Comparison of direct selective versus nonselective agar media plus LIM broth enrichment for determination of group B streptococcus colonization status in pregnant women.
BACKGROUND
Group B streptococcus (GBS) is the most common cause of early-onset neonatal sepsis in developed countries, and determination of the GBS colonization status in pregnant patients near term is essential for the provision of prophylactic measures to prevent early-onset disease.


OBJECTIVE
To determine if GBS recovery rates and/or result turnaround times for vaginal or combined vaginal/rectal swab specimens from pregnant patients near term are enhanced if swabs are inoculated initially onto selective versus nonselective agar media, in addition to the standard Centers for Disease Control and Prevention method.


METHODS
Prospective laboratory analysis.


METHODS
Urban health region/centralized diagnostic microbiology laboratory.


METHODS
Pregnant women presenting for routine obstetrical care and collection of vaginal or combined vaginal/rectal swab specimens for GBS testing at 35 to 37 weeks' gestation.


METHODS
Culture of specimens directly onto selective (5% sheep blood with colistin and nalidixic acid) or nonselective (5% sheep blood) agar media, in addition to LIM broth enrichment and terminal subculture.


METHODS
Group B streptococcus recovery rate and culture result turnaround time.


RESULTS
A total of 639 specimens were tested, with 128 (20%) positive for GBS. Sixty-three isolates were recovered on direct agar media at 24 hours, of which 16 (12.5%) were isolated on selective plates only. An additional 38 isolates were recovered at 48 hours from direct plates. Twenty-seven (21.1%) isolates that failed to grow on direct plates were recovered from the LIM broth subculture only. Three (2.3%) isolates not recovered from LIM broths were detected at 48 hours on the direct selective (2 isolates) and nonselective (1 isolate) agar plates. A 24-hour result turnaround time was achieved for 63 (49.2%) and 47 (36.7%) of the 128 culture-positive specimens for direct selective and nonselective plates, respectively (chi2 = 76.63, P <.001).


CONCLUSIONS
Use of direct selective agar media, in addition to LIM broth enrichment, for the determination of the GBS colonization status in pregnant patients near term results in decreased turnaround time for reporting positive results.
Elsayed
Sameer
S
Department of Pathology & Laboratory Medicine, University of Calgary, Calgary, Alberta. sameer.elsayed@cls.ab.ca
Gregson
Daniel B
DB
Church
Deirdre L
DL
D000362:Agar / Q000378:metabolism*; D000818:Animals; D002497:Centralized Hospital Services / Q000379:methods; D003091:Colistin / Q000378:metabolism; D003470:Culture Media; D005260:Female; D006801:Humans; D008403:Mass Screening / Q000379:methods; D008828:Microbiological Techniques / Q000379:methods; D009268:Nalidixic Acid / Q000378:metabolism; D011247:Pregnancy; D011251:Pregnancy Complications, Infectious / Q000175:diagnosis; D011446:Prospective Studies; D012002:Rectal Diseases / Q000175:diagnosis / Q000382:microbiology; D013048:Specimen Handling / Q000379:methods; D013290:Streptococcal Infections / Q000175:diagnosis*; D013292:Streptococcus agalactiae / Q000254:growth & development* / Q000302:isolation & purification*; D019037:Urban Health Services; D014623:Vaginal Diseases / Q000175:diagnosis / Q000382:microbiology; D016387:Women's Health
D003470:Culture Media; D009268:Nalidixic Acid; D000362:Agar; D003091:Colistin