Pseudomonas Testing

The genus Pseudomonas is a group of gram-negative, rod-shaped, non-spore forming, and aerobic microorganisms. They are the most common spoilage proteolytic microorganisms that can break down the protein and produce a variety of flavor and odor defects.

Figure 1. Electron micrograph of Pseudomonas and related contaminated foods

Pseudomonas can cause microbial food spoilage through undesirable changes in meat products particularly when there are high populations of bacteria in foods after the extended refrigerated storage. It can form green pigments on the surface of meat stored aerobically at the refrigeration temperature. Food spoilage is a serious global problem and leads to significant economic loss for the food industry. The foods that are often associated with Pseudomonas contamination include aerobically stored foods with a high water content and natural pH such as poultry, meat, and dairy products. Pseudomonas is ubiquitous in all types of environments with high adaptability and low nutrient requirements.

Pseudomonas can multiply at the refrigeration temperatures between 0 to 7℃. It is very important to control the initial amounts of Pseudomonas as low as possible on meat products at the beginning of the shelf life to limit the amount that can multiply and cause spoilage issues. The process of the sensory degradation in foods can occur more quickly with an initially high number of Pseudomonas. During the early growth phase of Pseudomonas, there are only minor biochemical changes in foods. After several days or weeks of refrigeration, the changes in foods become more apparent. Pseudomonas is sensitive to carbon dioxide and its growth is limited in reduced oxygen environments. The majority of Pseudomonas species are non-pathogenic, but some species such as P. aeruginosa may cause serious disease and infect a range of tissues and sites in humans. It is a common pathogen in drinking water.

It is estimated that in only four days Pseudomonas can grow from less than 10 CFU/g to 10⁵ CFU/g in foods at refrigerated storage under air conditions. The initial level of Pseudomonas should be below 100 CFU/g on meat products stored aerobically in order to maintain the proper sensory characteristics and shelf life results. The Pseudomonas and heterotrophic plate count level in drinking water is commonly set as 500 CFU/mL as an indicator of a sufficient detectable residual disinfectant.

Pseudomonas Testing of Food at Alfa Chemistry

The standard methods (EN/ISO and AOAC) that have been widely used to enumerate Pseudomonas are culture-based methods using general microbiological testing supplies. Selective or differential mediums are used to incubate Pseudomonas followed by the plate counting or the most probable number (MPN) technique to determine the level of Pseudomonas in samples. MPN method is a multi-step assay including presumptive, confirmed, and completed phases based on statistical analysis. We also have expertise in the sample preparation of a variety types of food matrices.

Alfa Chemistry offer accurate and validated testing platforms for the quantification and confirmation of Pseudomonas in various food samples to meet customers' needs. We also have experience working on different standards and regulations.

Platform: Plate counting or MPN technique

Limit of detection: <10 CFU/g

Sample type: Solid and liquid food samples

Sample size: 25 g