Antibody fragments can prevent colonization of teeth by Streptococcus mutans — a major pathogen implicated in the development of dental caries — but these fragments have a very short half-life in vivo. In July Nature Biotechnology, Carina Krüger and colleagues at Karolinska Institutet at Huddinge Hospital, Sweden, show that lactobacilli producing single-chain antibodies can be used for in situ therapeutic delivery of passive immunity at oral mucosal sites (Nat Biotechnol 2002, 20:702-706).

Krüger et al. expressed a single-chain Fv (scFv) antibody fragment encoding a streptococcal antigen I/II (SAI/II) adhesion molecule of Streptococcus mutans both on the surface of Lactobacillus zeae and as a secreted protein. In vitro, surface scFv-expressing lactobacilli agglutinated SAI/II-expressing S. mutans without affecting the corresponding SAI/II knockout strain. In addition, administration of scFv-expressing lactobacilli to a rat model of dental caries decreased both S. mutans counts and caries scores.

Lactobacilli are 'generally...

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