Characterization of the Microbial Population Present on a Short Ripening Mexican Artisanal Cheese

Introduction: There are a diversity of Mexican artisanal cheeses such as Poro cheese that is usually made with raw milk. However, the use of non-pasteurized milk represents an important risk to consumers’ health as it can contain pathogenic microorganisms.

Purpose: To characterize the autochthonous microbial population in Poro cheese using the ribosomal intergenic spacer analysis technique (RISA).

Methods: The bacterial population in Poro cheese obtained of Bejucal Ranch from Tabasco was characterized through total DNA extraction from milk, whey, curd and ripened cheeses (7, 30 and 60 days) in dry and rainy seasons. The DNA extracted from samples were used as templates for the PCR-RISA technique using ITSF (5’-GTCGTAACAAGGTAGCCGTA-3’) and ITSReub (5’-GCCAAGGCATCCACC-3’) primers. Cycling conditions were 95°C for 7 minutes, followed by 30 cycles at 95°C for 1 minute, 55°C for 1 minute and 72°C for 2 minutes, ending with 72°C for 7 minutes. The fingerprint was obtained and selected amplified products were purified and sequenced. Sequences were compared with the NCBI database to identify the bacterial population.

Results: In raw milk from dry and rainy season were identified Staphylococcus aureus, Bacillus subtilis and Comamonas testosteroni, Lactobacillus paraplantarum, Corynebacterium resistens, respectively. These microorganisms were not found on the later production process. Lactic acid bacteria (Streptococcus thermophilus, Lactobacillus delbrueckii subsp. bulgaricus and Lactococcus lactis) and opportunistic pathogen (Klebsiella pneumoniae) prevailed in the curd and in cheese samples at 7, 30, and 60 days of ripening in both seasons.

Significance: This study identified the composition of microbial populations during Poro cheese manufacture. Microorganisms such as lactic acid bacteria could be used as starter culture to provide the typical sensorial characteristics of Poro cheese made with pasteurized milk.