Salmonella causes enteric fever, septicemia, gastro enteritis

Salmonella typhoidal :

• s.typhi & s. Paratyphi
• Primary human parasite

Salmonella Non typhoidal :

• food poisoning group
• Animal parasite
• Also can infect humans
• Septicemia,localised infection, gastroenteritis

Morphology :

• Gram negative
• Rod shaped
• 1-3 micrometres X 0.5 micrometre
• Motile
• Aerobic
• Facultative anaerobic
• Non capsulated
• Non sporing

Culture media :

1. Mckonkey agar : non lactose fermenting pale colony
2. Deoxycholate citrate agar : black headed colony
3. Wilson and blair bismuth : jet black colony
4. Selenite F and tetrathionate : enrichment media

Biochemical Reaction :

1. Ferments glucose , mannitol, maltose
2. Ferments gas and acid
3. Lactose , sucrose, salicin not fermenting
4. IMVIC = “-,+,-,+”
5. Urea = not hydrolyzed
6. H2S = produced

Antigen structure :

1. “H” antigen
2. “O” antigen
3. “VI” antigen

Antigenic variation :

1. “H-O”variation

Phase variation :

Flagella may exhibit one or other of two alternative sets of Ag defined by 2 separate sets of genes in bacterial genome

• Phase 1 Ag : either specific for A species or shared by few species
• Phase 2 Ag : widely shared by many species

Strains that posses both phase are diphasic

Some like s.Typhi occur only in mono phasic

• V-W variation
• S-R variation

Clinical courses :

• Most common group : 5-20 yrs
• I.P. = 1-2 weeks

Onset : usually gradual with headache, constipation, diarrhoea and anorexia

Feature :

1. Bradycardia
2. Step ladder pyrexia
3. soft , palpable spleen
4. Hepatomegaly
5. Rose spot skin

Carrier :

• Convalescent carrier : 3 weeks to 3 months
• Temporary carrier : more than 3 months
• Chronic carrier : over a year

Lab diagnosis :