Definition

• Class Mollicutes (Latin, mollis, “soft”; cutis, “skin”).
• Divided into hemotrophic (formerly Haemobartonella and Eperythrozoon), which are discussed elsewhere, and non-hemotrophic types, which are discussed here.
• More than 80 genera; three families: Mycoplasmas, Ureaplasmas, and Acholeplasmas.
• Smallest (0.2–0.3 µm) and simplest procaryotic cells capable of self-replication.
• Fastidious, facultative anaerobic, gram-negative rods.
• Lack a cell wall; thus plastic, highly pleomorphic, fragile and sensitive to lysis by osmotic shock, detergents, alcohols, and specific antibody plus complement; enclosed by a trilayered cell membrane built of amphipathic lipids (phospholipids, glycolipids, lipoglycans, sterols) and proteins; therefore resistant to lysozyme and cell wall-inhibiting antibacterials; most require sterols for growth.
• Different from wall-defective or wall-less L-form bacteria, which can revert to the normal cell wall strain.
• Reproduce by binary fission; genome replication not necessarily synchronized with cell division, resulting in budding forms and chains of beads.
  • Small genome, typically 0.6–1.6 Mb.
  • Low genomic G + C content (23–40 mol%).
  • Small genome believed to be result of reductive evolution from a common gram-positive ancestor adapting to obligate parasitic life.
• Ubiquitous in nature as parasites, commensals, or saprophytes in animals, plants, and insects; many are pathogens of humans, animals, plants, and insects.

Pathophysiology

• Often part of the resident flora as commensals on mucous membranes of the upper respiratory, digestive, and genital tracts; pathogenicity and role in disease often controversial.
• Species show considerable host specificity.
• Mechanisms by which disease is caused are poorly understood.
• Some species attach to cells by specific receptors; small size and plastic nature enable them to adapt to the shape and contours of host cell surfaces.
• Intimate contact with host cells-necessary for assimilation of vital nutrients and growth factors (e.g., nucleic acid precursors), which organism cannot synthesize; along with the tendency of exogenous proteins to bind to mycoplasmal membrane may allow organism to evade the host's immune response; may incorporate host cell antigen onto mycoplasma membrane (capping) because lack of cell wall; conversely, mycoplasmal protein antigen may become incorporated onto surface of host cell, thereby involving host cell in deleterious immunologic reactions intended against the organism.
• Products produced during growth-capsular carbohydrate, hemolysins, proteolytic enzymes, ammonia, and endonucleases; accumulation of Mycoplasma metabolites (i.e., H₂O₂, NH₃) may contribute to cytopathic effects and tissue damage; cytotoxic glycoproteins and proteins have been isolated from the membranes of several species.
• Immune response-predominantly humoral; as with bacterial infections, IgM and IgA are first antibodies to appear, followed by IgG.
• Fibrinous exudate accompanying infections-protects organism from antibodies and antimicrobial drugs; contributes to chronicity.
• Secondary bacterial invaders-common (e.g., attachment to respiratory tract cells results in destruction of cilia, which predisposes patient to secondary bacterial infection).
• Sialidase, a virulence factor that promotes colonization, tissue invasion, and damage to host cells, varies in expression among strains of canine mycoplasma species.

Systems Affected

Incidence/Prevalence

• Frequent inhabitants of mucosal membranes; M. gateae and/or M. felis found in oral cavity or urogenital tract of 70–80% of healthy cats.
• Rate of isolation in diseased dogs much higher than in normal dogs (e.g., lung, uterus, prepuce).

Geographic Distribution

Ubiquitous

Signalment

Signs

Causes

• Mycoplasma flora of dogs-M. canis, M. spumans, M. maculosum, M. edwardii, M. cynos, M. molare, M. opalescens, M. feliminutum, M. gateae, M. arginini, M.bovigenitalium, M. mucosicanis, Acholeplasma laidlawii, and Ureaplasmas.

• Mycoplasma flora of cats-M. felis, M. gateae, M. feliminutum, M. arginini, M. pulmonis, M. arthritidis, M. gallisepticum, Acholeplasma laidlawi, and Ureaplasmas.

Risk Factors

• Commensals-occasionally cause systemic infection associated with immunodeficiency, immunosuppression, or cancer.
• Impaired resistance of the host-may allow organism to cross the mucosal barrier and disseminate (e.g., primary ciliary dyskinesia).
• Organism may be opportunistic-one factor in a multifactorial causal complex (e.g., impaired pulmonary clearance from viral infection may allow organism to establish infection in lungs as secondary opportunistic pathogen).
• Predisposing factors-stresses (e.g., reproductive problems associated with overcrowded operations) and other factors (e.g., urinary tumors and urinary calculi).
• Rate of isolation of organism in diseased dogs much higher than in normal dogs.

Differential Diagnosis

• Upper respiratory infection (dogs and cats)-viruses (parainfluenza virus, canine distemper, herpesvirus, feline calcivirus, reovirus); Chlamydia psittaci; bacteria (Bordetella bronchiseptica, staphylococci, streptococci, coliforms).
• Urinary tract infection (dogs and cats)-bacteria (staphylococci, streptococci, coliforms); fungus (Candida); parasites.
• Infertility, early embryonic death, abortion, stillbirths or weak newborns, and neonatal mortality (dogs)-bacteria (Brucella, Salmonella, Campylobacter, E. coli, streptococcus); viruses (canine herpesvirus, canine distemper, canine adenovirus); Toxoplasma gondii; endocrinopathies (progesterone deficiency, hypothyroidism).
• Prostatitis (dogs)-bacteria (E. coli, Brucella canis); fungi (Blastomyces, Cryptococcus).
• Arthritis (dogs and cats)-immune-mediated; bacteria (staphylococci, streptococci, coliforms, anaerobes); L-form bacteria; Rickettsia (Ehrlichia); Borrelia burgdorferi; fungi (Coccidioides, Cryptococcus, Blastomyces); protozoa (Leishmania); viruses (feline calicivirus).
• Conjunctivitis (cats)-feline herpesvirus; feline calicivirus; feline reovirus; Chlamydia psittaci; bacteria.

CBC/Biochemistry/Urinalysis

Other Laboratory Tests

• Serologic tests-complement fixation, agar gel immunodiffusion, ELISA; detect organism.
• Difficult to demonstrate in and from tissues.
• Extremely pleomorphic-in smears (e.g., conjunctival scrapings) seen as coccobacilli, coccal forms, ring forms, spirals, and filaments.
• Stains-stain poorly (gram-negative); preferred: Giemsa or other Romanowsky stain.
• Fluorescent antibody test-definitive diagnosis; isolate and identify or detect the organism in tissues; can submit cotton swabs placed in Hayflick broth medium or commercially available swabs; organisms fragile; refrigerate specimens and deliver to the laboratory within 48 hours; freeze to preserve longer.
• Culture urine sediment after centrifugation; fastidious, require complex growth media; form microcolonies having characteristic “fried egg” appearance.
• PCR of 16S rRNA.
• PCR-DGGE-used to identify difficult-to-culture or difficult-to-differentiate mycoplasma.

Imaging

Polyarthritis-no radiographic changes.

Diagnostic Procedures

• Polyarthritis-high numbers of non-degenerative neutrophils in synovial fluid.
• Prostatic fluid-inflammatory cells with negative bacterial culture.

Appropriate Health Care

Outpatient

Drug(s) Of Choice

• Sensitive to antibiotics that specifically inhibit synthesis in prokaryotes.
• Tetracyclines 22 mg/kg PO q8h.
• Doxycycline 5 mg/kg PO q12h.
• Pradofloxacin 5 mg/kg PO q12h.
• Chloramphenicol 40–50 mg/kg IV, IM, SC, PO q8–12h.
• No standardized procedure for in vitro antimicrobial susceptibility tests.
• Topical antibiotic-conjunctivitis.

Contraindications

• Topical steroid ointments-improper use for conjunctivitis may prolong infection and predispose patient to corneal ulceration.
• Tetracyclines-avoid use in animals <6 months of age.
• Tetracycline and chloramphenicol-avoid use in pregnant animals.

Precautions

Sulfonamides and -lactams-inhibit peptidoglycan synthesis; organism resistant because of lack of cell walls.

Alternative Drug(s)

• Gentamicin
• Kanamycin
• Spectinomycin
• Spiramycin
• Tylosin
• Erythromycin
• Nitrofurans
• Fluoroquinolones

Patient Monitoring

Treat for an extended period of time

Prevention/Avoidance

• No vaccines are available.
• Organism readily killed by drying, sunshine, and chemical disinfection.

Expected Course and Prognosis

Prognosis good in animals with competent immune systems and given appropriate antibiotic therapy.

Associated Conditions

M. pneumoniae-infects respiratory tracts in humans worldwide; causes mycoplasmal pneumonia, bronchitis, or upper respiratory infection; usually self-limited; rarely fatal.

Age-Related Factors

Tetracyclines-avoid in animals <6 months of age.

Zoonotic Potential

• Not generally considered zoonotic unless person is immunosuppressed.
• Reported development of suppurative mycoplasmal tenosynovitis in a veterinarian who was scratched by a cat being treated for colitis.
• Host specificity of mycoplasmas has been questioned by some; particularly between closely related species of mammals.

Pregnancy/Fertility/Breeding

Tetracycline and chloramphenicol-do not use in pregnant animals.

Synonyms

Pleuropneumonia-like organisms

Abbreviations

• ELISA = enzyme-linked immunosorbent assay
• PCR = polymerase chain reaction
• PCR-DGGE = polymerase chain reaction denaturing gradient gel electrophoresis

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