A RAPD based study revealing a previously unreported wide range of mesophilic and thermophilic spore formers associated with milk powders in China

• Twenty-five Chinese milk powders were evaluated for the presence of thermophilic and mesophilic spore-formers.
• A total of 738 isolates were clustered into more than 30 groups based on the RAPD profiles.
• Bacillus licheniformis was the most dominant bacterium followed by Geobacillus stearothermophilus.
• Twelve out of the nineteen bacteria belonged to previously unreported species.
• Mesophilic sporeformers were proved to be important milk powder contaminants.

Aerobic spore forming bacteria are potential milk powder contaminants and are viewed as indicators of poor quality. A total of 738 bacteria, including both mesophilic and thermophilic, isolated from twenty-five powdered milk samples representative of three types of milk powders in China were analyzed based on the random amplified polymorphic DNA (RAPD) protocol to provide insight into species diversity. Bacillus licheniformis was found to be the most prevalent bacterium with greatest diversity (~ 43% of the total isolates) followed by Geobacillus stearothermophilus (~ 21% of the total isolates). Anoxybacillus flavithermus represented only 8.5% of the total profiles. Interestingly, actinomycetes represented a major group of the isolates with the predominance of Laceyella sacchari followed by Thermoactinomyces vulgaris, altogether comprising of 7.3% of the total isolates. Out of the nineteen separate bacterial species (except five unidentified groups) recovered and identified from milk powders, twelve proved to belong to novel or previously unreported species in milk powders. Assessment and characterization of the harmful effects caused by this particular micro-flora on the quality and safety of milk powders will be worth doing in the future.