Feline mycobacterial disease in northern California: Epidemiology, clinical features, and antimicrobial susceptibility

Abstract

Background: Mycobacterial infections in cats are challenging to treat and incompletely described.

Hypothesis/objectives: To describe the features of mycobacterial infections in cats from northern California.

Animals: Nineteen cats, all with nontuberculous mycobacterial (NTM) infections; 4 with Mycobacterium avium infection, 15 with rapid-growing mycobacterial (RGM) infection.

Methods: Retrospective study. Cases with positive mycobacterial culture, species identification, and susceptibility testing were included. Descriptive statistics were used. Fisher's exact test and Mann-Whitney U test were used for comparisons between M avium and RGM infections (P ≤ .05).

Results: Rapid-growing mycobacterial cases included Mycobacterium smegmatis (9), Mycobacterium fortuitum (4), Mycobacterium abscessus (1), and Mycobacterium thermoresistibile (1). Mycobacterium avium infections were more likely than RGM infections to be disseminated (3/4 vs 0/15; P = .004). Disease of the skin/subcutis (15/15 vs 0/4; P < .001) and outdoor access (14/15 vs 0/4; P = .001) were primary features of RGM infections. Resistance to fluoroquinolones and aminoglycosides was common among M avium isolates. A high prevalence of resistance to third- and fourth-generation cephalosporins was noted in RGM species. Death/euthanasia was noted only in M avium cases (3/4). Twelve of 15 cats with RGM infection had available follow-up; 4 of these cats achieved remission.

Conclusions and clinical importance: The most prevalent RGM species isolated from cats from northern California are M smegmatis and M fortuitum. Susceptibility to prescribed antimicrobials does not appear to guarantee treatment success. Combination drug treatment is recommended. Repeat culture and susceptibility testing should be performed when disease is persistent/relapsing.

Keywords: antimicrobial; atypical bacteria; cutaneous; panniculitis; systemic; treatment.

FIGURE 1

Susceptibility patterns for Mycobacterium avium isolates identified in cats from northern California expressed as a percentage (susceptible, intermediate, and resistant, as defined by human breakpoints). Number of isolates tested against each antimicrobial is listed on the horizontal axis. ** Usually recommended antimicrobials: antimicrobials with proven in vivo efficacy against human M avium infections. Other additionally tested antimicrobials have been shown to have in vitro efficacy but lack definitively proven in vivo efficacy against human M avium infections

FIGURE 2

Susceptibility patterns for rapid‐growing nontuberculous mycobacterial (RGM) isolates identified in cats from northern California expressed as a percentage (susceptible, intermediate, and resistant, as defined by human breakpoints). Number of isolates tested against each antimicrobial is listed on the horizontal axis. TMS, trimethoprim sulfamethoxazole. A, Susceptibility patterns for Mycobacterium smegmatis isolates. B, Susceptibility patterns for Mycobacterium fortuitum isolates. ** The exact correlation between in vivo and in vitro efficacy has not been well delineated in human or feline RGM infections