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Journal of Clinical Microbiology, August 2005, p. 4303, Vol. 43, No. 8
0095-1137/05/$08.00+0     doi:10.1128/JCM.43.8.4303.2005

LETTER TO THE EDITOR

Liquid Granada Medium for Detection of Group B Streptococci


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LETTER
 
Heelan et al. (5) recently presented data on the sensitivity of a liquid Granada medium (9) (GBS broth) for detection of Streptococcus agalactiae. We have tested this medium, and it contains, as Granada medium, starch, proteose peptone 3, methotrexate, a Good’s buffer, serum, glucose, and selective agents. So, we agree with the authors that detection of orange-red colonies in GBS broth is 100% specific for the presence of beta-hemolytic group B streptococci (GBS). Nevertheless, some statements in this paper need clarification.

The authors claim that sometimes Granada agar lacks sensitivity for GBS detection, but no comparison between GBS broth and Granada agar is reported. In the two references cited to support this claim (3, 7), it is acknowledged that the batches of Granada agar used were probably spoiled (10). Moreover, the flurry of references (1, 2, 4, 6, 8, 9, 14, 15) that support a very good sensitivity of Granada agar to detect GBS are not mentioned.

Regarding sensitivity of GBS broth, the figures reported are somewhat confusing. One-hundred fifty-eight GBS strains were recovered from 580 swabs, but only in 108 cases were red colonies detected, so GBS broth sensitivity is 68.3% instead of the 87.8% or 90.3% reported. GBS pigment was not observed in 35 tubes that later (after subculture) proved to be positive (25% of all positives), and this figure makes the usefulness of this medium for direct GBS detection doubtful. When (study 1) GBS broth was used as a detection medium, 9 of 75 GBS strains (12%) were completely lost (positive in subculture from LIM broth but negative in subculture from GBS broth). When (study 2) GBS broth was used as a detection and transport medium, 6 of 83 GBS (7%) were also completely lost. This failure to detect (even after subculture) some GBS-positive vaginorectal samples can be an important drawback of GBS broth. Another fact is the dramatic failure of LIM broth to recover GBS (21 of 83 positive samples were lost in study 2) found in Heelan's work. This finding needs further evaluation, as enrichment in LIM broth is an accepted procedure for GBS detection in the Centers for Disease Control and Prevention guidelines (13).

Poor performance in detecting GBS could be explained by the fact that when liquid Granada media are kept refrigerated the starch precipitates (retrogradation) (16), producing an opaque white mass, where GBS colonies are sometimes barely noticeable. However, if not kept refrigerated the medium deteriorates in a few days (12). We have observed that when media containing folate antagonists (as methotretaxate) are used as transport media and swabs are kept in these media for several hours before starting incubation, the number of GBS CFU nosedives. This renders the use of such media as transport media unsafe. For these reasons, in our view, the use of liquid selective Granada media as transport media for detection of GBS colonization in pregnant women cannot be recommended.


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FOOTNOTES
 
Ed. Note: The authors of the published article did not respond.


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REFERENCES
 
    1
  1. Blanckaert, H., J. Frans, J. Bosteels, M. Hanssens, and J. Verhaegen. 2003. Optimisation of prenatal group B streptococcal screening. Eur. J. Clin. Microbiol. Infect. Dis. 22:619-621.[CrossRef][Medline]
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  2. Claeys, G., G. Verschraegen, and M. Temmerman. 2001. Modified Granada agar medium for the detection of group B streptococcus carriage in pregnant women. Clin. Microb. Infect. 7:22-24.
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  3. García Gil, E., M. C. Rodríguez, R. Bartolomé, B. Bejarano, L. Cabero, and A. Andreu. 1999. Evaluation of the Granada agar plate for detection of vaginal and rectal group B streptococci in pregnant women. J. Clin. Microbiol. 37:2648-2651.[Abstract/Free Full Text]
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  4. Gupta, C., and L. E. Riski. 2004. Comparison of two culture media and three sampling techniques for sensitive and rapid screening of vaginal colonization by group B streptococcus in pregnant women. J. Clin. Microbiol. 42:3975-3977.[Abstract/Free Full Text]
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  5. Heelan, J. S., J. Struminsky, P. Lauro, and C. J. Sung. 2005. Evaluation of a new selective enrichment broth for detection of group B streptococci in pregnant women. J. Clin. Microbiol. 43:896-897.[Abstract/Free Full Text]
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  6. Kelly, V. N., and S. M. Garland. 1994. Evaluation of new Granada medium (modified) for the antenatal detection of group B streptococcus. Pathology 26:487-489.[CrossRef][Medline]
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  7. Overman, S. B., D. D. Eley, B. E. Jacobs, and J. A. Ribes. 2002. Evaluation of methods to increase the sensitivity and timeliness of detection of Streptococcus agalactiae in pregnant women. J. Clin. Microbiol. 40:4329-4331.[Abstract/Free Full Text]
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  8. Rolland, C., B. Bailleux, S. Biausque, and L. Fortin. 2003. Evaluation du milieu Granada appliqué au despistage de Streptococcus agalactiae au huitème mois de grossese. Ann. Biol. Clin. (Paris) 61:705-708.[Medline]
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  9. Rosa, M., M. Perez, C. Carazo, J. I. Peis, L. Pareja, and L. Hernandez. 1992. New Granada medium for detection and identification of group B streptococci. J. Clin. Microbiol. 30:1019-1021.[Abstract/Free Full Text]
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  10. Rosa-Fraile, M. 2003. Granada agar sensitivity and detection of group B streptococcus. J. Clin. Microbiol. 41:4007.[Free Full Text]
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  11. Rosa-Fraile, M., J. Rodriguez-Granger, M. Cueto-Lopez, A. Sampedro, E. Biel Gaye, J. M. Haro, and A. Andreu. 1999. Use of Granada medium to detect group B streptococcal colonization in pregnant women. J. Clin. Microbiol. 37:2674-2677.[Abstract/Free Full Text]
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  12. Rosa-Fraile, M., J. Rodríguez-Granger, E. Camacho-Muñoz, and A. Sampedro. 2005. Use of unmodified starches and partial removal of serum to improve Granada medium stability. J. Clin. Microbiol. 43:1989-1991.[Abstract/Free Full Text]
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  13. Schrag, S., R. Gorwitz, K. Fultz-Butts, and A. Schuchat. 2002. Prevention of perinatal group B streptococcal disease. Revised guidelines from CDC. Morb. Mortal. Wkly. Rep. 51:1-22.[Medline]
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  14. Tamayo, J., J. L. Gomez Garces, and J. I. Alos. 2004. Evaluation of Granada agar plate for detection of Streptococcus agalactiae in urine samples from pregnant women. J. Clin. Microbiol. 42:3834-3836.[Abstract/Free Full Text]
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  15. Teese, N., D. Henessey, C. Pearce, N. Kelly, and S. Garland. 2003. Screening protocols for group B streptococcus: are transport media appropriate? Infect. Dis. Obstet. Gynecol. 11:199-202.[CrossRef][Medline]
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  16. Young, A. H. 1984. Fractionation of starch, p. 249-283. In R. L. Whistler, J. N. Bemiller, and E. F. Paschall (ed.), Starch: chemistry and technology, 2nd ed. Academic Press, Inc., New York, N.Y.
Manuel de la Rosa-Fraile*
Enrique Camacho-Muñoz
Microbiology Service
University Hospital Virgen de las Nieves
Granada 18014, Spain

* Phone: 34-958-020010, Fax: 34-958-020169, E-mail: manuel.rosa.sspa{at}juntadeandalucia.es

Journal of Clinical Microbiology, August 2005, p. 4303, Vol. 43, No. 8
0095-1137/05/$08.00+0     doi:10.1128/JCM.43.8.4303.2005





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