[Role of normal microflora in the throat in inhibition of adherence of pathogenic bacteria to host cells: in vitro competitive adherence between Corynebacterium pseudodiphtheriticum and Branhamella catarrhalis].

Our previous study showed the occurrence of Branhamella catarrhalis (B. catarrhalis) pulmonary infections which varies seasonally. To investigate the role of normal throat microflora in this seasonal variation of the occurrence of B. catarrhalis infection, seventy seven throat cultures were done in 45 patients with chronic pulmonary diseases from January to December in 1985. The isolation rate of Corynebacterium species as normal microflora was relatively higher in summer than in winter. Therefore in vitro competitive adherence to human epithelial cells between Corynebacterium pseudodiphtheriticum (C. pseudodiphtheriticum) and B. catarrhalis was done to examine bacterial interference. Preincubation or simultaneous incubation of C. pseudodiphtheriticum reduced the number of B. catarrhalis adherent to epithelial cells (p less than 0.02). The mean number of adherent C. pseudodiphtheriticum (average; 13.86) was higher than that (average; 1.22) of adherent B. catarrhalis. There was no antagonism in the growth on blood agar between C. pseudodiphtheriticum and B. catarrhalis. These findings suggest Corynebacterium species as normal throat microflora may interfere the adherence of B. catarrhalis to human epithelial cells and may protect against colonization and infection with B. catarrhalis. Bacterial interference of Corynebacterium species may be associated with the low occurrence of B. catarrhalis pulmonary infections in summer.