Katarina G. Mladenović

In vitro evaluation of the antimicrobial potential of Streptococcus uberis isolated from a local cheese from Southeastern Serbia

Streptococcus uberis is an environmental bacterium responsible for bovine mastitis. It is occasionally described as a human pathogen. In our study, the isolation was undertaken of lactic acid bacteria from a local cheese from Southeastern Serbia, produced in a traditional way. S. uberis (7 isolates) and S. agalactiae (1 isolate) were isolated from the cheese samples taken in the summer. the biochemical and physiological characteristics of the isolates were examined. Using tetracycline, chloramphenicol, novobiocin and rifampicin, the antibiotic susceptibility of the isolates was evaluated. the results demonstrated that all the isolates were susceptible to all the tested antibiotics, with a growth inhibition zone from 36-48 mm. also, the antagonism was examined of S. uberis kGPMF1-7 and S. agalactiae kFPMF8 isolates on the growth of Escherichia coli atCC 25922, Proteus mirabilis atCC 12453, Klebsiella oxytoca kGPMF1, Klebsiella ornithinolytica kGPMF8 and Aeromonas hydrophila, as indicator stains. the results were compared with the activities of chloramphenicol, streptomycin and tetracycline on the tested indicator stains. the strongest antagonism was demonstrated by all Streptococcus isolates on the growth of K. oxytoca kGPMF1 (growth inhibition zone from 12-20 mm) and the A. hydrophila (growth inhibition zone from 13-20 mm). When these results were compared with the results of the sensitivity of tested indicator stains to antibiotics, S. uberis kGPMF1-7 and S. agalactiae kGPMF8 isolates showed a moderate antagonistic effect. Due to the specific way cheese is made in from Sokobanja, these isolates probably originate from cows’ udders.

Effects of some potassium preservatives on physiological activities of selected food borne bacteria

The antibacterial activity of potassium metabisulphite, potassium benzoate, potassium propionate, and potassium nitrate were evaluated against 15 species of bacteria using diffusion and microdilution methods. Potassium metabisulphite showed the greatest activity (MIC varied in the range of 0.78 mg ml–1 to 3.12 mg ml–1), then potassium benzoate (6.25 mg ml–1 to 12.5 mg ml–1) followed by potassium propionate and potassium nitrate (6.25 mg ml–1 to 100 mg ml–1). Effects of potassium benzoate, potassium propionate, and potassium nitrate on the sugar fermentation, the effect of potassium benzoate on cell membrane permeability and on amylolytic activity of bacteria were tested. The results indicated inhibition of fermentation, loss of intracellular macromolecules (proteins) from treated cells, and inhibition of amylolytic activity.

The effects of environmental factors on planktonic growth and biofilm formation of Serratia odorifera and Serratia marcescens isolated from traditionally made cheese

In this study, the effects of different temperature, pH, salt and glucose concentrations on the planktonic growth, biofilm formation, and formed biofilm of Serratia odorifera and Serratia marcescens, isolated from traditionally made cheese, were investigated using spectrophotometric method. The investigated strains demonstrated best planktonic growth and biofilm formation in Tryptic soy broth. The limiting factors for the planktonic growth and biofilm formation were temperature below 4 °C and salt concentration above 4%. Temperature of 37 °C and 44 °C, as well as various concentrations of glucose, stimulated the planktonic growth of bacteria. Moderate influence on biofilm formation was demonstrated at 37 °C as well as at various concentrations of glucose. These results were in accordance with the origin of bacteria, since the isolates were obtained from cheese.