MRSA surveillance in a UK district hospital: measuring clinical isolates with MRSA is more useful than measuring MRSA bacteraemias.

The introduction of mandatory surveillance of meticillin-resistant Staphylococcus aureus (MRSA) bacteraemias and targets in England has led to reductions in most hospitals. However, reductions were difficult to demonstrate at Peterborough & Stamford Hospitals NHS Foundation Trust as MRSA bacteraemia was already an uncommon event. The authors questioned the efficacy of monitoring bacteraemias in a low-prevalence hospital, and this study sought to determine the accuracy of measuring bacteraemias compared with all clinical isolates (excluding bacteraemias; e.g. wound, sputa, urine) to assess the effectiveness of interventions. Over the six-year study period, a significant reduction was seen in MRSA in clinical specimens and new MRSA carriers identified by screening, whereas the MRSA bacteraemia rate remained at low levels. The measurement of clinical isolates may be more useful for assessment of the effectiveness of interventions now that MRSA bacteraemia rates have fallen to low levels almost universally across the UK.

Low concentrations of vancomycin stimulate biofilm formation in some clinical isolates of Staphylococcus epidermidis.

AIMS: To examine the response of Staphylococcus epidermidis isolates from prosthetic orthopaedic infections to vancomycin concentrations below the minimum inhibitory concentration. METHODS: Staphylococcal biofilms were grown in 96-well flat-bottomed cell culture plates under a variety of culture conditions and stained using an ammonium crystal violet solution. Optical density (450 nm wavelength) was recorded to estimate the biofilm density for each strain. Population analysis and time-kill studies were also performed on selected isolates. RESULTS: A range of responses were observed, including increased biofilm density at drug concentrations approaching the minimum inhibitory concentration. This increased density was associated with the presence of a more resistant population identified on population analysis but without an apparent effect on the time-kill curves. CONCLUSIONS: The ability of some strains to show increased biofilm density could be a factor in the failure of vancomycin therapy reported in some cases. The demonstration that low concentrations of vancomycin may increase the density of newly forming S epidermidis biofilms may indicate an area of potential concern in the use of vancomycin in orthopaedic implants and intravascular catheter locks, and may partially account for some cases of treatment failure.

Value of CT-guided biopsy in the diagnosis of septic discitis.

AIM: To determine the role of CT-guided biopsy in the management of cases of infective discitis. METHODS: Data were examined from a retrospective case series of CT-guided biopsies for the 5-year period ending June 2006. RESULTS: 98 CT-guided biopsies were performed in the study period on 103 patients. Malignancy was diagnosed in 49 episodes. Discitis and paravertebral abscess accounted for 27 cases. Culture was positive in nine of 25 (36%) samples received by the microbiology laboratory. Staphylococcus aureus (four cases) and Mycobacterium tuberculosis (three cases) were the most frequent organisms isolated, followed by group G streptococci and coagulase-negative staphylococci (one case each). Blood cultures were diagnostic in a further nine patients. The main reason for a negative culture was prior antimicrobial therapy. The biopsy changed management in 9/25 (36%) of cases. There were no reported adverse events. CONCLUSION: Septic discitis is a serious condition with a wide variety of infective causes. CT-guided biopsy is a useful tool when the diagnosis of infectious spinal infection is considered in terms of commencing and targeting therapy, and it is a safe and well-tolerated procedure.