Subtyping of Streptococcus dysgalactiae and Streptococcus uberis isolated from bovine mammary secretions by DNA fingerprinting.

Abstract

Streptococcus dysgalactiae and Streptococcus uberis isolated from mammary secretions of cows from Tennessee and New Zealand were subtyped using polymerase chain reaction-based DNA fingerprinting. Such DNA fingerprinting using primer 8.6d (5'-GTAACGCC3') resulted in categorizing 116 S. dysgalactiae isolates into 25 different subtypes, with 17 subtypes observed in isolates from Tennessee and eight in isolates from New Zealand. All S. dysgalactiae DNA fingerprint profiles, regardless of origin, contained 700- and 330-base pair fragments. The majority of S. dysgalactiae isolates (73%) from Tennessee belonged to two subtypes. The remaining 23 isolates belonged to 15 different DNA fingerprint subtypes. Streptococcus dysgalactiae isolates from New Zealand (n = 32) were grouped into eight different subtypes; 66% belonged to two subtypes. A characteristic feature of S. dysgalactiae isolates from New Zealand was the presence of a 270-base pair DNA fragment seen infrequently in S. dysgalactiae isolates from Tennessee. When primer OPE-4 (5'-GTGACATGCC-3') was used, DNA fingerprinting differentiated S. uberis from Tennessee (n = 28) and New Zealand (n = 30) into 20 subtypes; 14 subtypes were observed in isolates from Tennessee, and six in isolates from New Zealand. All S. uberis DNA fingerprint profiles, regardless of origin, contained 1100-, 640-, and 450-base pair fragments. A characteristic feature of S. uberis isolates from New Zealand was the presence of a 300-base pair DNA fragment seen infrequently in S. uberis isolates from Tennessee. The most common subtypes of S. dysgalactiae and S. uberis from Tennessee herds were isolated in milk from lactating cows during monthly herd surveys, in milk from cows with clinical mastitis, and in mammary secretions from cows during the periparturient period, and thus were not confined to one particular stage of lactation. These data suggest that S. dysgalactiae and S. uberis from New Zealand are distinct from those isolated from the USA, and that DNA fingerprinting can be used as an epidemiological tool to differentiate streptococci and identify important sources of these mastitis pathogens on dairy farms.