title: Genetic relatedness of levofloxacin-nonsusceptible Streptococcus pneumoniae isolates from North America.
abstract: We characterized 32 levofloxacin-nonsusceptible Streptococcus pneumoniae (LNSP) isolates obtained from a broad geographic region of North America over a 5-year period by using capsular serotypes, antimicrobial susceptibility profiles, BOX-PCR, multilocus sequence typing (MLST), and pulsed-field gel electrophoresis (PFGE). Sixteen international clones identified by the Pneumococcal Molecular Epidemiology Network also were included for comparison. Fifteen serotypes were represented, with serogroups 6, 9, 14, 19, and 23 accounting for 63% of isolates. Among isolates whose quinolone resistance-determining regions were sequenced, all contained gyrA and parC point mutations. Sixty-three percent were penicillin susceptible, and 84% were erythromycin susceptible. BOX-PCR analysis identified 39 different band patterns among 32 LNSP and 16 international clones and grouped 16 isolates, including 2 international clones, into seven unrelated groups of 2 to 4 isolates each. PFGE analysis identified 35 different band patterns among 32 LNSP and 16 international clones and grouped 21 isolates, including 3 international clones, into eight unrelated groups of 2 to 6 isolates each. MLST performed on 10 isolates identified five allelic profiles and separated 9 isolates into four groups of 2 to 3 isolates each. Overall, each typing method indicated that the LNSP were heterogeneous and that resistance to fluoroquinolones was not closely associated with a particular serotype or with coresistance to other antimicrobial classes and suggests that LNSP have likely arisen through independent mutational events as a result of selective pressure. However, seven LNSP were found to be related to three international clones by PFGE.
authors.affiliation: Department of Microbiology, University of Alabama at Birmingham, Birmingham, Alabama 35249, USA.
authors.forename: Crystal N
authors.initials: CN
authors.lastname: Johnson
authors.forename: William H
authors.initials: WH
authors.lastname: Benjamin Jr
authors.forename: Stephen A
authors.initials: SA
authors.lastname: Moser
authors.forename: Susan K
authors.initials: SK
authors.lastname: Hollingshead
authors.forename: Xiaotian
authors.initials: X
authors.lastname: Zheng
authors.forename: Marilyn J
authors.initials: MJ
authors.lastname: Crain
authors.forename: Moon H
authors.initials: MH
authors.lastname: Nahm
authors.forename: Ken B
authors.initials: KB
authors.lastname: Waites
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology; D000890:Anti-Infective Agents / Q000494:pharmacology*; D016667:Bacterial Capsules; D015373:Bacterial Typing Techniques; D024881:Drug Resistance, Bacterial; D016521:Electrophoresis, Gel, Pulsed-Field; D006801:Humans; D064704:Levofloxacin; D008826:Microbial Sensitivity Tests; D009656:North America; D015242:Ofloxacin / Q000494:pharmacology*; D011008:Pneumococcal Infections / Q000453:epidemiology* / Q000382:microbiology; D017422:Sequence Analysis, DNA; D012703:Serotyping; D013296:Streptococcus pneumoniae / Q000187:drug effects* / Q000235:genetics* / Q000302:isolation & purification
chemical_list: D000900:Anti-Bacterial Agents; D000890:Anti-Infective Agents; D064704:Levofloxacin; D015242:Ofloxacin