Patterns of multidrug resistance among methicillin-resistant hospital isolates of coagulase-positive and coagulase-negative staphylococci collected in the International Multicenter Study RESIST in 1997 and 1998

The primary purpose of the multicenter international study "RESIST" was to obtain an update on the degree of multidrug resistance among methicillin-re sistant staphylococci collected from a geographically diverse sample. A tot al of 3,307 staphylococcal isolates were recovered from single patients and primarily from clinical specimens that were collected at 20 collaborating regional health centers located in several countries in Europe, Asia, and L atin America during a 3- to 4-month period each in 1997 and 1998, All strai ns were deposited at the Laboratory of Molecular Genetics at ITQB/UNL in Oe iras, Portugal, for quality control and for testing by microbiological and molecular typing techniques; the Laboratory of Microbiology at The Rockefel ler University serving as organizational center. The majority of strains, 3 ,100, were methicillin-resistant, of which 1,749 were coagulase positive (m ethicillin-resistant Staphylococcus aureus, MRSA), and 1,351 were coagulase negative (methicillin-resistant coagulase negative staphylococci, MRCNS). The overall frequency of drug resistance traits among the 1,749 MRSA strain s was high (over 70% and up to and over 90% of the strains) to ciprofloxaci n, erythromycin, clindamycin, gentamicin, and tetracycline, and was somewha t less frequent to sulfamethoxazole-trimethoprim (45%), chloramphenicol (30 %), and rifampin (38%). None of the 3,307 staphylococcal isolates showed re duced susceptibility to vancomycin except for a single methicillin-resistan t coagulase-negative isolate. The great majority of staphylococci were also susceptible to the new antimicrobial Synercid, In contrast, resistance to teicoplanin was significant among methicillin-resistant strains of coagulas e-negative staphylococci, particularly among Staphylococcus haemolyticus. M RSA isolates showed marked geographic variation in their patterns of multir esistance, most likely reflecting the properties of unique multiresistant M RSA clones dominant in the hospitals that provided the MRSA isolates from t he various geographic areas. The multiresistance patterns of MRSA strains a nd strains of methicillin-resistant coagulase-negative staphylococci origin ating at the same country source also showed striking differences, suggesti ng that resistance to antimicrobial agents emerged under different antibiot ic pressures in these bacterial species.