Department of Medical Microbiology, National Polio Laboratory, University of Zimbabwe College of Health Sciences, P. O. Box A178, Avondale, Harare, Zimbabwe.
Faculty of Health Sciences, Institute of Infectious Diseases and Molecular Medicine, University of Cape Town, Room No. 3.22 Falmouth Building, Anzio Road, Observatory, Cape Town, 7925, South Africa.
BMC Infect Dis. 2021 Jan 28;21(1):125. doi: 10.1186/s12879-021-05820-6.
Streptococcus agalacticae (Group B Streptococcus, GBS) is one of the most important causative agents of serious infections among neonates. This study was carried out to identify antibiotic resistance and virulence genes associated with GBS isolated from pregnant women.
A total of 43 GBS isolates were obtained from 420 vaginal samples collected from HIV positive and negative women who were 13-35 weeks pregnant attending Antenatal Care at Chitungwiza and Harare Central Hospitals in Zimbabwe. Identification tests of GBS isolates was done using standard bacteriological methods and molecular identification testing. Antibiotic susceptibility testing was done using the modified Kirby-Bauer method and E-test strips. The boiling method was used to extract DNA and Polymerase Chain Reaction (PCR) was used to screen for 13 genes. Data was fed into SPSS 24.0.
Nine distinct virulence gene profiles were identified and hly-scpB-bca-rib 37.2% (16/43) was common. The virulence genes identified were namely hly 97.8% (42/43), scpB 90.1% (39/43), bca 86.0% (37/43), rib 69.8% (30/43) and bac 11.6% (5/43). High resistance to tetracycline 97.7% (42/43) was reported followed by 72.1% (31/43) cefazolin, 69.8% (30/43) penicillin G, 58.1% (25/43) ampicillin, 55.8% (24/43) clindamycin, 46.5% (20/43) ceftriaxone, 34.9% (15/43) chloramphenicol, and 30.2% (13/43) for both erythromycin and vancomycin using disk diffusion. Antibiotic resistance genes among the resistant and intermediate-resistant isolates showed high frequencies for tetM 97.6% (41/42) and low frequencies for ermB 34.5% (10/29), ermTR 10.3% (3/29), mefA 3.4% (1/29), tetO 2.4% (1/42) and linB 0% (0/35). The atr housekeeping gene yielded 100% (43/43) positive results, whilst the mobile genetic element IS1548 yielded 9.3% (4/43).
The study showed high prevalence of hly, scpB, bca and rib virulence genes in S. agalactiae strains isolated from pregnant women. Tetracycline resistance was predominantly caused by the tetM gene, whilst macrolide resistance was predominantly due to the presence of erm methylase, with the ermB gene being more prevalent. Multi-drug resistance coupled with the recovery of resistant isolates to antimicrobial agents such as penicillins indicates the importance of GBS surveillance and susceptibility tests. It was also observed that in vitro phenotypic resistance is not always accurately predicted by resistance genotypes.
无乳链球菌（B 群链球菌，GBS）是导致新生儿严重感染的最重要病原体之一。本研究旨在鉴定从感染 HIV 的孕妇和未感染 HIV 的孕妇的阴道样本中分离出的 GBS 菌株的抗生素耐药性和毒力基因。
从津巴布韦奇通圭扎和哈拉雷中央医院的 13-35 周妊娠的 HIV 阳性和阴性孕妇的 420 份阴道样本中获得了 43 株 GBS 分离株。使用标准细菌学方法和分子鉴定检测进行 GBS 分离株的鉴定试验。采用改良 Kirby-Bauer 法和 E 试验条进行抗生素敏感性试验。采用煮沸法提取 DNA，采用聚合酶链反应（PCR）筛选 13 种基因。数据输入 SPSS 24.0。
鉴定出 9 种不同的毒力基因谱，其中 hly-scpB-bca-rib 占 37.2%（16/43）。鉴定出的毒力基因分别为 hly 97.8%（42/43）、scpB 90.1%（39/43）、bca 86.0%（37/43）、rib 69.8%（30/43）和 bac 11.6%（5/43）。报告了对四环素的高耐药性 97.7%（42/43），其次是头孢唑啉 72.1%（31/43）、青霉素 G 69.8%（30/43）、氨苄西林 69.8%（30/43）、克林霉素 58.1%（25/43）、头孢曲松 46.5%（20/43）、氯霉素 34.9%（15/43）和红霉素和万古霉素均为 30.2%（13/43）。耐药和中度耐药分离株中的抗生素耐药基因显示出 tetM 97.6%（41/42）的高频率和 ermB 34.5%（10/29）、ermTR 10.3%（3/29）、mefA 3.4%（1/29）、tetO 2.4%（1/42）和 linB 0%（0/35）的低频率。atr 管家基因的阳性结果为 100%（43/43），而移动遗传元件 IS1548 的阳性结果为 9.3%（4/43）。
本研究显示，从孕妇中分离出的无乳链球菌菌株普遍存在 hly、scpB、bca 和 rib 毒力基因。四环素耐药主要由 tetM 基因引起，而大环内酯类耐药主要由 erm 甲基化酶引起，ermB 基因更为普遍。耐多药与青霉素等抗菌药物的耐药分离株的恢复表明，GBS 监测和药敏试验非常重要。还观察到，体外表型耐药性并不总是能准确预测耐药基因型。
