School of Public Health, Postgraduate Institute of Medical Education & Research, Chandigarh, India.
Indian J Med Res. 2011 Jun;133(6):674-80.
BACKGROUND & OBJECTIVES: Rheumatic fever (RF)/rheumatic heart disease (RHD) caused by Group A streptococcus (GAS) are more prevalent in north India as compared to the western world, where invasive diseases are common. This could be due to variation in the virulence of GAS in different geographic locations. Hence, we studied the virulence potential of GAS isolated from the throat of children from north India.
Fifty GAS isolated consecutively, from children with mild pharyngitis (20), severe pharyngitis (24) and asymptomatic pharyngeal carriers (6), were characterized by emm typing and opacity factor (OF). Adherence and internalization of GAS in HEp-2 cells and opsonophagocytosis in convalescent serum samples were studied.
Twenty emm types, six sequence types, and one non-typeable GAS were circulating in the community. emm type 74, 11, 68, StI129 and NS292 were most prevalent. Twenty seven (54%) GAS isolates were OF negative. Sixty five per cent of the most prevalent emm types were OF negative indicating their rheumatogenic potential. Adhesion of GAS ranged from 0.1 to 100 per cent. Forty eight per cent of GAS were highly adherent. Invasion of GAS in HEp-2 cells ranged between 0 to 30 per cent. Only 20 per cent isolates exhibited highest invasion. GAS were opsonophagocytosed with highly divergent efficiency ranging from 0 to 91.7 per cent. Nineteen GAS were not opsonophagocytosed and 15 multiplied during the assay. Isolates of the same emm type also varied in their virulence potential.
INTERPRETATION & CONCLUSIONS: GAS isolates from the throat of children from north India belonged to several emm types, majority were OF negative, excellent adherents but poor invaders. This explains why throat infections in these children tend to lead to ARF/RHD rather than invasive diseases. A few isolates exhibiting high invasion efficiency indicate that GAS throat cultures can also lead to invasive diseases.
由 A 组链球菌（GAS）引起的风湿热（RF）/风湿性心脏病（RHD）在印度北部比西方更为普遍，而西方常见的是侵袭性疾病。这可能是由于不同地理位置的 GAS 毒力存在差异。因此，我们研究了印度北部儿童咽喉分离的 GAS 的毒力潜力。
连续分离 50 株来自患有轻度咽炎（20 例）、重度咽炎（24 例）和无症状咽携带者（6 例）的儿童的 GAS，通过 emm 分型和不透明因子（OF）进行特征描述。研究 GAS 在 HEp-2 细胞中的黏附和内化以及恢复期血清样本中的调理吞噬作用。
社区中循环着 20 种 emm 型、6 种序列型和 1 种非定型 GAS。emm 型 74、11、68、StI129 和 NS292 最为流行。27 株（54%）GAS 分离株为 OF 阴性。65%最流行的 emm 型为 OF 阴性，表明其具有风湿性潜力。GAS 的黏附率为 0.1%至 100%。48%的 GAS 高度黏附。GAS 在 HEp-2 细胞中的侵袭率为 0%至 30%。只有 20%的分离株表现出最高的侵袭性。GAS 的调理吞噬作用效率差异很大，范围为 0%至 91.7%。19 株 GAS 不能被调理吞噬，15 株在检测过程中增殖。同一 emm 型的分离株其毒力潜力也存在差异。
来自印度北部儿童咽喉的 GAS 分离株属于几种 emm 型，大多数为 OF 阴性，是优秀的黏附剂，但侵袭性差。这解释了为什么这些儿童的咽喉感染往往导致 ARF/RHD，而不是侵袭性疾病。少数分离株表现出高侵袭效率表明，GAS 咽喉培养也可导致侵袭性疾病。
