In recent years, various plasmid-mediated resistance mechanisms that confer low-level resistance to quinolones (PMQR) have been described. These include enzymatic modification by the acetyltransferase AAC(6’)-Ib-cr, QepA active efflux pumps, and qnr genes, which have been associated with genes blaOXA-1, blaCTX-M-15 and blaTEM-1 genes.1 These determinants have frequently been found to be related to successful clones producing blaCTX-M-15 and blaOXA-48, such as sequence type (ST) 4052,3 or ST15 K. pneumoniae.4 In unsuccessful clones, an association of these determinants can also be found, such as an 3 years-outbreak in a hospital in Barcelona caused by ST14 K. pneumoniae.5 Nevertheless, the prevalence of these genes in non-extended-spectrum beta-lactamases (ESBL) or carbapenemases-producing isolates is unknown.
A previous study carried out by Rodríguez-Martínez et al.6 described a phenotypic detection algorithm for PMQR, which was validated in a collection of 99 isolates of Enterobacteriales of clinical origin from the University Hospital Virgen Macarena. Fifty-one isolates (51%) had at least one PMQR mechanism: qnrS, the most prevalent, appeared in 25 (49%) isolates, qnrB in 20 (39%) isolates, aac(6′)-Ib-cr in 9 (18%) isolates, oqxAB in 6 (12%) isolates, qnrA in 2 (4%) isolates and qnrD in 2 (4%) isolates. The phenotype compatible with the production of blaOXA-1 consists of an intermediate sensitivity or resistance to amoxicillin/clavulanic acid, decreased sensitivity to piperacillin/tazobactam according to CLSI breakpoints and synergy by disc diffusion between clavulanic and cefepime in the absence of ESBL enzymes. In order to estimate the frequency of the association between PMQR determinants and blaOXA-1 and blaTEM-1, 37 (37.3%) isolates with MIC values >8/4μg/ml to amoxicillin/clavulanic acid and >2μg/ml to cefepime were selected from the same collection. Screening of OXA-1 was performed by examining the synergy between discs of the amoxicillin/clavulanic and cefepime, and also by PCR, using specific primers for the blaOXA-1 gene.7 Twelve (32.4%) isolates were positive for blaOXA-1, including 8 (66.7%) K. pneumoniae (6 of them qnrB), 3 (25%) E. coli (1 qnrA and 1 qnrS) and 1 (8.3%) E. cloacae (qnrA). XbaI PFGE was used to study the clonal relatedness of K. pneumoniae isolates was studied by. Six isolates (75%) formed a cluster (less than 6 difference bands, 86% similarity using the Dice index) and shared the following determinants of resistance: all of them possessed aac(6′)Ib-cr and blaOXA-1; 5 (83%) also have qnrB, and 2 of them (33%) also carried blaCTX-M-15 and blaTEM-1. Two isolates from this group were selected for MLST (one isolate carrying blaOXA-1, qnrB1, aac(6′)-Ib-cr, and blaTEM-1; and the other isolate carrying blaOXA-1, qnrB1, aac(6′)-Ib-cr, blaTEM-1, and blaCTX-M-15) were assigned ST405. When these were also compared with the genetic profiles held at the Andalusian Reference Laboratory for molecular typing, they were found to share 85% similarity with isolates belonging to the same clone from other areas of Spain.
This clone with the genetic profile blaTEM-1, blaCTX-M-15 and blaOXA-1 was described for the first time in Casablanca (Morocco) in isolates collected between February 2007 and March 2008.8 The first description of ST405 with OXA-48 production was in Belgium (between January 2010 to April 2011) 4 isolates. These isolates also involved blaTEM-1 and blaCTX-M-15, and 3 of them additionally carried aac(6′)-Ib-cr and qnrB1.9 The largest single-centre outbreak to date, in the Hospital La Paz, Madrid,10 was caused by a ST405 producer of OXA-48 that also carried qnrB1 and aac(6′)-Ib-cr.2 The same clone was associated with two outbreaks in neonatology units in Andalusian hospitals (in the South of Spain) caused by isolated producers of CTX-M-15, but not of OXA-48.3
ST405 shares a series of determinants in every location where it has been detected: blaOXA-1, blaTEM-1 and aac(6′)-Ib-cr, even in non-ESBL or non carbapenemase-producing isolates, as well as having the characteristics of a successful clone. The dissemination of this clone seems to be associated with acquisition of determinants of low resistance to amoxicillin/clavulanic acid and quinolones, with acquisition of ESBL or carbapenemase genes occurring later. This clone could be more widely disseminated than initially thought, since there are few data available on cephalosporin- and carbapenems-susceptible isolates. In a recent study in our country, this was one of the 5 most important clones in the dissemination of carbapenemases in Spain, accounting for 13.5% of carbapenemases producers,11 and only 2 of the five non-carbapenemases-producers ST405 were susceptible to third-generation cephalosporins. It would be of interest to find out the real prevalence of this clone in resistant and wild type isolates in order to study the selective forces that drive its dissemination.
This work was supported by Plan Nacional de I+D+i 2013–2016 and Instituto de Salud Carlos III, Subdirección General de Redes y Centros de Investigación Cooperativa, Ministerio de Economía, Industria y Competitividad, Spanish Network for Research in Infectious Diseases (REIPI; RD16/0016/0001)-co-financed by European Development Regional Fund “A way to achieve Europe”, Operative Program Intelligent Growth 2014–2020.
