International Journal of Antimicrobial Agents 25 (2005) 501–507 Extended-spectrum -lactamases in Shigella flexneri from Argentina: first report of TOHO-1 outside Japan  Patricia Andres a , Alejandro Petroni a , Diego Faccone a , Fernando Paster´ an a , Roberto Melano a , Melina Rapoport a , Mariela Mart´ ınez b , Catalina Culasso c , Adriana Di Bella d , Bettina Irigoyen e , Jorgelina Mulki f , Adriana Procopio g , Martha von Specht h , Marcelo Galas a,∗ a Servicio Antimicrobianos, Dpto. Bacteriolog´ ıa, INEI-ANLIS ‘Dr. Carlos G. Malbr´ an’, Av. V´ elez Sarsfield 563 (1281), Buenos Aires, Argentina b Hospital de Pediatr´ ıa ‘JuanP. Garraham’, Buenos Aires, Argentina c Hospital de Ni ˜ nos de la Sant´ ısima Trinidad de C´ ordoba, Pcia. de C´ ordoba, Argentina d Hospital Nacional‘Prof. Dr. Alejandro Posadas’, El Palomar, Pcia.de Buenos Aires, Argentina e Hospital General de Agudos ‘Dr. Julio C. Perrando’, Resistencia, Pcia. de Chaco, Argentina f Hospital Materno Infantil de Salta, Pcia. de Salta, Argentina g Hospital de Ni ˜ nos ‘Dr. Ricardo Guti´ errez’, Buenos Aires, Argentina h Hospital P ´ ublico Provincial de Pediatr´ ıa, Posadas, Pcia. de Misiones, Argentina Received 12 November 2004; accepted 9 February 2005 This paper is dedicated to the memory of Dr. Alicia Rossi, who directed our Service and guided this work. Abstract A 9-year nation wide survey of the presence of extended-spectrum -lactamases (ESBLs) in Shigella flexneri is described. Ten of 9033 (0.1%) isolates produced ESBLs, which were characterized by isoelectric focusing, PCR and DNA sequencing. These were CTX-M-2 (five isolates), TOHO-1 (one isolate), SHV-2 (two isolates) and PER-2 (two isolates, the first report in S. flexneri world wide). The emergence of each ESBL type in S. flexneri was not restricted to a particular region of Argentina. TOHO-1 showed a more basic isoelectric point (8.4) than that previously found (7.8) and its encoding gene (bla TOHO-1a ) harboured a silent change, G825A, relative to the reported bla TOHO-1 . All the ESBL-encoding genes were transferred to Escherichia coli by conjugation. PFGE analysis indicated that the 10 ESBL-producing S. flexneri isolates were subtypes of a unique clone. © 2005 Elsevier B.V. and the International Society of Chemotherapy. All rights reserved. Keywords: Shigella flexneri; Resistance; -Lactamases; ESBL; CTX-M-2; TOHO-1 1. Introduction In Enterobacteriaceae, extended-spectrum -lactamases (ESBLs) constitute the major mechanism conferring resis- tance to expanded-spectrum cephalosporins world wide [1].  This work was presented in part at the 40th Interscience Conference on Antimicrobial Agents and Chemotherapy (ICAAC), Toronto, Ontario, Canada, September 17–20, 2000 (abstract 2011), and more recently, at the 44th ICAAC, Washington DC, USA, October 30–November 2, 2004 (ab- stract C2-1325). ∗ Corresponding author. Tel.: +54 11 4303 2812; fax: +54 11 4303 2812. E-mail address: mgalas@anlis.gov.ar (M. Galas). In Argentina, ESBLs are widely spread among enterobacte- rial isolates, CTX-M-2 being the most prevalent enzyme by far [2]. CTX-M-enzymes are an expanding family of ESBLs that preferentially hydrolyse cefotaxime over ceftazidime and are inhibited by -lactamase inhibitors such as clavulanic acid, sulbactam and tazobactam. Currently, this family com- prises 36 enzymes that were grouped in four clusters accord- ing to their amino acid identity; namely, the CTX-M-1 clus- ter; the CTX-M-2 cluster (hereafter referred to as CTXM2c); the CTX-M-8 cluster, and the CTX-M-9 cluster [2]. The first reported enzymes from the CTXM2c were CTX-M-2 and TOHO-1, described in Argentina [3] and Japan [4], re- 0924-8579/$ – see front matter © 2005 Elsevier B.V. and the International Society of Chemotherapy. All rights reserved. doi:10.1016/j.ijantimicag.2005.02.016