Clinical characteristics associated with isolation of small-colony variants of Staphylococcus aureus and Pseudomonas aeruginosa from respiratory secretions of patients with cystic fibrosis.

During a 3-month period, small-colony variant phenotypes of both Staphylococcus aureus and Pseudomonas aeruginosa were isolated from respiratory secretions of 8.2% and 9.2%, respectively, of 98 patients with cystic fibrosis, particularly those with advanced pulmonary disease and prolonged antibiotic exposure.

A global view of Staphylococcus aureus whole genome expression upon internalization in human epithelial cells.

BACKGROUND: Staphylococcus aureus, a leading cause of chronic or acute infections, is traditionally considered an extracellular pathogen despite repeated reports of S. aureus internalization by a variety of non-myeloid cells in vitro. This property potentially contributes to bacterial persistence, protection from antibiotics and evasion of immune defenses. Mechanisms contributing to internalization have been partly elucidated, but bacterial processes triggered intracellularly are largely unknown. RESULTS: We have developed an in vitro model using human lung epithelial cells that shows intracellular bacterial persistence for up to 2 weeks. Using an original approach we successfully collected and amplified low amounts of bacterial RNA recovered from infected eukaryotic cells. Transcriptomic analysis using an oligoarray covering the whole S. aureus genome was performed at two post-internalization times and compared to gene expression of non-internalized bacteria. No signs of cellular death were observed after prolonged internalization of Staphylococcus aureus 6850 in epithelial cells. Following internalization, extensive alterations of bacterial gene expression were observed. Whereas major metabolic pathways including cell division, nutrient transport and regulatory processes were drastically down-regulated, numerous genes involved in iron scavenging and virulence were up-regulated. This initial adaptation was followed by a transcriptional increase in several metabolic functions. However, expression of several toxin genes known to affect host cell integrity appeared strictly limited. CONCLUSION: These molecular insights correlated with phenotypic observations and demonstrated that S. aureus modulates gene expression at early times post infection to promote survival. Staphylococcus aureus appears adapted to intracellular survival in non-phagocytic cells.

High-density DNA probe arrays for identification of staphylococci to the species level.

Rapid and accurate identification and speciation of staphylococci clinical isolates is important for predicting medical pathology. We evaluated the ability of a high-density DNA probe array based on 16S rDNA sequences to identify Staphylococcus species. Correct identification was observed for 185 out of the 201 strains (92%). Of the 33 tested species, the array was able to correctly identify 30 of them. The total time required for identification of 4 isolates was 5 h. Such a tool represents a powerful method for routine microbiological diagnostic as well as for epidemiological studies.

Evaluation of a high-density oligonucleotide array for characterization of grlA, grlB, gyrA and gyrB mutations in fluoroquinolone resistant Staphylococcus aureus isolates.

Using high-density oligonucleotide array technology, 30 Staphylococcus aureus strains were studied for the presence of mutations in genes involved in fluoroquinolone resistance: grlA, gyrA, grlB and gyrB. For the two most important genes, gyrA and grlA, correlation with sequencing reached 95.1%. If all genes were considered, correlation was 88.8%.