Mycobacterium Marinum,may be a rare infectious bacteria but I can assure you it is very serious. Many of you know me as one of the oldest guys in the hobby/business. Set up my first SW aquarium in 1966 after 20 years in FW. Yup I'm that old, 79+, you know pushing 80. When I came down with a red streak shooting up my arm, my doctor said, blood poisoning, and treated me for that. During a follow up visit I showed him several rather large red bumps forming, two on the back of my hand, one on my forearm, one on the inside of my elbow, and one on my bicep. He didn't have a clew as to what they were and set another appointment for a week later. By that appointment the bumps were clearly like giant pimples that were seeping pus. The doctor called in other doctors in the clinic to get opinions. Pictures were taken, the open sores were probed with Q-tips and the resultant pus was put into several petri dishes for culture to ID the bacteria. The cultures were negative for any bacteria. They were scratching their brains. I was getting quite worried. The sores were growing in diameter. Did I mention they hurt like hell when touched.
I went in a couple of days later with the sores open, leaking pus, and obvious tissue devastation beneath the skin surface. This was obviously getting serious, it was a flesh eating bacteria. ONE of the observing doctors asked me if I had anything to do with aquariums. I said yes, they were my hobby. He said, "Mycobacterium Marinum"! This time when they cultured the swabs they put the petri dish into a heated chamber at body temp and the little jerks blossomed into a healthy living cultured ID'd as Mycobacterium Marinum. As it turns out Mycobacterium Marinum is a tough to get rid of bacteria resistant to antibacterial drugs. I don't remember the drug I was on but at that time they were $1 ea and I was taking 2 - 4 times a day, $240 per month. After a couple of months it was reduced to 4 a day until the pustules disappeared, healed.
Long ordeal, nothing to joke about. The guy with the lung infection could easily have died.
Point here is if you have something going on and your doctor can't ID the bacteria by culture, REMEMBER - Mycobacterium Marinum - must be cultured at body temp.