medical microbiology enterobacteriae

• What is the phylogenetic position of Enterobacterales?

  • Order: Enterobacterales
  • Family: Enterobacteriaceae (Genera: Salmonella, Escherichia, Shigella)
  • Family: Yersiniaceae (Genus: Yersinia)
  • Phylum: Proteobacteria
  • Order: Campylobacterales (Genera: Campylobacter, Helicobacter)

  
• What are the general morphological and biochemical characteristics of Enterobacterales?

  • 29 genera including Escherichia, Salmonella, Klebsiella, Enterobacter
  • Optimum temperature: 37 °C
  • Gram-negative, non-spore forming rods
  • Facultative anaerobes
  • Catalase positive
  • Oxidase negative
  • Nitrate reductase positive
  • Motile via peritrichous flagella (with a few exceptions)

  
• What is the G+C content and genome size of Enterobacteriaceae?

  G+C content 38-60%; genome size ~5 M bases
• What are the habitats and routes of infection for Enterobacteriaceae?

  • Habitats: gastrointestinal tract of humans, animals, and insects
  • Widespread environmental contamination: sewage, soil, water, plants, food
  • Routes of infection: oral, via wounds, urinary tract, respiratory tract

  
• 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 general 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)
  • Classification of Salmonella species is complex
• How can Salmonella be distinguished from E. coli and Shigella?

  • H2S production
  • Acid production during carbohydrate fermentation
  • Non-lactose fermenter
  • Indole test negative
• What color does Salmonella appear on XLD media?

  Black
• What are the phases of typhoidal Salmonella infection?

  1. 1st phase: slow fever, rose spots, mild bacteraemia
  2. 2nd phase: organism reaches gallbladder, formation of ulcers, haemorrhage, death (20%)
  3. Typhoid state: “muttering delirium” or “coma vigil”
• How many new cases of typhoid fever occur each year?

  ~15 million
• What is the global burden of non-typhoid Salmonella (NTS) infection?

  • ~94 million cases (155,000 deaths) each year
  • About 80 million estimated as foodborne origin
  • UK data: 8-9,000 confirmed cases per year
• What are the predominant serovars of non-typhoid Salmonella?

  • Salmonella Enteritidis
  • Salmonella Typhimurium
  • Salmonella Heidelberg
  • Salmonella Newport
• What is the primary route of NTS Salmonella infection?

  Faecal-oral transmission
• What are the main virulence factors of Salmonella?

  • Type 3 secretion systems (T3SSs)
  • SPI1: invasion of intestinal epithelial cells
  • SPI2: intracellular replication and systemic infection
• What is the mechanism of UPEC infection?

  Periurethral contamination with UPEC can occur after bowel movement or during sexual intercourse
• What are the types of urinary tract infections (UTIs) caused by UPEC?

  • Asymptomatic bacteriuria
  • Cystitis (bladder infection)
  • Pyelonephritis (kidney infection)
• What percentage of women experience a UTI in their lifetime?

  50%
• What is the major cause of CNS infections in infants under 1 month old?

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

  • Mild watery diarrhoea (typically ETEC)
  • Dysentery (typically EIEC)
  • Severe bloody diarrhoea (typically EHEC)
  • Persistent diarrhoea (typically EPEC, EAggEC)
  • Vomiting, abdominal pain, fever (all)
  • Haemolytic uraemic syndrome (HUS) only EHEC

  
• What are the characteristics of Enterotoxigenic E. coli (ETEC)?

  • Causes watery diarrhoea
  • High infectious dose: \(10^6\) organisms
  • Site of damage: small intestine; extracellular
  • Toxins: LT and ST
  • Treatment: self-limiting; oral rehydration

  
• What is the K-1 antigen synthesized by?

  1. 1 capsular antigens
• Why is K-1 antigen considered a major virulence factor?


  It is a homopolymer of sialic acid
• In which populations are K-1 strains commonly found?

  In the GI tract of pregnant women and newborns
• What is the prevalence of gastrointestinal infections caused by intestinal pathogenic E. coli (InPEC) in the UK?

  1 in 5 people are affected each year
• How is InPEC transmitted?

  By infected food and water or via person-to-person contact
• What symptoms are typically associated with ETEC infections?

  Mild watery diarrhoea
• What symptoms are typically associated with EIEC infections?


  Dysentery
• What symptoms are typically associated with EHEC infections?

  Severe bloody diarrhoea
• What symptoms are typically associated with EPEC and EAggEC infections?


  Persistent diarrhoea
• What symptoms are common to all pathotypes of InPEC?

  Vomiting, abdominal pain, and fever
• Which pathotype is associated with haemolytic uraemic syndrome (HUS)?

  EHEC
• What are the characteristics of ETEC infections?

  • Symptoms: Watery diarrhoea
  • Infectious dose: High (10^6 organisms)
  • Site of damage: Small intestine; extracellular
  • Toxins: LT and ST
  • Treatment: Self-limiting; oral rehydration; antibiotics (e.g. fluoroquinolones)

  
• What are the characteristics of EIEC infections?

  • Symptoms: Dysentery, bloody diarrhoea
  • Infectious dose: High (10^6-10^10 organisms)
  • Site of damage: Colon; intracellular
  • Toxins: None
  • Treatment: Oral rehydration; antibiotics (e.g. azithromycin)

  
• What are the characteristics of EAggEC infections?

  • Symptoms: Persistent diarrhoea
  • Infectious dose: High (10^10 organisms)
  • Site of damage: Colon; extracellular
  • Toxins: SPATEs (proteases), enterotoxins
  • Treatment: Self-limiting; oral rehydration; antibiotics (rarely)

  
• What are the characteristics of EPEC infections?

  • Symptoms: Diarrhoea
  • Infectious dose: High (10^8-10^10 organisms)
  • Site of damage: Colon; extracellular
  • Toxins: Proteases
  • Treatment: Self-limiting; oral rehydration; antibiotics (rarely)

  
• What are the characteristics of EHEC/STEC infections?

  • Symptoms: Bloody diarrhoea, kidney disease
  • Infectious dose: Low (50-500 organisms)
  • Site of damage: Colon; extracellular
  • Toxins: Shiga toxin (Stx)
  • Treatment: None at present

  
• What is the function of the type 3 secretion system (T3SS) in EPEC/EHEC?

  It enables the bacterium to export proteins directly into the host cell
• What is the primary cause of shigellosis worldwide?

  1. flexneri and S. sonnei
• How many cases of shigellosis occur annually worldwide?

  Over 190 million cases