|Year : 2001 | Volume
| Issue : 2 | Page : 1-4
Colonization of pregnant women and their newborn infants with group-B streptococci
AA Kulkarni , SG Pawar , CA Dharmadhikari , RD Kulkarni
Department of Microbiology, Government Medical College, Miraj - 416 410, Maharashtra, India
Department of Microbiology, Government Medical College, Miraj - 416 410, Maharashtra, India
As group B streptococci (GBS) prevalence varies from place to place and this organism is responsible for serious infections in newborns such as septicaemia and meningitis, the present study was carried out to find the prevalence of GBS in pregnant women and their neonates. From June 1998 to April 1999 a total of 317 pregnant women and their neonates were examined for GBS. GBS colonization rate was 2.52% and 1.26% in pregnant women and their neonates respectively. Four sites - viz. throat, external ears, external nares and stump of umbilicus from neonates were found to be equally colonized by GBS immediately after birth and at the time of discharge from hospital, except the umbilicus which was not swabbed at the time of discharge. None of the neonates developed GBS related sepsis. Selective broth medium (SBM) was found to be a superior transport method over Stuart transport medium and filter paper method. All the isolates were sensitive to Ampicillin, Erythromycin, Penicillin followed by Chloramphenicol 66.6% (12/18). All the strains were resistant to Gentamicin, followed by Tetracycline 94.4% (17/18) and Kanamycin 88.8% (16/18).
|How to cite this article:|
Kulkarni A A, Pawar S G, Dharmadhikari C A, Kulkarni R D. Colonization of pregnant women and their newborn infants with group-B streptococci. Indian J Med Microbiol 2001;19:1-4
|How to cite this URL:|
Kulkarni A A, Pawar S G, Dharmadhikari C A, Kulkarni R D. Colonization of pregnant women and their newborn infants with group-B streptococci. Indian J Med Microbiol [serial online] 2001 [cited 2019 Jun 24];19:1-4. Available from: http://www.ijmm.org/text.asp?2001/19/2/1/6929
Streptococci have an important position in clinical medicine as human pathogens. Among them group A streptococci had a special place as a causative agent of important clinical diseases and syndromes till recently. Other members of this family are now coming to light as human pathogens and group B streptococcus (GBS) has emerged as an important pathogen within the last few decades.
GBS is a well-recognized pathogen in veterinary medicine because of its role as a causative agent of bovine mastitis. Of late, it has become apparent that this organism contributes to such serious diseases as septicaemia and meningitis in the newborn infants. GBS is also known to cause a wide variety of complications in pregnancy. The source of the organism in most of these cases is the maternal genital or gastrointestinal tract or both.
Maternal colonization by GBS at delivery is almost always demonstrable in cases of early onset neonatal infections.
Thus identification of maternal colonization by GBS at labour is the most desirable element of a selective intrapartum chemoprophylactic strategy.
The prevalence of GBS in pregnant women varies from place to place as reported by several workers the world over.,,,,, The present study was undertaken with the following objectives :
a) To find out the prevalence of GBS colonization in pregnant women at the time of labour and in their neonates.
b) To estimate the frequency of neonatal acquisition of GBS at various body sites.
c) To correlate the risk factors, if any, contributing to GBS colonization.
d) To find out the efficacy of three different transport systems used for GBS isolation.
e) To study the antibiogram of the isolates (GBS) with a view to determine the pattern of antibiotic resistance.
| ~ Material and Methods|| |
Three hundred and seventeen pregnant female patients at labour and their neonates were examined for GBS colonization from June 1998 to April 1999.
From each mother four low vaginal swabs were taken prior to first pelvic examination (no antiseptic preparation of the perineum or vulva was carried out before swabbing). Two rectal swabs were also collected from each mother. A total of four samples were collected from each newborn infant immediately after birth viz. external ear swab, nasal swab, throat swab and umbilical swab. Again at the time of discharge from hospital, similar swabs except the umbilical swab were collected.
Transport of swabs
Three vaginal swabs were transported to the laboratory by three different methods- Stuart transport medium, filter paper technique, and selective broth medium (SBM). In brief, the selective medium consisted of nalidixic acid 15µg/ml, gentamicin sulfate 8µg/ml in Todd- Hewitt broth with 5% sheep blood. Remaining vaginal swab was used for Gram stain. Of the two rectal swabs, one was transported to the laboratory in SBM while the remaining one was used for Gram stain. All swabs from neonates were transported in Stuart transport medium to the laboratory.
Processing of specimens
All swabs were plated on 5% sheep blood agar and incubated at 37oC, in candle jar for 18 - 24 hours. Plates were further incubated for 24 hours before being declared as negative.
Presumptive identification of GBS
Typical colony morphology, hippurate hydrolysis and CAMP test identified GBS. The colony is usually gray, soft, shiny, convex, moist, regular and about 1mm in diameter and surrounded by a small hazy zone of beta haemolysis.
Confirmation of GBS
Identified strains were further confirmed by serogrouping. For the extraction of cell wall antigen, Lancefield's (hot acid) method of extraction was adopted. The grouping of GBS was done by counterimmunoelectrophoresis (CIEP) method. The grouping antisera that were used for CIEP were raised locally by immunizing healthy adult rabbits. In brief, standard strains of Streptococcous group A, B, C, D, F and G were grown in 200 mL Todd- Hewitt broth for 16 to 18 hours. Plate culture was done to test for purity. The cells were centrifuged, resuspended in 10 mL 0.85% saline, formalin (0.4%) added and the suspension was left in refrigerator for 24 hours. To prepare grouping sera, rabbits were immunised with suspension (diluted 20 times with saline) by injecting 1 mL intravenously each day for 5 successive days in first week, 2 mL each day for 5 successive days in third week and 4 mL in fifth week. Five days after the last injection, ear vein blood was collected and tested by capillary pipette precipitin method. If satisfactory precipitin reaction was obtained with extracts of strains of homologous group, the rabbit blood was collected. Sera were tested with homologous and heterologous streptococci for specificity and titre. The isolated strains were also confirmed by C.M.C.H., Vellore, Tamil Nadu.
The isolates were tested for antibiotic sensitivity by disc diffusion method of Kirby- Bauer by employing the following drugs on 5% sheep blood agar- Ampicillin (10 µg/disc), Penicillin (10 Units/ disc), Erythromycin (15 µg/ disc), Gentamicin (10 µg/ disc), Chloramphenicol (30 µg/ disc) & Kanamycin (30 µg/ disc).
| ~ Results|| |
GBS colonization rate in pregnant women at labour and in neonates was 2.52% (8/317) and 1.26% (4/317) respectively (frequency of transmission 50%). Among eight GBS colonized mothers, GBS was isolated in three cases from vagina only (37.5%), in two cases from rectum only (25.0%), and in three cases from both vagina and rectum (37.5%). From four GBS colonized neonates, only one site, either throat, external ears, external nares and stump of umbilicus was found to be colonized immediately after birth and at the time of discharge from hospital.
Only one risk factor has been seen in two GBS colonized mothers (i.e. in one case premature delivery and in the other case premature rupture of membranes), associated with GBS transmission.
GBS isolation rate by using 3 different transport systems was as follows- by filter paper technique and by Stuart transport medium, 1.26% (4/317) each and 1.89% (6/317) by selective broth medium (SBM).
All isolates were sensitive to Ampicillin, Erythromycin and Penicillin followed by Chloramphenicol 66.6% (12/18). All isolates were resistant to Gentamicin, followed by Tetracycline (17/18) 94.4%, and Kanamycin (16/18) 88.8%.
| ~ Discussion|| |
The group- B streptococci (GBS) are known to cause a wide variety of infections in adults, but clinical interest in these bacteria mainly relates to their ability to cause serious neonatal illness, especially meningitis and sepsis. In developed countries these organisms are the leading cause of neonatal sepsis and meningitis with a case fatality rate of 40 to 80%.  The reason for this is not clear. However, in developing countries like India, the problem has not been adequately studied and there are only a few reports available,,, In the present study all the females were from lower socioeconomic group and in 18 to 38 years of age group.
In adult women, GBS carriage in the genital tract, perineal skin and gastrointestinal tract is of great importance in view of its significance in GBS neonatal infection, whether asymptomatic mucous membrane colonization or symptomatic invasive infection (early onset septicaemia, meningitis etc.).  In the present study we found that both vagina and rectum were the prime sites of GBS colonization. These two sites act as reservoir as well as source of GBS infection to neonates.
The density of maternal colonization at delivery was found to be an important predictor of vertical transmission of GBS to the neonate. Colonized infants born to heavily colonized untreated mothers tend to be colonized at multiple sites more frequently than were colonized infants born to untreated mothers with moderate and light colonization. Nosocomial spread of GBS also occurs in the nursery, but it accounts for a much smaller proportion of neonatal disease than does maternal transmission. In the present study we found that only one site from neonates was colonized by GBS. None of the neonate developed GBS related sepsis. Thus an invasive attack rate was found to be zero percent which might be due to passive immunization of newborns via transplacental transfer of type specific serum antibodies from their mothers. Also there was complete absence of GBS colonization in neonates of non colonized mothers, and this probably indicates that nosocomial transmission of GBS was not a major problem in this hospital. Although desirable, it was not possible to follow up our cases in this study.
Considerable work has been done to determine the risk factors involved in GBS carriage. A number of factors are involved, like- maternal urinary tract infection, premature or prolonged rupture of membranes, premature delivery, peak intrapartum fever greater than 37.5oC, while some workers give weightage to lack of type specific antibodies by neonates due to failure of transplacental transfer of these antibodies. This is responsible for GBS colonization, or in turn GBS disease in the newborn. We found two cases having a single risk factor- premature delivery in first case and premature rupture of membrane in second case associated with GBS colonization.
For better isolation of GBS from clinical material the use of transport medium has revealed the critical consideration. Several workers tried different methods of transportation of clinical specimens from patients to the laboratory.,,, In the present study we compared 3 different transport methods to find out their efficacy in GBS isolation namely, Stuart transport medium, filter paper technique & selective broth medium (SBM). We found SBM was the most effective method for GBS isolation than the other two as it inhibits the normal vaginal flora without any inhibitory effect on isolation of GBS. One more reason is that, it acts as both transport as well as enrichment media for GBS. Since it requires sheep blood, which is not routinely available in every laboratory, filter paper technique and Stuart transport medium were found to be effective for GBS isolation.
All the isolates were sensitive to Ampicillin, Erythromycin and Penicillin, followed by Chloramphenicol. Resistance was seen with Gentamicin, followed by Tetracycline & Kanamycin. The limitation of disc diffusion method in case of GBS sensitivity is that in many instances, GBS demonstrates tolerance to penicillin in that it has high minimum bactericidal concentration (MBC) though the MIC may be in the sensitive stage. The MBC can be reduced by the addition of Gentamicin; i.e. Gentamicin has synergistic action along with penicillin. This fact cannot be demonstrated if only a disc diffusion test is used to determine antimicrobial susceptibility.
| ~ Acknowledgement|| |
We are thankful to Dr. M.K. Lalitha, Professor and Dr. K.N. Brahmadathan, Professor, Department of Microbiology, C.M.C.H. Vellore, for supplying the standard strains of streptococci and also for serogrouping of the isolated strains.
We also thank Dr. Geeta Mehta, Professor & Head, Department of Microbiology, L.H.M.C., New Delhi, for supplying some of the standard strains of streptococci.
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