Bacterial resistance to tetracycline: mechanisms, transfer, and clinical significance

Abstract

Tetracycline has been a widely used antibiotic because of its low toxicity and broad spectrum of activity. However, its clinical usefulness has been declining because of the appearance of an increasing number of tetracycline-resistant isolates of clinically important bacteria. Two types of resistance mechanisms predominate: tetracycline efflux and ribosomal protection. A third mechanism of resistance, tetracycline modification, has been identified, but its clinical relevance is still unclear. For some tetracycline resistance genes, expression is regulated. In efflux genes found in gram-negative enteric bacteria, regulation is via a repressor that interacts with tetracycline. Gram-positive efflux genes appear to be regulated by an attenuation mechanism. Recently it was reported that at least one of the ribosome protection genes is regulated by attenuation. Tetracycline resistance genes are often found on transmissible elements. Efflux resistance genes are generally found on plasmids, whereas genes involved in ribosome protection have been found on both plasmids and self-transmissible chromosomal elements (conjugative transposons). One class of conjugative transposon, originally found in streptococci, can transfer itself from streptococci to a variety of recipients, including other gram-positive bacteria, gram-negative bacteria, and mycoplasmas. Another class of conjugative transposons has been found in the Bacteroides group. An unusual feature of the Bacteroides elements is that their transfer is enhanced by preexposure to tetracycline. Thus, tetracycline has the double effect of selecting for recipients that acquire a resistance gene and stimulating transfer of the gene.

Use of antimicrobials in veterinary medicine and mechanisms of resistance

“…Surprisingly, the tetX gene has not been detected in bacteria other than anaerobic Bacteroides spp. where the TetX protein is inactive [52,67].…”

Physico-Chemical Properties and Microbiological Quality of Borehole Water in Four Crowded Areas of Benin City, Nigeria, During Rainfalls

“…Resistance to tetracyclines arose worldwide as a consequence of its extensive usage as a broad spectrum antibiotic and an anti-parasitic drug (43). Over time, gram positive and gram negative isolates acquired resistance attributes to tetracycline through two main mechanisms, tetracycline efflux and ribosomal protection (42).…”

“…The most predominant resistant pattern was DOCRAMPR. Multidrug resistance among members of the enterobacteriaceae family is common (42). Resistance to tetracyclines arose worldwide as a consequence of its extensive usage as a broad spectrum antibiotic and an anti-parasitic drug (43).…”

Cancer stem cell hypothesis: a brief summary and two proposals

“…Technically, it is accomplishable to favor the growth of one cell line while killing other cell lines. For example, we can incorporate the tet R gene into the genome of the seeding cells and at the presence of tetracycline, which is used clinically in treating infections, the seeded stem-like cells may overgrow the CSCs (Speer et al 1992;Matthess et al 2005). Subsequently, after successfully replacement, the seeded stem-like cells could be eradicated by adding 'drug two' which would activate the suicide genes incorporated before seeding.…”