Bacterial Infections in Cats


Methicillin Resistant Staphylococcus aureus infections of cats

Veterinarians have been lucky over the last decade or so in not having to deal with methicillin resistant staphylocccus aureus (MRSA) infections very often. It is likely that this situation will change over the next few years as MRSA infections are being reported more commonly in pets. In most cases these infections are thought to be contracted by the pet due to association with an infected human but it also appears that pets can be a reservoir for the infection in households and much more rarely a source of infection for previously uninfected humans. There are two forms of MRSA that are recognized in people, community acquired MRSA and hospital acquired MRSA. In general, hospital acquired MRSA is much worse and can lead to organ failure and death fairly rapidly, despite treatment, in some patients. So far, the pet cases that have been reported appear to be the community acquired form of MRSA. Cats infected with MRSA may have difficult to treat abscesses or lymph node swelling not explained by other diagnoses. Dogs have more of a tendency to have inapparent infections affecting the nasal passages but can have severe abscesses or other signs of an infectious process. At the present time the main thing to remember about MRSA and pets is that they are usually infected by a family member who has the disease but that it may be difficult to clear it from the household without treating pets who are infected. So if you or someone you have close contact with is diagnosed with MRSA and it is hard to eliminate, you may want to be sure that a pet is not harboring the Staph bacteria and keeping the infection going in the household. It is also important to keep in mind that most Staph infections in dogs and cats are caused by Staphococcus intermedius, so just the word "staph" should not set off alarm bells immediately. Dr Mike Richards, DVM 9/02/2006


Campylobacteriosis causes gastrointestinal disease in many species of animals and is considered to be a zoonotic disease, usually associated with poor sanitation practices around infected dogs or cats. The bacteria is a gram negative rod (corkscrew shaped) that is usually highly motile. It can be cultured using anerobic techniques but is present in many normal animals so it is hard to determine for sure if it is the disease agent based on culture results. It can cause no disease (asymptomatic carriers) to pretty severe diarrhea that can be hemorrhagic. Vomiting can also occur. The disease usually lasts about 2 weeks but some chronic cases are reported. It is unclear how quickly reinfection can occur. It most commonly affects young kittens and immune compromised cats. Several antibiotics are effective against campylobacter in most cases. These include: enrofloxacin at 5mg/kg bid x 5 days, doxycycline 5mg/kg q12 to 24 hours x 15 to 21 days, erythromycin 10mg/kg every 8 hours x 10 to 14 days. Most of the commonly used antiseptics will kill campylobacter in the environment. Keeping the environment as dry as possible is helpful, too --- so using paper towels and antiseptic spray to clean cages is better than hosing them out, for instance. I hope this is helpful. Mike Richards, DVM 1/24/2003


Question: Dear Dr. Richards:

First, I apologize for probably not spelling "meningitis" correctly! I wrote to you last January, and the help and advice you gave me regarding Zithromax RX for cats has saved not only many of my cats, but by passing it on to my local vets, saved many, many other cats, and I can't thank you enough for that.

Unfortunately a few of the cats died from menengitis. This was confirmed by a cat I sent to Michigan State Univ. But I don't really understand how they contract it or if there is anything I can do to prevent it. Some of the cats had recovered (and I thought completely) from inner ear or upper respiratory ailments, then would later show neurological symptoms and die. A couple of the cats died within 36 hours since I noticed a problem, 3 I had to have euthanized. Just yesterday, after 6 months of no more deaths, a cat who I brought through an inner ear infection a month ago, died. He had the same neurological symptoms. Last weekend he was playful and fine, and then Tuesday I noticed changes and late last night he died.

I of course, keep asking myself, what have I missed? Got him past the inner ear and upper respiratory with Clavamox and Prednisone ( I use Zithromax as the "big guns").

Any information would be deeply appreciated. When these cats get sick, I sit with them all through the night and as much of the day as I can and it is heartbreaking to see them go through this.

Thank you so much for this wonderful service you are providing. There is no worse feeling than that of being helpless when you see suffering. Knowing about the Zithromax did more than words can convey.

Respectfully, Christina

Answer: Christina-

I have tried to research this topic for you to see if there was a particularly likely cause of the meningitis that was diagnosed at Michigan State. I think that you best option might be to ask your veterinarian to check with the pathologist to get his or her opinion of the most likely underlying cause and to ask whether the meningitis seemed like the primary problem or if it might have occurred as another disease progressed to the point that it was affecting all of the body's systems. In some cases it simply isn't possible to make a diagnosis and this may not be as helpful, but it is really worth asking, at least.

The most common causes of meningitis in cats are probably feline infectious peritonitis virus and toxoplasmosis. These are possible problems whenever cats live in multi-cat households, so they are probably the prime suspects. Cats can develop meningitis as a result of rabies and even meningitis as a reaction to rabies vaccination is reported, but I can't remember seeing a case of this. I have heard that roundworm migration can lead to meningitis in some cats and there is evidence that many cats do not develop the strong immunity to these worms that dogs develop with age, so that seems like a possible problem, as well. Routine deworming (once or twice a year) is probably a good idea in a multi-cat household. Cats do get several forms of bacterial meningitis but these are uncommon. Fungal infection, especially cryptococcosis, may cause meningitis but is also uncommon.

In your cats there may be a higher chance for bacterial meningitis than in the average housecat. Bacterial meningitis usually occurs because of bite wounds or infections that occur near the spinal cord or in areas in which spread into the meninges is possible, such as inner ear infections or severe sinus infections. I think that this would be an unusual problem and not one that would be likely to affect more than a few cats in your household over time, though. If you persistently see meningitis over time it would be a really good idea to look for an underlying cause that might be contributing to the cat's susceptibility, such as feline leukemia virus infection or feline immunodeficiency virus infection. We do seem to see really bad upper respiratory infections in some groups of cats that do not have these viruses present, though. I am guessing that the cats in some multiple cat households pass bacterial infections back and forth and sometimes these become stronger due to the continued opportunity to grow.

Feline infectious peritonitis (FIP) can be hard to rule in or rule out in many cases. There is not yet a reliable blood test for this disease and while it can usually be diagnosed during a post mortem examination this is not always true. It may be a good idea to consider having the pathologists at MSU examine another cat, if you see a similar case in the future.

The last possibility is some sort of toxin. I can't actually think of one that would lead to these signs but it would be hard to rule that possibility out with repeated occurrences of problems in one household. It is something to think about but not something that is likely, at all.

I guess that I am leaning towards the bacterial meningitis secondary to inner ear infection or sinusitis and that these problems are most likely to be caused as a secondary problem due to the upper respiratory viruses. It might help to consider intranasal vaccination for rhinotracheitis and calcivirus, since there are some reports of this helping to control the infections better in multi-cat households. I haven't actually tried this approach personally, though -- so I really don't have any idea how much more effective it might be.

I wish that I could help you more with this.

Mike Richards, DVM 1/9/2002 L form Bacteria and multiple abscesses

Question: Dear Dr. Richards,

I'm a new subscriber to your VetInfo newsletter. My wife and I came across the website while researching a puzzling illness one of our cats has. The website mentions the "L-form" bacteria as a possible cause of multiple abscesses in cats. Let me give you a brief case history and perhaps you can suggest if the "L-form" is what's causing our cat's problem:

- "Whitey" is a healthy (at least up until now) 5-yr old male short-hair (pure white), neutered, all shots up to date. - Three weeks ago his left rear foot appeared swollen. Mainly one of the toes. - It formed an abscess, the vet drained it and prescribed Clavamox and Antirobe. - The toe finally healed up. - Within a week, another abscess formed further up the leg, the vet opened it and inserted a drain. - Now that that's on the mend, other smaller abscesses are forming up and down the leg.

Fever was 104 at first, now closer to 103 F. White count around 8000, high the vet says, but not as high as they expected. Cultures for aerobic and anaerobic bacteria were negative. Inspection of the puss under a microscope was also negative.

The head vet at the local animal hospital is now suspecting a fungus. I have printed our the VetInfo article on L-Form. Does that sound like what's going on? The vet says cancerous lesions don't move around.

We'd appreciate any ideas you can suggest. Vet bills are probably approaching $800 and the poor cat is soooo tired of being sick! Our local vet is top notch, but we need all the help we can get.

Thanks so much. Charles

Answer: Charles- L-form bacteria are not a common problem, but they are one of the things to think about when there are abscesses that do not respond to the typical antibiotics used for bite wounds and sterile cultures from these wounds. These bacteria do not grow in normal cultures so they are not found, even though they are present. I am not sure that I completely understand L-form bacteria, but I think they are considered to be a sort of mutant bacteria that may be produced after treatment with an antibiotic, such as penicillin, that damages cell walls. Since these can't be easily cultured, the usual tactic is to put cats on doxycycline or some other tetracycline, which usually will kill this bacteria.

There are a several other odd bacterial infections that do not grow well on normal cultures and have to be considered. We see Mycobacterium marinum here in the tidewater area of Virginia and other mycobacterium species, such as M. fortuitum and M chelonei can also cause abscesses resistant to antibiotic treatment. These are organisms related to Mycobacterium tuberculosis, which you might recognize as the cause of tuberculosis, so sometimes looking for a lung infection through X-rays can be helpful in determining if these bacteria are present. Sometimes the organism can be seen on smears of the exudate using special stains (so a degree of suspicion for the organism is necessary). These do sometimes respond to treatment with enrofloxacin or other fluorquinolone antibiotics and sometimes to sulfa-trimethoprim combinations (hard to use in cats because they cause excessive salivation when administered) and gentamicin, an injectable antibiotic. I am not sure if isoniazid or rifampin, used for tuberculosis, would be helpful, or not. So far, we have not had to resort to these as we see these infections most commonly in dogs and have been able to get results using one or the other of the previously mentioned antibiotics.

Actinomyces and nocardiosis may be hard to find with normal culture techniques, too. Nocardiosis can usually be identified by looking for the organism in smears from the abscessed area, though. At least that is what the books say. I can't recall ever finding it but it is more common farther south and in the Southwest. It is supposed to respond best to sulfa/trimethoprim combination antibiotics. Actinomyces also shows up in smears from the abscessed site. We have seen this organism. We do not routinely do anaerobic cultures on our initial cultures of abscesses and it is necessary to do this in order to grow Actinomyces. These bacteria sometimes respond to doxycycline but are usually treated with penicillins or penicillin derivatives.

In our area, I think that these less common bacterial infections are more likely than fungal infections, but I have heard that fungal infections are more common just a little south of us, which would be closer to you, so your vet may be thinking a fungus is more likely where you are.

Since there isn't a reliable test for L-form bacteria they are usually eliminated as a possibility by treating for the possibility they are there, using doxycycline or tetracyclines, which are not among the first choice antibiotics for bite wounds in cats.

We have seen moving draining tracts from foreign bodies in several patients, as well. The most frustrating one was a dog that lived in a boat construction facility and who got a small piece of fiberglass in it's paw. We treated an abscess there, including surgical exploration and found nothing. We treated several more abscesses before finally finding the piece of fiberglass just behind the dog's shoulder blade. I am certain it was the same foreign body that just moved from the toe to the shoulder as there was a clear path of abscessation along the way. If your cat hangs around a workbench or other place problems like this might occur, it would be worth considering, too.

Good luck with this. Abscesses that recur or that don't respond to treatment can be very frustrating but usually it is possible to find a solution, eventually. It doesn't hurt to take X-rays to rule out an underlying osteomyelitis (bone infection), if that hasn't been done, or if it was done early in the diagnostic process.

Mike Richards, DVM 9/23/2000

Last edited 01/17/08


Michael Richards, D.V.M. co-owns a small animal general veterinary practice in rural tidewater Virginia. Dr. Richards graduated from Iowa State University's College of Veterinary Medicine in 1979, and has been in private practice ever since. Dr. Richards has been the director of the PetCare Forum...