Abstract
Dermatophilosis is a form of dermatitis caused by the bacterium Dermatophilus congolensis. The disease usually presents as localized purulent dermatitis, crusty hair masses or widespread matting of the hair. This condition is most common in domestic ruminants; but it can also affect other wild animals and humans. Antimicrobial therapy is used in many regions to treat clinical dermatophilosis with varying results. In this study, we aimed to assess the antimicrobial susceptibility of D. congolensis isolates. Fifty-two isolates were obtained from animals showing clinical signs of the disease at farms in St. Kitts. The isolates were then confirmed as D. congolensis by phenotypic tests, PCR and MALDI-TOF Mass Spectrometry. Furthermore, minimum inhibitory concentrations (MIC) of 16 antimicrobial agents were determined, using the broth microdilution method. Although most antimicrobials showed MICs in line with published values, the tetracycline results displayed a clear bimodal distribution over the tested range, with most isolates showing low MICs and 6 isolates much higher values (+/− 100-fold increase). These results indicate the presence of acquired tetracycline resistance in D. congolensis on the island of St. Kitts. Whether the current observation has implications for efficacy of treating the disease must be confirmed in further research.
Highlights
Dermatophilus congolensis is a facultatively anaerobic actinomycete that can infect a wide range of animals as well as humans, leading to the skin disease dermatophilosis, commonly referred to as mycotic dermatitis, rain rot, rain scald or streptotrichosis [1,2,3,4]
All the 52 isolates were subjected to antimicrobial susceptibility testing, but the results summarized in Table 1 show only 34 isolates reflecting a single isolate from each animal
Few studies have assessed the normal antimicrobial susceptibility of D. congolensis and the most detailed one is at least 25 years old; the current results provide additional insights in both intrinsic susceptibility and potential acquired resistance against various antimicrobial agents
Summary
Dermatophilus congolensis is a facultatively anaerobic actinomycete that can infect a wide range of animals as well as humans, leading to the skin disease dermatophilosis, commonly referred to as mycotic dermatitis (erroneously as it is not a mycosis), rain rot, rain scald or streptotrichosis [1,2,3,4]. The first reported case of dermatophilosis was in Congo in 1915: the disease has since been described worldwide, it is mainly present in areas with hot and/or humid climates. It is most often associated with cattle, sheep, goats and horses; and causes economic loss due to damaged hides, loss of body condition, poor health, secondary infections, high culling rates or, in rare cases, death [3,5]. Dermatophilosis is a zoonotic disease, manifesting as keratolysis, pustules or exudative scaly lesions in humans [6]. Due to the diagnostic procedures not being well-developed, it is likely that this condition is underdiagnosed in humans [5]
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