavily colonized enterocytes may have intracellular bacteria
- mucosal erosions are present
E. coli EPEC key virulence factor
- eae (enterocyte attaching and effacing)
o encodes an intimin which allows bacteria to attach
E. coli EPEC dogs
- increasingly recognized
- may mimic typical parvovirus presentation
E. coli Uropathogenic
- infections opportunistic: ascending from urethra
- intracellular infections
- many virulence factors
E. coli uropathogenic virulence factors
- fimbriae: P. fimbriae protect against phagocytosis
- flagella: swimming up kidneys from bladder
- siderophores: aerobacin (acquisition of iron)
- alpha hemolysi: pore-forming
E. coli Septicemic virulence factors
- fimbriae
- capsule
- siderophores
- endotoxin
- colicin V
E. coli APEC virulence factors
- fimbriae
- invasins
- hemolysins
- siderophores
E. coli piglet diarrhea
- F4 E.coli
- Neonatal diarrhea (more often affects gilt litters)
- Youn piglet diarrhea (until weaning)
- Post-weaning diarrhea
Treatment of E. coli piglet diarrhea
- Antimicrobials (based on AST if possible)
- Fluid therapy
Management of E. coli piglet diarrhea
- Keep barn clean: build-up of pathogens=RISK factor
- Keep piglets warm (30-34degrees C for unweaned) and DRY
E. coli calf scours
- Calves and sheep (F5 E. coli)
- Receptors only expressed in first 1 week of life
- Watery and NOT bloody
- Polymicrobial infections common: cause expression of F5 receptors in older calves
o Rotavirus
o Cryptosporidium parvum - *other strains of E. coli can cause systemic infections in calves (ascending from umbilicus)
E. coli edema disease (pigs)
- Peracute disease
- Differential diagnosis for Clostridoides difficile
- Fecal-oral transmission
- Following attachment to intestinal epithelium=production of a Shiga-toxin
E. coli edema disease (pigs): peracute disease
- Often found dead
- Edema of eyelids, forehead, stomach and spiral colon
- Neurological signs: infarctions of brain
E. coli hamburger disease (humans)
- Severe, bloody diarrhea in people
- Associated with the O157:H7 strain
- Important foodborne pathogen (most commonly beef)
- Fecal-oral transmission can result in zoonotic spread
o Contaminated water or direct contact with animals
E. coli hamburger disease (humans): severe, bloody diarrhea
- Hemorrhagic colitis
- Hemolytic-uremic syndrome
o Hemolytic anemia
o Kidney failure
o thrombocytopenia
E. coli mastitis (cattle)
- coliform mastitis
- major cause of mastitis in well managed herds
- E. coli shed in feces and enters teat from environment
- Presentation varies (mild to severe)
- Some cows respond to invasion early and clear E. coli from teat
- Some are slower=allows cells to multiply
- *30-40% of severely affected become bacteremic
Coliform
- Relating to gram-negative rod-shaped bacteria (ex. E. coli) found in intestine
- Used as indicators of fecal contamination
E. coli mastitis (cattle): cows that are slower and allow cells to multiply
- Multiply in teat
- Endotoxin released from dead cells
- Leads to cytokine storm and systemic inflammation
E. coli mastitis (cow) treatment
- systemic and intramammary antibiotics
E. coli mastitis (cow) management
- removing organic bedding materials that support E. coli growth
Colibacillosis
- infection with avian-pathogenic E. coli
o make their way into the egg - constellation of symptoms
- found in environment, from hens feces and exploding eggs
o gas produced by bacteria can cause egg to burst
Symptoms of colibacillosis
- Omphalitis: often involves yolk sac
- coli-septicemia
- swollen-head syndrome
- air sacculitis
omphalitis
- inflammation of navel
E. coli omphalitis (chickens and turkeys) numerous presentations
- dead embryos
- swelling and edema of navel
- distended abdomen
- *’mushy chicks’: body wall overlying yolk sac degenerates
E. coli omphalitis (chickens and turkeys): treatment
- Antimicrobials (area of debate)
E. coli omphalitis (chicken and turkeys): management
- Keep things clean (discard eggs and exploders)
- Disinfecting eggs within 2 hours of laying
- Good quality diets may help
- Possible vaccination
E. coli UTI (dogs)
- 14% of dogs (most commonly spayed females) have UTIs, 50% implicated with E. coli
- Less common in cats than dogs
- Classified by anatomical site
Lower UTI
- Bladder and urethra
- Sporadic cystitis
- Recurrent cystitis
Sporadic cystitis: lower UTI
- Female otherwise healthy, non-pregnant
- No anatomical or functional abnormalities or relevant co-morbidities
- NOT a repeat infection
Upper UTI
- Kidney and ureter
Treatment of UTI if sporadic cystitis
- Can treat empirically
- *collect urine to culture
Treatment of UTI if anything else
- MUST be based on susceptibility tests
Treatment of UTI
- Antibiotic therapy depends on site of infection
- Addressing underlying disease
Management of UTI
- Get a diagnosis!
o Why does this animal have a UTI? - Address underlying disease!
Sample collection
- Diarrhea: colonic tissue for histopathology
- Mastitis: milk
- Omphalitis: samples from dead chicks (inner viscera)
- Mortality event: whole animals (pathological lesions, histology, culture)
- UTI: aseptically collect urine (preferably cystocentesis)
Lab ID
- Easy to grow with standard cultures
- *MacConkey provides very useful first clue
- Biochemical tests
- MALDI-TOF
- Molecular methods
- NAAT tests: to help ID pathogenic types
- Histology to ID/characterize lesions
Zoonotic/interspecies transmission: food borne transmission
- Enterohemorrhagic E. coli
o Maintained by healthy cattle, shed in feces
o Cattle unaffected=LACK TOXIN RECEPTOR - *possibly a source of antimicrobial resistance
Zoonotic/interspecies transmission: animal to human to animal to human
- Less well defined=UNDERSTUDIED
Standard precautions to prevent zoonotic/interspecies transmission
- Hand washing
- PPE
Treatment options
- Must be guided by susceptibility testing
Drugs to avoid/intrinsic resistance
- ALL enterobacterales intrinsically resistant to
o Benzylpencillin
o Glycopeptides
o Fusidic acid
o Macrolides
o Lincosamides
o Streptogramins
o Rifampin
Resistance is emerging! Be aware of
- Broad spectrum beta-lactamases
- Fluroquinolone resistance
