ABSTRACT
Control of harmful bacteria in food, aquaculture, pharmaceuticals, agriculture, hospitals and recreation water pools are of great global concern. Marine bacteria are an enormous source of bio-controlling agents. The aim of this study was to identify and optimize the growth conditions including effect of different biotic and abiotic factors on antimicrobial activity of strain DK1-SA11 isolated from Qingdao Bay of China Yellow Sea. Microscopic characterization, API[registered sign] 20E and 50 CHB kit base carbohydrates utilization, 16S rDNA and DNA gyrB gene sequencing studies identified the bacterium as Bacillus subtilis subsp. spizizenii DK1-SA11. Antimicrobial spectrum of cell free supernatant [CFS] has shown antimicrobial activities against all test strains including methicillin-resistant Staphylococcus aureus, E. coli O157:H7, Candida albicans, Klebsiella pneumoniae, Listeria monocytogenes, Vibrio parahaemolyticus, E. coli, Pseudomonas fluorescens, Salmonella typhimurium and Vibrio cholerae. Among all the media tested, Marine Broth 2216 was found to be the best medium for bacterial growth and production of antibacterial compounds. The other optimum conditions for growth were pH:7 and incubation temperature: 25[degree sign] C with >/= 180 rpm for 60-72 h. Out of 49 different carbohydrates tested, D-mannose increases the antibacterial activity by 33.3% while Darabitol decreases it by 44.4%. Crude CFS showed activity even after three months of storage below -20[degree sign] C and boiling for 10 min, whereas it loses 100% of its antimicrobial activity after enzymatic treatments of lipase, trypsin and papain. The production of antimicrobial compounds and broad spectrum of antimicrobial activity against all tested pathogens suggested that the strain DK1-SA11 can be used as a source for probiotics, synbiotics and antibiotics
ABSTRACT
To determine the effect of physical and chemical stress factors e.g. antibiotics, NaCI, glucose, heat shock, cold shock and sonic waves on biofilm formation by icaA positive and negative strains of Methicillin resistant Staphylococcus [S.] aureus. Experimental study. Microbiological Analytical Centre, Pakistan Council of Scientific and Industrial Research [PCSIR] Laboratories Complex, Karachi, from January to December 2010. One strain of Staphylococcus aureus labelled as FA was isolated from a food sample and the other strain labelled as CL was a clinical strain. Biofilm assays were performed in brain-heart infusion [BHI] medium and in BHI supplemented with 7% NaCI, 5% glucose, or sub-inhibitory concentrations of Vancomycin, Oxacillin, Ampicillin, Tetracycline, Erythromycin, Rifampicin and Ciprofloxacin. Polymerase chain reaction [PCR] was used for screening of the icaA and mecA genes. The FA and CL were identified as MRSA carrying mecA gene. The strain FA showed biofilm formation without any treatment and was found to carry icaA gene contrary to CL, that does not contain this gene therefore, is unable to produce biofilm under normal conditions without any stress. The use of sub-lethal doses of cell wall active antibiotics, exposure to 7% NaCI, sonication, and heat shock were found to augment biofilm quantity in FA, an icaA positive strain and induce biofilm mode of growth in CL, an icaA negative strain. Anti-protein synthesis antibiotics did not show any effect on biofilm formation process in icaA positive or negative strains. There is a role of anti-cell wall factors i.e. sonication, heat shock, NaCI and antibiotics in the induction of biofilm mode of growth in MRSA and Methicillin sensitive S. aureus. The factors which partially damage bacterial cell wall, equally, induce biofilm formation in icaA positive or negative S. aureus