You’re right, sometimes it is potentially dangerous! The bacteria we use can be deadly if they infect us and aren’t treated. Occasionally we grow up large amounts of the bacteria – for example to make stocks for future experiments – and here we have to be really careful.
There are lots of precautions in place to keep us safe though. The main one is that we work in a specially designed lab. This lab always has air flowing through it, and up into the safety cabinets that we do our experiments. The infectious bacteria are very small and the danger comes mainly from breathing in little droplets of liquid with the bacteria inside. These droplets would be very lightweight though, so the air flow makes sure droplets are always carried away from us! We wear two pairs of thin gloves when we work in these cabinets as well, so if any bacteria gets on our hands, we can take off a pair and still be wearing gloves underneath. We also wear a disposable gown, and plastic coverings to go on our shoes – to stop and bacteria getting on our clothes and being taken outside of the lab. And we wash our hands very throughly after every experiment! Lastly, we make sure to use strains of bacteria that we know we can treat with strong antibiotics in case there is an accident, although we can’t always be sure of this when we use samples we take from patients infected with other types of TB bacteria.
All of these safety precautions mean that normally I don’t worry too much when I do my experiments, although I know I always have to be careful!