Influence of sub-MICs of B-Lactam Antibiotics, Growth Rate, and Iron Limitation on the Surface Structures of Klebsiella Pneumoniae

Abstract

Chemostat culture makes it possible to control growth rate and nutrient availability. It was used in this study to mimic some of the conditions which are characteristic of bacterial growth in vivo. The pattern of expression of one of the porin proteins of K. pneumoniae was shown to vary with changes in growth rate and iron availability. This could have important implications in antibiotic resistance. High molecular weight iron regulated outer membrane proteins (IRMP's)were expressed in iron limited chemostats at both slow and fast growth rates but the amount of the bacterial iron chelator enterochelin detected in the media was reduced at the slow growth rate. When iron was not the growth rate limiting nutrient but was reduced almost to these levels the IRMP's were expressed only by fast growing cells. The evidence suggests that acquisition of iron is less physiologically stressful in slow compared to fast growing cultures. The amount both of cell free and of cell associated capsular polysaccharide produced by slow growing iron limited chemostat cultures of K. pneumoniae was significantly greater than in faster growing cultures. Slow growth rates are characteristic of bacteria adapted to persistence in vivo and encapsulation may be of particular importance in protecting these bacteria from clearance by host defence mechanisms. There was little effect of growth rate on the lipopolysaccharide ladder... pattern.