| Antibiotic resistance and multidrug resistance in Streptococcus pneumoniae has increased in both the U.S. and other countries. We studied a total of 412 isolates of S. pneumoniae collected between 1995 and 1997 in Washington State including 368 isolates from a statewide study of invasive disease, 37 isolates from a pediatric carriage study, and 7 isolates from the Washington State Health Department. Antibiotic resistance, including multidrug resistance, was most prevalent in the S. pneumoniae isolated from children ≤5 years and elderly ≥65 years of age. Out of seventy tetracycline resistant S. pneumoniae tested, five isolates, representing five serotypes (12, 22, 6A, 19F, and 23), carried the tetO gene. Two additional 19F isolates, from the same patient, carried both tetM and tetO genes and the remaining 63 isolates carried only the tetM gene. The tetO gene was not mobile at detectable levels in vitro (<10-9/recipient) while the tetM gene was. From thirty-four erythromycin resistant isolates, twenty-six S. pneumonide carried the mef gene, six isolates carried the ermB gene, and two isolates carried both ermB and mef genes. The mef gene was mobile and transferred to S. pneumoniae and/or E. faecalis recipients using different donors. In addition, the mef gene was newly identified in four genera, Corynebacterium, Enterococcus, Micrococcus, and Streptococcus .;Using pulsed-field gel electrophoresis (PFGE) with three restriction enzymes, IS1167 and mef restriction fragment length pattern (RFLP), twenty multidrug resistant isolates had identical or highly related PFGE and RFLP patterns, suggesting that they represented a new multiresistant clone. The same clone was found in Alaska and Eastern Canada. The clone isolates carried both the tetM and mef genes and are thought to have accounted for part of the increase in pneumococcal multidrug resistance that was seen during the 1995--1997 Washington State surveillance study. |
