In the present study, 13 Salmonella Infantis strains, which have been originated from Turkey, were selected due to their clinical and industrial relevance, sufficient biofilm producing capability and multidrug resistance. Although all tested strains were built up of thin pellicle, optimum pellicle formation has occurred at 28 °C. All S. Infantis biofilms were categorized as ‘bdar’ morphotype following the incubation at both 20 and 28 °C, while they were categorized as ‘saw’ morphotype at 37 °C. Under a certain incubation temperature (28 °C), 84.62% of strains have formed strong biofilm structures. By using the disk diffusion method, high levels of resistance have been observed among tested bacteria against nalidixic acid (100%), spectinomycin (100%), streptomycin (92.3%), tetracycline (92.3%), kanamycin (76.9%) and neomycin (76.9%). Further studies were performed with S. Infantis DMC 12 strain, due to its capability to produce biofilm and multidrug resistance phenotype. Gentamycin (>64 µg/mL, 2 × MIC) and tetracycline (>128 µg/mL, 4 × MIC) were determined as the most effective antibiotics against biofilm formation. The biofilm forms have showed increased antimicrobial resistance when it was compared to the planktonic bacteria. The highest resistance rates of the biofilm bacteria were observed to neomycin (12 × MIC) followed by spectinomycin (10 × MIC) and streptomycin (10 × MIC). Biofilm structure was induced as a result of nalidixic acid, spectinomycin, tetracycline and neomycin treatment at sub-MIC concentrations of tested antibiotics.

Nisin production of three bioengineered strains, (LAC338, LAC339 and LAC340) with immunity (nisFEG) and/or regulation (nisRK) genes of nisin biosynthesis on plasmids in the Lactococcus lactis LL27 nisin producer, was evaluated under pH-controlled and pH-uncontrolled batch fermentations. Optimization studies showed that fructose and yeast extract yielded the highest nisin activity. The strains LAC338, LAC339, and LAC340 produced 24, 45, and 44% more nisin, respectively, than wild-type L. lactis LL27 after 12-h incubation. However, sharp decreases in the yield of nisin were observed at the late phase of fermentation with LAC339 and LL27 in contrast to LAC340 and LAC338 strains for which the high level of nisin could be maintained longer. Obviously, increasing the copy number of the regulation genes together with immunity genes in the nisin producers retarded the loss of nisin in the late phase of the fermentation.

The aim of this work was to detect technological characteristics of fifty strains of lactococci previously isolated in Turkey in order to use them as components of starter formulations. All the lactococcal strains were low acid producers from lactose except L. lactis subsp. lactis MBLL9. 22, 17 and 11 strains of L. lactis presented low, moderate and strong proteolytic activity, respectively. Three out of 50 strains (L. lactis subsp. lactis MBLL1, MBLL9 and MBLL57) were determined to be bacteriocin producers. The strains L. lactis subsp. lactis MBLL1 and MBLL9 were found to be lacticin 481-like producers, whereas MBLL57 was a nisin-like producer, according to their partial characterization data. L. lactis strains were tested against 61 lactic phages for their phage-resistance properties. Eleven strains exhibited a sensitive phenotype against different phages, whereas the remaining 39 strains were completely resistant to all phages. Among the L. lactis subsp. lactis biovar. diacetylactis strains, 5 strains were defined as high, 3 strains as medium and 7 strains as low-level diacetyl producers. L. lactis strains were found to have 1-10 plasmids with molecular weights from 1.9 to 29.2 kb.