The Ecology, Biology and Pathogenesis of Acinetobacter spp.: An Overview

Diversity, biology and evolution of IncQ-family plasmids

Tetracycline Antibiotics: Mode of Action, Applications, Molecular Biology, and Epidemiology of Bacterial Resistance

Tetracyclines were discovered in the 1940s and exhibited activity against a wide range of microorganisms including gram-positive and gram-negative bacteria, chlamydiae, mycoplasmas, rickettsiae, and protozoan parasites. They are inexpensive antibiotics, which have been used extensively in the prophlylaxis and therapy of human and animal infections and also at subtherapeutic levels in animal feed as growth promoters. The first tetracycline-resistant bacterium, Shigella dysenteriae, was isolated in 1953. Tetracycline resistance now occurs in an increasing number of pathogenic, opportunistic, and commensal bacteria. The presence of tetracycline-resistant pathogens limits the use of these agents in treatment of disease. Tetracycline resistance is often due to the acquisition of new genes, which code for energy-dependent efflux of tetracyclines or for a protein that protects bacterial ribosomes from the action of tetracyclines. Many of these genes are associated with mobile plasmids or transposons and can be distinguished from each other using molecular methods including DNA-DNA hybridization with oligonucleotide probes and DNA sequencing. A limited number of bacteria acquire resistance by mutations, which alter the permeability of the outer membrane porins and/or lipopolysaccharides in the outer membrane, change the regulation of innate efflux systems, or alter the 16S rRNA. New tetracycline derivatives are being examined, although their role in treatment is not clear. Changing the use of tetracyclines in human and animal health as well as in food production is needed if we are to continue to use this class of broad-spectrum antimicrobials through the present century.

Comparative Biology of IncQ and IncQ-Like Plasmids

Plasmids belonging to Escherichia coli incompatibility group Q are relatively small (approximately 5 to 15 kb) and able to replicate in a remarkably broad range of bacterial hosts. These include gram-positive bacteria such as Brevibacterium and Mycobacterium and gram-negative bacteria such as Agrobacterium, Desulfovibrio, and cyanobacteria. These plasmids are mobilized by several self-transmissible plasmids into an even more diverse range of organisms including yeasts, plants, and animal cells. IncQ plasmids are thus highly promiscuous. Recently, several IncQ-like plasmids have been isolated from bacteria found in environments as diverse as piggery manure and highly acidic commercial mineral biooxidation plants. These IncQ-like plasmids belong to different incompatibility groups but have similar broad-host-range replicons and mobilization properties to the IncQ plasmids. This review covers the ecology, classification, and evolution of IncQ and IncQ-like plasmids.