title: Novel Streptococcus infantarius subsp. infantarius variants harboring lactose metabolism genes homologous to Streptococcus thermophilus.
abstract: Streptococcus infantarius subsp. infantarius belongs to the Streptococcus bovis/Streptococcus equinus complex (SBSEC) commonly associated with human and animal infections. We elucidated the lactose metabolism of S. infantarius subsp. infantarius predominant in African fermented milk products. S. infantarius subsp. infantarius isolates (n = 192) were identified in 88% of spontaneously fermented camel milk suusac samples (n = 24) from Kenya and Somalia at log₁₀ 8.2-8.5 CFU mL⁻¹. African S. infantarius isolates excreted stoichiometric amounts of galactose when grown on lactose, exhibiting a metabolism similar to Streptococcus thermophilus and distinct from their type strain. African S. infantarius subsp. infantarius CJ18 harbors a regular gal operon with 99.7-100% sequence identity to S. infantarius subsp. infantarius ATCC BAA-102(T) and a gal-lac operon with 91.7-97.6% sequence identity to S. thermophilus, absent in all sequenced SBSEC strains analyzed. The expression and functionality of lacZ was demonstrated in a β-galactosidase assay. The gal-lac operon was identified in 100% of investigated S. infantarius isolates (n = 46) from suusac samples and confirmed in Malian fermented cow milk isolates. The African S. infantarius variant potentially evolved through horizontal gene transfer of an S. thermophilus-homologous lactose pathway. Safety assessments are needed to identify any putative health risks of this novel S. infantarius variant.
authors.affiliation: Laboratory of Food Biotechnology, Institute of Food, Nutrition and Health, ETH Zurich, Schmelzbergstrasse 7, 8092 Zurich, Switzerland.
authors.forename: Christoph
authors.initials: C
authors.lastname: Jans
authors.forename: Andrea
authors.initials: A
authors.lastname: Gerber
authors.forename: Joséphine
authors.initials: J
authors.lastname: Bugnard
authors.forename: Patrick Murigu Kamau
authors.initials: PM
authors.lastname: Njage
authors.forename: Christophe
authors.initials: C
authors.lastname: Lacroix
authors.forename: Leo
authors.initials: L
authors.lastname: Meile
mesh_terms: D000818:Animals; D002162:Camelus; D043302:Cultured Milk Products / Q000382:microbiology*; D004269:DNA, Bacterial / Q000235:genetics / Q000302:isolation & purification*; D005690:Galactose / Q000378:metabolism; D005838:Genotype; D007630:Kenya; D007763:Lac Operon; D007785:Lactose / Q000378:metabolism*; D010641:Phenotype; D017422:Sequence Analysis, DNA; D012998:Somalia; D013291:Streptococcus / Q000235:genetics* / Q000302:isolation & purification / Q000378:metabolism; D048249:Streptococcus thermophilus / Q000235:genetics* / Q000378:metabolism; D001616:beta-Galactosidase / Q000235:genetics / Q000378:metabolism
chemical_list: D004269:DNA, Bacterial; D001616:beta-Galactosidase; D007785:Lactose; D005690:Galactose