NEW Product MAY 2006
STREPTO B ID
NEW chromogenic media available !
STREPTO B ID
NEW PRODUCT in the bMx offer
SECOND in the NEW PREVENTION range
dedicated to the
“Screening of Strepto B for pregnant women”
PRESCRIBE CONFIDENCE…
…COMPLETE RANGE promoted globally
Todd Hewitt Broth+ATBs
+
Bouillon Todd Hewitt + Antibiotiques- Réf. 42 116
STREPTO B ID
Photo 1/2- rev.0 – 2002/11/05
+
Slidex STREPTO B
=
Greater reliability
Validated solution
38
Prevention of perinatal Group B streptococcal infections:
Evaluation of a new chromogenic medium Strepto B ID
C. Roure, V. Fiaty, Y. Gilles, H. Salord, S. Tigaud,
Hôpital de la Croix-Rousse, Laboratoire de Microbiologie, Lyon, France
P798
ABSTRACT
Objective: The aim of this prospective study was to compare a method using the new
chromogenic agar Strepto B ID (bioMérieux SA, France), Granada agar (Biomedics) and
Columbia blood agar with colistin-nalidixic acid (BA-CNA) (bioMérieux), to detect vaginal
colonization by group B streptococci (GBS) in pregnant women.
Method: Specimens for GBS screening received over a 3 month period from pregnant women
(683 vaginal swabs and 41 urine), 13 newborn gastric fluids at two hospitals were included and
tested during this study. These specimens were cultured in parallel onto the three media by
direct inoculation and after enrichment in Todd-Hewitt + antibiotics broth. Each medium was
observed after 24 and 48hrs of incubation.
Results: Overall GBS was detected in 255 cases (35%) on at least one medium after
enrichment. Before and after enrichment, the sensitivity was 45.8% and 93.3% for Strepto B ID,
39.6% and 82.9% for Granada, 45.4% and 92.5% for BA-CNA respectively at 24hrs. Prolonged
incubation (48hrs) enabled to increase the sensitivity: before and after enrichment, the sensitivity
was 55.8% and 99.2.% for Strepto B ID, 52.5% and 92.9% for Granada, 52.9% and 96.7% for
BA-CNA. Regarding the specificity, the Granada medium method gave 99.8% versus 97.3% for
the Strepto B ID after enrichment and 48 hrs of incubation.
Conclusion: These findings show that the Strepto B ID medium, the first chromogenic medium
to detect GBS, is more sensitive than the Granada medium. However, the Granada medium
method is more specific after enrichment and 48 hrs of incubation.
The enrichment phase increases significantly the GBS sensitivity of detection especially with
Strepto B ID. This new medium is easy to use due to the incubation under aerobic conditions.
Figure 1: GBS vaginal specimens collection
GBS colonies are pale pink to red, round and pearly
RESULTS
Group B streptococcus is detected in 35% of the samples, whatever the
medium.
A total of 737 samples (683 vaginal swabs, 41 urine collections and 13 gastric
fluids) were cultured, both directly and after previous selective enrichment
(Todd Hewitt broth + antibiotics, bioMérieux, France) onto:
• Strepto B ID agar (bioMérieux, France)
• Granada medium (BIOMEDICS, Spain)
• Columbia CNA + 5% sheep blood agar (bioMérieux, France)
Culture plates were incubated at 38°C in aerobic (Strepto B ID, Columbia CNA)
or anaerobic conditions (Granada) and interpreted after a period of incubation
of
both
24 and 48 hours.
Suspected colonies (red or pink on Strepto B ID [Fig. 1], red or orange on
Granada, beta-hemolytic on Columbia-CNA) were GBS confirmed using a
Slidex agglutination test (bioMérieux, France).
Negative predictive values (reading at 48 hours) are 80.8 % (Strepto B ID) and
79.8% (Granada) without enrichment, and 99.4 % (Strepto B ID) and 96%
(Granada) with previous enrichment.
Table 1: Sensitivity of detection for Strepto B ID and Granada media
Sensitivity of
False
True
Incubation
detection
negative
positives
period
[CI at 95%]
s
45.5%
24 hrs
116
139
[39.4% - 51.7%]
Strepto B ID
56.1%*
48 hrs
143
112
[49.8% - 62.1%]
38.4%
24 hrs
98
157
[32.6% - 44.7%]
Granada
52.2%
48 hrs
133
122
[45.9% - 58.3%]
93.3%
24 hrs
238
17
[89.4% - 95.8%]
Strepto B ID
98.8%
48 hrs
252
3
[96.5% - 99.6%]
81.2%
24 hrs
207
48
[75.8% - 85.6%]
Granada
92.2%
48 hrs
235
20
[88.1% - 94.9%]
Without enrichment
MATERIAL AND METHODS
Sensitivity of detection at 48 hours without enrichment on Strepto B ID,
Granada and Columbia CNA media are respectively 56.1%, 52.2% and 52.9%.
This sensitivity reaches 98.8%, 92.2%, 96.7% after previous enrichment.
Whatever the method and the incubation period, the sensitivity of Strepto B ID
medium is significantly higher than for the other two media.
* Example of interpretation: without previous enrichment of a Strepto B-positive sample, there are
56.1 possibilities out of 100 to detect a strain from this micro-organism on Strepto B ID medium,
after a 48-hr period of incubation .
With enrichment
Reading at 24 hrs
With enrichment
Strepto B ID medium performance was compared to Granada medium and to
Columbia CNA + 5% sheep blood, with and without previous selective
enrichment, using biological samples.
Incubation
period
True
positives
False
negative
s
24 hrs
116
1
48 hrs
143
12
24 hrs
98
0
48 hrs
133
0
24 hrs
238
6
48 hrs
252
13
24 hrs
207
0
48 hrs
235
1
Strepto B ID
OBJECTIVES
GBS remains a leading cause of serious neonatal infections despite great
progress in perinatal GBS disease prevention. The CDC recommends the use
of a screening method for GBS colonization in pregnant women to identify
candidates for intra-partum prophylaxis. Strepto B ID is a new, ready-to-use,
chromogenic medium, designed for rapid identification of GBS. The aim of the
study was to evaluate the biological performance of Strepto B ID on clinical
samples.
Without enrichment
Table 2: Positive predictive values of Strepto B ID and Granada media, with and wi
enrichment.
Granada
Strepto B ID
Granada
PPV
[CI at 95%]
99.1%
[95.2% - 99.9%]
92.3%*
[86.8% - 95.6%]
100%
[96.1% - 100%]
100%
[97.1% - 100%]
97.5%
[94.7% - 98.9%]
95.1%
[91.7% - 97.1%]
100%
[98.1% - 100%]
99.6%
[97.6% - 99.9%]
* Example of interpretation: without previous enrichment of a Strepto B-positive sample, there are
92.3 possibilities out of 100 that the colonies showing a characteristic coloration (pale pink to red)
on Strepto B ID medium, after a period of incubation of 48 hrs, are Group B Streptococcal strains .
CONCLUSION
The systematic screening for Group B
Streptococci carriage is recommended at the
end of pregnancy, ideally between the 34th
and the 38th week of amenorrhea, in order to
prevent neonatal Group B streptococcal
infections. Culture techniques from vaginal
cavity swabbing are currently the best.
Strepto B ID appears to be a very effective
medium for the screening of Group B
Streptococci.
As for every chromogenic medium, a trained
eye is necessary to pinpoint characteristic
colonies.
According to the results obtained during this
study, Strepto B ID is more sensitive than
Granada medium.