EHEC and Salmonella: Pathogenesis, Symptoms, and Treatment

EHEC: Pathogenesis and Clinical Presentation

Enterohemorrhagic Escherichia coli (EHEC) interacts with intestinal colon cells by establishing a close bond, causing the dissolution of cell membranes and glandular epithelium, alongside extensive destruction of microvilli.

Transmission and Symptoms

EHEC is associated with the consumption of undercooked ground beef, milk, and unpasteurized fruit juices. Located in the intestine, it causes hemorrhagic colitis, abdominal cramps, and bloody, watery diarrhea, typically without fever.

Hemolytic Uremic Syndrome (HUS)

HUS, associated with serogroup O157:H7, is non-invasive; blood in the stool is caused by the action of the verotoxin.

ECEA Characteristics

Enteroaggregative E. coli (ECEA) is located in the small intestine and is a common cause of childhood diarrhea in underdeveloped countries. Symptoms include persistent vomiting, watery diarrhea, and dehydration. It is characterized by plasmid-mediated aggregative adherence, shortened microvilli, mononuclear infiltration, hemorrhage, and decreased fluid absorption.

Salmonella Species

• Salmonella typhi
• Salmonella typhimurium
• Salmonella enteritidis

Pathogenicity Mechanisms

Salmonella can invade and replicate in M cells (microfold cells) located in Peyer's patches of the small intestine:

• Binding: Mediated by specific pili.
• Secretion Systems: Two type III secretion systems are utilized.
• SPI-1: Introduces invasion proteins, forming membrane ruffles.
• SPI-2: Facilitates systemic disease.
• Evasion: Employs Acid Tolerance Response (ATR) genes, superoxide dismutase, and catalase to survive digestive action.

Epidemiology and Clinical Manifestations

Salmonella Epidemiology: S. Typhi and S. paratyphi have humans as their exclusive reservoir. Risk factors include decreased gastric pH and immunocompromised status.

Salmonella Diseases: Includes enteric fever, nausea, vomiting, diarrhea, abdominal cramps, rectal bleeding, and bacteremia.

Salmonella Typhi

The reservoir is human. It produces a systemic infection known as typhoid fever. Bacteria reach the small intestine, enter the bloodstream, multiply in the gut, and are excreted in feces. The incubation period is 10 to 14 days.

Symptoms and Treatment

Symptoms include fever, malaise, headache, constipation, myalgia, and bradycardia. Antibiotic treatment is required.

Salmonella Enteritidis

Symptoms appear 8 to 48 hours after ingestion, including nausea, headache, vomiting, and profuse diarrhea. Symptoms typically resolve in 2 to 3 days. It is invasive, causes enterocolitis, and is associated with the consumption of raw eggs and unpasteurized milk. Serological methods are used for identification. Antibiotic treatment may be necessary for infants, though it can sometimes prolong symptoms and bacterial excretion. A carrier state may occur.