Gram-Negative Bacilli and Gastrointestinal Diseases

Gram-Negative Bacilli: Gastrointestinal Diseases

• Gram-negative bacilli cause food poisoning, diarrhea, dysentery, and cholera.
• Objectives of the study include causes, diagnosis & prevention of gastrointestinal diseases, specifically focusing on food poisoning, diarrhea, dysentery, and cholera.

Enterobacteriaceae Properties

• Gram-negative rods
• Ferment glucose with acid production
• Reduce nitrates into nitrites
• Oxidase negative
• Divided into two main groups based on lactose action: Lactose Fermenters (LF) and Lactose Non-Fermenters (LNF).

Lactose Fermenter: Escherichia coli

• Diseases: Urinary tract infection (UTI), sepsis, neonatal meningitis, traveler's diarrhea
• Habitat: Human colon
• Transmission: Colonizes vagina and urethra, ascending UTI, acquired during birth, fecal-oral route in diarrhea.
• Diagnosis: Gram-negative rods, ferment lactose, indole-positive.
  • Predisposing factors in women include proximity of anus to vagina/urethra, short urethra, urinary tract abnormalities (strictures, valves, stones), and in-dwelling catheters. Colonization of the vagina can lead to neonatal meningitis.

Lactose Fermenter: Klebsiella pneumoniae

• Diseases: Pneumonia, UTI, sepsis
• Habitat: Human upper respiratory and enteric tracts
• Transmission: Inhalation of respiratory droplets, ascending spread of fecal flora to the urinary tract.
• Diagnosis: Gram-negative rods, polysaccharide capsule, citrate-positive.
  • Predisposing factors to pneumonia are chronic pulmonary diseases, and catheterization predisposes to UTI.

Lactose Fermenter: Enterobacter cloacae & Serratia

• Diseases: Hospital-acquired pneumonia, UTI, sepsis
• Characteristics: Enteric gram-negative rods similar to K. pneumoniae but motile.
• Key Feature: Highly antibiotic resistant

Lactose Fermenter: Citrobacter

• Characteristics: Enteric gram-negative rod similar to E. coli, citrate positive.
• Habitat: Found in human feces and various clinical specimens.
• Relevance: Occasionally causes neonatal meningitis.

Non-Lactose: Salmonella typhi

• Disease: Typhoid fever
• Habitat: Human colon only
• Transmission: Fecal-oral route
• Diagnosis: Facultative gram-negative rods, non-lactose-fermenting, produces H2S.
  • Predisposing factors include decreased stomach acid due to antacids/gastrectomy, chronic carrier state established in gallbladder, fecal-oral spread to others.

Salmonella enteritidis (Salmonella enterica)

• Diseases: Enterocolitis, sepsis with metastatic abscesses
• Habitat: Enteric tract of humans and animals (chickens, livestock)
• Transmission: Fecal-oral route
• Diagnosis: Facultative gram-negative rods, non-lactose-fermenting, produces H2S, motile.

Shigella Species

• Diseases: Enterocolitis (dysentery)
• Habitat: Human colon only
• Transmission: Fecal-oral route
• Diagnosis: Facultative gram-negative rods, non-lactose-fermenting, nonmotile.
  • Pathogenicity: Invades the ileum and colon mucosa, endotoxin in cell wall causing sepsis (rare). Low infectious dose (1–10 organisms) due to resistance to stomach acid.

Proteus Species

• Diseases: UTI, sepsis
• Habitat: Human colon and environment (soil, water)
• Transmission: Ascending spread of fecal flora to urinary tract
• Diagnosis: Facultative gram-negative rods, non-lactose-fermenting, highly motile, produce urease.
  • Pathogenesis: Endotoxin causes fever and shock (sepsis). Urease degrades urea to produce ammonia (↑pH), facilitating bladder entry. Predisposing factors include vaginal colonization, urinary catheters, and urinary tract abnormalities.

Yersinia pestis

• Disease: Bubonic and pneumonic plague.
• Habitat: Wild rodents (e.g., rats)
• Transmission: Flea bite
• Diagnosis: Small gram-negative rods with bipolar staining. One of the most virulent organisms (very low ID50).

Explore the role of gram-negative bacilli in gastrointestinal diseases such as food poisoning, diarrhea, dysentery, and cholera. This quiz covers properties of Enterobacteriaceae, particularly Escherichia coli, and their diagnosis and prevention. Test your knowledge about these important pathogens and their implications in human health.