Isolation and Identification from Subgingival Dental Plaque Samples of Bacteria with Low Susceptibility to Chlorhexidine and Phenoxyethanol

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Abstract
Subgingival plaque samples from 19 patients with chronic periodontitis were exposed to various concentrations of phenoxyethanol, chlorhexidine and a mixture of both. Organisms surviving at concentrations lower than the minimum inhibitory concentrations of the antimicrobial agents were isolated and identified: these were designated the ‘most-resistant organisms’. In the case of the plaque samples exposed to phenoxyethanol, most (78 per cent) of the isolates were streptococci; Gram-negative obligate anaerobes were recovered from only one of the samples. From the samples exposed to chlorhexidine, streptococci were again the most frequently encountered organisms, comprising 48 per cent of the 27 isolates. However, Gram-negative obligate anaerobes accounted for a high proportion (33 per cent) of the isolates. The organisms recovered from the samples exposed to a combination of phenoxyethanol and chlorhexidine were similar to those found in samples exposed to phenoxyethanol alone. Hence, streptococci accounted for 82 per cent of the isolates and no Gram-negative obligate anaerobes were recovered. These results imply that the use of chlorhexidine alone as an adjunct to the mechanical treatment of chronic periodontitis may permit the survival of organisms implicated in the aetiology of chronic periodontitis. In contrast, the use of phenoxyethanol alone, or in combination with chlorhexidine, would in general permit the survival of only those organisms compatible with gingival health.