Cold-active antibacterial and antifungal activities and antibiotic resistance of bacteria isolated from an alpine hydrocarbon-contaminated industrial site

Selection pressure in hydrocarbon-contaminated soils may lead not only to increased microbial resistance to antibiotics, but also to increased capacity of the soil indigenous population to produce antimicrobial compounds. Therefore, we studied the antibiotic resistance pattern and antibacterial and/or antifungal activities of 47 bacterial strains isolated from an industrial alpine site heavily polluted with petroleum hydrocarbons. Resistance to penicillin was more widespread (49%) than resistance to chloramphenicol or rifampicin (28%) or streptomycin (26%). Only 9% of the strains were resistant to tetracycline. The ability to produce cold-active (10 °C) antimicrobial compounds was tested by using human pathogenic bacteria (Escherichia coli, Shigella flexneri, Salmonella enterica, Pseudomonas aeruginosa, Staphylococcus aureus) and yeasts (Candida albicans, Cryptococcus neoformans) as indicator microorganisms. About two-thirds of the 47 tested strains produced compounds that inhibited growth of at least one indicator microorganism. Six strains inhibited growth of both bacteria and yeast indicators; 12 and 16 strains showed either antibacterial or antifungal activity, respectively. The most versatile bacteria with regard to multiple antibiotic resistance and antimicrobial activity belonged to Actinobacteria or Gammaproteobacteria. The antimicrobial compounds produced by three Pseudomonas spp. and two Serratia spp. strains were characterized in more detail by TLC and HPLC. Depending on the sensitivity of growth inhibition to enzymes, the compounds produced by the three pseudomonads contained a proteinaceous component.