New culture media for the isolation of Streptococcus mutans and Lactobacillus in the saliva of head- and neck-irradiated patients

Abstract

The reduction in salivary flow in patients subjected to head and neck irradiation induces changes in the oral microflora and increases the risk of oral mucosal infections. The frequent presence of fungi, particularly Candida, in the oral environment of these patients complicates identification of the most important cariogenic bacteria with the commercial CRT Bacteria (Ivoclar Vivadent) culture media. Such identification is important for the application of chemical measures to control cariogenic bacteria in these patients, since it has been shown that simple fluoride application is unable to control caries in this population.

Objective: The aim of this study was to obtain a simple medium that inhibits Candida spp. growth and allows the specific growth of Streptococcus mutans and Lactobacillus spp. Thus, reliable counts of cariogenic species can be achieved.

Materials and methods: Stimulated saliva samples from 30 head- and neck-radiotherapy patients were seeded in commercial CRT Bacteria culture medium and in two different media designed by our group: mitis salivarius bacitracin agar (MSBA), containing 5% potassium tellurite and fluconazole 64 microg/ml (MSBTPF) for the isolation of Streptococcus; and Man, Rogosa and Sharpe (MRS) agar, containing bacitracin 0.2 U/ml and fluconazole 32 microg/ml (MRSBF) for the isolation of Lactobacillus spp.

Results: Candida growth was inhibited 100% in the media developed in this study. In all the samples seeded, growing of colonies in MRSBF was identified as Lactobacillus, while in CRT Bacteria for Lactobacillus spp. this species was only isolated in 48.1% of the samples. S. mutans was identified in 71.4% of the colonies that grown in MSBTPF medium, while in CRT Bacteria for S. mutans, this species was only identified in 35% of the colonies obtained.

Conclusion: The culture medium developed in the present study was able to inhibit the 100% of Candida spp. growth. These new media permit reliable counts of cariogenic bacteria in irradiated patients.