Purpose: To evaluate seasonal influence on microbial isolates from artisanal Chihuahua cheese elaborated with raw milk.
Methods: Samples of raw milk, curd, cheddaring and cheese were collected during three seasons of the year from a Mennonite farm. Cheese was aged on the laboratory, and a portion was taken every 30 d during 270 d. From a total of 11 types of samples, decimal dilutions were prepared to spread 100 μl on MRS and Elliker agar and incubated at 25 and 42°C. Isolated gram-positive colonies were selected to DNA extraction and amplification of 16S rRNA gene. RFLP analysis was made by the restriction enzyme MboI.
Results: A total of 181 bacterial isolates were analyzed, and the highest numbers were isolated from cheese samples. There was a prevalence of cocci strains (151), and only 30 bacilli strains. Analysis of 16S rRNA gene by RFPL allows the identification of 11 different groups with different band pattern. Bacterial strains isolated during autumn were located on categories 1, 2, 4 (all bacilli) and 10 and 11 (both cocci); while winter isolates were located in groups 3 (cocci) and 8 (bacilli); summer strains belong to group 7 (cocci). Groups 5, 6 and 9 (all cocci) are formed by strains isolated during the three seasons, which might be strains typical of the dairy environment.
Significance: Analysis of the microbial isolates of native Chihuahua cheese by 16S rRNA gene shows the marked influence of the season on strain distribution, but there are also strains that prevail on the dairy samples independently of the season.