Salmonella

Two important serotypes: typhimurium, and typhi.

Characteristics/Epidemiology

Typhi is exclusively human.

Other salmonella can be associated with food (egg and poultry) or pet turtle.

Pathogenesis/Transmission

Classification

All strains are called Salmonella enterica. The species is divided based on serotype.

Serotypes are based on the cell wall (O), flagellar (H), and capsular (Vi, analogous to K) antigens.

Pathogenesis

Development of disease depends on

• Infectious dose (strain dependent)
• Bacterial factors
• Host factors (achlorhydria, sickle cell disease, reduced cell-mediated immunity)

Ingestion of salmonellae in small intestine

   -> Enter epithelial cells by endocytosis (induced by bacterial protein)

   -> Phagocytosis by macrophages in the sub-mucosa

   -> Multiply intracellularly

   -> Spread to reticuloendothelial system by macrophages

   -> Cause lymphoid hyperplasia and hypertrophy

   -> Re-enter bowel via liver and gall bladder

   -> Inflammation and increase cAMP

   -> Active fluid secretion and diarrhoea

Clinical significance

Gastroenteritis

Caused by serotype enteriditis and typhimurium

Symptoms

• Fever, abdo cramp
• Nausea, vomiting, and nonbloody diarrhoea

Develops within 48 hours of ingestion

Generally self-limiting (48 to 72 hours)

Enteric (typhoid) fever

Caused by serotype typhi (uncommonly by other types)

Severe, life-threatening systemic illness

Symptoms

• Fever
• Abdominal symptoms
• Chills, sweats
• Headache
• Weakness, myalgia, anorexia
• Sore throat, cough
• 30% has rose spots - faint maculopapular rash on trunk

Incubation 5 to 21 days.

Mortality 15% if untreated. <1% if treated with antibiotics.

Last for 3-4 weeks.

Complication

• Intestinal haemorrhage
• (rarely) focal infection
• (rarely) endocarditis
• (uncommon) Chronic carrier (e.g. in gallbladder)

Other infections

• Sustained bacteremia (esp when atherosclerotic plaque infected)
• Abdominal infections (esp hepatobiliary tract, spleen)
• Osteomyelitis
• Septic arthritis

Laboratory identification

Most strains are Lac-.

Produce gas and acid during fermentation of glucose.

Produce H2S from sulfur containing amino acid.

Multiple flagella over the cell surface

Facultative, intracellular.

Survives in phagocytic cells.

Can be isolated on MacConkey agar.

Treatment

First line: ceftriaxone

Second line: fluoroquinolone (e.g. ciprofloxacin)

Prevention/immunity

Food and personal hygeine.

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Bibliography:

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