Genetic Diversity of the tet (M) Gene in Tetracycline-Resistant Clonal Lineages of Streptococcus pneumoniae

Abstract

The aim of the present study was to examine the stability and evolution of tet(M)-mediated resistance to tetracyclines among members of different clonal lineages of Streptococcus pneumoniae. Thirty-two tetracyclineresistant isolates representing three national (Spanish serotype 14, Spanish serotype 15, and Polish serotype 23F) and one international (Spanish serotype 23F) multidrug-resistant epidemic clones were all found to be tet(M) positive and tet(O), tet(K), and tet(L) negative. These isolates all carried the integrase gene, int, which is associated with the Tn1545-Tn916 family of conjugative transposons. High-resolution restriction analysis of tet(M) products identified six alleles, tet(M)1 to tet(M)6: tet(M)1 to tet(M)3 and tet(M)5 in isolates of the Spanish serotype 14 clone, tet(M)4 in both the Spanish serotype 15 and 23F clones, and tet(M)6, the most divergent allele, in the Polish 23F clone. This indicates that tet(M) variation can occur at the inter-and intraclone levels in pneumococci. Two alleles of int were identified, with int1 being found in all isolates apart from members of the international Spanish 23F clone, which carried int2. Susceptibility to tetracycline, doxycycline, and minocycline was evaluated for all isolates with or without preincubation in the presence of subinhibitory concentrations of tetracyclines. Resistance to tetracyclines was found to be inducible in isolates of all clones; however, the strongest induction was observed in the Spanish serotype 15 and 23F clones carrying tet(M)4. Tetracycline was found to be the strongest inducer of resistance, and minocycline was found to be the weakest inducer of resistance.The gram-positive pathogen Streptococcus pneumoniae (the pneumococcus) is a major cause of pneumonia, otitis media, and meningitis (12). The evolution and broad global distribution of multiple antibiotic resistance determinants in bacteria have resulted in a situation in which pneumococci are commonly resistant to penicillin, the broad-spectrum cephalosporins, macrolides, lincosamides, co-trimoxazole, chloramphenicol, and tetracyclines, as well as rifampin (11), sulphonamides (42), and fluoroquinolones (13,24,30), making the treatment of serious pneumococcal disease increasingly difficult (17,22). The transformable nature of S. pneumoniae (which has played an important role, along with point mutations) in the evolution of resistance [1,4,11,13,24,30] has in no small part also led to a population structure characterized by free genetic exchange, punctuated by clonal expansion of successful variants. The best studied of these are the Spanish 23F, Spanish 6B, and French/ Spanish 9V14 multidrug-resistant clones that have now spread intercontinentally (see reference 10 for a recent review).One class of antimicrobial agents found most often in clinical use is the tetracyclines, broad-spectrum bacteriostatic drugs shown to be active against pneumococci (33). In some European (9, 16, 23), Asian (35,36,41,47), and African (31, 52), countries lack of susceptibility to tetracyclines...

Molecular Epidemiology of Pneumococcal Carriage among Children with Upper Respiratory Tract Infections in Hanoi, Vietnam

“…Thirteen tet(M)-containing strains were fully susceptible to tetracycline, suggesting the presence of a nonfunctional tetracycline resistance gene. A similar observation has previously been reported by Doherty et al (10).…”

Molecular Epidemiology of Penicillin-Susceptible Non-β-Lactam-Resistant Streptococcus pneumoniae Isolates from Greek Children

“…So far, no other tetracycline resistance determinants have been on May 11, 2018 by guest http://jcm.asm.org/ described; therefore, the underlying mechanism remains unclear. Also in line with the Vietnamese study is the isolation of tet(M)-containing but tetracycline-susceptible strains in Greece, suggesting the presence of a nonfunctional or unexpressed tetracycline resistance gene (2,9). A similar phenomenon was seen for the PBP genes.…”

Evidence for the predominance of a single tet(M) gene sequence type in tetracycline-resistant Ureaplasma parvum and Mycoplasma hominis isolates from Tunisian patients

“…Comparative sequence analysis of tet(M) in several mycoplasma isolates from Russia showed that the gene was completely identical in 11 of 13 M. hominis clinical strains (Soroka et al, 2002). By contrast, using a high-resolution restriction analysis, tet(M) variation in S. pneumoniae was shown to occur at both the inter-and intraclone levels (Doherty et al, 2000), suggesting that tet(M) may evolve differently depending on the bacterial species. However, comparative analyses of several S. pneumoniae tet(M) sequences available in GenBank revealed a divergence rate of no more than 2 % (data not shown).…”