Phylogeny and species identification of the family Enterobacteriaceae based on dnaJ sequences.

Phylogenetic relations within the family Enterobacteriaceae were analyzed using partial dnaJ sequences of 165 strains belonging to 93 species from 27 enterobacterial genera. The dnaJ phylogeny was in relative agreement with that constructed by 16S rDNA sequences, but more monophyletic groups were obtained from the dnaJ tree than from the 16S rDNA tree. The degree of divergence of the dnaJ gene was approximately 6 times greater than that of 16S rDNA. Also, the dnaJ gene showed the most discriminatory power in comparison with tuf and atpD genes, facilitating clear differentiation of any 2 enterobacterial species by dnaJ sequence analysis. The application of dnaJ sequences to the identification was confirmed by assigning 72 clinical isolates to the correct enterobacterial species. Our data indicate that analysis of the dnaJ gene sequences can be used as a powerful marker for phylogenetic study and identification at the species level of the family Enterobacteriaceae.

Emerging multiple mutations and high-level fluoroquinolone resistance in methicillin-resistant Staphylococcus aureus isolated from ocular infections.

We investigated the prevalence of mutations in the gyrA, gyrB, grlA, and grlB genes in 21 clinical isolates of methicillin-resistant Staphylococcus aureus recovered from ocular infections. These isolates were classified into 16 groups on the basis of pulsed-field gel electrophoresis (PFGE) patterns. Among these nonidentical strains, 9 different combinations of mutations were observed. We observed an unusually high frequency of mutations: 10 (62.5%) of the isolates had four or five mutations, 5 (31.3%) of the isolates had double mutations, and 1 isolate had a single mutation. Different mutations were detected in strains of the same PFGE type, and this is consistent with the independent acquisition of mutations. The minimun inhibitory concentrations values ranged from 0.5 to 512 microg/mL for levofloxacin and 0.125 to 128 microg/mL for gatifloxacin. Only 1 isolate was found to be susceptible to both agents. These results suggest that application of high concentration fluoroquinolone ophthalmic solutions selects for isolates presenting such mutations that may result in a high level of resistance to fluoroquinolones.