Exposición a Estreptococo del grupo B en mujeres mexicanas en edad reproductiva

Genomic analysis of virulence factors and antimicrobial resistance of group B Streptococcus isolated from pregnant women in northeastern Mexico

Introduction

Group B Streptococcus (GBS) causes infections in women during pregnancy and puerperium and invasive infections in newborns. The genes lmb, cylE, scpB, and hvgA are involved with increased virulence of GBS, and hypervirulent clones have been identified in different regions. In addition, increasing resistance of GBS to macrolides and lincosamides has been reported, so knowing the patterns of antibiotic resistance may be necessary to prevent and treat GBS infections. This study aimed to identify virulence genes and antibiotic resistance associated with GBS colonization in pregnant women from northeastern Mexico.

Methods

Pregnant women with 35–37 weeks of gestation underwent recto-vaginal swabbing. One swab was inoculated into Todd-Hewitt broth supplemented with gentamicin and nalidixic acid, a second swab was inoculated into LIM enrichment broth, and a third swab was submerged into a transport medium. All samples were subcultured onto blood agar. After overnight incubation, suggestive colonies with or without hemolysis were analyzed to confirm GBS identification by Gram staining, catalase test, hippurate hydrolysis, CAMP test, and incubation in a chromogenic medium. We used latex agglutination to confirm and serotype GBS isolates. Antibiotic resistance patterns were assessed by Vitek 2 and disk diffusion. Periumbilical, rectal and nasopharyngeal swabs were collected from some newborns of colonized mothers. All colonized women and their newborns were followed up for three months to assess the development of disease attributable to GBS. Draft genomes of all GBS isolates were obtained by whole-genome sequencing. In addition, bioinformatic analysis to identify genes encoding capsular polysaccharides and virulence factors was performed using BRIG, while antibiotic resistance genes were identified using the CARD database.

Results

We found 17 GBS colonized women out of 1154 pregnant women (1.47%). None of the six newborns sampled were colonized, and no complications due to GBS were detected in pregnant women or newborns. Three isolates were serotype I, 5 serotype II, 3 serotype III, 4 serotype IV, and 2 serotype V. Ten distinct virulence gene profiles were identified, being scpB, lmb, fbsA, acp, PI-1, PI-2a, cylE the most common (3/14, 21%). The virulence genes identified were scpB, lmb, cylE, PI-1, fbsA, PI-2a, acp, fbsB, PI-2b, and hvgA. We identified resistance to tetracycline in 65% (11/17) of the isolates, intermediate susceptibility to clindamycin in 41% (7/17), and reduced susceptibility to ampicillin in 23.5% (4/17). The tetM gene associated to tetracyclines resistance was found in 79% (11/14) and the mel and mefA genes associated to macrolides resistance in 7% (1/14).

Conclusions

The low prevalence of colonization and the non-occurrence of mother-to-child transmission suggest that the intentional search for GBS colonization in this population is not justified. Our results also suggest that risk factors should guide the use of intrapartum antibiotic prophylaxis. The detection of strains with genes coding virulence factors means that clones with pathogenic potential circulates in this region. On the other hand, the identification of decreased susceptibility to antibiotics from different antimicrobial categories shows the importance of adequately knowing the resistance patterns to prevent and to treat GBS perinatal infection.

Infective endocarditis caused by Streptococcus agalactiae in a native aortic valve, complicated by meningitis and cerebral embolism

We present a case of infective endocarditis associated with community-acquired Streptococcus agalactiae in an immune competent patient. The endocarditis affected the native aortic valve with perforation of the coronary cusp and was complicated by a cerebral embolism. The use of intravenous ampicillin produced a satisfactory clinical and echocardiographic recovery despite not receiving a valve replacement. In addition to reporting an extremely rare case, this paper confirms that the opportune identification of endocarditis caused by S. agalactiae and the selection of appropriate antibiotics can prevent the necessity of cardiac surgery, usually required in such cases.

High-virulence clone of group B streptococci unable to grow at high temperatures is present in serotypes other than type III

Highly virulent clonotypes of serotype III seem to cause much of the perinatal morbidity and mortality attributed to Streptococcus agalactiae (group B streptococci, GBS), One of these clonal types, designated the "high-virulence clone" (HVC), was identified by its inability to grow at 40 degrees C in a chemically defined medium. In the present study, this inability to grow at high temperatures was used as a marker to identify HVC in a sample of 286 Mexican GBS isolates. Forty-three isolates (15%) were identified as belonging to this clone: 15 were invasive isolates, 33 were serotype III (77%), and 10 were of serotypes other than type III (23%). These results demonstrate that HVC is more prevalent in Mexico than previously reported and that this clone is not restricted to serotype III isolates.