Elsevier

Maturitas

Volume 85, March 2016, Pages 5-10
Maturitas

Molecular characterization and antimicrobial susceptibility of hemolytic Streptococcus agalactiae from post-menopausal women

https://doi.org/10.1016/j.maturitas.2015.11.007Get rights and content

Highlights

  • The distribution of serotypes in postmenopausal women is similar to that of pregnant population.

  • Reduced sequence type variability is observed in postmenopausal women than in pregnant population.

  • The most common sequence types are ST-19 and ST-23, mainly related to colonization.

  • Antimicrobial resistance percentages are somewhat higher in postmenopausal women.

  • Characterization of strains in different populations is necessary for the development of candidate vaccines.

Abstract

Purpose

Streptococcus agalactiae (Group B streptococcus, GBS) is increasingly recognized as a pathogen in adult populations, including the elderly. Appropriate treatment involves antibiotics. An alternative to this strategy would be the administration of a polysaccharide vaccine therefore the capsular serotypes and molecular characterization of circulating strains needs to be known. Few studies have been conducted in this population.

Methods

One hundred and seven GBS isolates collected from vagino-rectal swabs from 600 post-menopausal women were analysed for their capsular type, antimicrobial resistance and genetic relatedness (multilocus sequence typing, MLST).

Results

The colonization rate was 17.8%. Capsular type III was predominant (34.6%), followed by type V (22.4%). The most frequent sequence type (ST) was 19 (23.3%), followed by 23 (18.7%), 1 (16.8%) and 17 (12.1%). Isolates were assembled into three phylogenetic groups from ST-19, ST-23 and ST-17 founders. All isolates were susceptible to penicillin, whereas resistance to erythromycin and clindamycin was recorded in 23.4% and 20.6% of isolates, respectively.

Conclusions

In our setting, the GBS colonization rate in postmenopausal women is similar to that reported in others populations studied. The population structure of these isolates is highly diverse and contains different STs. These data can contribute to the future development of a polysaccharide vaccine for preventing GBS infection in older adults.

Introduction

Streptococcus agalactiae (group B streptococci, GBS) is the most common etiologic agent of neonatal sepsis [1]. Severe GBS infections are increasingly recognized in adults, mainly in the elderly and in individuals compromised by underlying medical conditions, with reported incidence rates ranging from 4.4 to 23 cases per 100,000 adults [2], [3], [4], [5].

The incidence is higher in patients over the age of 60 years. Primary bacteraemia is the most frequent form of invasive GBS disease, followed by skin and soft-tissue infection, pneumonia and urinary tract infections [3], [4], [5]. The prevalence of colonization reported among healthy elderly adults (20–25%) is similar to that among women of child-bearing age [3], [6].

The incidence of neonatal early onset GBS infections has nose-dived since the generalized use of intrapartum antibiotic prophylaxis in GBS-colonized pregnant women [7]. In contrast, there are no strategies to prevent GBS infection in infants aged over 7 days (late-onset GBS disease) or in adult patients [8], and several studies have reported an increase in the rate of GBS invasive infections among adults over the past few years [2], [9], [10].

The most promising approach for the prevention of GBS-induced invasive disease is the development of an effective vaccine to prevent infection not only in neonates but also in the elderly [4], [11], [12].

Numerous studies have analyzed the variability of colonization by GBS, but most have focused on pregnant women [13], and only a few have investigated the prevalence of colonization among non-pregnant adults [3], [6]. Investigation of the distribution of capsular serotypes and sequence types (STs) among GBS infection strains in neonates and pregnant women has revealed strong differences between these populations, suggesting that some GBS lineages are more prone to cause disease in neonates than in the women. Fewer data are available on the serotypes and MLSTs of strains colonizing the elderly and causing infections in this population. The objective of this study was to assess the GBS colonization rate and GBS antibiotic resistance profile in post-menopausal women in our area, using capsular serotyping and MLST to study possible correlations between capsular types and clonal complexes of GBS colonizing isolates.

Section snippets

Methods

The study was approved by the ethics committee of Virgen de las Nieves University Hospital in Granada (Southern Spain) in April 2010. Sample size calculation was performed to get a 3% accuracy, with a confidence interval 95% and assuming a prevalence of colonization GBS in adults 15% [14] Six hundred consecutive post-menopausal women attending the Emergency Department of the hospital for non-infectious conditions between March 2011 and February 2012 were enrolled in the study (none of them

Results

GBS were recovered from 107 (17.8%) out of the 600 vaginal-rectal specimens studied. The distribution of capsular types is shown in Table 1.

The most frequent types were Ia, III and V, which together accounted for 77.6% of strains. None of the isolates belonged to types VI, VII, VIII or IX. In one case (0.9%), the serotype of the strain could not be determined. The proportion of strains non-typeable by serological methods was not determined in our study, which exclusively used molecular capsular

Discussion

There has been little research on the prevalence of GBS colonization in post-menopausal women, which was found to be 17.8% in the present study, slightly higher than the prevalence of 15.9% detected in pregnant women in the same area between 2009 and 2011 [20].

The distribution of capsular types was similar in both population groups, with serotype III being the most frequent [20]. However, in comparison to the distribution generally reported in colonized pregnant women in Europe, we found a

Conflicts of interest

The authors declare no conflict of interest.

Funding

The authors declare funding received by University Hospital Virgen de las Nieves (Granada) in study design; in the collection, analysis and interpretation of data for this article.

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