This page of The Last of Us game guide contains information on how to kill a bloater. Those monsters are the largest and the most durable type of infected in the game. We advise on how to defeat bloaters during mandatory encounters with those monsters.
If possible, a better solution is to simply sneak by the bloater or run away in case of detection. This will decrease che chances of you dying and will save you a lot of valuable resources.
A bloater appears for the first time during High School Escape stage. Those monsters will appear in more difficult encounters in later parts of the game.
A bloater is a very powerful enemy that can throw exploding spores. You will quickly die if you stand in the poisonous substance for too long, which is why you should try to run around as much as possible.
During the encounter, pay attention to the runners accompanying the bloater. Try to take them out as quickly as possible.
Focus your attacks on the bloater once all of the "regular" infected are gone. It is worth to hide behind cover and try to hit the enemy with a Molotov cocktail. If you are successful, the enemy will be set on fire, becoming defenses for several seconds. You can then shoot the enemy several times and finish off with a bomb.
If the bloater manages to survive your Molotov cocktail and bomb attacks, or if you do not have these items in your inventory at all, take single shots aimed at the enemy and then quickly run away to avoid getting hit by its spores. You cannot allow the bloater to approach you in melee range, as it will result in a quick death of the protagonist.