Who is responsible for the hotel being bitten by rats?

First of all, you and the hotel are a service contract or a consumption contract.

Secondly, judging from the Law on the Protection of Consumer Rights and Interests, Article 18 of the Law on the Protection of Consumer Rights and Interests stipulates that business operators should ensure that the goods or services they provide meet the requirements of protecting personal and property safety. For goods and services that may endanger personal and property safety, consumers should be given a true explanation and a clear warning, and the methods of correctly using goods or receiving services and the methods of preventing harm should be explained and marked.

Operators of hotels, shopping malls, restaurants, banks, airports, stations, ports, theaters and other places of business shall fulfill their obligations of safety protection for consumers.

Finally, judging from the incident itself, since you were bitten by a mouse in the hotel, as long as you didn't bring the mouse in yourself, the hotel certainly didn't fulfill its obligation to protect personal and property safety and should bear corresponding responsibilities, so it should compensate you for medical expenses and other losses.

PS: Since there are rats, the hotel's hygiene should be unqualified, and the hotel should pay administrative responsibility, and may be fined, closed for rectification and so on.