Overview
ISO 10705-2:2000 - "Water quality - Detection and enumeration of bacteriophages - Part 2: Enumeration of somatic coliphages" is an international laboratory standard that specifies a validated culture-based method for detecting and counting somatic coliphages in water, sediment, sludge extracts and shellfish extracts. The method expresses results as plaque‑forming particles (pfp or pfu) per unit volume and is part of the ISO 10705 series on bacteriophage detection.
Keywords: ISO 10705-2, somatic coliphages, water quality standard, bacteriophage detection, phage enumeration, plaque assay.
Key topics and technical requirements
- Scope and applicability: Method applicable to all kinds of water and extracts (sediment, sludge, shellfish). Preconcentration for very low counts is noted as a separate requirement/standard.
- Principle: Sample is mixed with a semi‑solid nutrient medium, inoculated with an appropriate host strain, plated on solid medium, incubated and plaques counted to give pfp per unit sample.
- Host strains and reference materials:
- Escherichia coli strain C (ATCC 13706) for low-bacterial-content samples.
- Nalidixic-acid-resistant E. coli WG5 (ATCC 700078) for samples with high background bacteria.
- Bacteriophage phiX174 (ATCC 13706-B1) recommended for reference material and quality control.
- Media and diluents: Uses Modified Scholtens' Broth (MSB), peptone‑saline diluent (or ISO 6887 compliant diluent). Annex A contains media and reagent details.
- Equipment and conditions: Thermostatic incubation (typically (36 ± 2) °C), shaking incubator, spectrophotometer, nephelometric flasks, membrane filters (0.2 µm), controlled freezers for stock cultures. Safety: handle cultures in biohazard cabinet; chloroform is carcinogenic - alternatives recommended.
- Procedure variants: Standard plaque count, methods for high bacterial background, low phage counts (dilution/concentration considerations), and a presence/absence test. Annexes B and C provide descriptive background and detailed culturing notes (e.g., phiX174).
Practical applications
- Routine water quality monitoring for faecal viral indicators in drinking water, recreational waters and wastewater.
- Environmental surveillance of viral contamination pathways (sediments, sludges, shellfish).
- Quality assurance in water treatment and disinfection studies where somatic coliphage is used as a viral process indicator.
- Research laboratories developing or comparing bacteriophage detection and concentration methods.
Who should use it
- Environmental and public‑health microbiology laboratories
- Water utilities and wastewater treatment operators
- Shellfish safety testing labs
- Regulatory agencies and standards bodies
- Research groups studying viral indicators and waterborne pathogen removal
Related standards
- ISO 10705-1: Enumeration of F-specific RNA bacteriophages
- ISO 10705-3: Concentration methods (under development at time of publication)
- ISO 10705-4: Enumeration of bacteriophages infecting Bacteroides fragilis
This standard is essential for accredited labs performing standardized somatic coliphage enumeration for regulatory compliance, surveillance and process evaluation.