Salmonella Typhi / Paratyphi
Motile Gram-negative bacilli
Identification & Growth
Identification
- S. Typhi: weak H₂S on TSI, citrate-negative, ornithine-negative, no gas
- Confirmation by serotyping (O9, Hd and Vi antigens)
Growth Conditions
- Blood and bone marrow culture in the first week; stool culture from the second to third week
Clinical Significance
- Typhoid and paratyphoid fever — notifiable disease in Brazil
Intrinsic Resistance
- Do not report aminoglycosides, first/second-generation cephalosporins or cephamycins: ineffective in vivo despite in vitro susceptibility
Bench Alerts
- Screen for low-level fluoroquinolone susceptibility with the pefloxacin disk, per EUCAST/BrCAST
- Immediate notification to public health surveillance
Clinical Notes
Clinical presentations
- Causes enteric fever (typhoid/paratyphoid) with prolonged fever, abdominal pain, hepatosplenomegaly, and possible intestinal perforation.
- Can progress to sustained bacteremia and an asymptomatic chronic gallbladder carrier state.
- Severe complications include gastrointestinal hemorrhage, encephalopathy, and myocarditis.
Specimens and collection
- Blood culture has the highest yield in the first week of illness, before antibiotic initiation.
- Stool culture and bone marrow aspirate culture increase diagnostic sensitivity, especially after prior antimicrobial use.
- Serologic tests (Widal) have low specificity and should not replace culture for diagnostic confirmation.
Epidemiology and at-risk populations
- Fecal-oral transmission via contaminated water and food, endemic in regions with inadequate sanitation.
- Travelers to endemic areas (South Asia, sub-Saharan Africa) constitute a relevant risk population in non-endemic countries.
- It is a notifiable disease in many countries, including Brazil, requiring immediate communication to epidemiological surveillance.
Resistance and therapeutic implications
- Fluoroquinolone resistance and multidrug-resistant (MDR) strains are widely described in endemic regions, including extensively drug-resistant (XDR) strains in South Asia.
- Third-generation cephalosporins and azithromycin are therapeutic options for fluoroquinolone-resistant strains.
- Individual susceptibility testing is mandatory given the variable and increasing regional resistance pattern.
Bench and reporting notes
- Isolation requires serologic confirmation with specific antisera for O, H, and Vi antigens.
- Immediate mandatory notification to public health authorities is required upon laboratory confirmation.
- Differentiate Salmonella Typhi/Paratyphi from non-typhoidal serotypes in the report, as clinical and public health implications differ substantially.
Sources
Educational decision-support content. It does not replace laboratory validation, current guidelines or review by the responsible professional.
FAQ: Frequently Asked Questions
How to identify Salmonella Typhi / Paratyphi in the lab?
Salmonella Typhi / Paratyphi is identified through s. typhi: weak h₂s on tsi, citrate-negative, ornithine-negative, no gas, confirmation by serotyping (o9, hd and vi antigens).
What are the intrinsic resistances of Salmonella Typhi / Paratyphi?
This organism is naturally resistant to do not report aminoglycosides, first/second-generation cephalosporins or cephamycins: ineffective in vivo despite in vitro susceptibility. These drugs should not be reported as susceptible.
Where is Salmonella Typhi / Paratyphi commonly found?
It is typically associated with typhoid and paratyphoid fever — notifiable disease in brazil.
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