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Objectives: Linezolid resistance mediated by the cfr gene represents a global concern due to its dissemination among multiresistant nosocomial pathogens such as MRSA and Enterococcus. In the present work, we have evaluated the in vitro transmission of cfr pSCFS7-like plasmids from two Staphylococcus epidermidis ST2 strains (SE45 and SE50) isolated in Spanish hospitals, to clinical MRSA and Enterococcus spp. isolates obtained in Japan, a country in which cfr has not been detected yet. We have also investigated alternative mechanisms of horizontal gene transfer involved in the spread of the cfr gene.Methods: MRSA (n = 16) and Enterococcus spp. (n = 8) clinical isolates were used as recipients in conjugative experiments. Bacteriophage-mediated transmission was tested using MR83a phage and N315, COL and Mu50 strains. A transformation assay was carried out using a natural competent strain derived from N315.Results: The SE45 strain was able to transfer the cfr gene to all strains tested, while transmission from SE50 was observed only to a few strains and with less efficiency. No transmission was observed to Enterococcus spp. isolates. Even though conjugation is thought to be the main mechanism of cfr dissemination, we have demonstrated that transduction can be considered an alternative pathway for transmission of the cfr gene between MRSA strains. However, the results suggest an absence of transmission by natural transformation.Conclusions: Linezolid resistance mediated by cfr vectors, such as pSCFS7-like plasmids, can be efficiently transferred to clinical MRSA in Japanese isolates. After reaching the staphylococcal pool, the cfr gene could be spread among MRSA strains by either conjugation or transduction. [ABSTRACT FROM AUTHOR]

The aim of the study was to investigate biofilm formation in Gram negative bacteria and to quantify biofilm production applying a new developed technique that made possible to compare results about biofilm formation within the different Gram negative bacteria species. A total of 153 Gram negative strains corresponding to 12 different bacterium species were studied applying a variation of the optic density measurement technique reported by Stepanovic et al. Data obtained with optic density analysis allow to classify microorganisms in strong biofilm developers, moderate biofilm developers, weak biofilm developers and no biofilm developers. The results were expressed in two ways, using in both cases the same statistical method: without standardization, where controls were different depending on the day optic density measurements were performed, and standardized using a correction factor, using the same control for every strain of all our bacterium species in our study, which allows result homogenization. The obtained results in our study after data analysis and standardization show that over the 153 Gram negative strains in our study, 105 of them were no biofilm developers, representing 63.75% of all the studied bacterium genera. We consider that standardization and quantification of biofilm development in Gram negative bacteria can be useful in clinical practice, because biofilm development ability can lead or focus the gold treatment of pathologies produced by these microorganisms.

Objectives: High-level penicillin resistance in Streptococcus pneumoniae requires extensive re-modulation of the penicillin-binding proteins (PBPs), and murM gene function is also required for the expression of resistance. In this work, we determined whether specific changes in PBPs were associated with specific MurM variants., Methods: Two collections of highly penicillin-resistant (MIC 2-8 mg/L) isolates, including 10 early (1997-1998) and 23 contemporary (2002-2004) isolates, were studied., Results: Most of the isolates belonged to clones Spain(6B)-2 (13 strains), Spain(23F)-1 (10 isolates) and Spain(14)-5 (20 isolates). Different protein variants of MurM (MA, MB5, MB6, MB9 and MB10), PBP1A (A-C), PBP2B (A-D) and PBP2X (A-C) were recognized, including two murM alleles not previously described. Particular [MurM-PBP1A-2B-2X] allelic combinations were predominant among the different clones, including [MA-B-B-B] for old (MIC 2 mg/L) and [MB10-C-A-B] for recent (MIC 4-8 mg/L) Spain(6B)-2 isolates, [MA-A-C-A] for Spain(23F)-1 and [MB5-A-A-A] in Spain(14)-5 isolates., Conclusions: Although S. pneumoniae has a basic recombinational population structure, our results indicate remarkable conservation of PBPs and MurM protein types within each clone. This suggests that particular PBPs-MurM combinations tend to be preserved and may have an independent evolutionary history in particular clones.

Aims: The aim of this study was to analyse the nucleotide sequences of regions encoding the penicillin-binding domains of pbp1A, pbp2B and pbp2X genes and murM alleles from 14 selected amoxicillin-resistant Streptococcus pneumoniae isolates (MICs 8-16 mg/L) obtained in Spain., Methods: PFGE and dideoxynucleotide chain termination sequencing were used., Results: Analysis of PFGE profiles showed that the amoxicillin-resistant S. pneumoniae strains belonged to six different PFGE patterns including the Spain23F-1, Spain6B-2, Spain9V-3 and Spain(14)-5 international clones; however, 8 of the 14 strains belonged to the Spain9V-3 clone. These strains showed the typical changes in penicillin-binding proteins (PBPs) 1A and 2X and had 10 unique changes in the 590-641 region of PBP2B as described previously. Transformation experiments tried to incorporate the transpeptidase domain of PBP2B including the 590-641 region associated with amoxicillin-resistant pneumococci. Sequencing of the pbp2B genes revealed that part of the 3' region of the pbp2B sequence encoding a region of the domain (around amino acid 514-538 to the C terminus of PBP2B) did not recombine with the R6 pbp2B gene. The murM sequence analysis showed that 6, 6 and 2 amoxicillin-resistant S. pneumoniae strains had murMA, murMB5 and murMB6 alleles, respectively. However, strains with murMB5 or murMB6 alleles showed a single mutation (N537D) in the 537-581 region of PBP2B, while strains with the murMA allele had 12 unique changes., Conclusions: Ten unique changes in the 590-641 region of PBP2B and no specific murM alleles were found in S. pneumoniae strains isolated in Spain with an amoxicillin MIC>or=8 mg/L (MICs from 6 to 12 mg/L by 1 mg/L step dilution). In addition, the presence of specific mutations in PBP2B seems to play a key role in the presence of different murM alleles in these amoxicillin-resistant pneumococcal strains.