Enterobacterales Quiz

Enterobacterales Overview

• Enterobacterales are a wide taxonomic order of bacteria
• Dr. Yang Yu MD PhD FRCPC provided the original slide deck

Agenda

• Introduction and Overview
• General Characteristics of Enterobacterales
• Medically Important Species
• Diagnosis and Treatment
• Prevention and Control

Learning Objectives

• Describe general characteristics of the order Enterobacterales, including biochemical testing, microscopic Gram staining and macroscopic appearances
• Describe methods for detecting Enterobacterales in clinical specimens, comparing culture-based vs. culture-independent tests
• List common solid culture media for Enterobacterales (blood, MacConkey, xylose-lysine-deoxycholate (XLD), Salmonella-Shigella (SS) and Hektoen enteric agar)
• Describe the importance of STEC infection and available lab diagnosis methods
• Describe Salmonella infection, including typhoid and non-typhoid, and typhoid prevention
• Describe antimicrobial resistance features in Enterobacterales and its impact on treatment and infection prevention and control (IPAC)
• Describe foodborne infection surveillance and outbreak investigation

General Characteristics of Enterobacterales

• Gram negative bacilli
• More than 50 genera, hundreds of species
• Aerobic and facultative anaerobic growth
• Non-spore forming
• Ferment glucose (acid ± gas)
• Reduce nitrate (NO₃) to nitrite (NO₂)
• Catalase positive
• Oxidase negative

Clinically Important Gram Negative Bacteria

• Enterobacterales (glucose fermenters)
• Non-glucose fermenters
• Gram-negative cocci
• Gram-negative coccobacilli
• Pseudomonas
• Acinetobacter
• Haemophilus
• Neisseria (H. influenzae, N. meningitis, N. gonorrhoeae)

Enterobacterales - Ubiquitous & Opportunistic Bacteria

• Ubiquitous in soil, water, vegetation and gut flora across animals and humans
• Some are strict human pathogens (e.g., Salmonella typhi, Yersinia pestis)
• Some are opportunistic pathogens (e.g., Escherichia coli, Klebsiella pneumoniae, Proteus mirabilis)

Enterobacterales - Structure & Virulence Factors

• Structural components of cells, including:
  • Flagella (H antigen)
  • Capsule (K or Vi antigen)
  • Lipopolysaccharide (LPS) or endotoxin
  • Common antigen
  • Outer membrane
  • Periplasmic space
  • Lipoprotein
  • Peptidoglycan
  • Inner membrane
  • Cytoplasm
  • O polysaccharide
  • Lipid A (endotoxin)
• Common virulence factors include endotoxins, capsules, and secretion systems

Traditional Bacterial Identification

• Methods for identifying bacteria rely on biochemical properties (e.g., PRG acid, PR-L, PR-M, Methyl Red, VP, Indole, Ureases, Citrates, TSI, Gas, H₂S)

Automated Bacterial Identification System

• Automated testing systems exist to identify bacteria rapidly and help with diagnosis

Medically Important Species - Specific examples

• Escherichia coli (opportunistic)
• Klebsiella pneumoniae (pneumonia)
• Proteus mirabilis (infections)
• Salmonella enterica
• Shigella spp.
• Yersinia pestis (plague)
• Y. enterocolitica
• Other species (e.g., Citrobacter freundii, Citrobacter koseri, Enterobacter aerogenes, Enterobacter cloacae, Morganella morganii, Serratia marcescens)

Escherichia coli - Gastroenteritis

• Common part of the human and animal gut flora
• Associated with various diseases, including gastroenteritis
• Some strains cause watery diarrhea, vomiting, and dehydration
• Some serotypes are associated with more severe illnesses like hemorrhagic colitis, and hemolytic uremic syndrome (HUS), caused by strains such as E. coli O157:H7
• Extraintestinal infections include urinary tract infections (UTIs) neonatal septicemia, meningitis, bacteremia, and HAI including ventilator-associated pneumonia

Escherichia coli Associated with Gastroenteritis (Specific types)

• Enterotoxigenic E. coli (ETEC)
• Enteropathogenic E. coli (EPEC)
• Enteroaggregative E. coli (EAEC)
• Shiga toxin-producing E. coli (STEC)
• Enteroinvasive E. coli (EIEC)

Shiga Toxin-Producing E.coli (STEC)

• Nomenclature: Shiga toxin-producing E. coli (STEC), Verocytotoxin-producing E. coli (VTEC), Enterohemorrhagic E. coli (EHEC)
• All STEC strains produce Shiga toxin 1 (Stx1) and/or 2 (Stx2)

Shiga toxin-producing E. coli (STEC) - Human Disease

• O157:H7 is the most common serotype among human cases, with the 2000 Walkerton water contamination incident as a notable example
• Non-O157 strains also cause HUS and foodborne outbreaks (e.g., 2011 E. coli 0104:H4, 2007 E. coli 0121)

STEC Infection

• Ranges from mild diarrhea to hemorrhagic colitis with severe complications like HUS
• HUS is characterized by acute renal failure, thrombocytopenia, and microangiopathic hemolytic anemia
• Occurs in children under 10
• Foodborne outbreaks associated with undercooked meat, unpasteurized milk or juice and contaminated vegetables

E. coli Associated with Extraintestinal Infections

• Pathogens originate in the colon and may migrate to the kidney, bladder or prostate
• Uropathogenic E. coli (UPEC) produce adhesins (P pili, AAF/I, AAF/III) helping them adhere to urinary tract cells
• Leading to urinary tract infections (UTIs), neonatal meningitis (K1 antigen), septicemia, and other intraabdominal infections

Salmonella Species

• Genus Salmonella has two species—Salmonella enterica and S. bongari
• Salmonella enterica accounts for almost all human infections
• Common serovars include S. typhi, a cause of typhoid fever
• Animals are the main reservoir for most non-typhoidal Salmonella

Salmonella Species - Clinical Presentation

• Clinical presentation includes gastroenteritis, septicemia and typhoid fever
• Includes focal infections (osteomyelitis, meningitis, brain abscess, endocarditis)

Typhoid Fever Pathogenesis

• Bacteria are ingested
• Bacteria multiply in small intestine, Peyer's patches
• Septicemia through lymphatic and mesenteric nodes
• Multiplication in macrophages of liver, spleen and bone marrow
• Symptoms include fever, abdominal pain, and potentially complications like cholecystitis

Shigella Species

• Four species: S. dysenteriae, Shigella flexneri, Shigella boydii; and Shigella sonnei.
• DNA analysis shows they are bio-groups in E. coli, not distinct species.
• S. dysenteriae produces Shiga toxin, causing damage to glomerular endothelial cells, potentially leading to renal failure (HUS)
• Human reservoir for Shigella

Shigella Species - Transmission and Symptoms

• Fecal-oral transmission through contaminated hands or food
• Common in young children or male homosexual adults
• Symptoms include abdominal cramps, diarrhea, fever, bloody stools

Yersinia Species

• Three human pathogens: Y. pestis, Y. enterocolitica, Y. pseudotuberculosis
• Y. pestis is associated with the plague (endemic/pandemic)
• Transmitted animal-to-human usually via infected fleas
• Two clinical presentations: bubonic plague and pneumonic plague

Yersinia enterocolitica and Y. pseudotuberculosis

• Cause gastroenteritis, often with complications such as appendicitis or mimics
• Ingestion of contaminated food or water
• Symptoms include fever diarrhea and abdominal pain
• May lead to other issues like septicemia, arthritis, intra-abdominal abscess, hepatitis, and or osteomyelitis

Klebsiella Species

• K. pneumoniae and Klebsiella oxytoca are common causes of community and hospital-acquired pneumonia, characterized by mucoid colonies due prominent capsules
• Infections include wound and soft tissue infections along with UTIs and septicaemia
• K. granulomatis is the agent of granuloma inguinale

Diagnosis

• Specimens include stool, blood, urine, and bone marrow
• Culture media used include blood agar, MacConkey, and other selective media
• Culture-independent methods exist for detection
• Methods for STEC diagnosis include Sorbitol MacConkey (SMAC) or CHROMagar cultures, Enzyme-linked immunosorbent assays (EIAs), and polymerase chain reaction (PCR)
• Identification of specific toxins or genes

Treatment and Antimicrobial Susceptibility

• Some STEC infections and Salmonella gastroenteritis cases in immunocompetent hosts may not need antibiotics
• Antibiotic resistance is increasing among Enterobacterales (ESBL, CRE, AmpC).

Prevention and Control of Enteric Infections

• Education on food safety and preparation
• Infection control procedures like handwashing, and proper disposal of contaminated material
• Vaccines (Salmonella)
• Water treatment and food safety protocols
• Surveillance helps to detect and contain outbreaks

Surveillance Programs

• Canada uses various programs for monitoring foodborne illnesses, including FoodNet Canada, the National Enteric Surveillance Program, and PulseNet Canada

Pathogen Laboratory Surveillance Programs

• PulseNet uses molecular subtyping methods such as pulsed-field gel electrophoresis (PFGE) and whole genome sequencing (WGS) to track and analyze bacteria

WGS process

• WGS is a laboratory procedure that determines the precise order of a microorganism's DNA bases
• Provides a highly detailed fingerprint to investigate links between individual cases, and helps to identify outbreaks much faster.

Test your knowledge on Enterobacterales and their implications in food-borne illnesses. This quiz covers key characteristics, strains, and mechanisms of diarrhea related to this important group of bacteria. Assess critical aspects like STEC infections and their symptoms.