Clinical Use of 16S rRNA Gene Sequencing To IdentifyMycoplasma felisandM. gateaeAssociated with Feline Ulcerative Keratitis

Abstract

Routine bacterial cultures of corneal scrapings from seven cats with either ulcerative feline keratitis, keratomalacia, or both yielded colonies which were identified by 16S rRNA gene sequencing as Mycoplasma felis (six cases) and Mycoplasma gateae (one case). Identification of the pathogens allowed the use of less empirical and more organism-specific therapy.Mycoplasma species are part of the normal flora of the conjunctiva and upper respiratory tract of cats (1,5,16,21,25). However, Mycoplasma species have been implicated as etiological agents of feline conjunctivitis, lower respiratory tract infections, and polyarthritis (7,9,11,12,13,19,20). Historically, the detection of Mycoplasma in and diagnosis of cases of feline conjunctivitis and ulcerative keratitis have been based on clinical presentation and judgment, the observation of small basophilic inclusion bodies in stained cytology preparations of epithelial cells, and culture of clinical specimens. However, cytology is not specific for Mycoplasma, and culture for Mycoplasma is not a particularly sensitive test. The routine antimicrobial agents (usually triple-antibiotic ointments and gentamicin) used by veterinarians to treat feline ulcerative keratitis empirically are not effective against Mycoplasma. In addition, other antimicrobial agents (e.g., tetracycline and chloramphenicol), if given topically, can cause cats so much irritation that treatment must be discontinued. Therefore, veterinarians and their feline patients could benefit from rapid and accurate identification of Mycoplasma involved in feline ulcerative keratitis so that Mycoplasma-specific antimicrobial agents can be administered as soon as possible.Clinical presentations. From March 2000 to March 2004, seven cats with severe stromal ulcerative keratitis, keratomalacia, or both were examined, cultured for bacteria routinely encountered in a clinical microbiology laboratory, and treated by a veterinary ophthalmologist. These cases were unusual because (i) each case presented as severe stromal ulcerative keratitis, keratomalacia, or both and (ii) corneal specimens from each of the cases were culture positive for growth which was suggestive of Mycoplasma. Four cats had a history of recent feline herpetic keratitis or concurrent corneal ulcerations which were typical of feline herpetic keratitis. All of the cats had recently received systemic or topical corticosteroids prior to presentation, or had received either topical or systemic antibiotics which were not effective against Mycoplasma. Three representative cases are presented here. Case 1.A 15-year-old Birman cat presented with a classical dendritic herpetic ulcer in the right eye and a large corneal ulcer with central necrosis and diffuse corneal vascularization in the left eye (Fig. 1A). Prior to presentation, both eyes had been treated with topical prednisolone for an unknown length of time. The treatment with prednisolone likely had activated a latent herpesvirus infection. Corneal scrapings from the left eye were submitted for routine b...

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