ISO 7899-1:1998

Overview

ISO 7899-1:1998 - "Water quality - Detection and enumeration of intestinal enterococci - Part 1: Miniaturized method (Most Probable Number)" defines a laboratory procedure for detecting and enumerating major intestinal enterococci in surface water and wastewater using a miniaturized Most Probable Number (MPN) approach in 96‑well microtitre plates. The method targets typical faecal enterococci (E. faecalis, E. faecium, E. durans, E. hirae) and uses enzymatic fluorescence (MUD hydrolysis) for positive identification after incubation at 44 °C. This standard is not suitable for drinking water or waters with expected counts below 15 per 100 ml.

Key topics and requirements

• Principle: Inoculate diluted samples into wells containing dehydrated MUD/SF medium; incubate and detect fluorescence (4‑methylumbelliferyl‑β‑D‑glucoside hydrolysis) under UV (366 nm). Results reported as MPN/100 ml.
• Sample handling: Follow ISO 5667 series and ISO 8199 guidance for sampling, preservation and lab practice.
• Culture media & diluents: Specifies MUD/SF medium composition (including nalidixic acid, thallium acetate, TTC, MUD) and a Special Diluent (synthetic sea salt). Media sterilization and microtitre plate dehydration procedures are given.
• Apparatus: 96‑well non‑fluorescent microtitre plates, 8‑channel multipipettes, thermostatic incubator at 44 °C ±0.5 °C, UV observation chamber (Wood’s lamp 366 nm). Safety warnings for toxic reagents (thallium salts, N,N‑dimethylformamide) and UV exposure.
• Procedure: Prepare serial dilutions (protocols for fresh/brackish and sea water), distribute 200 µl inoculum per well, incubate 36–72 h, read wells showing blue fluorescence as positive.
• Result expression: Record characteristic number (pattern of positive wells), compute MPN and 95% confidence intervals using statistical tables or software (examples in annexes). If no positives, report as “< n/100 ml” per dilution scheme.
• Quality control: Annexes cover performance data, manufacturing quality criteria for pre‑prepared microtitre plates, calibration plates and performance characteristics.

Applications and users

• Environmental microbiology laboratories performing water quality testing, routine monitoring of surface waters, recreational (bathing) water compliance, and wastewater treatment plant monitoring.
• Public health agencies, environmental regulators, water utilities, and manufacturers of microbiological test kits for enterococci detection.
• Useful where sample volumes are limited or samples have high suspended solids (miniaturized MPN is suited for turbid waters).

Related standards

• ISO 7899-2 (membrane filtration method for enterococci)
• ISO 5667 series (water sampling)
• ISO 8199 (enumeration of microorganisms)

Keywords: ISO 7899-1, intestinal enterococci, water quality, Most Probable Number, MPN, microtitre plate, MUD/SF medium, enterococci detection, surface water, wastewater.