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Antimicrobial Agents and Chemotherapy, September 2007, p. 3205-3211, Vol. 51, No. 9
0066-4804/07/$08.00+0     doi:10.1128/AAC.00625-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Occurrence of Tetracycline Resistance Genes among Escherichia coli Isolates from the Phase 3 Clinical Trials for Tigecycline

Margareta Tuckman,¹ Peter J. Petersen,¹ Anita Y. M. Howe,² Mark Orlowski,² Stanley Mullen,² Karen Chan,^1, Patricia A. Bradford,¹ and C. Hal Jones^1*

Infectious Diseases Discovery Research,¹ Vaccines Discovery Research, Wyeth Research, Pearl River, New York²

Received 11 May 2007/ Returned for modification 8 June 2007/ Accepted 2 July 2007

Tigecycline, a member of the glycylcycline class of antibiotics, was designed to maintain the antibacterial spectrum of the tetracyclines while overcoming the classic mechanisms of tetracycline resistance. The current study was designed to monitor the prevalence of the tet(A), tet(B), tet(C), tet(D), tet(E), and tet(M) resistance determinants in Escherichia coli isolates collected during the worldwide tigecycline phase 3 clinical trials. A subset of strains were also screened for the tet(G), tet(K), tet(L), and tet(Y) genes. Of the 1,680 E. coli clinical isolates screened for resistance to classical tetracyclines, 405 (24%) were minocycline resistant (MIC 8 µg/ml) and 248 (15%) were tetracycline resistant (MIC 8 µg/ml) but susceptible to minocycline (MIC 4 µg/ml). A total of 452 tetracycline-resistant, nonduplicate isolates were positive by PCR for at least one of the six tetracycline resistance determinants examined. Over half of the isolates encoding a single determinant were positive for tet(A) (26%) or tet(B) (32%) with tet(C), tet(D), tet(E), and tet(M), collectively, found in 4% of isolates. Approximately 33% of the isolates were positive for more than one resistance determinant, with the tet(B) plus tet(E) combination the most highly represented, found in 11% of isolates. The susceptibilities of the tetracycline-resistant strains to tigecycline (MIC₉₀, 0.5 µg/ml), regardless of the encoded tet determinant(s), were comparable to the tigecycline susceptibility of tetracycline-susceptible strains (MIC₉₀, 0.5 µg/ml). The results provide a current (2002 to 2006) picture of the distribution of common tetracycline resistance determinants encoded in a globally sourced collection of clinical E. coli strains.

Published ahead of print on 9 July 2007.

Present address: Discovery Neurosciences, Wyeth Research, Princeton, New Jersey.

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• Kelesidis, T., Karageorgopoulos, D. E., Kelesidis, I., Falagas, M. E. (2008). Tigecycline for the treatment of multidrug-resistant Enterobacteriaceae: a systematic review of the evidence from microbiological and clinical studies. J Antimicrob Chemother 0: dkn311v1-10 [Abstract] [Full Text]