Yes, bacteria can grow in coffee makers. In fact, coffee makers are often a breeding ground for bacteria because they are warm and moist, two conditions that bacteria need to thrive. The most common type of bacteria found in coffee makers is Pseudomonas aeruginosa, which can cause infections in people with weakened immune systems. To prevent bacterial growth in your coffee maker, be sure to clean it regularly with soap and water. You should also descale it every few months to remove any build-up of minerals that could provide a food source for bacteria.