Differential response of lymphocytes to biofilm derived Streptococcus mitis cells

0120 Differential response of lymphocytes to biofilm derived Streptococcus mitis cells
N. PARAHITIYAWA, N. BANDARA, J.Y.Y. YAU, R. WATT, W.K. LEUNG, L. JIN, and L.P. SAMARANAYAKE, The University of Hong Kong, Hong Kong SAR, China

Biofilms, or surface attached microbial communities, are responsible for many localized and systemic diseases especially among immunocompromised hosts. Cells dislodged from such biofilms may enter the systemic circulation and have the propensity to invade distant organs and tissues. It is well recognised that biofilms are highly resistant to antimicrobials compared with their free-floating planktonic counterparts. Yet, how the cellular defences of the body interact with biofilm derived bacteria, is ill understood.

Objectives: This preliminary study compared the response of peripheral blood lymphocytes (PBL) to the biofilm derived (BF) and, planktonic cells (PC) of Streptococcus mitis, an organism commonly seen in bacteraemic states.

Methods: Human PBL were harvested from two systemically healthy adults using the Ficoll Paque layering method. Biofilms and planktonic cultures of Streptococcus mitis were grown in polystyrene well plates and culture tubes under standard conditions. The response of harvested lymphocytes to bacterial assault was measured at different time points using the XTT reduction assay.

Results: Biofilm growth was evident at 24 and 48 hours. At both time points, the XTT reduction response of PBL-BF and PBL-PC was significantly higher than PBL alone. For the 24 hour old cultures, the time-curve for XTT reduction assays showed that PBL-BF response was consistently lower than that for PBL-PC. As time passed the activity reached a plateau but the PBL –BF endpoint activity remained lower than that of PBL-PC. The response was reversed with 48 hour grown cultures where PBL-BF response was higher than PBL-PC response.

Conclusion: The data from this pilot experiment suggests that the biofilm constituent cells, particularly the young (24 hrs), stimulate PBL to a lesser extent than the older biofilm cells or their planktonic counterparts. This may explain to some degree their sluggish clearance and persistence in the bloodstream.

0120 淋巴细胞对生物膜来源的链球菌肺炎双球菌细胞的差异性反应

N. PARAHITIYAWA, N. BANDARA, J.Y.Y. YAU, R. WATT, W.K. LEUNG, L. JIN, 及 L.P. SAMARANAYAKE，香港大学，中国香港特别行政区

生物膜，或附着于表面的微生物群落，是许多局部和系统性疾病的成因，尤其是在免疫抑制宿主中。从此类生物膜上脱离的细胞可能进入全身循环，并具有侵犯远端器官和组织的倾向。生物膜相较于其自由浮动的浮游生物，对抗菌剂的抵抗力极强。然而，身体细胞的防御机制与生物膜来源细菌的相互作用仍不甚明了。

研究目标：本初步研究比较了外周血淋巴细胞（PBL）对生物膜来源（BF）和浮游细胞（PC）的链球菌肺炎双球菌的反应。

研究方法：采用Ficoll Paque分层法从两名全身健康的成年人中采集PBL。在标准条件下，于聚苯乙烯培养板和培养管中培养链球菌肺炎双球菌的生物膜和浮游培养物。通过XTT还原法在不同时间点测量收集到的淋巴细胞对细菌攻击的反应。

研究结果：在24小时和48小时均观察到生物膜的生长。在这两个时间点，PBL-BF和PBL-PC的XTT还原反应均显著高于单独的PBL。对于24小时培养物，XTT还原反应的时间曲线显示，PBL-BF的反应始终低于PBL-PC。随着时间的推移，活性达到平台期，但PBL-BF的终点活性仍低于PBL-PC。在48小时培养的细胞中，反应情况相反，PBL-BF的反应高于PBL-PC的反应。

研究结论：本初步实验的数据表明，生物膜组成部分的细胞，尤其是年轻的（24小时）细胞，对PBL的刺激程度低于较老的生物膜细胞或其浮游生物。这可能在一定程度上解释了它们在血液中的清除缓慢和持久性。