Antimicrobial resistance among Streptococcus pneumoniae in the United States: have we begun to turn the corner on resistance to certain antimicrobial classes?
BACKGROUND
Antimicrobial resistance has emerged as a major problem in Streptococcus pneumoniae in the United States during the past 15 years. This study was undertaken to elucidate the current scope and magnitude of this problem in the United States and to assess resistance trends since 1994-1995.


METHODS
A total of 1817 S. pneumoniae isolates obtained from patients with community-acquired respiratory tract infections in 44 US medical centers were characterized during the winter of 2002-2003. The activity of 27 antimicrobial agents was assessed. In addition, selected isolates were examined for the presence of mutations in the quinolone-resistance determining regions (QRDRs) of parC and gyrA that resulted in diminished fluoroquinolone activity. The results of this survey were compared with the results of 4 previous surveys conducted in a similar manner since 1994-1995.


RESULTS
Overall rates of resistance (defined as the rate of intermediate resistance plus the rate of resistance) were as follows: penicillin, 34.2%; ceftriaxone, 6.9%; erythromycin, 29.5%; clindamycin, 9.4%; tetracycline, 16.2%; and trimethoprim-sulfamethoxazole (TMP-SMX), 31.9%. No resistance was observed with vancomycin, linezolid, or telithromycin; 22.2% of isolates were multidrug resistant; 2.3% of isolates had ciprofloxacin MICs of >or=4.0 microg/mL. It was estimated that 21.9% of the isolates in this national collection had mutations in the QRDRs of parC and/or gyrA, with parC only mutations occurring most often (in 21% of all isolates). Trend analysis since 1994-1995 indicated that rates of resistance to beta -lactams, macrolides, tetracyclines, TMP-SMX, and multiple drugs have either plateaued or have begun to decrease. Conversely, fluoroquinolone resistance among S. pneumoniae is becoming more prevalent.


CONCLUSIONS
It appears that, as fluoroquinolone resistance emerges among S. pneumoniae in the United States, resistance to other antimicrobial classes is becoming less common.
Department of Pathology, University of Iowa College of Medicine, Iowa City, IA 52242, USA. gary-doern@uiowa.edu
Gary V
GV
Doern
Sandra S
SS
Richter
Ashley
A
Miller
Norma
N
Miller
Cassie
C
Rice
Kristopher
K
Heilmann
Susan
S
Beekmann
D000293:Adolescent; D000328:Adult; D000368:Aged; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D002648:Child; D002675:Child, Preschool; D027081:DNA Gyrase / Q000235:genetics; D027101:DNA Topoisomerase IV / Q000235:genetics; D024881:Drug Resistance, Bacterial; D006801:Humans; D007223:Infant; D008826:Microbial Sensitivity Tests; D008875:Middle Aged; D009154:Mutation; D011008:Pneumococcal Infections / Q000188:drug therapy / Q000453:epidemiology / Q000382:microbiology; D013296:Streptococcus pneumoniae / Q000187:drug effects* / Q000235:genetics; D014481:United States / Q000453:epidemiology
D000900:Anti-Bacterial Agents; D027101:DNA Topoisomerase IV; D027081:DNA Gyrase