Ahmed, Mushtaq; (1996) Physiological studies on environmental and hospital isolates of 'Enterococcus' species. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

The physiology of environmental and hospital isolates of Enterococcus was studied. A total of 78 isolates of Enterococcus were tested for antimicrobial activity against Listeria innocua NCTC 11288; 17.94 percent showed positive activity. Some environmental and hospital isolates showed strong antimicrobial activity against selected Enterococcus isolates but they did not show activity against pathogenic strains of some other species. Antibiotic sensitivity of Enterococcus isolates to a number of antibiotics including β-lactams, glycopeptides, aminoglycosides and other antibiotics used for the treatment of enterococcal infections was measured. Both environmental and hospital isolates showed resistance to aminoglycosides while these isolates were susceptible to β-lactams and glycopeptides. The main emphasis of this work was to determine the heat tolerance of enterococci. The heat tolerance of stationary phase cells of enterococci grown at 37°C or 45°C was determined at 65°C, 67.5°C and 70°C for half an hour. The heat tolerance of exponential phase cells of barley isolate E. faecium BAR1 and hospital isolate E. faecalis MI2 grown at 37°C or 45°C was determined at 55°C, 60°C and 62.5°C. The stationary phase cells were more resistant to heat than the exponential cells. Both stationary and exponential phase cells were found to be more resistant to heat when grown at above optimum temperatures. The heat tolerance of exponential cells of barley isolate E. faecium BAR1 and hospital isolate E. faecalis MI2 grown at pHs 5.0, 6.0, 8.0 and 9.0 was investigated. The environmental isolate grown at these pHs showed more resistance to heat than the hospital isolate. The heat tolerance of exponential cells of E. faecium BAR1 and E. faecalis MI2 grown at 37°C in 6.5% NaCl broth was studied. Also the heat tolerance of agar grown cells exposed to 10.5% and 15% NaCl broth overnight was investigated at 55°C, 60°C and 62.5°C. Both isolates either grown in 6.5% NaCl broth or exposed to various salt concentrations were found to be more resistant to heat than the cells grown without high salt concentrations. The heat tolerance of an industrial isolate of E. faecium and barley isolate E. faecium BAR1 was determined in malt extract at 60°C, 70°C, 80°C and 90°C. Cells of both isolates in malt extract showed more resistance to heat than the cells in maximum recovery diluent. The heat tolerance of heat shocked cells of E. faecium BAR1 and E. faecalis MI2 was studied. The exponential cells were heat shocked at 50°C for 15 minutes. The heat tolerance was determined at 55°C, 60°C and 62.5°C. The heat shocked cells of the environmental isolate showed more resistance to heat than the hospital isolate. Agar grown cells of the 4 Enterococcus isolates E. faecium MA1, E. faecium BAR1, E. faecium W1 and E. faecalis MI2 were exposed to 50°C or 52°C overnight. The heat tolerance of these isolates was determined at 65°C, 67.5°C and 70°C. The agar grown cells were more resistant to heat than the broth grown exponential phase cells. Whole-cell protein profiles of all the enterococcal isolates were also analyzed on SDS polyacrylamide gels. The river water and the barley isolates each showed two distinct banding patterns. The wheat and rice isolates could not be distinguished on their banding patterns. Hospital isolates were found to be similar to each other in banding patterns but they were distinct from the environmental isolates. Protein samples prepared from heat shocked cells were analyzed on SDS- polyacrylamide gels but no heat shock proteins were seen.

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