Prescribing antibiotics in diabetic foot infection: what is the role of initial microscopy and culture of tissue samples?^*

Abstract

The aim of this study was to evaluate the role of microscopy, Gram stain and the culture of tissue samples in the antibiotic treatment of patients with diabetic foot infection. A retrospective review of patients with a diabetic foot infection was undertaken. Data analysed included the severity of infection, antibiotic prescribing patterns, microscopy and culture results. A total of 71 patients were included, from whom 114 tissue samples were collected. Gram stain results were in agreement with final culture results in 45·8% (n = 54) of samples. Overall sensitivity and specificity of the Gram stains were low (74·5% and 69·8%, respectively), although the specificity for Gram-negative rods was high (98·5%). The presence or absence of 'pus cells' on microscopy was a poor predictor of culture results. Empirical prescribing of antibiotics was in accordance with local policy in 31·1% of patients, improving to 86·8 % following culture results. Microscopy, a skilled laboratory procedure, was generally a poor predictor of tissue culture results. However, the presence of Gram-negative rods was suggestive of isolation in the culture of such organisms and could allow the early broadening of antibiotic treatment. Despite initial poor compliance of empirical antibiotic treatment regimens, prescribing was adjusted in light of culture results, suggesting these were important for clinicians.

A retrospective analysis of the microbiology of diabetic foot infections at a Scottish tertiary hospital

“…The aim was to investigate whether the microbiological profile of diabetic foot infections at a Scottish hospital was comparable to previously published reports. The literature suggests that in the UK Staphylococci, particularly S. aureus, are most commonly isolated from DFIs [16][17][18][19], and the findings of this study support this. A previous prospective culture-based microbiological analysis of 20 Scottish DFI samples also identified S. aureus as the most common microorganism, present in 40% of samples [11].…”

“…The reasons for this remain unclear but could reflect a variety of environmental, clinical or personal factors [26]. The frequency of samples with no significant growth (38%) is broadly comparable with that found in similar studies in the UK [16,19], and similar to that reported for the only other Scottish analysis of the microbiology of DFIs (45%) performed at the same hospital [11]. Given the potential breadth of associated factors and limited sample size, it was not surprising that our descriptive analysis of gender and anatomical sample site did not reveal any clear association with the broad pattern of microbiological growth observed.…”

“…Antimicrobial resistance is a common finding in DFIs, with meta-analyses estimating the global prevalence of methicillin-resistant S. aureus in DFIs to be 15-30% [8,9]. Previous studies in the UK have reported higher rates, ranging from 19.9 to 57.9% [16][17][18][19]. Reassuringly this analysis did not report the isolation of any MRSA and, where investigated, a high degree of sensitivity to flucloxacillin was observed.…”

Feasibility of Percutaneous Bone Biopsy as Part of the Management of Diabetic Foot Osteomyelitis in a 100% Neuropathic, Grade 3 IDSA/IWGDF Population on an Outpatient Basis

“…6,20 No anaerobes were cultured. In most cultures, the microorganisms grown were staphylococci, in accordance to the literature 3,5,7,17,21 reported in the North America and European countries, which identified Staphylococcus aureus as the most predominant pathogen cultured in DFO. Of note, in 5 BB in our series, isolates were Staphylococcus sp that could be a contaminant.…”

“…Almost three quarters of the bone cultures were positive, which is consistent with previous studies, where positivity varies between 67.7% and 93%. 5,8,17,18 An antibiotic-free window has been regarded in most of our cases. There were 2 cases in which the BB had been done under antibiotic therapy, prescribed for another infection.…”