División de Investigación en Salud y División de Auxiliares de Diagnóstico, Unidad Médica de Alta Especialidad Hospital de Especialidades No. 25, Instituto Mexicano del Seguro Social, Monterrey, Nuevo León, México.
Laboratorio de Inmunología y Virología, Facultad de Ciencias Biológicas, Universidad Autónoma de Nuevo León, San Nicolás de los Garza, Nuevo León, México.
PLoS One. 2022 Mar 16;17(3):e0264273. doi: 10.1371/journal.pone.0264273. eCollection 2022.
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.
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.
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).
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.
B 群链球菌（GBS）可导致孕妇和产褥期妇女感染，并导致新生儿侵袭性感染。lmb、cylE、scpB 和 hvgA 基因与 GBS 的毒力增加有关，并且已经在不同地区鉴定出了超毒力克隆。此外，已经报道了 GBS 对大环内酯类和林可酰胺类抗生素的耐药性增加，因此了解抗生素耐药模式可能对于预防和治疗 GBS 感染是必要的。本研究旨在鉴定与墨西哥东北部孕妇 GBS 定植相关的毒力基因和抗生素耐药性。
35-37 周妊娠的孕妇进行直肠阴道拭子采样。一个拭子接种于含庆大霉素和萘啶酸的 Todd-Hewitt 肉汤中，另一个拭子接种于 LIM 富集肉汤中，第三个拭子浸入运输培养基中。所有样本均经孵育后进行次代培养，对有或无溶血的可疑菌落进行分析，通过革兰氏染色、触酶试验、马尿酸水解试验、CAMP 试验和在显色培养基中孵育来确认 GBS 的鉴定。我们使用乳胶凝集试验来确认和血清型 GBS 分离株。通过 Vitek 2 和药敏纸片扩散法评估抗生素耐药模式。对一些定植母亲的新生儿进行脐周、直肠和鼻咽拭子采集。对所有定植的孕妇及其新生儿进行为期三个月的随访，以评估与 GBS 相关的疾病发展情况。使用全基因组测序获得所有 GBS 分离株的基因组草图。此外，使用 BRIG 进行生物信息学分析，以鉴定编码荚膜多糖和毒力因子的基因，使用 CARD 数据库鉴定抗生素耐药基因。
我们在 1154 名孕妇中发现了 17 名 GBS 定植的孕妇（1.47%）。在 6 名采样的新生儿中未发现定植，孕妇和新生儿均未发现与 GBS 相关的并发症。3 株为血清型 I，5 株为血清型 II，3 株为血清型 III，4 株为血清型 IV，2 株为血清型 V。确定了 10 种不同的毒力基因谱，其中 scpB、lmb、fbsA、acp、PI-1、PI-2a、cylE 最为常见（3/14，21%）。鉴定的毒力基因包括 scpB、lmb、cylE、PI-1、fbsA、PI-2a、acp、fbsB、PI-2b 和 hvgA。我们发现 65%（11/17）的分离株对四环素耐药，41%（7/17）对克林霉素中介耐药，23.5%（4/17）对氨苄西林耐药性降低。在 79%（11/14）的分离株中发现了与四环素耐药相关的 tetM 基因，在 7%（1/14）的分离株中发现了与大环内酯类耐药相关的 mel 和 mefA 基因。
定植率低且母婴传播未发生表明，在该人群中有意寻找 GBS 定植是没有意义的。我们的结果还表明，应根据危险因素指导使用产时抗生素预防。检测到编码毒力因子的基因的菌株意味着具有致病潜力的克隆在该地区循环。另一方面，不同抗菌类别的抗生素敏感性降低的鉴定表明，充分了解耐药模式对于预防和治疗围产期 GBS 感染非常重要。
