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Antimicrobial Agents and Chemotherapy, January 2002, p. 119-124, Vol. 46, No. 1
0066-4804/01/$04.00+0     DOI: 10.1128/AAC.46.1.119-124.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.

Prevalence of Single Mutations in Topoisomerase Type II Genes among Levofloxacin-Susceptible Clinical Strains of Streptococcus pneumoniae Isolated in the United States in 1992 to 1996 and 1999 to 2000

Todd A. Davies,1 Alan Evangelista,1 Sharon Pfleger,1 Karen Bush,2 Daniel F. Sahm,3 and Raul Goldschmidt2*

Ortho-McNeil Pharmaceutical,1 The R.W. Johnson Pharmaceutical Research Institute, Raritan, New Jersey 08869,2 Focus Technologies, Herndon, Virginia 201713

Received 20 June 2001/ Returned for modification 13 August 2001/ Accepted 14 October 2001

Levofloxacin resistance in Streptococcus pneumoniae is rare, requiring at least two mutations in the quinolone resistance-determining region (QRDR) of topoisomerase IV and DNA gyrase. The prevalence of single QRDR mutations in these genes is unknown. Of 9,438 levofloxacin-susceptible pneumococci from the TRUST 4 surveillance study (1999–2000), 528 strains (MICs of 0.5 to 2.0 µg/ml) were selected for analysis. For comparison, 214 levofloxacin-susceptible strains (MICs of 0.5 to 1 µg/ml) isolated between 1992 and 1996 were analyzed. Oligonucleotide probe assay and DNA sequencing were used to detect QRDR mutations leading to changes at Ser79 and Asp83 in ParC, Ser81 in GyrA, and Asp435 in ParE, the most frequently found substitutions among levofloxacin-resistant strains. Among the 1992 to 1996 isolates only one strain (levofloxacin MIC, 1 µg/ml) had a mutation (Ser79 to Phe in ParC). No single mutations were found among 270 TRUST 4 strains with levofloxacin MICs of 0.5 µg/ml. Among 244 strains for which levofloxacin MICs were 1 µg/ml, 15 strains (6.1%) had a parC mutation and 3 strains (1.2%) had a parE mutation. Of 14 strains for which levofloxacin MICs were 2 µg/ml, 10 strains (71%) had a parC mutation; no parE mutations were found. No gyrA mutations were detected. It was estimated that 4.5% of the 9,438 levofloxacin-susceptible TRUST 4 isolates (MICs, <=0.06 to 2 µg/ml) had a single parC or parE QRDR mutation. Although there has been an increase in the prevalence of single-step mutants, the increase may have been overestimated due in part to differences in geographical distribution for the two sets of isolates.

* Corresponding author. Mailing address: The R. W. Johnson Pharmaceutical Research Institute, 1000 Route 202, Raritan, NJ 08869. Phone: (908) 704-5516. Fax: (908) 526-3047. E-mail: rgoldsch{at}prius.jnj.com.

Antimicrobial Agents and Chemotherapy, January 2002, p. 119-124, Vol. 46, No. 1
0066-4804/01/$04.00+0     DOI: 10.1128/AAC.46.1.119-124.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.



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