Antibiotic Susceptibility

Antibiotic Susceptibility of Group B Streptococcus Isolated in Hawaii
By Xiaotian Zheng, PhD, DLS Microbiology Director, Thomas Reppun, MD, DLS Associate Medical Director, Seema Singh, MPH, Microbiologist (ASCP) and Terrie Koyamatsu, MT (ASCP) – 2002

Group B streptococcus (GBS) is a commensal of the gastrointestinal and genital tracts. It has been found in up to 30% of pregnant women. However, this organism is also a leading cause of serious neonatal infections. Intrapartum antibiotic prophylaxis is effective in reducing colonization and early-onset GBS disease. Recommendations published by the Centers for Disease Control and Prevention (CDC) included utilization of IV penicillin G or ampicillin, with erythromycin and clindamycin as alternatives for those who are penicillin intolerant.

Since GBS strains resistant to penicillin and other b-lactams have not been recognized, antibiotic susceptibility testing is not performed routinely for this organism. However, recently, studies have shown that the prevalence of GBS resistance to the alternative erythromycin and clindamycin has increased in many areas of the country.

In order to obtain data for Hawaii, we conducted a study to test antimicrobial resistance for GBS collected with standard culture methodology, including selected broth enrichment media; our positive rate for intrapartum GBS screening is 23%. A total of 50 consecutively collected GBS clinical isolates obtained in our laboratory were tested for their susceptibility to selected antimicrobial agents. All the patients were adult patients. The collection sources included rectal/vaginal, urine, wound, and throat samples. Our test results are shown in Table 1.

Table 1. Antibiotic susceptibility results of GBS obtained in Hawaii (total number of isolates = 50).

100 %100 %98 %88 %26 %

Our results demonstrated the universal susceptibility to penicillin drugs and local GBS resistance to antibiotics recommended for the patients who are penicillin intolerant.


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  4. Morales, W., et al. 1999. Change in antibiotic resistance of group B streptococcus: impact on intrapartum management. Am J Obstet Gynaecol 181:310-314.