In Vitro Synergism between Azithromycin or Terbinafine and Topical Antimicrobial Agents against Pythium insidiosum

Abstract

bWe describe here in vitro activity for the combination of azithromycin or terbinafine and benzalkonium, cetrimide, cetylpyridinium, mupirocin, triclosan, or potassium permanganate. With the exception of potassium permanganate, the remaining antimicrobial drugs were active and had an MIC 90 between 2 and 32 g⁄ml. The greatest synergism was observed for the combination of terbinafine and cetrimide (71.4%). In vivo experimental evaluations will clarify the potential of these drugs for the topical treatment of lesions caused by Pythium insidiosum. Pythium insidiosum is the main oomycete pathogen associated with severe diseases in humans and animals, particularly horses and dogs. In humans, clinical presentations include ocular, cutaneous⁄subcutaneous, vascular, and disseminated pythiosis. While underlying diseases, such as thalassemia and hemoglobinopathy syndrome, have been observed in cutaneous, vascular, and disseminated forms of disease, ocular pythiosis can affect otherwise healthy individuals. Moreover, no underlying diseases have been observed with animal pythiosis, for which most cases are associated with pyogranulomatous disease in subcutaneous tissue or in a gastrointestinal form (1, 2).Treating pythiosis remains a challenge because this microorganism produces hyaline hyphae similar to those of true fungi but is unable to synthesize ergosterol, which is the direct or indirect main target of most antifungal drugs. Consequently, there are no definitive treatment protocols for this disease, and despite some contradictory results, P. insidiosum can be considered intrinsically resistant to most antifungal drugs (2-4). The most commonly used effective clinical management of pythiosis is aggressive surgical resection, such as amputation, and surgical debridement of skin lesions. Unfortunately, surgical interventions are not always possible, and a high rate of recurrence has been observed. Additionally, immunotherapy cure rates can reach approximately 55% and 80% in humans and horses, respectively (2, 3, 5). Independent of the use of single or combination therapies, the best cure rates are associated with rapid diagnosis and early treatment (1, 2). Regardless of the therapy of choice, little attention has been given to the specific topical treatment of pythiosis lesions.Considering the high tissue concentrations achieved by azithromycin and terbinafine and the above context, this study aimed to assess the in vitro activity for combinations of azithromycin or terbinafine (systemic therapeutic options) and benzalkonium, cetrimide, cetylpyridinium, mupirocin, triclosan, or potassium permanganate (topical therapeutic options).We evaluated the susceptibility of 20 isolates of P. insidiosum from equine pythiosis cases and the reference strain ATCC 58637. Clinical isolates were previously identified by a nested PCR assay (6). The drugs (final concentrations tested in the wells) azithromycin (0.06 to 32 g⁄ml), benzalkonium chloride (0.25 to 32 g⁄ml), alkyltrimethylammonium bromide (cetrimide) (0.5 to 32 g⁄ml), cetylpyrid...

The effect of fennel essential oil and trans-anethole on antibacterial activity of mupirocin against Staphylococcus aureus isolated from asymptomatic carriers

“…Itaqui et al . investigated the interactions between azithromycin and terbinafine in combination with MUP in order to reduce the therapeutic doses of systemic and local treatment against Pythium insidiosum responsible for ocular, cutaneous/subcutaneous, vascular and disseminated pythiosis [30]. Sato et al .…”

Recent update in diagnosis and treatment of human pythiosis

“…Historically, saturated solution of potassium iodide (SSKI; one mL orally three times per day for up to three months) has been used to successfully treat localized skin/subcutaneous disease (Krajaejun et al, 2006b;Imwidthaya, 1994). Several antibacterial drugs that inhibit protein synthesis can inhibit the growth of P. insidiosum (Brazilian strains) in vitro including azithromycin, tigecycline, clarithromycin, linezolid, nitrofurantoin, chloramphenicol, quinupristin/dalfopristin, clindamycin, josamycin, miltefosine, sutezolid, retapamulin, tiamulin, and valnemulin (Loreto et al, 2011;Mahl et al, 2012;Jesus et al, 2014;Jesus et al, 2016;Itaqui et al, 2016;Loreto et al, 2019). Azithromycin demonstrated potent in vivo activity in an experimental model of pythiosis (Jesus et al, 2016;Loreto et al, 2018).…”

Review of methods and antimicrobial agents for susceptibility testing against Pythium insidiosum

“…However, administration of terbinafine, usually in combination with itraconazole, has shown a favorable response in only a few pythiosis patients [7,72,117,120]. MICs of terbinafine varied (range: 0.5-128 μg/ml), depending on P. insidiosum strains tested (i.e., different genotypes) and the susceptibility methods used (i.e., broth dilution and radial growth) [69,72,86,87,88,95,107,109,117,121,122,123,124,125,126,127,132] (Table 1). Because P. insidiosum lacks the ERG1-encoding gene [69], it is still mysterious about how terbinafine exhibits antimicrobial activity against some strains of this pathogen.…”

“…Macrolides suppress the peptidyl transferase or block the ribosome exit tunnel of a nascent peptide [143]. Broth microdilution-based MIC ranges of the macrolide drugs against P. insidiosum have been reported (Table 2): clarithromycin, 0.05-64 μg/ml; azithromycin, 0.02-32 μg/ml; erythromycin, 1-32 μg/ml; roxithromycin, 2-128 μg/ml; josamycin, 2-64 μg/ml; and tilmicosin, 4-128 μg/ml [9,79,80,88,106,107,123,124,125,139,140]. The agar diffusion method with macrolides demonstrated different inhibition zones of P. insidiosum (Table 2): azithromycin (22.1-29.2 mm), clarithromycin (20.5-28.3 mm), erythromycin (22.9 mm), roxithromycin (18.9 mm), and tilmicosin (17.6 mm) [9,88,141].…”