Enterobactericeae

• What are the main aims of studying Enterobacterales and Campylobacterales?

  To describe structural, physiological, biochemical, and genetic characteristics of bacteria and viruses, diseases caused, virulence mechanisms, and environmental roles.
• What is the general morphological and biochemical characteristics of Enterobacterales?

  • Emended family Enterobacteriaceae
  • 29 genera including Escherichia, Salmonella, Klebsiella, Enterobacter
  • Gram-negative, non-spore forming rods
  • Facultative anaerobes, catalase positive, oxidase negative
  • Motile via peritrichous flagella
• What is the optimum temperature for Enterobacterales?

  37ºC
• What is the G+C content and genome size of Enterobacterales?

  G+C content is 38-60%; genome size is > 5M bases.
• What are the common habitats of Enterobacteriaceae?

  • Gastrointestinal tract of hosts (humans, animals, insects)
  • Widespread in sewage, soil, water, plants, and food
• What are the routes of infection for Enterobacterales?

  Oral, via wounds, urinary tract, and respiratory tract.
• What diseases are commonly caused by Enterobacterales?

  Diarrhea, sepsis, urinary tract infections, CNS infections.
• How many people are affected by food-borne illness in the UK each year?

  1 million people.
• What percentage of urinary tract infections (UTIs) are caused by E. coli?

  70%.
• What are the characteristics of the genus Salmonella?

  • 2 species, 7 subspecies, ~2,600 serovars
  • Some serovars are host-restricted (e.g., Typhi for humans)
  • Most serovars infect a wide range of hosts (e.g., Typhimurium)
• What is the difference in lactose fermentation between Salmonella and E. coli?

  Salmonella is a non-lactose fermenter, while E. coli ferments lactose.

  
• What selective media can distinguish Salmonella from E. coli and Shigella?

  XLD media and SS media.

  
• What are the phases of Typhoid fever caused by S. Typhi?

  1. First phase: slow fever, rose spots, mild bacteremia
  2. Second phase: organism reaches gallbladder, formation of ulcers, hemorrhage, death (20% mortality)
• What is the global burden of non-typhoid Salmonella (NTS) cases each year?

  Approximately 94 million cases.

  
• What are the predominant serovars of non-typhoid Salmonella?

  Salmonella enteritidis, Salmonella typhimurium, Salmonella heidelberg, Salmonella Newport.
• What are the main virulence factors of Salmonella?

  • Type 3 secretion systems (T3SSs)
  • Encoded on Salmonella pathogenicity island (SPI)
  • T3SS acts as a molecular ‘syringe’ to transfer proteins to host cells

  
• What is the primary route of NTS Salmonella infection in the UK?

  Fecal-oral transmission.
• What are the characteristics of the genus Escherichia?

  • First isolated in 1919 by Theodore Escherich
  • Five species: E. albertii, E. coli, E. fergusonii, E. hermanii, E. vulneris
  • E. coli colonizes the mammalian GI tract shortly after birth
• How many different serotypes of E. coli are there?

  Approximately 700.
• What are the types of urinary tract infections (UTIs) caused by E. coli?

  • Asymptomatic bacteriuria
  • Cystitis (bladder infection)
  • Pyelonephritis (kidney infection)

  
• What is the percentage of women who experience a UTI in their lifetime?

  50%.
• What is the mechanism of UPEC infection?

  UPEC can contaminate the periurethral area after bowel movements or sexual intercourse.
• What is the major cause of CNS infections in infants?

  Meningitis-associated E. coli (MNEC).
• What are the symptoms of intestinal pathogenic E. coli (InPEC)?

  • Mild watery diarrhea (ETEC)
  • Dysentery (EIEC)
  • Severe bloody diarrhea (EHEC)
  • Persistent diarrhea (EPEC, EAggEC)
  • Vomiting, abdominal pain, fever
• What are the characteristics of ETEC?

  • Causes watery diarrhea
  • High infectious dose: \(10^6\) organisms
  • Site of damage: small intestine; extracellular
  • Toxins: LT and ST
  • Treatment: self-limiting; oral rehydration
• What are the characteristics of EIEC?

  • Causes dysentery, bloody diarrhea
  • High infectious dose: \(10^6\) to \(10^{10}\) organisms
  • Site of damage: colon; intracellular
  • Treatment: oral rehydration
• What are the characteristics of EAggEC?

  • Causes persistent diarrhea
  • High infectious dose: \(10^{10}\) organisms
  • Site of damage: colon; extracellular
  • Treatment: self-limiting; oral rehydration; antibiotics (rarely)
• What are the genetic features of the genus Shigella?

  • 4 species: S. dysenteriae, S. flexneri, S. boydii, S. sonnei
  • S. dysenteriae causes the most severe infections
  • S. flexneri is the most frequent in developed countries
• What is the annual global incidence of shigellosis?

  Approximately 190 million cases.
• What is the primary transmission route for Shigella?

  Fecal-oral route and person-to-person spread.
• What are the clinical presentations of shigellosis?

  • Aggressive watery or mucoid/bloody diarrhea
  • Fever and stomach cramps
  • Symptoms begin 1-2 days after ingestion
• What is the infectious dose for Shigella?

  10-100 organisms.
• What are the virulence factors of Shigella?

  • Plasmid-borne factors (pINV)
  • Type 3 secretion system (T3SS)
  • Chromosomal factors including enterotoxins and siderophores

  
• What is the pathogenesis of Shigella?

  • Invades and destroys large intestine epithelium
  • Crosses epithelium via M cells and induces uptake by macrophages
  • Kills macrophages and escapes to the epithelium's basolateral surface
• What is the role of T3SS in Shigella infection?

  • Allows injection of proteins directly into host cells
  • Pivotal to infection process

  
• What is the significance of the SHI-1 chromosomal factor in Shigella?

  It encodes enterotoxins.
• What is the role of SHI-2 and SHI-3 in Shigella?

  They encode siderophores.

  
• What is the function of Stx-phage p27 in Shigella?

  It encodes shiga toxin.
• How long does shigella typically resolve in?

  1. 7 days
• Which age group is most affected by shigella?

  Children under 5 years