Evolution in action: dissemination of tet(X) into pathogenic microbiota

Tetracycline Antibiotics and Resistance

“…This activity was subsequently characterized as a flavin-dependent monooxygenase, encoded by an expanding family of tet(X) orthologs, capable of covalently inactivating all tetracyclines with the addition of a hydroxyl group to the C-11a position located between the C and B rings of the tetracycline core (Fig. 1) (Speer et al 1991;Yang et al 2004;Moore et al 2005;Grossman et al 2012;Aminov 2013). Because Bacteroides species are obligate aerobes, it is not surprising that the oxidoreductases encoded by tet(X) and its orthologs tetX1 and tetX2 do not confer resistance in the isolates in which they were originally found (Whittle et al 2001).…”

“…The environmental origin of tet(X) is suggested by its iden-tification in Sphinogbacterium spp., a Gramnegative soil bacterium that expresses a functional Tet(X) (Ghosh et al 2009). Further, the presence of tet(X) and genes encoding similar tetracycline-inactivating activities, also known as "tetracycline destructases," in agricultural and aquacultural bacteria ensures the persistence of this resistance mechanism in the food chain, facilitating crossover into human pathogens (Aminov 2013;Forsberg et al 2015). Because of the conjugative nature of tet(X)containing plasmids and transposons, recent reports of tet(X) in Enterobacteriaceae and Pseudomonadaceae hospital urinary tract infection (UTI) isolates in Sierra Leone, and tet(X) in A. baumannii in a Chinese hospital, are of concern with regard to the spread of this mechanism (Leski et al 2013;Deng et al 2014).…”

Biotic acts of antibiotics

“…Although it is on the list of reserve drugs, its use is steadily increasing (Huttner et al, 2012). Regrettably, similar to the fate of other antibiotics, the efficiency of tigecycline may start to deteriorate due to the penetration of tigecycline resistance into pathogenic microbiota (Aminov, 2013). …”

Resistance to the tetracyclines and macrolide-lincosamide-streptogramin group of antibiotics and its genetic linkage – a review

“…Dissemination of tet(X) resistance gene is of special concern because it confers resistance also against third generation tetracycline tigecycline [36]. Although the use of this antibiotic is strictly regulated, tet(X) has already been observed among pathogenic bacteria [37], and sequence similarity of flanking regions around tet(X) suggest that its spread is most likely due to horizontal transfer of transposons from the CTnDOT family [38].…”