Increased complexity of the species composition of lactic acid bacteria in human feces revealed by alternative incubation condition

Denaturing gradient gel electrophoresis (DGGE) of DNA fragments generated by PCR with primers specific for lactic acid bacteria (LAB) was applied to investigate various media and incubation conditions to recover LAB from human feces. Samples were plated on selective and nonselective media and incubated under standard condition (37°C, anaerobiosis) for fecal LAB as well as alternative condition (30°C, 2% O₂). PCR-DGGE analyses of resuspended bacterial biomass (RBB) obtained from agar plates revealed that the species composition of the recovered LAB was affected more strongly by the incubation condition than by the used medium. It was observed that food-associated LAB, such as Lactobacillus sakei and Leuconostoc mesenteroides, hitherto not described as intestinal inhabitants, are more easily selected when the alternative incubation condition is used. Identification of randomly picked colonies grown under the alternative condition showed that L. sakei is one of the predominant food-associated LAB species, reaching counts of up to 10⁶ CFU/g feces. Comparison of the results of bacteriological culture with those obtained by PCR-DGGE analysis of the RBB showed that investigation of RBB is a fast and reliable method to gain insight into the species composition of culturable LAB in feces.