Antibiotic-resistant Bacterial Infections in Cats

PetMD Editorial
May 31, 2010
3 min read
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L-Form Bacterial Infections in Cats

L-form bacterial infections are caused by bacterial variants with defective or absent cell walls. That is, L-form bacteria are defective variations of bacterial cells, which can be almost any type of bacteria. L-forms are different from most other forms of bacteria in the respect that cell walls are an important component of organized cell division. While L-forms are still able to divide, creating more of themselves, they lack the same organizational structure as bacteria with cell walls. L-forms replicate without regard to size, big and small, rather than being of one standard size. They have been found throughout nature, in humans, animals, and plants.

L-form bacteria are formed as a spontaneous variant of bacteria, or when cell wall synthesis is inhibited or impaired by antibiotics (e.g., penicillin), specific immunoglobulins, or lysosomal enzymes that degrade the cell walls. They can be induced from virtually all gram- positive and negative bacteria under suitable conditions. They occur sporadically in cats, and are most common in free-roaming cats of all ages.

Symptoms and Types

The site of infection is typically a surgical or bite wound. Other signs of L-form bactera infection include:

  • Cellulitis (infection of the skin and underlying tissues)
  • Fever
  • Arthritis
  • Synovitis (inflammation of synovial membrane, the soft tissue that lines the surfaces within the joints that possess cavities [e.g., elbow, wrist, knee])


Bites, scratches, or trauma may allow the organism to enter the skin and subcutaneous tissue. Formation is also encouraged by antibiotic treatment of the host, resistance of the host, suitability of the site for establishment of the infective bacterium, and relatively low to moderate virulence of the infecting bacterium.


L-form bacteria are difficult organisms to isolate and identify. Using a process of differential diagnosis, which is guided by deeper inspection of the apparent outward symptoms, ruling out each of the more common causes until the correct disorder is settled upon and can be treated appropriately, the veterinarian will make a diagnosis by putting all of the signs and symptoms together, along with any consistent laboratory results, to come to a conclusion. Your doctor will also collect some of the fluid from any draining lesions, as well as joint fluid for analysis.


Gentle cleaning of the wound will help to degrade the fragile L-form organisms. In most cases, doctors allow the open wounds to heal by secondary intention; that is, the open edges of the wound are not intentionally closed (e.g., by stitches), but are allowed to heal by themselves, growing new tissue over the wound. The main treatment in this case is by cleansing the wound, applying antibiotic ointment to the wound, and applying fresh bandages.

Your veterinarian will prescribe medications such as antibiotics to treat the symptoms as well as the disease; however, these organisms are resistant and difficult to target with antibiotics. The fever usually breaks within 24-48 hours. In many cases, arthritic symptoms continue to persist. 

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