Evaluation of the Granada Agar Plate for Detection of Vaginal and Rectal Group B Streptococci in Pregnant Women

Abstract

Granada medium was evaluated for the detection of group B streptococci (GBS) in vaginal and rectal swabs compared with selective Columbia blood agar and selective Lim broth. From May 1996 to March 1998, 702 pregnant women (35 to 37 weeks of gestation) participated in this three-phase study; 103 (14.7%) of these women carried GBS. In the first phase of the experiment (n = 273 women), vaginorectal specimens were collected on the same swab; the sensitivities of Granada tube, selective Columbia blood agar, and Lim broth were 31.4, 94.3, and 74.3%, respectively. In the second and third phases (n = 429 women), vaginal and rectal specimens were collected separately; the sensitivities of Granada plate, selective Columbia blood agar, and Lim broth (subcultured at 4 h on selective Columbia agar in the second phase and at 18 to 24 h in Granada plate in the third phase) were 91.1, 83.9, and 75%, respectively, in the second phase and 88.5, 90.4, and 63.5%, respectively, in the third phase. There were no statistically significant differences in GBS recovery between the Granada agar plate and selective Columbia blood agar, but the Granada plate provided a clear advantage; the characteristic red-orange colonies produced overnight by GBS can be identified by the naked eye and is so specific that further identification is unnecessary. The use of the Granada tube and Lim broth did not result in increased isolation of GBS. In conclusion, the Granada agar plate is highly sensitive for detecting GBS in vaginal and rectal swabs from pregnant women and can provide results in 18 to 24 h.

Comparison of Various Culture Methods for Isolation of Group B Streptococcus from Intrapartum Vaginal Colonization

“…Three different isolation methods were evaluated. [1,3] i. One swab was used for direct culture onto 5% sheep blood agar (SBA) medium (Fi-Tech Chemechtron Pvt.…”

“…G roup B Streptococcus (GBS) or Streptococcus agalactiae, a Gram positive beta hemolytic cocci, is one of the most common causes of neonatal sepsis throughout the world. [1] Early-onset disease, evident during the first 6 days of life is acquired by neonates through the vertical transmission from colonized mothers either by ascending route or by acquisition during passage through birth canal. [2] GBS colonizes genitourinary tract of 10-40% of all pregnant women, [2] however, there are substantial geographical and racial differences in the incidence of early-onset disease.…”

Evaluation of Group B Streptococcus Differential Agar for detection and isolation of Streptococcus agalactiae

“…Such modified media include Granada medium (GM) [3,5], on which b-haemolytic strains of S. agalactiae produce orange-to-salmon colonies [3], thereby allowing identification of GBS in a single step. GM shows a sensitivity of > 90% for the detection of GBS [6][7][8][9], although there have been reports of lower sensitivity [10] that may be explained by poor storage conditions in the laboratory or during transportation [11]. However, the occurrence (1-3%) of non-pigmented GBS strains, as well as possible masking of the orange colour in GM by the saprophytic flora that normally colonises the vagina, make alternative procedures desirable.…”

“…The usefulness of GM for the detection of GBS has been demonstrated previously [6,9,11]. Moreover, the use of selective broth for the isolation and detection of GBS has been reported to have good sensitivity, although the technique is timeconsuming [9].…”

Estudo retrospectivo sobre a prevalência de Streptococcus agalactiae em gestantes em um município do interior do Rio Grande do Sul, Brasil

“…A coleta de material para a cultura tem se mostrado mais eficaz quando realizada no terço inferior do trato genital e na região anal da gestante, com swab, sendo que os meios de cultura seletivos que inibem o crescimento de outras bactérias acabam aumentando em 50% a positividade das culturas para S. agalactiae 2 . A utilização da placa com ágar Granada demonstra ser altamente sensível para a detecção de EGB em swab vaginal e retal de mulheres grávidas e pode fornecer resultados em 18 a 24 horas 6 .…”