Clearly, the fish will only be able to fight back if conditions are improved and all efforts are made to keep the numbers of bacteria as low as possible. So really any anti-bacterial treatments should be seen as supportive treatment for the fish's own immune system and what we are trying to do is to tilt the balance of health back in the fish's favour. There are broadly four treatment methods for bacterial infections. On their own baths are only likely to be effective for relatively minor bacterial infections such as fin rot or situations when just one or two fish have minor ulcerations. This supposes that any underlying problems are resolved or treated.
Baths are unlikely to resolved severe cases.
If there is no sign of healing within a week to ten days a change of treatment is vital. These are specially prepared foods containing antibiotics. In the UK they are only available with a veterinary prescription. While the use of medicated food has obvious advantages, the disadvantages are the slight delay while the food is ordered and processed, very sick fish may not be eating and there is widespread resistance to the most commonly used antibiotics. It is possible to prepare your own medicated food by top-dressing ordinary food with an appropriate antibiotic.