Overview
ISO/TS 11059:2009 - Milk and milk products - Method for the enumeration of Pseudomonas spp. - is a technical specification published jointly by ISO and IDF. It defines a microbiological plate-count method to detect and enumerate both pigmented and non‑pigmented psychrophilic Pseudomonas species in milk, milk products and dairy environmental samples. The method specifies selective media, incubation conditions, colony counting rules and biochemical confirmation steps to ensure reliable identification and quantification.
Key topics and technical requirements
- Scope: Enumeration of Pseudomonas spp. in milk, milk products and dairy environmental samples (psychrophilic strains included).
- Selective medium: Penicillin and pimaricin agar (PPA) is used to isolate Pseudomonas; the specification provides the basic medium composition and preparation steps plus inhibitor solutions (penicillin and pimaricin/natamycin).
- Incubation: Plates incubated aerobically at 25 °C ± 1 °C for 48 h ± 2 h.
- Inoculation and dilutions: Surface inoculation of 0.1 ml per plate using decimal dilutions of the initial suspension prepared according to ISO 6887-5.
- Counting rules: Retain plates with fewer than 150 colonies for counting; select five colonies at random per retained plate for confirmation.
- Confirmation tests: Biochemical confirmation includes the oxidase test (oxidase reagent produces violet/purple within 5–30 s if positive) and glucose fermentation in glucose agar (absence of acidification indicates non-fermentative profile typical of Pseudomonas).
- Quality control: Performance testing of media (productivity and selectivity) with reference strains (e.g., P. fluorescens, P. aeruginosa, E. coli, S. aureus) and criteria for productivity/selectivity are specified.
- Apparatus and procedures: References to general microbiological practice and equipment (ISO 7218, ISO/TS 11133 series) and sampling guidance (ISO 707/IDF 50).
Applications and users
Practical uses include:
- Dairy quality control and shelf‑life studies - monitoring spoilage organisms that grow at refrigeration temperatures.
- Product release testing and routine microbiological surveillance for milk, cheese, cream and other dairy products.
- Environmental monitoring of dairy processing facilities to detect psychrophilic Pseudomonas reservoirs.
Primary users: microbiology laboratories in dairy companies, food safety and regulatory laboratories, contract testing labs, and researchers studying dairy spoilage and refrigeration‑adapted bacteria.
Related standards
This specification is essential for laboratories performing accurate enumeration of Pseudomonas in dairy matrices and supports consistent, harmonized testing for food quality and safety.