Epidemiol Health.  2014;36:e2014022. 10.4178/epih/e2014022.

Efflux-mediated resistance identified among norfloxacin resistant clinical strains of group B Streptococcus from South Korea

• Dang TN
• Srinivasan U
• Britt Z
• Marrs CF
• Zhang L
• Ki M
• Foxman B

• KMID: 2380566
• DOI: http://doi.org/10.4178/epih/e2014022

Abstract

OBJECTIVES
Group B Streptococcus (GBS), a common bowel commensal, is a major cause of neonatal sepsis and an emerging cause of infection in immune-compromised adult populations. Fluoroquinolones are used to treat GBS infections in those allergic to beta-lactams, but GBS are increasingly resistant to fluoroquinolones. Fluoroquinolone resistance has been previously attributed to quinolone resistance determining regions (QRDRs) mutations. We demonstrate that some of fluoroquinolone resistance is due to efflux-mediated resistance.
METHODS
We tested 20 GBS strains resistant only to norfloxacin with no mutations in the QRDRs, for the efflux phenotype using norfloxacin and ethidium bromide as substrates in the presence of the efflux inhibitor reserpine. Also tested were 68 GBS strains resistant only to norfloxacin not screened for QRDRs, and 58 GBS strains resistant to ciprofloxacin, levofloxacin or moxifloxacin. Isolates were randomly selected from 221 pregnant women (35-37 weeks of gestation) asymptomatically carrying GBS, and 838 patients with GBS infection identified in South Korea between 2006 and 2008. The VITEK II automatic system (Biomerieux, Durham, NC, USA) was used to determine fluoroquinolone resistance.
RESULTS
The reserpine associated efflux phenotype was found in more than half of GBS strains resistant only to norfloxacin with no QRDR mutations, and half where QRDR mutations were unknown. No evidence of the efflux phenotype was detected in GBS strains that were resistant to moxifloxacin or levofloxacin or both. The reserpine sensitive efflux phenotype resulted in moderate increases in norfloxacin minimum inhibitory concentration (average=3.6 fold, range=>1-16 fold).
CONCLUSIONS
A substantial portion of GBS strains resistant to norfloxacin have an efflux phenotype.

Keyword

Fluoroquinolones; Norfloxacin; Ciprofloxacin; Levofloxacin; Moxifloxacin; Mutations; Efflux; Minimum inhibitory concentration

MeSH Terms

Adult
beta-Lactams
Ciprofloxacin
Ethidium
Female
Fluoroquinolones
Humans
Korea
Levofloxacin
Microbial Sensitivity Tests
Norfloxacin*
Phenotype
Pregnant Women
Reserpine
Sepsis
Streptococcus*
Ciprofloxacin
Ethidium
Fluoroquinolones
Norfloxacin
Reserpine
beta-Lactams