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Bacteria may adhere to and develop biofilm structures onto dairy surfaces trying to protect themselves from adverse conditions such as pasteurization and CIP processes. Thus, biofilms are considered common sources of food contamination with undesirable bacteria. The purpose of this study was to evaluate the diversity of the microbiota attached to stainless steel surfaces in pre-and post-pasteurization pipe lines of a milk-processing plant. Seventy Gram-positive isolates were identified as Enterococcus faecalis (33), Bacillus cereus (26), Staphylococcus hominis (8), Staphylococcus saprophyticus (2), and Staphylococcus epidermidis-Staphylococcus aureus (1) species. Fifty-five Gram-negative isolates were identified to the species Escherichia coli (18), Klebsiella pneumoniae (13), Acinetobacter calcoaceticus (6), Serratia marcescens (6), Enterobacter spp. (5), Pseudomonas aeruginosa (4), Escherichia vulneris (2), and Proteus mirabilis (1). Fifty-five different strains were detected by the RAPD technique. These were subjected to an in vitro assay to evaluate their biofilm-forming capability. E. faecalis (7), A. calcoaceticus (4), K. pneumoniae (3), S. hominis (3), and P. aeruginosa (2) were the species in which more biofilm producer strains were encountered. The adhered microbiota was also assessed by the PCR-DGGE culture-independent technique. This analysis revealed a greater bacterial diversity than that revealed by culturing methods. In this way, in addition to the bacteria detected by culturing, DNA bands belonging to the genera Chrysobacterium and Streptomyces were also identified. This study emphasizes that knowledge of attached Dairy Sci. & Technol. (2016) 96:27-38 DOI 10.1007

Klila, an Algerian cheese produced in steppe and mountainous areas, is proving increasingly popular with consumers. It is traditionally made with ewe, goat or cow milk, leading to a product with high dry matter content (> 90%). In this work, we have characterized three different Klila cheeses made with the three different milks using physico-chemical and microbiological parameters. A triangle test was also performed on naïve consumers, and the three types of Klila were clearly distinguished by sensory analysis. They exhibited distinct features, in particular very low Aw (< 0.5) and pH values (< 4.5) preserving them from pathogens. Lactobacilli and enterococci were counted at low levels (< 4 log (cfu)/g) as well as some spore-forming bacteria (< 3 log (cfu)/g). Colonies were picked from MRS and BEA media. They were identified by sequencing and characterized on their ability to produce lactic acid and using REP-PCR. Lb plantarum was the main species isolated, followed by Pediococcus pentosaceus, Leuconostoc pseudomesenteroïdes and Lactobacillus fermentum. The Enterococcus genus was dominated by Ec durans, Ec faecium and Ec hirae. Among these two main populations, different subgroups were observed by means of the REP-PCR profiles and the lactic acid production of the isolates. Some strains were found in two and even three cheeses. We suppose that these microbes are representative of the environmental context in which Klila is produced.

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, 2.5 × 10 5 and 9.7 × 10 7 cfu/cm 2 , respectively, in the different units. Phenotypic identification of isolates revealed predominance of Gram-positive bacilli belonging to Bacillus and notably the Bacillus cereus group, at maximal levels of 72 and 21% respectively. The other Gram-positive microflora included Staphylococcus (30%) and Micrococcus (10%). In contrast, the incidence of the Gram-negative bacteria was relatively low. Two genera, identified as Pseudomonas (9%) and Enterobacter (6%), were found only in two dairies. Three dairies were Gram-negative bacteria-free. That should be the result of common contamination sources or highly environmental selective pressure. Further studies have to address these hypotheses. Treatment of experimental Bacillus cereus sensu lato strains biofilms with a 50, 100 and 150 ppm of quaternary ammonium disinfectant, showed a significant resistance of biofilms to this product even after long exposure time (15 min). This study emphasized the importance of aerobic spore-forming bacteria in dairy-processing equipment as they are able to built recalcitrant biofilms on the inside equipment surfaces with subsequent resistance to conventional CIP system and potential transfer to pasteurized milk. Therefore, in order to reduce the contamination levels of spore-forming bacteria and improve the quality and shelf life of the product, these dairies have, besides improvement in the hygienic status of the plant equipments, also to monitor either the pasteurization process or the contamination from raw material (that is, milk powder).