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Pulsed-Field Fingerprinting of Vaginal Group B Streptococcus in Pregnancy

From the Departments of Obstetrics and Gynecology, and Food Microbiology and Toxicology and Food Science, University of Wisconsin, Madison, Wisconsin; Centers for Disease Control and Prevention, Atlanta, Georgia; and Department of Pathology, Meriter Hospital, Madison, Wisconsin.

Address reprint requests to: Helen H. Kay, MD, Edward Hospital, 801 South Washington Street, Naperville, IL 60540; E-mail: hkay{at}edward.org.

	ABSTRACT

TOP ABSTRACT MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 
OBJECTIVE: There is more to be learned about the epidemiology of group B ß-hemolytic streptococci infections in pregnancy. In this study, we investigated the discriminating capabilities of pulsed-field gel electrophoresis of group B streptococci strains from pregnant patients and mother/ infant pairs of patients compared with serotyping.

METHODS: Forty-two vaginal strains of group B streptococci cultured from pregnant patients in the third trimester and strains from 20 mother/infant pairs with documented newborn group B streptococci infection were studied. Isolates were serotyped by the Lancefield capillary precipitin method and molecularly characterized by counterclamped homogeneous electrical field pulsed-field gel electrophoresis with rarely cutting restriction enzymes.

RESULTS: Nine of the 13 serotypes of group B streptococci identified thus far in the scientific literature (Ia, Ia/c, Ib, Ib/c, II, IIc, III, V, and NT/c) were represented among the 62 isolates. Among the 42 maternal isolates, eight serotypes were represented, and among the 20 mother/infant isolates, six serotypes were represented. Serotypes of mother/ infant isolates matched in nine of the ten pairs. Restriction endonuclease profiles, or digests, from the 42 maternal isolates resulted in 25 unique profiles that were arranged into five major groups based on the overall relatedness. Each group was comprised of one predominant serotype. The 20 mother/infant paired isolates displayed nine unique restriction endonuclease profiles and nine of the ten paired isolates showed indistinguishable restriction endonuclease profiles between mother and infant.

CONCLUSION: Deoxyribonucleic acid profiling using pulsed-field gel electrophoresis is more discriminating of group B streptococci strains than serotyping because of the different yet closely related patterns within each restriction endonuclease profile group that are linked to one specific serotype. Pulsed-field gel electrophoresis can refine our epidemiologic studies of group B streptococci transmission and acquisition.

Group B streptococcus (S agalactiae) infection is the most common cause of sepsis in newborns in North America and Europe.¹ The most predictive factor of group B streptococcus infection in the neonate is exposure to the organism via the maternal genital tract. Infections in newborns by group B streptococci may result in pneumonia, bacteremia, meningitis, and death in rare instances. Meningitis can lead to significant morbidity, resulting in severe neurologic damage.²

Group B streptococcus organisms are asymptomatically harbored in 14–40% of pregnant women, commonly in the gastrointestinal tract, and may colonize the genitourinary tract by secondary spread.³ Therefore, unless pregnant women are screened for group B streptococcus carriage, they usually do not know that they are colonized.⁴ At the time of birth, group B streptococcus is vertically transmitted to the neonate, and it is estimated that 50% or more of newborns exposed to group B streptococcus will become colonized if the mother is a carrier.⁵

The prevalence of neonatal group B streptococcus infection is one to two per 1000 live births, and approximately 7000 cases of neonatal streptococcal septicemia occur in the United States each year.⁶ Of these, 25–50% will have significant adverse outcomes, including a death rate of 5–10%.⁷ Through much effort and debate, two main screening protocols have emerged. One, from the Centers for Disease Control and Prevention (CDC),⁸ is based on uniform screening of pregnant women at 36–37 weeks’ gestational age, and the second, from The American College of Obstetricians and Gynecologists (ACOG), focuses on risk factors such as preterm labor, preterm rupture of membranes, or chorioamnionitis.⁹ Neither of these screening protocols is without drawbacks, as both approaches overtreat patients and may miss at-risk patients. The current standard of care dictates antibiotic coverage in labor for patients with screen-positive cultures for group B streptococcus or patients with risk factors. Because of this widespread antibiotic use, the emergence of antibiotic-resistant strains of streptococci has become a real concern.¹⁰

All five group B streptococcus serotypes (Ia, Ib, Ic, II, and III) are associated with early-onset disease. However, serotype III, a small subset of all group B streptococci (1–3%), is most often associated with neonatal late-onset sepsis and meningitis.¹¹ Identification via serotyping is not currently feasible on a clinical basis because of costs and time constraints. Therefore, if more refined, efficient, and cost-effective protocols could be developed, we could potentially better select those patients to treat who would be at highest risk of neonatal sepsis and meningitis.

Pulsed-field gel electrophoresis utilizes restriction endonucleases to determine the relatedness among bacterial strains. It is a sensitive and exact molecular technique. In contrast, serotyping is based on characterization of cell surface carbohydrate antigens and may be a cruder, less reliable method. This study evaluated pulsed-field gel electrophoresis with rarely cutting restriction endonucleases to characterize vaginally isolated group B streptococcus from pregnant women, as well as from mother/infant pairs with documented neonatal sepsis. Comparisons to the gold standard of serotyping were done. We determined the discriminating capability of pulsed-field gel electrophoresis to better define genomic subtypes of colonized pregnant women and their infected newborns that may help us refine our antibiotic treatments. Other investigators have suggested that the present serological classification of group B streptococcus is inadequate and that the epidemiologic understanding of group B streptococcus disease can only be achieved through genomic classification.¹²

	MATERIALS AND METHODS

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Isolates of vaginal group B streptococcus were anonymously obtained from the hospital microbiology laboratory after they had been isolated from third trimester inpatients and outpatients from the two obstetric hospitals in Madison, Wisconsin, from October 1998 to June 1999. There was no direct patient contact, and clinical charts were not reviewed. Group B streptococcus cultures were obtained from outpatients as part of routine antenatal screening. Cultures from inpatients were obtained as part of the evaluation for preterm labor, preterm premature rupture of membranes, or intrapartum sepsis. Isolates were obtained with a swab culturette (Becton Dickinson Microbiology Systems, Sparks, MD) from the lower vagina, perineum, and perianal region. The group B streptococcus samples were first streaked onto blood agar media (5% sheep blood) (Becton Dickinson) and then placed in selective group B streptococcus broth (Lim broth; Becton Dickinson). The broth was incubated at 37C for 24 hours and then streaked onto blood agar plates and incubated for 24 hours at 37C. Colonies qualifying phenotypically as group B streptococcus were isolated and gram stained using Escherichia coli (American Type Culture Collection strain 25922) as a negative control and a catalase reaction for Staphylococcus aureus (American Type Culture Collection strain 29213) as a positive control. Further confirmation was obtained using API 20 biochemical test strips (BioMerieux Vitak Inc., Hazelwood, MO) and the cyclic adenosine monophosphate test using S aureus negative control. Strains that were positive for group B streptococcus by all tests were then sent to JAE at the CDC for serotyping. In addition, anonymous isolates from mother/infant pairs with documented neonatal sepsis were generously provided by JAE. These 20 isolates were collected over a 12-year period and stored in defibrinated sheep blood at -65C. Mother/infant isolates were obtained from the mother’s vagina, cervix, or breast milk as per CDC records. Neonatal isolates were obtained from gastric aspirates, cerebral spinal fluid, blood cultures, or lung aspirates. Serotyping was also performed at the CDC.

Serotyping was done by the Lancefield capillary precipitin method,¹³ which is the most commonly used method across the country.

Contour-clamped homogeneous electrical field pulsed-field gel electrophoresis was conducted as previously described.^14,15 For selection of an acceptable rarely cutting restriction endonuclease, genomic deoxyribonucleic acid (DNA) from group B streptococcal DNA within agarose plugs was separately digested with ApaI, AscI, EcoRI, DraI, HindIII, NotI, SgrAI, SacI, SfiI, SmaI, XbaI, or XhoI (Promega Co., Madison, WI) according to the instructions of the manufacturer. Restriction fragments were resolved in 1% electrophoresis grade agarose (Seakem Gold; FMC BioProducts, Rockland, ME) using a CHEF DRII system (Bio-Rad Laboratories, Hercules, CA) at 6 V/cm with pulse times ramped from 1 to 15 seconds (AscI, NotI, SacI, Sfi1, SgrAI, XbaI, and XhoI), 1–25 seconds (ApaI, DraI, EcoRI, and HindIII), or 5–50 seconds (SmaI) over 24 hours with the running buffer temperature maintained at 14C. The size standard used on all gels was genomic DNA from E coli G5244 digested with XbaI. An E coli digest was used because it is a standard reference yielding a narrow range of molecular weights encompassing all observed bands in this study. After electrophoresis and staining in ethidium bromide (0.5 µg/ml), the resulting restriction endonuclease digestion profiles were recorded using the Molecular Analyst software system (Bio-Rad Laboratories) and analyzed using the Fingerprinting Plus software system (Bio-Rad Laboratories) based on the Dice coefficient correlation:

To establish proficiency with genomic fingerprinting, contour-clamped homogeneous electrical field pulsed-field gel electrophoresis was performed on isolates of group B streptococcus. Restriction endonucleases with specificity for "A" and "T" in the recognition sequence, such as XbaI (5'-TkCTAGA-3'), were selected, based on the likelihood that genomic DNA of streptococci are relatively high in G and C, and such a rarely cutting enzyme would produce discernible restriction endonuclease digestion profiles.¹⁶ Enzymes with specificity for recognition sequences of eight base pairs or greater in length, such as NotI (5'-GCGGCCGC-3') and SfiI (5'GGCCNNNNNGGCC-3'), were also evaluated. With the exceptions of SmaI and XhoI, the other enzymes tested were not desirable because either too many or too few fragments were generated or because the resulting restriction endonuclease digestion profiles were ambiguous. The restriction endonuclease digestion profiles produced from SmaI digestions will henceforth be described, although both SmaI and NotI produced similar results. The 42 maternal isolates and the 20 mother/infant restriction endonuclease digestion profiles were separately compared (Figures 1 and 2, respectively) by use of the Fingerprinting Plus software (Bio-Rad Laboratories). Pulsed-field gel electrophoresis was performed three times for each specimen, and results were reproducible.

View larger version (67K): [in this window] [in a new window]   Figure 1. Serotype and restriction endonuclease digestion profiles profiles of 42 group B streptococci strains isolated from patients in the third trimester. NT = not typeable. Benson. Clonality of Group B-Hemolytic Streptococcus. Obstet Gynecol 2002.

View larger version (49K): [in this window] [in a new window]   Figure 2. Serotype and restriction endonuclease digestion profiles profiles of 20 group B streptococci strains isolated from 10 mother/infant pairs. Benson. Clonality of Group B-Hemolytic Streptococcus. Obstet Gynecol 2002.

	RESULTS

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Among the 42 maternal isolates, eight serotypes were represented (excluding NT) (Figure 1). Among the 20 mother/infant isolates, six different serotypes were represented. The serotypes of mother/infant isolates matched in nine of the 10 pairs (Figure 2).

Digestion of genomic DNA from group B streptococcus using SmaI generated from eight to 18 (circa 30.8–304 kb in length) readily discernible restriction fragments (Figures 1 and 2). The restriction endonuclease digestion profiles from 42 maternal isolates (Figure 1) resulted in 25 unique profiles as determined by Dice analysis (see horizontal bars directly to the left of the electrophoresis gel results). Six of the 25 profiles were duplicated (three pairs, one triplet, and two groups of seven indistinguishable restriction endonuclease digestion profiles—strains 1–7 and strains 20–26) (see vertical bars directly to the left of the electrophoresis gel results). The 42 restriction endonuclease digestion profiles were arranged into five major groups (A–E) based on the overall relatedness (Figure 1). These five groups were delineated using Dice coefficients by the Fingerprinting Plus software. Within each of these five restriction endonuclease digestion profile groups there was one predominant serotype.

The restriction endonuclease digestion profiles from 20 mother/infant isolates (strains 43–62) displayed nine unique restriction endonuclease digestion profiles by Dice analysis (Figure 2) (see horizontal bars directly to the left of the electrophoresis gel results). Seven of the nine profiles were duplicated (six pairs and one group of six indistinguishable restriction endonuclease digestion profiles) (see vertical bars directly to the left of the electrophoresis gel results), and only two of the profiles were singularly unique (strains 45 and 54). Each of the six pairs of indistinguishable restriction endonuclease digestion profiles were from six individual mother/infant pairs. The group of six indistinguishable restriction endonuclease digestion profiles (strains 57–62) was comprised of three mother/infant isolates—in other words, nine of the ten mother/infant-paired isolates showed indistinguishable restriction endonuclease digestion profiles.

The eight restriction endonuclease digestion profiles identified in the ten infected neonates from the CDC were identified among the pregnant women screened during pregnancy in our institution. This indistinguishable similarity was carried over despite the fact that the neonates and these pregnant women were geographically remote and disparate from each other.

	DISCUSSION

TOP ABSTRACT MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 
The parallel result between serotyping and DNA subtyping in this study is an interesting finding. In other words, similar and/or indistinguishable restriction endonuclease digestion profiles are closely linked to dominant serotypes despite originating from geographically diverse sources—ie, the CDC in Atlanta, Georgia, and two hospitals in Madison, Wisconsin. We found five main groups of restriction endonuclease digestion profiles that are each closely linked to one predominant serotype. There are a few exceptions where isolates of the same serotype had substantially dissimilar restriction endonuclease digestion profiles. For example, strain 8 in Figure 1 had a serotype of Ia/c, similar to others in group E, but had a restriction endonuclease digestion profile unrelated to others in group A, and strains 55 and 56 (Figure 2) from mother/infant pair 6 had different serotypes but indistinguishable restriction endonuclease digestion profiles. It is possible, although unlikely, that these specimens were mislabeled in the past, or that there was contamination or laboratory error. It is also possible that there was a gain or loss of a plasmid in these organisms or that there was more than one source of infection with more than one strain. Despite these, the parallel grouping of specific restriction endonuclease digestion profiles with singular serotypes was a consistent finding and supports pulsed-field gel electrophoresis as a technology to characterize group B streptococcus isolates, although serotyping has been the gold standard to date.

We found that DNA profiling using pulsed-field gel electrophoresis is more discriminating of group B streptococcus strains than serotyping because of the different yet closely related patterns within each restriction endonuclease digestion profile group that are linked to one specific serotype (eg, group "E" restriction endonuclease digestion profiles in Figure 1). In other words, more numbers of unique restriction endonuclease digestion profile patterns (25) can be found among the eight serotype groups represented here, in essence a three-fold increase in discriminating power. Indeed, some strains were nontypeable by serotyping techniques, but all were typeable by pulsed-field gel electrophoresis. Because of this, pulsed-field gel electrophoresis may refine our epidemiologic studies of group B streptococcus transmission and acquisition because it will enable us to more accurately follow transmission from a patient of interest knowing the restriction endonuclease digestion profile pattern of the group B streptococcus isolate. Obviously, the more unique the restriction endonuclease digestion profile, the easier it will be to track its transmission. Other investigators have performed clonal analysis on group B streptococcus isolates to study the epidemiology of neonatal sepsis using isoenzyme electrophoresis, but with less refinement than we currently find with pulsed-field gel electrophoresis.¹⁸ Blumberg et al¹⁹ investigated restriction endonuclease analysis of chromosomal DNA and DNA restriction fragment length polymorphisms of ribosomal ribonucleic acid genes. Their results are consistent with ours: Serotyping is suboptimal in discriminatory capacity. They reported that serotype III isolates belonged to at least four ribotypes and concluded that reproducible molecular epidemiologic methods should prove useful for studying the epidemiology of group B streptococcus infections.

The current results by serotyping and pulsed-field gel electrophoresis confirm the direct transmission of group B streptococcus from mother to infant. Only one pair out of the ten showed a discrepancy between the mother/ infant serotype, and a second pair showed a discrepancy between the mother/infant restriction endonuclease digestion profiles. Therefore, either serotyping or pulsed-field gel electrophoresis could allow us to track the transmission and hence the epidemiology of group B streptococcus infection. Although the issue of transmission and acquisition in a neonate may appear obvious now, there exists the possibility that other routes of transmission may exist but are not appreciated at this time.

Pulsed-field gel electrophoresis may also be used to study reinfection by antibiotic resistant strains of group B streptococcus. Similar analyses using enzyme electrophoretic analysis by Quentin et al²⁰ identified clones of infected neonates in France that differed from clones of infected neonates in the United States. Therefore, more refined pulsed-field gel electrophoresis group B streptococcus characterization could potentially aid in identification of patients who are at higher risk for neonatal sepsis through isolation and identification of strains known to be recovered more frequently from septic neonates—ie, strains that are more virulent. In this study, we were able to identify eight unique restriction endonuclease digestion profiles from the septic neonates compared with five unique serotypes. These sepsis-related restriction endonuclease digestion profiles were also identified in some but not all of the 42 pregnant women screened in our institution, suggesting that perhaps not all women with a positive group B streptococcus isolate will have the same propensity to transmit and infect a neonate. Furthermore, our findings suggest that there may be strains of group B streptococcus that may not normally cause disease in healthy individuals even if they carry the strains. Clearly, additional studies on larger numbers of group B streptococcus strains will be needed to test this observation, which may enable us to refine our current use of antibiotic prophylaxis and decrease the emergence of antibiotic-resistant strains. Since pulsed-field gel electrophoresis is based on software analysis of genomic DNA digested by restriction endonuclease digestion, it is a technique that could be standardized between different laboratories or possibly in established national reference laboratories. Hence, a pulsed-field gel electrophoresis profiling of each strain of group B streptococcus isolated from any pregnant woman could be reliably characterized and potentially classified into a pathogenic versus a nonpathogenic strain, an exercise that could have clinical significance.

The group B streptococcus strains isolated from our population are similar to those defined nationally. Predominant serotypes of group B streptococcus strains previously received by the CDC are predominantly Ia/c and III, along with serotype V, which has shown a dramatic increase in prevalence in recent years.¹⁷ Strains isolated from pregnant women in the present study reflect that same trend, with mostly Ia/c (17 isolates) and III (16 isolates) serotypes, but also some occurrence of serotype V (eight strains). Although serotype III isolates of group B streptococcus have been responsible for the predominance of neonatal late sepsis and meningitis,¹¹ we found that other serotypes are also involved in cases of neonatal sepsis (Ia/c, Ia, Ib, and II). We did not, however, identify any serotype V strains among the mother/infant pairs tested. Therefore, the pathogenicity of this particular serotype in clinical practice might be further elucidated by pulsed-field gel electrophoresis given its discriminating characterization.

In conclusion, pulsed-field gel electrophoresis has the potential to characterize group B streptococcus strains in a clinical setting. Any test to encourage more discriminating antibiotic usage based on the pathogenicity of certain strains would ultimately lead to less drug resistance. Future studies could evaluate considerably more strains to substantiate the feasibility of using pulsed-field gel electrophoresis to identify those patients carrying a pathogenic strain of group B streptococcus who would benefit from treatment and/or prophylaxis.

	Footnotes

 
JBL is currently affiliated with the United States Department of Agriculture, Agricultural Research Service, Eastern Regional Research Center, Wyndmoor, Pennsylvania.

PII S0029-7844(02)02139-7

Received December 20, 2001. Received in revised form March 15, 2002. Accepted April 4, 2002.

	REFERENCES

TOP ABSTRACT MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 
1. Committee on Technical Bulletins of the American College of Obstetricians and Gynecologists. Group B streptococcal infections in pregnancy. ACOG technical bulletin no. 170. Washington, DC: American College of Obstetricians and Gynecologists, 1992.

2. Levinson ME, Trestman I, Quach R, Sladowski C, Floro CN. Quantitative bacteriology of the vaginal flora in vaginitis. Am J Obstet Gynecol 1979;133:139–44.[Medline]

3. Larsen B, Galask RP. Vaginal microbial flora: Composition and influences of host physiology. Ann Intern Med 1982;96:926–30.

4. Baker CJ, Clark DJ, Barrett FF. Selective broth medium for isolation of group B streptococci. Appl Microbiol 1973; 26:884–5.[Medline]

5. Baker CJ. Group B streptococcal infections in neonates. Pediatr Rev 1979;1:5–15.[Abstract/Free Full Text]

6. Schuchat A, Deaver-Robinson K, Plikaytis BD, Zangwill K, Mohle-Boetani J, Wenger J, et al. Multistate case-control study of maternal risk factors for neonatal group B streptococcal disease. Pediatr Infect Dis J 1994;13:623–9.[Medline]

7. Zangwill KM, Schuchat A, Wenger JD. Group B streptococcal disease in the United States, 1990: Report from a multistate active surveillance system. Mor Mortal Wkly Rep CDC Surveill Summ 1992;41(SS-6):25–32.

8. Prevention of perinatal group B streptococcal disease: A public health perspective. MMWR Morb Mortal Wkly Rep 1996;45:1–24.[Medline]

9. Committee on Obstetric Practice. Prevention of early-onset group B streptococcal disease in newborns. ACOG committee opinion no. 173. Washington, DC: American College of Obstetricians and Gynecologists, 1996.

10. Morales WJ, Dickey SS, Bornick P, Lim DV. Change in antibiotic resistance of group B streptococcus: Impact on intrapartum management. Am J Obstet Gynecol 1999; 181:310–4.[Medline]

11. Dinsmoor MJ. Group B streptococcus infection. In: Queenan JT, ed. Management of high risk pregnancy. Oxford, England: Blackwell Scientific, 1990:326–32.

12. Dmitriev AV, Pak JV, Suvorov AN, Totolian AA. Analysis of pathogenic group B streptococci by pulsed field gel electrophoresis. In: Horaud T, Bouvet A, Leclercq R, eds. Streptococci and the host. New York: Plenum Press,1997: 351–3.

13. Lancefield RC. Serological differentiation of specific types of bovine hemolytic streptococci (group B). J Exp Med 1934;61:335–49.

14. Brosch R, Chen J, Luchansky JB. Pulsed-field fingerprinting of listeriae: Identification of genomic divisions for Listeria monocytogenes and their correlation with serovar. Appl Environ Microbiol 1994;60:2584–92.[Abstract/Free Full Text]

15. Howard PJ, Harsono KD, Luchansky JB. Differentiation of Listeria monocytogenes, Listeria ivanovii, and Listeria seeligeri by pulsed-field gel electrophoresis. Appl Environ Microbiol 1992;58:709–12.[Abstract/Free Full Text]

16. McClelland M, Jones R, Patel Y, Nelson M. Restriction endonucleases for pulsed field mapping of bacterial genomes. Nucleic Acids Res 1987;15:5985–6005.[Abstract/Free Full Text]

17. Elliott JA, Farmer KD, Facklam RR. Sudden increase in isolation of group B streptococci, serotype V, is not due to emergence of a new pulsed-field gel electrophoresis type. J Clin Microbiol 1998;36:2115–6.[Abstract/Free Full Text]

18. Helmig R, Uldbjerg N, Boris J, Kilian M. Clonal analysis of Streptococcus agalactiae isolated from infants with neonatal sepsis or meningitis and their mothers and from healthy pregnant women. J Infect Dis 1993;168:904–9.[Medline]

19. Blumberg HM, Stephens DS, Licitra C, Pigott N, Facklam R, Swaminathan B, et al. Molecular epidemiology of group B streptococcal infections: Use of restriction endonuclease analysis of chromosomal DNA and DNA restriction fragment length polymorphisms of ribosomal RNA genes (ribotyping). J Infect Dis 1992;166:574–9.[Medline]

20. Quentin R, Huet H, Wang FS, Geslin P, Goudeau A, Selander RK. Characterization of Streptococcus agalactiae strains by multilocus enzyme genotype and serotype: Identification of multiple virulent clone families that cause invasive neonatal disease. J Clin Microbiol 1995;33:2576–81.[Abstract]

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