Resistance-nodulation-cell division

An alternative to most of these mechanisms is the existence of efficient efflux systems, so that toxic concentrations of the drug are not achieved. There are three major families of proton-dependent multidrug efflux systems (1) the major facilitator superfamily, (2) the small multidrug resistance family, and (3) the resistance/nodulation/cell division family (Paulsen et al. 1996). It should be emphasized that several of these systems are involved not with antibiotic efflux but with, for example, acriflavine, chlorhexidine, and crystal violet. An attempt is made only to outline a few salient features of the resistance/nodulation/cell division family that mediates antibiotic efflux, and these are given in Table 3.3 (Nikaido 1996). They consist of a transporter, a linker, and an outer membrane channel. 

Summary of Resistance/Nodulation/-Cell Division Family... 

S. Magnet, P. Courvalin, and T. Lambert, Resistance-nodulation-cell division-type efflux pump involved in aminoglycoside resistance in Acinetobacter baumannii strain BM4454, Antimicrob. Agents Chemother., 45 (2001) 3375-3380. 

Infection of host cells is achieved as bacteria are released from the unwalled tips of infection threads (Fig. 1C) into newly formed nodule initials (Newcomb, 1981 Sutton, 1983). While infection of cells in indeterminate nodules appears to be solely throu infection threads, a second mode of infection through subsequent division of previously infected cells can occur in determinate nodules. The proliferation of the infection thread into legume host cells involves a delicate balance between bacterial penetration and plant wall resistance (Long and Cooper, 1988). Only 40 to 60% of all nodule cells are infected, and in effective associations this occurs without inducing a disease resistance response. To date one of the least well-understood phases of symbiosis is that of how infection thread growth is regulated and why cellular infection is selective. 

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