生物膜（15）_与宿主共存

Researchers often note that, once biofilms are established, planktonic bacteria may periodically leave the biofilm on their own. When they do, they can rapidly multiply and disperse. There is a natural pattern of programmed detachment of planktonic cells from biofilms. This means that biofilms can act as what Costerton refers to as “niduses病源” of acute infection. Because the bacteria in a biofilm are protected by a matrix, the host immune system is less likely to mount a response to their presence.²⁷

But if planktonic bacteria are periodically released from the biofilms, each time single bacterial forms enter the tissues, the immune system suddenly becomes aware of their presence. It may proceed to mount an inflammatory response that leads to heightened disease symptoms. Thus, the periodic release of planktonic bacteria from some biofilms may be what causes many chronic relapsing infections.

浮游细菌首先从生物膜内游出，沾黏新的区域。免疫系统对生物膜识别度低，但对出来的浮游细菌识别高，马上用细胞因子引发炎症。人类就用药杀死刚出来的浮游细菌。这就是很多慢性病反复发作原因。

As Matthew R. Parsek of Northwestern University describes in a 2003 paper in the Annual Review of Microbiology, any pathogen that survives in a chronic form benefits by keeping the host alive.²⁸ After all, if a chronic bacterial form simply kills its host, it will no longer have a place to live. So according to Parsek, chronic infection often results in a “disease stalemate疾病僵局” where bacteria of moderate virulence are somewhat contained by the defenses of the host. The infectious agents never actually kill the host, but the host is never able to fully kill the invading pathogens either.

为了生物膜为了与宿主共存，病原体并未真正杀死宿主，宿主也没有根本性杀死病原体。于是病原体与宿主陷入僵局。

Parsek believes that the optimal way for bacteria to survive under such circumstances is in a biofilm, stating that “Increasing evidence suggests that the biofilm mode of growth may play a key role in both of these adaptations. Biofilm growth increases the resistance of bacteria to killing and may make organisms less conspicuous to the immune system…. ultimately this moderation of virulence may serve the bacteria’s interest by increasing the longevity of the host.”