The rapid emergence of antibiotic-resistant (ART) pathogens is a major threat to public health. While the surfacing of ART food-borne pathogens is alarming, the magnitude of the antibiotic resistance (AR) gene pool in food-borne commensal microbes is yet to be revealed. Incidence of ART commensals in selected retail food products was examined in this study. The presence of 10(2)-10(7) CFU of ART bacteria per gram of foods in many samples, particularly in ready-to-eat, 'healthy' food items, indicates that the ART bacteria are abundant in the food chain. AR-encoding genes were detected in ART isolates, and Streptococcus thermophilus was found to be a major host for AR genes in cheese microbiota. Lactococcus lactis and Leuconostoc sp. isolates were also found carrying AR genes. The data indicate that food could be an important avenue for ART bacterial evolution and dissemination. AR-encoding plasmids from several food-borne commensals were transmitted to Streptococcus mutans via natural gene transformation under laboratory conditions, suggesting the possible transfer of AR genes from food commensals to human residential bacteria via horizontal gene transfer.

The importance of conjugation as a mechanism to spread biofilm determinants among microbial populations was illustrated with the gram-positive bacterium Lactococcus lactis. Conjugation triggered the enhanced expression of the clumping protein CluA, which is a main biofilm attribute in lactococci. Clumping transconjugants further transmitted the biofilm-forming elements among the lactococcal population at a much higher frequency than the parental nonclumping donor. This cell-clumping-associated high-frequency conjugation system also appeared to serve as an internal enhancer facilitating the dissemination of the broad-host-range drug resistance gene-encoding plasmid pAM␤1 within L. lactis, at frequencies more than 10,000 times higher than those for the nonclumping parental donor strain. The implications of this finding for antibiotic resistance gene dissemination are discussed.Lactococci are important fermentation starter cultures. As commensal organisms, they are widely distributed (19, 37) and can be found coexisting with many other organisms, including pathogens, in natural and food-processing environments, most commonly in the form of mixed-culture ecosystems. However, to date information regarding lactococcal biofilm formation is very limited (30). The contribution of commensal organisms in mixed-culture biofilm development involving pathogens and other risks associated with these biofilms have not been fully explored.Lactococci are susceptible to various gene transfer mechanisms (13). Many important traits, including lactose utilization, the proteolytic system, bacterial phage resistance, and nisin production and immunity, are associated with mobile elements. Of particular interest, a cell-clumping-associated high-frequency conjugal gene transfer system has been reported in two similar settings involving Lactococcus lactis strains ML3 and 712. In both cases, the conjugative elements, i.e., the sex factor in 712 and pRS01 in ML3, mobilized the transfer of the Lac plasmid to the recipient cells by forming plasmid cointegrates. Some of the conjugation progenies exhibited cell autoaggregation. When these clumping cells served as donors in the second round of mating, they transferred the Lac plasmid 10 2 to 10 7 times more efficiently than the original donor strain (1, 10, 40). Divalent ions were required for autoaggregation, and proteinase treatments significantly decreased both cell clumping (Clu ϩ ) and high-frequency conjugation (41). Strain MG1363 is a nonclumping, plasmid-cured derivative of strain 712 with the sex factor retained in the chromosome. A cluA gene, which encoded a putative cell surface protein containing the well-conserved hexapeptide LPXTGE, was cloned from the sex factor. Expression of the CluA protein through upstream fusion of a lactococcal heat shock promoter in MG1363 partially restored cell aggregation (16).It is anticipated that the biofilm environment would be suitable for gene transfer events such as conjugation and transformation. However, a two-way relationship was recently demonst...

The outgrowth of spoilage organisms, including molds and yeasts, results in significant financial loss to the food industry and wastes natural resources. The objective of this study was to develop a rapid, specific, and sensitive real-time PCR method for detecting spoilage molds during screening of raw materials and final product quality control analysis. The 18S rRNA gene was used to develop PCR primers and probe. With this set of primers and probe, less than 1,000 mold cells per milliliter of orange juice (10 cells per reaction) were detected with the real-time PCR system within 6 to 7 h. No cross-reactivity was found with other common foodborne bacteria, yeasts, or food ingredients. This technique is significantly faster than current detection and identification procedures, which take from days to weeks.

In the paper by Wang et al. (2006), the following error appeared.On p. 228, Streptococcus thermophilus (S. thermophilus) was incorrectly described as Staphylococcus thermophilus on three occasions. The publishers apologize for this error.