Severe bilateral optic neuritis associated with prolonged linezolid therapy

1114 isolate 4 as donor, transconjugants were selected on MacConkey agar with 2 mg/L cefotaxime and 50 mg/L nalidixic acid. Both types of bla CTX-M-14-carrying plasmids proved to be conjugative (Figure 1a) and harboured the bla CTX-M-14 gene on an EcoRI-fragment of ∼18 kb. All three S. Enteritidis isolates showed closely related XbaI-PFGE-patterns, determined as previously described. 2 The only difference in the fragment patterns was an extra band of ∼75 kb in the cefotaxime-resistant isolates 2 and 3 (Figure 1b), which hybridized with the CTX-M-14 probe (data not shown). Based on these observations, it was assumed that the child was infected with a strain which developed an ESBL phenotype during the treatment. Because data were not available about intestinal flora of the patient before the bacteraemic episode, we cannot exclude the possibility that the child acquired an invasive cefotaxime-susceptible and a cefotaxime-resistant S. Enteritidis as well as an ESBL-producing E. coli at the same time before hospital admission. Simultaneous transmission of ESBL-producing E. coli with susceptible Salmonella enterica from a common source has been previously reported 3 in a Salmonella outbreak in a summer camp. None of the samples from campers or food-handlers yielded resistant salmonellae and, in contrast with our case, no person received antibiotic therapy. The family of the CTX-M-type ESBLs comprises 40 enzymes, subclassified into five major groups by their similar amino acid sequences: CTX-M-1, M-2, M-8, M-9 and M-25 groups. 4 Salmonella isolates have been found to express CTX-M-2, M-3, M-4 and M-9 enzymes in serotypes Typhimurium and Enteritidis isolated in South America and Europe. 4 Until now, CTX-M-14 has been described in several enterobacterial species, but not in Salmonella isolates. 5 In Spain, the only report of a CTX-M-type production in Salmonella was that described by Simarro et al. 1 in 1997. In this study, four Salmonella enterica Virchow strains were reported with CTX-M-9 production in Barcelona and Murcia. Furthermore, CTX-M-14 β-lactamase has previously been found in the northwest area of Spain 6 in different E. coli strains, causing infections in 17 patients. Our findings provide the first evidence of CTX-M-14 β-lactamase in Salmonella enterica serotype Enteritidis. The observation that the bla CTX-M-14 gene is located on a conjugative plasmid which can transfer in vitro between E. coli and Salmonella Enteritidis strongly suggests that such transfer events can also occur in vivo.