Overview
SIST ISO 19250:2011 - Water quality - Detection of Salmonella spp. specifies a standardized laboratory method for the detection (presumptive or confirmed) of Salmonella spp. in water samples. The standard addresses sample preparation (including membrane filtration where needed), non‑selective pre‑enrichment, selective enrichment, plating on selective agars, and biochemical/serological confirmation. It is intended for use where water is a possible vehicle of Salmonella infection (drinking, recreational, surface, agricultural and waste waters) and can be applied during routine monitoring, epidemiological investigations and outbreak response.
Key technical topics and requirements
- Scope and safety: Tests must be performed in properly equipped laboratories by trained personnel; special precautions apply when testing for S. Typhi and S. Paratyphi.
- Sampling guidance: While sampling itself is outside the method, samples should follow ISO 19458 and be representative and correctly stored/transported; typical volumes for drinking and bathing water range from 1 000 ml to 5 000 ml.
- Pre‑enrichment: Use buffered peptone water (BPW) for pre‑enrichment (e.g., 18 ± 2 h at 36 ± 2 °C) to recover low numbers or injured cells; membrane filters can be added to BPW after filtration of larger volumes.
- Selective enrichment: Inoculate selective broths such as Rappaport‑Vassiliadis with soya (RVS) and Muller‑Kauffmann tetrathionate‑novobiocin (MKTTn) with incubation regimes (e.g., RVS ~41.5 °C, MKTTn ~37 °C for about 24 h) to suppress background flora.
- Plating and isolation: Plate onto xylose lysine deoxycholate (XLD) agar plus a complementary selective agar (lab’s choice, e.g., brilliant green or bismuth sulfite) and inspect after ~24 h.
- Confirmation: Presumptive colonies require biochemical (e.g., TSI, lysine decarboxylation, urea) and serological tests to confirm Salmonella spp.
- Limitations: The method may not recover all strains (notably some S. Typhi/Paratyphi) and may require alternative media for epidemiological needs. MPN approaches are possible by adjusting BPW volumes.
Practical applications and users
SIST ISO 19250:2011 is used by:
- Public health and clinical laboratories conducting environmental surveillance
- Water utilities and drinking water laboratories monitoring water safety
- Environmental testing labs assessing recreational and surface waters
- Wastewater and agricultural testing facilities
- Epidemiologists and outbreak response teams requiring standardized detection protocols
Benefits include reproducible detection, alignment with international best practice, and compatibility with outbreak investigations that require reliable presence/absence results.
Related standards
- ISO 6579 - detection of Salmonella in food/animal feeding stuffs (horizontal method)
- ISO 19458 - sampling for microbiological analysis of water
- ISO 7218, ISO 8199, ISO 7704 - general microbiology and membrane filtration guidance
- ISO/TS 11133 series - media quality and performance testing
Keywords: SIST ISO 19250:2011, Salmonella detection, water quality, selective enrichment, buffered peptone water, RVS, MKTTn, XLD agar, membrane filtration, microbiological water testing.