Cross-reactivity indices (CRIs) of 28 isolates of Moraxella bovis recovered from outbreaks of infectious bovine keratoconjunctivitis in Argentina (A, 11 isolates), Brazil (B, 7), and Uruguay (U, 10) between 1983 and 2000 were estimated. Hyperimmune sera were produced in rabbits and antibody titres determined with each isolate. Isolates showing CRIs3 70 were placed in the same group. Group I had 13 isolates (A, 1; B, 6; U, 6); group II had 6 isolates (A, 4; U, 2); groups III, IV, and V had 2 isolates each, recovered in Argentina; group VI had 2 isolates, from Uruguay; and group VII had 1 isolate, from Brazil. The CRIs3 70 between vaccine strains and isolates recovered before and after 1990 were 58% and 42%, 50% and 50%, and 33% and 67% with vaccine strains 2419, 2358, and 2439, respectively. Isolate 273, from Uruguay, showed CRIs > 70 with 78% of the isolates and is recommended as the vaccine strain.

O objetivo do presente estudo foi determinar a relação genética entre rep-PCR de 52 linhagens Staphylococcus aureus isoladas de infecções mamárias em quatro fazendas leiteiras da região leiteira central da Argentina. Os resultados foram comparados com a atividade in vitro dos antimicrobianos freqüentemente utilizados no tratamento da mastite bovina. Foram observados 12 diferentes perfis de antimicrobianos. Do total de linhagens, 45% foram suscetíveis a todos os antibióticos ensaiados. A caracterizacão por rep-PCR pode diferenciar com sucesso as linhagens de S. aureus de origem bovina. Num primeiro nível de similaridade (50%) foram definidos cinco grupos denominados de I a V. A maioria das estirpes (75%) agruparam-se no grupo I. Os resultados sugerem que os genotipos foram similares. Os genotipos não foram asociados com os perfis de antimicrobianos na maioria dos isolados. O presente estudo descreve os genotipos responsáveis pelos casos de mastites na região central da Argentina. O melhor conhecimento da distribução das linhagens infectantes em fazendas leiteras poderia auxiliar na formulacão de estratégias para o controle de infecção. Além disso a suscetibilidade aos antimicrobianos de linhagens de S. aureus deve ser usada para montear a selecão de drogas efetivas para a terapia intramamária. | The aim of this study was to assess by rep-PCR the genetic relationship of 52 S. aureus strains isolated from mammary infections collected in four herds located in the central dairy region of Argentina. Results were compared with the in vitro activity of antimicrobial drugs frequently used for treating bovine mastitis. Twelve different antimicrobials patterns were observed. Forty eight percent of the strains were susceptible to all antimicrobials tested. rep-PCR typing could successfully differentiate S. aureus strains of bovine origin. At a first level of similarity (50%), it could be defined 5 clusters namely I to V. Most of the strains (75%) were grouped in cluster I. The results may suggest that genotypes were similar in the different herds. Agreement between antibiotic patterns and rep-profiles was not observed for most isolates. The present report describes the genotypes responsible for the mastitis cases in the central dairy region of Argentina. A better knowledge of infective strains distribution in dairy herds might help in formulating strategies to control of infection. Furthermore, antimicrobial susceptibility of S. aureus should be used as guide to select effective drugs to therapy in intramammary infections.