A critical step in any epidemiologic research concerning nosocomial infections is the precise identification of the responsible pathogen. The present work utilized a molecular approach -plasmids identification, restriction length polymorphism DNA analysis, and random amplified polymorphic DNA- for the characterization of 6 nosocomial outbreaks due to 52 strains of methicillin-resistant Staphylococcus aureus (MRSA). In these episodes, the clinic-epidemiologic and phenotypic analysis (antibiotype) pointed to a nosocomial infection. Through molecular analysis it was possible to establish, in a very precise way, clonality due to MRSA strains in 2 of the studied outbreaks; the same type of analysis allowed to eliminate a MRSA clonal origin in the remainder 4 episodes. The antibiogram was not an useful analytic tool due to its poor discriminatory power. Also, through a PCR procedure, it was possible to identify the presence of the gen mecA in every of the 52 MRSA strains studied.

The in vitro activity of trospectomycin sulfate was compared with those of several antimicrobials, against 301 anaerobic bacteria and 613 aerobic Gram-positive cocci. Trospectomycin was about 4- to 32-fold more active than was spectinomycin. Trospectomycin exhibited consistently good activity against all Bacteroides fragilis group isolates, except Bacteroides vulgatus, and against all other anaerobes comparable or higher to that of clindamycin. The trospectomycin's activity was most similar to that of vancomycin, even against methicillin-resistant Staphylococcus aureus and methicillin-resistant Staphylococcus epidermidis.

The in vitro activity of 10 antibiotics was determined for 231 strains of methicillin resistant (MRSA) Staphylococcus aureus. Oxacillin was a very good antibiotic to determine methicillin-resistance. Its agreement with methicillin-resistance was in all the strains tested. On the contrary, the correlation with nafcillin was established only in 95% of the strains tested. Cloxacillin and flucloxacillin are not good methicillin-resistance indicators. The strains tested against macrolides, such as erythromycin, and lincosamides, such as lincomycin and clindamycin presented a susceptibility of 68, 78, and 80%, respectively. All tested strains were susceptible to vancomycin.