Enterobacteriaceae and Campylobacteraceae

• What is the order that includes the family Enterobacteriaceae?

  Enterobacterales
• What are the characteristics of the Enterobacteriaceae family?


  • 29 genera including type genus *Escherichia*
  • Optimum temperature: 37°C
  • Gram-negative, non-spore forming rods
  • Facultative anaerobes
  • Catalase positive
  • Oxidase negative
  • Nitrate reductase positive
  • Motile via peritrichous flagella
  • DNA genome characteristics: G+C content 38%-60%; genome size ~5M bases
• Where are Enterobacteriaceae commonly found?


  In the gastrointestinal tract of hosts including humans, animals, and insects
• What are common routes of infection for Enterobacteriaceae?


  Oral, via wounds, urinary tract, and respiratory tract
• What diseases are associated with Enterobacteriaceae?


  Diarrhoea, sepsis, urinary tract infections, CNS and brain infections
• Why are Enterobacteriaceae considered among the most pathogenic organisms?


  They are often encountered and can cause severe diseases
• What are the characteristics of the genus Salmonella?


  • 2 species; 7 subspecies; >2600 serovars
  • Some serovars are host-restricted
  • Most serovars infect a wide range of hosts
  • Non-lactose fermenter
  • Indole test negative
• How can Salmonella be distinguished from E. coli/Shigella?


  By $H_2S$ production and acid production during carbohydrate fermentation
• What is the annual incidence of typhoid fever caused by *S. Typhi*?


  ~15 million new cases each year
• What are the phases of typhoid fever caused by *S. Typhi*?


  1st phase: Slow fever, rose spots, mild bacteraemia; 2nd phase: Organism reaches gallbladder, formation of ulcers, haemorrhage, death (20%)
• What is the impact of non-typhoid *Salmonella* (NTS) globally?


  ~94 million cases and 155,000 deaths each year
• What are the predominant serovars of NTS in the UK?


  *Salmonella* Enteritidis, *Salmonella* Typhimurium, *Salmonella* Heidelberg, *Salmonella* Newport
• What is the typical disease caused by NTS in healthy individuals?


  Self-limiting enteritis
• How does *Salmonella* invade the host?


  By crossing the epithelial barrier via phagocytic cells or direct uptake
• What are the main virulence factors of *Salmonella*?


  Type 3 secretion systems (T3SS) and Salmonella pathogenicity islands (SPI)
• What is the route of transmission for NTS *Salmonella* infections?


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


  • First isolated in 1919 by Theodor Escherich
  • Five species: *E. albertii, E. coli, E. fergusonii, E. hermanii, E. vulneris*
  • *E. coli* colonizes mammalian GI tract shortly after birth
  • Over 700 different serotypes (O, H, K), most are harmless
• What are the pathotypes of pathogenic *E. coli*?


  InPEC (intestinal infections) and ExPEC (extra-intestinal infections)
• What are the types of intestinal infections caused by *E. coli*?


  • Enteroaggregative *E. coli* (EAEC)
  • Enteroinvasive *E. coli* (EIEC)
  • Enterotoxigenic *E. coli* (ETEC)
  • Shiga toxin-producing *E. coli* (STEC)
  • Enterohaemorrhagic *E. coli* (EHEC)
• What is the prevalence of UTIs caused by uropathogenic *E. coli* (UPEC) in women?


  75% of UTIs are caused by UPEC
• What types of UTIs exist?


  Asymptomatic bacteriuria, cystitis, pyelonephritis
• How does UPEC infection occur?


  Periurethral contamination with UPEC can occur after bowel movement or during sexual intercourse
• What is the major virulence factor of meningitis-associated *E. coli* (MNEC)?


  1. 1 capsular antigens
• What is the impact of *Shigella* species globally?


  Over 190 million cases of shigellosis annually worldwide
• What is the primary route of transmission for *Shigella*?


  Faecal-oral route and person-to-person spread
• What are the symptoms of shigellosis?


  Aggressive watery or mucoid/bloody diarrhoea, fever, and stomach cramps
• What is the infectious dose of *Shigella*?


  Low infectious dose (10-100 organisms)
• How does *Shigella* invade the host's large intestine?


  By crossing the epithelium via M cells and inducing uptake by macrophages
• What is the role of the type 3 secretion system (T3SS) in *Shigella* pathogenesis?


  T3SS allows the bacterium to inject proteins directly into the host cell
• What are the four species of *Shigella* based on serological typing?


  • *S. dysenteriae* - most severe
  • *S. flexneri* - most frequent
  • *S. boydii* - confined to Indian sub-continent
  • *S. sonnei* - mildest infection
• What is the recommended first-line treatment for shigellosis?


  Fluoroquinolones, such as ciprofloxacin
• What is the mechanism of *Shigella* pathogenesis?


  *Shigella* kills macrophages and escapes to reach the epithelium’s basolateral surface
• What is the clinical presentation of *Shigella* infection?


  Aggressive watery or mucoid/bloody diarrhoea, fever, and stomach cramps
• What is the role of plasmid-borne factors in *Shigella* pathogenesis?


  They code for type 3 secretion system (T3SS) which is pivotal to infection
• What are the symptoms of intestinal pathogenic *E. coli* (InPEC)?


  • Mild watery diarrhoea (ETEC)
  • Dysentery (EIEC)
  • Severe bloody diarrhoea (EHEC)
  • Vomiting, abdominal pain, fever (all)
  • Haemolytic uraemic syndrome (HUS) (EHEC)
• What are the types of urinary tract infections (UTIs)?

  • Asymptomatic bacteriuria
  • Cystitis (Bladder infection)
  • Pyelonephritis (Upper ureter infection, kidney infection)
• What are the types of intestinal pathogenic *E. coli* (InPEC) and their characteristics?

  | Pathotype | Symptoms | Infectious Dose | Site of Damage | Toxins | Colonisation Factor | Treatment |

  | --- | --- | --- | --- | --- | --- | --- |

  | ETEC | Watery diarrhoea | High (10^6) | Small intestine | LT and ST | - | Self-limiting; oral rehydration; antibiotic |

  | EIEC | Dysentery, bloody diarrhoea | High (10^6 - 10^10) | Colon | None | pINV (T3SS) | Oral rehydration; antibiotics |

  | EAggEC | High infectious dose: 10^10 organisms | Colon | SPATEs (protease), enterotoxins | - | Self-limiting; oral hydration; antibiotics |

  | EPEC | Diarrhoea | High (10^6-10^10) | Colon | Proteases | - | Self-limiting, oral rehydration; antibiotics (rarely) |

  | EHEC/STEC | Bloody diarrhoea, kidney disease | - | Colon | Shiga toxin (Stx) | A/E lesions (LEE pathogenicity island) | None at present |
• What is the clinical presentation of Shigellosis?


  Aggressive watery or mucoid/bloody diarrhoea, fever, and stomach cramps
• How long does it take for symptoms of Shigellosis to begin after ingestion?


  1. 2 days
• What is the typical duration of Shigellosis in immunocompetent individuals?


  1. 7 days