In Jainism, even microorganisms are living beings (jiva), so killing them is also considered himsa (violence).

But Jain dharma also teaches practical minimisation of harm, not complete impossibility of harm. So the answer is:

1. Principle in theory

• Every life, however small – bacteria, water-bodied beings, nigodas (micro‑organisms) – is a jiva.
• Intentionally killing or carelessly destroying them is paap (bad karma).
• So “Can Jains kill microorganisms?” – Ideally: no. One should avoid and minimise such killing as far as realistically possible.

2. How this works in daily life

In practice, some harm to microorganisms is unavoidable in worldly life (samsar), so Jain conduct focuses on reducing it:

• Boiling and filtering water

Jains are told to drink boiled, filtered water. Boiling does kill many micro‑organisms, but: - unboiled water contains far more living beings - by boiling + filtering, the total number harmed is reduced So this is accepted as a lesser himsa done for survival, with awareness and restraint.

• Food and fermentation

- Fermented foods (old curd, yeast, alcohol, etc.) involve huge growth of microorganisms, so they are mostly discouraged or restricted. - Where something is allowed (like fresh curd in some households), it is with rules like: fresh only, before sunset, not kept long – again to limit microbial life and its destruction.

• Water, soil, farming, etc.

- Harming water-bodied micro‑organisms is called udambhi‑himsa and should be avoided as much as possible. - Traditional Jains avoid farming because ploughing soil kills countless insects and microorganisms.

3. The Jain approach in simple words

• Every microorganism is a soul → killing it is also violence.
• Total zero‑killing is impossible while living a normal life.
• So Jain dharma teaches:

- avoid direct, intentional killing - avoid activities that destroy huge numbers of micro‑organisms (e.g., unnecessary fermentation, wastage, pollution) - when harm is unavoidable for basic survival (drinking, basic cooking, hygiene), do it in the least violent way, with awareness, repentance (pratikraman), and effort to improve.

So: Jains should not “freely” or “casually” kill microorganisms. Where some destruction of them is unavoidable for survival, it is done carefully, to minimize violence and karmic bondage, not to justify it.