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Abstract
Background
Group B Streptococcus (Streptococcus agalactiae, GBS) is a major cause of severe infections in neonates, including bacteremia, pneumonia, and meningitis, and is generally vertically transmitted from a colonized, pregnant woman to her infant. Penicillin is the drug of choice to treat GBS infections, because GBS strains are uniformly susceptible to penicillin. Recently, however, penicillin resistant GBS strains have been reported and the rates of erythromycin and clindamycin resistance have increased. We evaluated the perineal colonization rates and antimicrobial susceptibility of GBS strains isolated from pregnant and non-pregnant women.
Methods
The antibiotic susceptibilities of a total of 180 GBS strains isolated from two university hospitals and one reference laboratory between May 2008 and January 2009 were determined using disk diffusion and broth microdilution methods. The presence of erythromycin resistance genes was confirmed by PCR.
Results
The average colonization rate of pregnant women was 5.5%. The overall colonization rates of pregnant and non-pregnant women ranged between 5.5% and 7.5%. All 180 GBS strains were susceptible to penicillin. Fifty strains (27.8%) were resistant to erythromycin, whereas 78 (41.1%) were resistant to clindamycin. The ermB gene was identified in 40 isolates and 44 isolates had constitutive macrolide-lincosamide-streptogramin B resistance phenotypes.
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Fig. 1.
MLS genotype analysis of erythromycin-resistant GBS strains. Lane M: 100 bp DNA ladder marker; Lane 1,2,4,5: Negative patient's strains; Lane 3,6,7,10: ermB gene positive strains; Lane 8: Negative control; Lane 9: ermA/TR gene positive strains; Lane 11: mefA/E gene positive strains; Lane 12: Positive control.
Table 1.
Disc diffusion susceptibility test results of 180 GBS strain
| Antibiotics | % susceptible |
|---|---|
| Penicillin | 180/180 (100) |
| Ampicillin | 180/180 (100) |
| Clindamycin | 102/180 (58.9) |
| Erythromycin | 130/180 (72.2) |
| Cefazolin | 180/180 (100) |
| Vancomycin | 180/180 (100) |
| D-test | 3∗/6 |
Table 2.
Microbroth dilution antimicrobial susceptibility test results of 180 GBS strains
| Antibiotics | MIC (μg/mL)50/90∗ | MIC range |
|---|---|---|
| Penicillin | ≤0.06/≤0.06 | ≤0.06 |
| Oxacillin | ≤0.5/≤0.5 | ≤0.5 |
| Cefotaxime | ≤0.06/≤0.06 | ≤0.06 |
| Cefoxitin | 4/4 | 2∼4 |
Table 3.
MicroScan MIC susceptibility test of 47 erythromycin nonsusceptible GBS strains∗
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