Detection and differentiation of staphylococcal contamination of clinical surfaces using denaturing gradient gel electrophoresis

Multiple-Locus Variable Number Tandem Repeat Analysis (MLVA) and Tandem Repeat Sequence Typing (TRST), helpful tools for subtyping Staphylococcus lugdunensis

Staphylococcus lugdunensis is an emergent virulent coagulase-negative Staphylococcus that is increasingly responsible for severe infections. In an attempt to generate informative sequence data for subtyping S. lugdunensis, we selected and sequenced seven polymorphic variable number of tandem repeats (VNTRs) to develop two new methods: a classic length-based multiple-locus VNTR analysis (MLVA) method and a tandem repeat sequence typing (TRST) method. We assessed their performances compared to two existing methods, multilocus sequence typing (MLST) and multivirulence-locus sequence typing (MVLST) for 128 isolates from diverse clinical settings and geographical origins. The clustering achieved by the four methods was highly congruent, with MLVA discriminating within clonal complexes as defined by MLST. Indeed, MLVA was highly discriminant compared to MLST and MVLST in terms of number of genotypes as well as diversity indexes. Sequencing of the seven VNTRs showed that they were stable, and analysis of sequence polymorphisms provided superior discriminatory power. The typeability, reproducibility, and epidemiological concordance of these new methods were excellent. Of note, no link between clustering and clinical settings was identified. This study demonstrates that MLVA and TRST provide valuable information for molecular epidemiological study of S. lugdunensis, and represent promising tools to distinguish between strains of homogenous lineages in this clonal species.

Multiple approaches to microbial source tracking in tropical northern Australia

Microbial source tracking is an area of research in which multiple approaches are used to identify the sources of elevated bacterial concentrations in recreational lakes and beaches. At our study location in Darwin, northern Australia, water quality in the harbor is generally good, however dry-season beach closures due to elevated Escherichia coli and enterococci counts are a cause for concern. The sources of these high bacteria counts are currently unknown. To address this, we sampled sewage outfalls, other potential inputs, such as urban rivers and drains, and surrounding beaches, and used genetic fingerprints from E. coli and enterococci communities, fecal markers and 454 pyrosequencing to track contamination sources. A sewage effluent outfall (Larrakeyah discharge) was a source of bacteria, including fecal bacteria that impacted nearby beaches. Two other treated effluent discharges did not appear to influence sites other than those directly adjacent. Several beaches contained fecal indicator bacteria that likely originated from urban rivers and creeks within the catchment. Generally, connectivity between the sites was observed within distinct geographical locations and it appeared that most of the bacterial contamination on Darwin beaches was confined to local sources.

Evaluation of the bacterial distribution within the biofilm by denaturing gradient gel electrophoresis in the rat model of urinary catheters

PURPOSE

Most nosocomial urinary tract infections are related to urinary catheters and their biofilm. For the research in this province, animal models are needed to explain the host-pathogen interactions and have an advantage in controlling external interference. This study investigated the validity of the denaturing gradient gel electrophoresis (DGGE) technique for identification of bacteria in a rat model of urinary catheter biofilm.

METHODS

After cutting with aseptic technique, the 24-gauge polyurethane IV catheter was placed in the female rat bladder through the urethra. The catheters were kept in the bladder for 2, 4, or 6 weeks for each group. The genomic DNA was isolated from harvested biofilm of the extracted catheter, and DGGE was performed. The band patterns of DGGE results were analysed, and the sequences were compared using the BLAST from the NCBI.

RESULTS

The results show that Pseudomonas aerusinosa, Escherichia coli, Enterococcus spp., and Corynebacterium sp. were the dominant bacterial species, regardless of the indwelling periods, and other species of bacteria, including Burkholderia and Achromobacter, were identified. The changes in bacterial distribution for the different indwelling periods were non-specific.

CONCLUSIONS

This study using rat model of urinary catheter suggests that DGGE is a useful method in the analysis of the bacterial community in biofilms. Molecular techniques, including DGGE, are valuable to identify fastidious bacteria in the urinary catheter biofilm. This study may be used as fundamental data for studies involving human materials hereafter.