Does deathtouch apply when a creature deals damage to multiple blockers during combat?

Deathtouch causes any amount of damage dealt by the creature with deathtouch to be considered lethal damage (CR 702.2b). This means even 1 point of damage from a deathtouch creature is enough to destroy any creature it damages, regardless of that creature's toughness.

When an attacking creature with deathtouch is blocked by multiple creatures, the attacking player assigns combat damage among the blockers in a chosen order (CR 509.2). The damage must be assigned in order, and normally you must assign enough damage to "kill" each blocker before moving to the next — but because deathtouch makes even 1 damage lethal, you only need to assign 1 damage to each blocker before moving on (CR 510.1d, 702.2b).

This interaction means a deathtouch attacker can efficiently kill multiple blockers simultaneously, since every creature that receives even 1 damage from it will be destroyed (assuming no regeneration, indestructible, or similar effects).

Example: Your 1/1 Snake with deathtouch attacks and is blocked by a 3/3 and a 4/4. You assign 1 damage to the 3/3 and 1 damage to the 4/4. Both are destroyed at end of combat because deathtouch makes even 1 damage lethal to each of them.

Note that deathtouch only applies to damage actually dealt — if a blocker is assigned 0 damage (e.g., due to damage ordering rules), it is not destroyed. The creature must actually receive the damage for deathtouch to trigger destruction.