I haven't had a moment to listen to the recordings, but I will give you my opinion on your question regarding Janny and her possible pneumonia. Is it contagious? It depends. In addition to mycoplasmosis causing lung infections (such as pneumonia), there are dozens of gram positive and gram negative genera of bacteria that can contribute to the development of pneumonia (an infection that caused by bacteria or a virus) in rats and humans. The infection causes inflammation in the lungs which leads to the airsacs at the end of the bronchial tree to become filled with fluid or pus and may affect both lungs (double pneumonia), one lung (single pneumonia) or it can be contained in certain lobes (lobar pneumonia).
Mycoplasma is a sneaky, unusual and nasty little bacteria. It is in the genus of mollicute bacteria, unlike other bacteria that often have a cell well, mycobacterium lack a true cell wall around their cell membranes. This lack of a cell wall actually works to the bacteria's advantage and makes it difficult for antibiotics to penetrate and kill mycobacterium. Most modern antibiotics are amalgamated so that they specifically target and attack via cell wall synthesis but if the bacterium lacks a cell wall to attack, the antibiotic does a pretty crappy job of killing and completely eliminating mollicute bacteria from the body and tissues. This is why macrolide antibiotics like azithromyacin and tetracyclines like doxycycline work really well on mycoplasmosis. The class of these two medications are examples of bacterostatic antibiotics since they work by impeding the growth of bacteria by inhibiting bacterial protein synthesis. This method of blocking protein synthesis disrupts how amino acids bind, basically breaking the amino acid chain and starving the bacteria of energy/food. This in turn slows their growth and starvation eventually kills them off.
Bactericidal antibiotics target and kill by inhibiting cell wall synthesis; a bacteria with a damaged cell wall cannot undergo binary fission and this will cause the bacteria to die. Some examples of bactericidal antibiotics are penicillins (eg amoxicillin) and fluoroquinolones (eg enrofloxicin/baytril). There are also antibiotics that have both bactericidal and bacterostatic activity such as ciprofloxacin, which is also a class of fluoroquinolone. There's even debate as to whether giving a bactericidal antibiotic and bacterostatic antibiotic together can negate the benefit of both antibiotics and make them less effective or render them inactive. However in some situations combinations can be synergistic. For example combining doxycycline (bacterostatic) and baytril (bactericidal) seem to work well together, but combining something like amoxicillin clavanate (bactericidal) and doxycycline (bacterostatic) could potentially buffer the action of amoxicillin clavanate which can make it less effective or may render it ineffective. So it's always a good idea to speak to a veterinarian before mixing and matching different antibiotics since doing so could cause the medication to be ineffective or it may lead to antibiotic resistance.
Okay, enough about how antibiotics work lecture lol sorry!... so, is pneumonia contagious? If it is caused by a secondary infection (a secondary infection is an infection that occurs during or after the treatment of an active infection) due to an animals resistance that has been compromised or an immunodeficiency created from the stress of the body fighting an active and/or untreated mycobacterium infection, the answer is "possibly".
Secondary infections, like any infection, can be spread through the aspiration of respiratory droplets containing the pathogen (eg streptococcus spp.) or via the mouth and eyes. It's important to remember that the majority of rats carry mycobacterium (mycoplasma, myco) and the only environment you will find mycoplasma-free rats would be in a laboratory setting. With that said, it is safe to assume that Janny and your other girls are all carrying mycoplasma pulmonis and that they all have an active infection (which may or may not display symptoms).
As you know, rats are stoic but very hardy creatures that are incredible at disguising illness for a period of time. Until the infection begins to severely impact their systems (respiratory, cardiovascular, etc. ) we usually won't see many outward signs except for maybe excessive sneezing or nasal congestion. When an infection is this advanced to where we are seeing clear symptoms, we are opening the door to numerous, opportunistic bacterium in an already compromised animal. When this happens it is called a secondary infection.
What ever caused the secondary infection in Janny (if that is the case here), regardless of all of your girls having mycoplasmosis, Janny's infection could possibly be passed to her cage mates via sneezes, food, urine, etc. There's not much you can do to prevent that from occurring and I would strongly advise against anyone separating their rats (ofcourse unless otherwise directed by a veterinarian) since that can cause additional and unwanted stress, exasperating symptoms and advancing the infection.
With all of that said, my advice would be to begin Janny on azithromyacin (have it compounded by Wedgewood at 200mg/ml) and enrofloxicin (baytril). I would also simultaneously treat your other girls with a doxycycline and baytril combination to nip what sounds like an upper respiratory infection before it becomes a lower respiratory infection. Janny and the ladies should be on these meds for 6 to 8 weeks and I would lean more toward 8 weeks over 6.
I hope that this helps for now and I will get back to you after I have a chance to review the videos if I think of any other suggestions! Lots of smooches and scritches to Janny and the girls! ❤