Colonisation index of the oral cavity: A novel technique for monitoring colonisation defence

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Abstract
The constancy of oropharyngeal flora in healthy people is based on intact defence against colonisation. Conditions which can interfere with this defence are underlying disease and medical interventions, and may be associated with alterations in the oropharyngeal flora. The oral flora was assessed by means of a modified oral rinse method based on pre-enrichment in nutrient medium. The colonisation index of the oral cavity was defined as the sum of the log10 of the concentrations of a particular microorganism isolated from one ml of oropharyngeal washing specimens, divided by the number of oral washings. This index was evaluated as an indicator of (decreased) colonisation defence by comparing a group of healthy volunteers with a group of post-surgery head and neck oncology patients. Oral colonisation indices for Enterobacteriaceae, Pseudomonadaceae and Acinetobacter spp. as well as for Staphylococcus epidermidis were statistically significantly higher in the patient group compared to the volunteers. This clear reduction in colonisation defence, resulting in a high carriage rate of potentially pathogenic Gram-negative bacilli, may be a result of the combination of underlying disease (cancer) and surgical intervention (debulking or radical resection of tumor).