E. coli Infections Quiz

Gram-Negative Bacteria

• Gram-negative bacteria use biochemical pathways to metabolize carbohydrates and generate energy through two main processes: fermentation and aerobic respiration (oxidation).
• Fermentation is an anaerobic process, while aerobic respiration is an aerobic process.

Enterobacteriaceae: Non Lactose Fermenters

• This group includes bacteria like Salmonella, Shigella, Yersinia, and Proteus.
• They are characterized as not fermenting lactose.

Enterobacteriaceae: Lactose Fermenters

• Escherichia coli, Klebsiella, Citrobacter, Enterobacter spp., and Serratia belong to this group.
• These bacteria ferment lactose.

Other Non Lactose Fermenters

• Pseudomonads, Vibrio, and Acinetobacter are examples of non-lactose fermenting bacteria.

Escherichia coli (E. coli)

• Commonly found in the colon.
• Used as a marker for fecal contamination in water quality.
• Mostly motile.
• Possesses adhesive fimbriae, sex pili, and O, H, and K antigens.
• O antigens share significant cross-reactivity with Shigella species.
• Several virulence factors. including lipopolysaccharide (LPS) for example the O side chains, capsule (K), and flagella (H), contribute to its pathogenicity.
• Different E. coli subtypes cause various diseases such as gastroenteritis (e.g., ETEC, EIEC, EPEC, EHEC, and Enteroadherent).
• E. coli have self-limiting diseases that causes watery diarrhea, abdominal cramps, malaise, nausea potentially without vomiting

Escherichia coli (E. coli) - Virulence Factor

• Lipopolysaccharide (LPS)
• Capsule (K)
• Flagella (H)

Escherichia coli (E. coli) - Culture growth

• MacConkey Agar (MAC) is a differential medium.
• Bile salts and crystal violet inhibit Gram-positive organisms.
• Lactose is a fermentable carbohydrate enabling differentiation.
• Lactose fermenters appear as pink colonies, while non-fermenters remain colorless.

Escherichia coli (E. coli) - Uropathogenic E. coli (UPEC)

• The most common cause of UTIs in humans.
• Strains vary slightly in immunocompetent and immunocompromised patients.
• Adherence to the urinary epithelial mucosa is facilitated by various factors (eg, pili).
• Other virulence factors such as cytolysins (hemolysins) inhibit phagocytosis.
• Aerobactin aids in iron chelation.

Escherichia coli (E. coli) - Gastrointestinal E. coli

• Categorized into five groups based on virulence factors, clinical characteristics, epidemiology. Different O and H serotypes are important
• ETEC, EIEC, EPEC, EHEC, and Enteroadherent (EAEC/DAEC).

Escherichia coli (E. coli) - ETEC

• Common cause of traveler's diarrhea, especially in tropical climates.
• Associated with stomach acidity, protective mechanism against infection
• Produces a heat-labile toxin (LT) similar to Vibrio cholerae toxin.
• Causes hypersecretion of electrolytes and fluids into the intestinal lumen.
• Self-limiting disease.

Escherichia coli (E. coli) - EIEC

• Rare in developed countries compared to ETEC or EPEC.
• Produces dysentery with direct penetration.
• Transmission via the fecal-oral route.
• Often misidentified.
• Symptoms include fever, severe abdominal cramps, malaise, and watery diarrhea.
• Nonmotile strains that do not ferment lactose are common.

Escherichia coli (E. coli) - EPEC

• Has an adhesive property
• Adheres to human epithelial cells and causes low-grade fever, malaise, vomiting, and diarrhea.
• Mucus-containing diarrhea without blood.
• Commonly observed in children <1 year old.

Escherichia coli (E. coli) - EHEC

• Serotype O157:H7.
• Linked to hemorrhagic diarrhea, colitis, HUS (hemolytic uremic syndrome).
• Produces verotoxin 1 and 2.
• Symptoms include watery to bloody diarrhea, abdominal cramps, and low-grade fever.
• Toxin detection in stool is essential.

Escherichia coli (E. coli) - Enteroadherent (EAEC/DAEC)

• Associated with diarrheal syndromes and UTIs.
• DAEC strains may cause cystitis.
• EAEC strains cause watery diarrhea.
• Identification is based on "stacked-brick" cell growth patterns in cultures.

Escherichia coli (E. coli) - Extraintestinal Infections

• Primary cause of septicemia and meningitis in neonates (~40%).
• Newborn infection commonly acquired through the birth canal.
• Capsular antigen K1 shares similarity with N. meningitidis group B.

Klebsiella spp

• Klebsiella pneumoniae is the most common isolated species.
• Possesses a large polysaccharide capsule.
• Frequently found in the intestinal tracts of humans and animals.
• Associated with HAIs (hospital-acquired infections), pneumonia, wound infections, and UTIs.
• Gram-negative rods, nonmotile, have a polysaccharide capsule.
• Lactose fermenters, facultative anaerobes
• Cultures present as moist, mucoid colonies on media like MacConkey agar; on blood agar, they have slimy appearances.

Klebsiella spp. - Diseases

• UTIs
• Pneumonia
• Septicemia

Treatment of Klebsiella and other Gram Negative bacteria

• Antibiotic choices vary by the organism and patient condition
• Antibiotic treatment may be difficult because the infections are frequently caused by drug resistance strains

Salmonella

• Gram-negative, facultative anaerobes that resemble other enteric bacteria.
• Colonies on selective/differential media (MAC) are clear and colorless, non-lactose fermenting.
• Potential black centers on media with H2S indicators.
• Produce significant infections in humans and other animals. Common species are S. Typhi and S. Paratyphi.

Salmonella - Epidemiology

• Worldwide variation in incidence.
• Presence in a variety of sources.
• Various serotypes in animals and humans.

Salmonella - Clinical Infections

• Gastroenteritis is prominent.
• Enteric fever.

Salmonella - Diagnosis

• Specimen collection (e.g., stool).
• Culture on selective media.
• Blood and urine cultures are done.

Salmonella - Treatment

• Complicated infections may require specific antibiotics.

Shigella

• Gram-negative, non-motile, non-encapsulated, bacillus
• Important strains are S. sonnei, S. flexneri, and S. dysenteriae.
• Causes bacillary dysentery.

Shigella - Clinical Infections

• Shigellosis is characterized by short-term, self-limiting diarrhea with possible fever.

Shigella - Diagnosis

• Specimens include fresh stool, mucus flecks, rectal swabs, and cultures on selective media (e.g., Hektoen enteric agar).

Shigella - Treatment

• Antibiotic treatment can shorten the illness.
• Reserve the antibiotics for severe cases.

Pseudomonas

• Gram-negative, aerobic bacilli (rods).
• Includes various species, some produce water-soluble pigments.
• P. aeruginosa commonly causes infections in debilitated patients (e.g., cystic fibrosis).

Pseudomonas - P. aeruginosa

• Small, gram-negative rod with a single polar flagellum
• Aerobic, not fermenting lactose
• Oxidase positive
• Produces greenish pigment that fluoresces under UV light.

Pseudomonas - Virulence Factors

• Flagella: aiding in attachment.
• Biofilms: increasing pathogen resistance.
• Enzymes which break down host tissues.
• LPS (lipopolysaccharide): causing endotoxic shock.
• Exoenzymes S, T, U, and Y

Pseudomonas - Clinical Manifestations

• Localized and systemic infections.
• Endocarditis, pneumonia, meningitis.
• Often affecting patients with severe burns or compromised immune systems.

Pseudomonas - Treatment

• Broad-spectrum antibiotics are typically used
• Drug resistant infections may require more aggressive treatments

Acinetobacter

• Gram-negative, coccobacilli / bacilli (rod-shaped)
• Primarily non-motile, oxidase negative, catalase positive, aerobic.
• Two major groups: saccharolytic and asaccharolytic.
• Common in nosocomial infections (hospital acquired infections).

Acinetobacter - Epidemiology

• Ubiquitous and frequently present in the environment and the skin, but mostly colonizes the hospital setting during prolonged stays.

Acinetobacter - Virulence Factor

• Ability to produce a capsule increasing resistance against chemical disinfectants.
• Associated with various infections (e.g., UTI).