Characterization of constitutive microflora of biofilms in dairy processing lines

The biofilm status of pasteurization lines of a commercial plant (CP) and an experimental dairy plant (EDP) was evaluated. Samples were collected after cleaning-in-place systems from different segments of pasteurization lines over a period of 6 months. A total of 105 and 36 isolates from CP and EDP, respectively, were selected, on the basis of colony morphology and Gram's reaction. Biochemical differentiation of organisms in biofilms revealed the predominance of the genus Bacillus in both plants (59 and 64% in the CP and EDP, respectively). The other Gram-positive microflora of the commercial plant included Lactobacillus spp., Streptococcus spp. and Staphylococcus spp., while the EDP only had Micrococcus spp. in addition to Bacillus spp. The incidence of Gram-negative genera also revealed the presence of Shigella spp. Escherichia coli and Enterobacter aerogenes in both plants. On the other hand, Klebsiella spp. were only present in samples from the EDP. Further characterization of the isolates indicated the presence of psychrotropic microflora at a level of 38 and 75% in post-pasteurization segments of the CP and EDP, respectively. In addition, the percentage of heat-resistant organisms in the pre-pasteurization segment was 17%, as compared to 21% in post-pasteurization segments. Antibiotic susceptibility of selected isolates indicated maximum resistance of the isolates against carbenicillin (90% in CP and 75% in EDP), followed by cloxacillin (86% in CP and 89% in EDP), cephaloridine, novobiocin and vancomycin, indicating the presence of multiple antibiotic-resistant microflora that can be shed into the final product. Thus, the study reveals that all plants should be regularly evaluated for the prevalence of biofilms.