Susceptibility in vitro of canine methicillin-resistant and -susceptible staphylococcal isolates to fusidic acid, chlorhexidine and miconazole: opportunities for topical therapy of canine superficial pyoderma

Antimicrobial use guidelines for canine pyoderma by the International Society for Companion Animal Infectious Diseases (ISCAID)

BACKGROUND

Canine pyoderma is one of the most common presentations in small animal practice, frequently leading to antimicrobial prescribing.

OBJECTIVES

To provide clinicians with antimicrobial treatment guidelines for staphylococcal pyoderma, including those involving meticillin-resistant staphylococci. Guidance on diagnosing surface, superficial and deep pyoderma and their underlying primary causes, is included. Recommendations aim to optimise treatment outcomes while promoting responsible antimicrobial use.

MATERIALS AND METHODS

Evidence was gathered from a systematic literature review of English-language treatment studies for canine pyoderma up to 23 December 2023. Quality was assessed using SORT criteria and combined with authors' consensus evaluation. Recommendations were voted on in an iterative process, followed by a Delphi-style feedback process before final agreement by the authors.

RESULTS

Cytology should be performed in all cases before antimicrobials are used. Topical antimicrobial therapy alone is the treatment-of-choice for surface and superficial pyodermas. Systemic antimicrobials should be reserved for deep pyoderma and for superficial pyoderma when topical therapy is not effective. Systemic therapy, with adjunctive topical treatment, is initially provided for 2 weeks in superficial and 3 weeks in deep pyoderma, followed by re-examination to assess progress and manage primary causes. First-choice drugs have expected efficacy against the majority of meticillin-susceptible Staphylococcus pseudintermedius; for all other drugs, laboratory testing should confirm susceptibility and exclude suitability of safer alternatives. As culture and susceptibility testing are essential for rationalising systemic therapy, laboratories and practices should price them reasonably to encourage use. Proactive topical therapy using antiseptics may help prevent recurrences.

CONCLUSIONS AND CLINICAL RELEVANCE

The accessibility of the skin offers excellent, achievable opportunities for antimicrobial stewardship.

Antimicrobial activity of ear cleanser products against biofilm and planktonic phases of Staphylococcus spp. and Pseudomonas spp. isolated from canine skin and ear infections

BACKGROUND

Staphylococcus spp., and Pseudomonas spp., including multidrug resistant staphylococci are frequent isolates from canine otitis externa and atopic dermatitis. The ability of these bacteria to form biofilms significantly contributes to the chronic nature of otitis. To manage microbial overgrowth, ear cleanser products are commonly used. It is important therefore, to measure their antibiofilm effects. In this study, six ear cleansers (EpioticⓇ SIS, EpioticⓇ Advanced, CleanauralⓇ, OtifreeⓇ, PeptivetⓇ and SonotixⓇ) were evaluated against clinical isolates of Pseudomonas aeruginosa, methicillin resistant and sensitive Staphylococcus aureus and Staphylococcus pseudintermedius. Antibiofilm activity was measured using a colorimetric assay that detects viable cells through the reduction of thiazolyl blue tetrazolium bromide (MTT). Additionally, minimum inhibitory concentration (MIC) of Epiotic SIS and Epiotic Advanced were determined using a broth micro-dilution assay to assess their ability to inhibit bacteria in the planktonic state.

RESULTS

Epiotic (SIS and Advanced), Cleanaural and Peptivet showed high antibiofilm activity, with Otifree and Sonotix showing moderate to low antibiofilm activity. Notably, Otifree was significantly less effective at inhibiting methicillin-resistant S. aureus compared to methicillin-sensitive strains. P. aeruginosa biofilms were less effectively disrupted by some ear cleansers, and the MIC results indicated that less diluted solutions were required to inhibit this isolate compared to the staphylococcal species. Differences in the antibacterial effects between Epiotic SIS and Epiotic Advanced solutions could also be detected from the MIC assays suggesting differences in formulations can affect antimicrobial efficacy.

CONCLUSIONS

Commonly used canine ear cleanser products showed variable activity against multidrug resistant and sensitive Staphylococcus spp. and P. aeruginosa isolates in both biofilm and planktonic phases. The observed differences between bacterial strains and cleanser formulations highlight the importance of selecting appropriate products for targeted microbial control, which can lead to more effective management of chronic otitis externa and atopic dermatitis in dogs.

Antimicrobial Strategies Proposed for the Treatment of S. pseudintermedius and Other Dermato-Pathogenic Staphylococcus spp. in Companion Animals: A Narrative Review

The treatment of dermato-pathogenic Staphylococcus spp., particularly Staphylococcus pseudintermedius, in companion animals presents significant challenges due to rising antimicrobial resistance. This review explores innovative strategies to combat these infections. We examined novel antimicrobials and the repurposing of existing drugs to enhance their efficacy against resistant strains. Additionally, we evaluate the potential of natural products, nanomaterials, and skin antiseptics as alternative treatments. The review also investigates the use of antimicrobial peptides and bacteriophages, highlighting their targeted action against staphylococcal pathogens. Furthermore, the role of adjuvants in antibiotic treatments, such as antimicrobial resistance breakers, is discussed, emphasizing their ability to enhance therapeutic outcomes. Our analysis underscores the importance of a multifaceted approach in developing effective antimicrobial strategies for companion animals, aiming to mitigate resistance and improve clinical management of staphylococcal skin infections.

Evaluation of residual antibacterial effects on canine skin surface and hair following treatment with five commercial mousse products against Staphylococcus pseudintermedius

BACKGROUND

Antibacterial effect studies of commercial antiseptics typically have evaluated hair and not the skin.

OBJECTIVES

To evaluate the antibacterial effects of mousse products on both canine skin and hair.

ANIMALS

Fifteen short-haired and eight long-haired dogs without skin disease.

MATERIALS AND METHODS

Five mousses were applied once: (1) 2% chlorhexidine and 2% miconazole; (2) 0.05% phytosphingosine; (3) 2% salicylic acid and 10% ethyl lactate; (4) 3% chlorhexidine and 0.5% climbazole; and (5) 2% chlorhexidine and 1% ketoconazole. Skin swabs and hair were collected from application sites before treatment, and at 1 h and at Day (D)2, D4, D8, D10 and D14 post-treatment. Skin swabs and hair were placed on Mueller-Hinton plates inoculated with Staphylococcus pseudintermedius inoculum suspension. Inhibition zones were measured after incubation.

RESULTS

Inhibition was not noted with mousses 2 and 3. In mousse 5, inhibition zone sizes produced by swabs from long- and short-haired dogs were not significantly different (p = 0.105), and all swabs and hair produced inhibition until D14, regardless of hair length. By contrast, in mousse 1, inhibition zones produced by swabs from long-haired dogs were smaller than those from short-haired dogs (p < 0.001), and swabs from long-haired dogs produced a shorter duration of bacterial inhibition than hair.

CONCLUSIONS AND CLINICAL RELEVANCE

The antibacterial effects of mousse 5 were not affected by hair length. Hair may be acceptable for evaluating effects on the skin in short-haired dogs. However, long hair may interfere with product distribution and duration of bacterial inhibition. Therefore, the evaluation of hair alone may overestimate clinically relevant antibacterial effects.

A retrospective study of treatment, outcome, recurrence and concurrent diseases in 190 dogs with anal sacculitis

BACKGROUND

Few studies report the treatment and recurrence rate in anal sacculitis (AS).

OBJECTIVES

Retrospective study reporting the management, recurrence and concurrent diseases in dogs with AS in a primary care practice.

ANIMALS

One hundred and ninety privately owned dogs in Sweden.

MATERIALS AND METHODS

Clinical records of dogs diagnosed with AS between 2018 and 2021 were reviewed, and management, time until clinical resolution, number of recurrent episodes and comorbidites were recorded.

RESULTS

The 190 dogs developed 290 episodes of AS. The most common management, in 235 of 290 (81.0%) episodes, was flushing ± infusion of an antimicrobial product into the sacs ± prescription of a nonsteroidal anti-inflammatory drug (NSAID), providing resolution in 213 of 235 (90.6%) episodes. Median time to resolution was one week (range 1-16 weeks), with resolution seen within one week in 205 of 290 (70.7%) episodes. A single episode of AS developed in 126 of 190 (66.3%) dogs. Dogs with concurrent cutaneous allergic disease were more likely (p < 0.001) to have recurrence of AS when compared to dogs with other comorbidities. Cutaneous allergic disease occurred more often (p < 0.001) in dogs with AS than in the practice population.

CONCLUSIONS AND CLINICAL RELEVANCE

Local treatment of the anal sacs ± systemic NSAID was the most common treatment, inducing clinical resolution in the majority of dogs. Cutaneous allergic disease was the most common concurrent diagnosis, with higher recurrence rate of AS compared to other diseases and occurring in higher prevalence than in the practice population. Further studies are needed to determine if management of cutaneous allergic disease would reduce the risk of AS.

Exploring Efflux as a Mechanism of Reduced Susceptibility towards Biocides and Fluoroquinolones in Staphylococcus pseudintermedius

Staphylococcus pseudintermedius is the main bacterial cause of skin and soft tissue infections (SSTIs) in companion animals, particularly dogs. The emergence of methicillin-resistant S. pseudintermedius (MRSP) strains, frequently with multidrug resistance phenotypes is a public health concern. This study aimed to evaluate efflux, a resistance mechanism still poorly characterized in S. pseudintermedius, as a contributor to biocide and fluoroquinolone resistance. Susceptibility to the efflux pump substrates ethidium bromide (EtBr), tetraphenylphosphonium bromide (TPP) and ciprofloxacin (CIP) was evaluated by minimum inhibitory concentration (MIC) determination for 155 SSTIs-related S. pseudintermedius in companion animals. EtBr and TPP MIC distributions were analyzed to estimate cut-off (COWT) values. The effect of the efflux inhibitors (EIs) thioridazine and verapamil was assessed upon MICs and fluorometric EtBr accumulation assays, performed with/without glucose and/or EIs. This approach detected a non-wild type population towards TPP with increased efflux, showed to be strain-specific and glucose-dependent. Resistance to fluoroquinolones was mainly linked to target gene mutations, yet a contribution of efflux on CIP resistance levels could not be ruled out. In sum, this study highlights the relevance of efflux-mediated resistance in clinical S. pseudintermedius, particularly to biocides, and provides a methodological basis for further studies on the efflux activity on this important pathogen of companion animals.

In Vitro Antimicrobial Activity of Piper betle Leaf Extract and Some Topical Agents against Methicillin-Resistant and Methicillin-Susceptible Staphylococcus Strains from Canine Pyoderma

As multidrug-resistant methicillin-resistant staphylococci (MRS) is becoming more prevalent in canine pyoderma, the discovery of new therapeutic options is required. This study aimed to test the antimicrobial activity of crude Piper betle leaf extract and some topical antimicrobial agents against canine Staphylococcus clinical strains by determining the minimum inhibitory concentration (MIC) and the minimum bactericidal concentration (MBC). The results showed that the mean MICs of chlorhexidine, miconazole, crude P. betle leaf extract, azelaic acid, and benzoyl peroxide against Staphylococcus strains were 1.41, 1.62, 252.78, 963.49, and 1342.70 mg/L, respectively. Therefore, betel leaf extract demonstrated a superior efficacy to azelaic acid and benzoyl peroxide. Furthermore, the ratio of MBC/MIC of betel leaf extract was 1.75, indicating its bactericidal action. When applied to methicillin-resistant S. pseudintermedius (MRSP) and methicillin-susceptible S. pseudintermedius (MSSP), betel leaf extract was equally efficient towards both groups. S. pseudintermedius strains were more susceptible to betel leaf extract than S. schleiferi subsp. coagulans. In gas chromatography-mass spectrometry analysis, eugenol and hydroxychavicol appeared to be the major components of betel leaf extract. Given its efficacy, dogs with pyoderma could benefit from the use of betel leaf extract as a topical antimicrobial alternative.

Canine pyoderma: mecA persists autogenous bacterin formulation from meticillin-resistant Staphylococcus pseudintermedius (MRSP) and S. aureus (MRSA)

OBJECTIVE

Autogenous Staphylococcus pseudintermedius bacterins can reduce prescribing of antimicrobials in the management of canine recurrent pyoderma. However, increasing prevalence of meticillin-resistant, mecA-positive S. pseudintermedius (MRSP) raises concern over dispersal of mecA through bacterin therapy. We investigated the presence and integrity of mecA in bacterin formulations after manufacturing.

MATERIAL AND METHODS

Twenty clinical isolates (12 MRSP, 7 MR-S. aureus, 1 meticillin-susceptible SP) were investigated. Pellets from overnight growth were washed 3 times with 0.5 % phenol saline, followed by addition of 0.1 ml 10 % formal-saline to 10 ml phenol-saline. Sterility was confirmed, and DNA extracted using both a standard genomic extraction kit and one recommended for formalin-fixed tissue samples (FFPE). The presence of mecA was determined after PCR and its integrity examined in 5 randomly selected samples after sequencing.

RESULTS

In all bacterins from meticillin-resistant isolates, mecA was detected following FFPE extraction; products aligned fully to a reported mecA sequence. After standard DNA extraction, mecA was seen in 16/19 samples.

CONCLUSION

Persistence of mecA in MRSP bacterins suggests that dispersal of this important resistance mediator through therapy may be possible. While the ability of skin bacteria to uptake naked DNA remains unclear, it seems prudent to only formulate autogenous bacterins from mecA-negative S. pseudintermedius to avoid unnecessary spread of mecA.

Antibacterial and Antivirulence Activity of Manuka Honey against Genetically Diverse Staphylococcus pseudintermedius Strains

Staphylococcus pseudintermedius is an important member of the skin microbial community in animals and can cause opportunistic infections in both pets and their owners. The high incidence of antimicrobial resistance in S. pseudintermedius highlights that this opportunistic zoonotic pathogen can cause infections which require prolonged and intensive treatment to resolve. Manuka honey has proven efficacy against many bacterial pathogens and is an accepted topical treatment for infections in both veterinary and clinical practice, and so it is a particularly appropriate antimicrobial for use with zoonotic pathogens such as S. pseudintermedius. Here, we demonstrate that not only is manuka honey highly potent against novel multidrug-resistant S. pseudintermedius isolates, it also acts synergistically with clinically relevant antibiotics. In addition, manuka honey modulates S. pseudintermedius virulence activity, even at subinhibitory concentrations. In a clinical setting, these attributes may assist in controlling infection, allowing a more rapid resolution and reducing antibiotic use.

Staphylococcus pseudintermedius causes opportunistic infections in dogs. It also has significant zoonotic potential, with the emergence of multidrug resistance leading to difficulty treating both animal and human infections. Manuka honey has previously been reported to inhibit many bacterial pathogens, including methicillin-resistant Staphylococcus aureus, and is successfully utilized in both clinical and veterinary practice. Here, we evaluated the ability of manuka honey to inhibit strains of S. pseudintermedius grown alone and in combination with antibiotics, as well as its capacity to modulate virulence within multiple S. pseudintermedius isolates. All 18 of the genetically diverse S. pseudintermedius strains sequenced and tested were inhibited by ≤12% (wt/vol) medical-grade manuka honey, although tolerance to five clinically relevant antibiotics was observed. The susceptibility of the isolates to four of these antibiotics was significantly increased (P ≤ 0.05) when combined with sublethal concentrations of honey, although sensitivity to oxacillin was decreased. Virulence factor (DNase, protease, and hemolysin) activity was also significantly reduced (P ≤ 0.05) in over half of isolates when cultured with sublethal concentrations of honey (13, 9, and 10 isolates, respectively). These findings highlight the potential for manuka honey to be utilized against S. pseudintermedius infections.

IMPORTANCEStaphylococcus pseudintermedius is an important member of the skin microbial community in animals and can cause opportunistic infections in both pets and their owners. The high incidence of antimicrobial resistance in S. pseudintermedius highlights that this opportunistic zoonotic pathogen can cause infections which require prolonged and intensive treatment to resolve. Manuka honey has proven efficacy against many bacterial pathogens and is an accepted topical treatment for infections in both veterinary and clinical practice, and so it is a particularly appropriate antimicrobial for use with zoonotic pathogens such as S. pseudintermedius. Here, we demonstrate that not only is manuka honey highly potent against novel multidrug-resistant S. pseudintermedius isolates, it also acts synergistically with clinically relevant antibiotics. In addition, manuka honey modulates S. pseudintermedius virulence activity, even at subinhibitory concentrations. In a clinical setting, these attributes may assist in controlling infection, allowing a more rapid resolution and reducing antibiotic use.

A pilot study of the in vitro antimicrobial activity and in vivo residual activity of chlorhexidine and acetic acid/boric acid impregnated cleansing wipes

BACKGROUND

Topical antimicrobials are recommended for first line treatment of surface and superficial infections in dogs. This is especially important given the increasing prevalence of antimicrobial resistant infections. Antimicrobial wipes have become popular, but there are a lack of controlled studies assessing their in vitro antimicrobial and in vivo residual activity. We aimed to assess the antimicrobial efficacy of two commercial antimicrobial wipes against frequently isolated pathogens. Ten clinical and one reference isolate each of meticillin-susceptible Staphylococcus pseudintermedius (MSSP), meticillin-resistant S. pseudintermedius (MRSP), Escherichia coli (EC), extended spectrum beta-lactamase (ESBL) producing E. coli (ESBL-EC), Pseudomonas aeruginosa (PA) and Malassezia pachydermatis (MP) were tested using a modified Kirby-Bauer technique. Each isolate was tested against 6 mm discs of chlorhexidine (CHX) and acetic acid/boric acid (AABA) wipes, and positive and negative controls either overnight (bacteria) or for 3 days (Malassezia). Healthy dogs were treated with the wipes and distilled water on a randomised flank (n = 5 each). Hair samples (1 cm; 0.1 g) taken at days 0, 1 and 3 were inoculated with an isolate of each organism. Zones of inhibition (ZI) were measured.

RESULTS

All isolates produced confluent growth with AABA and control wipes, except for the cleansing wipes and MP (median ZI 12 mm; 95% CI 8.2-15.8). The median (95% CI) CHX wipe ZIs (mm) were: MP 48.0 (47.0-49.0), MSSP 15.6 (14.2-17.0), MRSP 14.0 (13.6-14.4), EC 13.6 (12.0-15.2) and ESBL-EC 10.0 (9.4-10.6). PA showed confluent growth. The differences between the bacterial isolates was significant (Kruskal-Wallis p < 0.0001; post-tests MSSP = MRSP = EC > EBSL-EC > PA). Confluent growth was visible with all the hair samples.

CONCLUSION

CHX but not AABA showed in vitro efficacy against MSSP, MRSP, EC and MP. ESBL-EC were less susceptible and there was no activity against PA. There was no residual activity on hair. Additional studies are required to determine efficacy of these products in clinically affected patients.

Genetic resistance determinants to fusidic acid and chlorhexidine in variably susceptible staphylococci from dogs

BACKGROUND

Concern exists that frequent use of topically-applied fusidic acid (FA) and chlorhexidine (CHX) for canine pyoderma is driving clinically relevant resistance, despite rare description of FA and CHX genetic resistance determinants in canine-derived staphylococci. This study aimed to determine minimum inhibitory concentrations (MICs) and investigate presence of putative resistance determinants for FA and CHX in canine-derived methicillin-resistant (MR) and -susceptible (MS) staphylococci. Plasmid-mediated resistance genes (fusB, fusC, fusD, qacA/B, smr; PCR) and MICs (agar dilution) of FA and CHX were investigated in 578 staphylococci (50 MR S. aureus [SA], 50 MSSA, 259 MR S. pseudintermedius [SP], 219 MSSP) from Finland, U.S.A., North (NUK) and South-East U.K. (SEUK) and Germany. In all isolates with FA MIC ≥64 mg/L (n = 27) fusA and fusE were amplified and sequenced.

RESULTS

FA resistance determinants (fusA mutations n = 24, fusB n = 2, fusC n = 36) were found in isolates from all countries bar U.S.A. and correlated with higher MICs (≥1 mg/L), although 4 SP isolates had MICs of 0.06 mg/L despite carrying fusC. CHX MICs did not correlate with qacA/B (n = 2) and smr (n = 5), which were found in SEUK SA, and SP from NUK and U.S.A.

CONCLUSIONS

Increased FA MICs were frequently associated with fusA mutations and fusC, and this is the first account of fusB in SP. Despite novel description of qacA/B in SP, gene presence did not correlate with CHX MIC. Selection pressure from clinical use might increase prevalence of these genetic determinants, but clinical significance remains uncertain in relation to high skin concentrations achieved by topical therapy.

Residual antibacterial activity of canine hair treated with five mousse products against Staphylococcus pseudintermedius in vitro

BACKGROUND

Topical therapy alone can be effective in the treatment of canine pyoderma. Topical products are commercially available as shampoos, sprays, wipes and mousses. To date, no studies have evaluated the efficacy of commercially available mousse products in the treatment of canine pyoderma.

OBJECTIVE

To determine the residual antibacterial activity of canine hairs treated with mousse products containing different active ingredients.

ANIMALS

Fifteen client-owned dogs with no history of dermatological disease.

METHODS AND MATERIALS

Dogs were treated once with five mousse products [(i) 2% chlorhexidine and 1% ketoconazole, (ii) 2% chlorhexidine and 2% miconazole, (iii) 3% chlorhexidine and 0.5% climbazole, (iv) 2% salicylic acid 10% ethyl lactate and (v) phytosphingosine HCl 0.05%; control]. Hair samples were collected from each treatment area before application, one hour after application and on days 2, 4, 7, 10 and 14 post-treatment. Collected hairs were weighed and plated on Mueller-Hinton agar plates streaked with a Staphylococcus pseudintermedius isolate showing no antimicrobial resistance. Plates were incubated for 24 h and bacterial growth inhibition zones around the hairs were measured.

RESULTS

Mousses 1, 2 and 3 created significant inhibition zones up to Day 10 when compared to pre-treatment samples. On Day 14, only mousse 3 produced a significant zone of inhibition when compared to the pre-treatment sample. Mousses 4 and 5 showed no statistical difference between any of the samples.

CONCLUSIONS AND CLINICAL IMPORTANCE

These results suggest that three of the mousse products had residual activity in inhibiting S. pseudintermedius growth in vitro for at least 10 days.

Activity In Vitro of Clotrimazole against Canine Methicillin-Resistant and Susceptible Staphylococcus pseudintermedius

Emergence of multidrug-resistance in Staphylococcus pseudintermedius (SP) has increased interest in topical therapy as an alternative to systemic antibiotics in canine pyoderma. The antifungal imidazole, clotrimazole, is contained in numerous licensed canine ear preparations. Its in vitro activity against SP has not been evaluated, although previous studies have shown that the related imidazole, miconazole, has significant anti-staphylococcal efficacy. We therefore determined minimum inhibitory concentrations (MICs) of clotrimazole amongst 50 SP isolates (25 methicillin-resistant [MR]SP and susceptible [MS]SP) collected from dogs in Germany during 2010–2011 using an agar dilution method (CLSI VET01-A4). MICs amongst MRSP and MSSP were comparable (MIC₅₀ and MIC₉₀ = 1mg/L for both groups, p = 0.317); overall, 49 isolates had MIC = 1 mg/L and one had MIC = 0.5 mg/L. The relatively low MICs obtained in this study are likely to be exceeded by topical therapy and thus further clinical evaluation of clotrimazole use in canine superficial pyoderma and otitis externa caused by MRSP and MSSP is now warranted.

Opportunities for topical antimicrobial therapy: permeation of canine skin by fusidic acid

BACKGROUND

Staphylococcal infection of the canine epidermis and hair follicle is amongst the commonest reasons for antimicrobial prescribing in small animal veterinary practice. Topical therapy with fusidic acid (FA) is an attractive alternative to systemic therapy based on low minimum inhibitory concentrations (MICs, commonly <0.03 mg/l) documented in canine pathogenic staphylococci, including strains of MRSA and MRSP (methicillin-resistant Staphylococcus aureus and S. pseudintermedius). However, permeation of canine skin by FA has not been evaluated in detail. This study aimed to define the degree and extent of FA permeation in canine skin in vitro from two sites with different hair follicle density following application of a licensed ophthalmic formulation that shares the same vehicle as an FA-betamethasone combination product approved for dermal application in dogs. Topical FA application was modelled using skin held in Franz-type diffusion cells. Concentrations of FA in surface swabs, receptor fluid, and transverse skin sections of defined anatomical depth were determined using high-performance liquid chromatography and ultraviolet (HPLC-UV) analysis.

RESULTS

The majority of FA was recovered by surface swabs after 24 h, as expected (mean ± SEM: 76.0 ± 17.0%). FA was detected within 424/470 (90%) groups of serial sections of transversely cryotomed skin containing follicular infundibula, but never in 48/48 (100%) groups of sections containing only deeper follicular structures, nor in receptor fluid, suggesting that FA does not permeate beyond the infundibulum. The FA concentration (mean ± SEM) in the most superficial 240 μm of skin was 2000 ± 815 μg/g.

CONCLUSIONS

Topically applied FA can greatly exceed MICs for canine pathogenic staphylococci at the most common sites of infection. Topical FA therapy should now be evaluated using available formulations in vivo as an alternative to systemic therapy for canine superficial bacterial folliculitis.

Discovery of potential antifungal triazoles: design, synthesis, biological evaluation, and preliminary antifungal mechanism exploration

A series of triazoles as miconazole analogues was designed, synthesized and characterized by IR, NMR, MS and HRMS. All the newly prepared compounds were screened for their antifungal activities against five kinds of fungi. The bioactive assay showed that most of the synthesized compounds exhibited good or even stronger antifungal activities in comparison with the reference drugs miconazole and fluconazole. In particular, the 3,4-dichlorobenzyl derivative 5b showed a comparable or superior activity against all the tested fungal strains to standard drugs, and formed a supramolecular complex with CYP51 via the hydrogen bond between the 4-nitrogen of the triazole nucleus and the histidine residue. Preliminary experiments revealed that both of the active molecules 5b and 9c could intercalate into calf thymus DNAs, which might block DNA replication to exhibit their powerful antifungal abilities. Further studies indicated that compound 5b might be stored and transported by human serum albumin through hydrophobic interactions, specific electrostatic interactions and hydrogen bonds. These results strongly suggested that compound 5b could serve as a promising antifungal candidate.

New insights on the antibacterial efficacy of miconazole in vitro

Miconazole is a broad-spectrum antifungal used in topical preparations. In the present investigation the minimal inhibitory concentration (MIC) of miconazole for eighty wild type strains of gram-positive and gram-negative bacteria isolated from infected skin lesions was assessed using a modified agar dilution test (adapted to CLSI, Clinical Laboratory Standards Institute). 14 ATCC reference strains served as controls. Miconazole was found efficacious against gram-positive aerobic bacteria (n=62 species), the MICs against Staphylococcus (S.) aureus, S. spp., Streptococcus spp. und Enterococcus spp. ranged between 0.78 and 6.25 μg/mL. Interestingly, there were no differences in susceptibility between methicillin-susceptible (MSSA, 3) methicillin-resistant (MRSA, 6) and fusidic acid-resistant (FRSA, 2) S. aureus isolates. Strains of Streptococcus pyogenes (A-streptococci) (8) were found to be slightly more sensitive (0.78-1.563 μg/mL), while for gram-negative bacteria, no efficacy was found within the concentrations tested (MIC >200 μg/mL). In conclusion, for the gram-positive aerobic bacteria the MICs of miconazole were found within a range which is much lower than the concentration of miconazole used in topical preparations (2%). Thus topically applied miconazole might be a therapeutic option in skin infections especially caused by gram-positive bacteria even by those strains which are resistant to antibiotics.

Interaction of chlorhexidine with trisEDTA or miconazole in vitro against canine meticillin-resistant and -susceptible Staphylococcus pseudintermedius isolates from two UK regions

BACKGROUND

Topical therapy is an important alternative to systemic antibacterial therapy for treatment of canine superficial pyoderma in light of the emergence of multidrug-resistant staphylococci. Chlorhexidine is widely used in shampoo products alone or in combination with miconazole or tromethamine-ethylenediaminetetraacetic acid (trisEDTA). Comparisons of these combinations have not been made.

HYPOTHESIS/OBJECTIVES

To determine minimum inhibitory concentrations (MICs) of combinations of chlorhexidine/miconazole and chlorhexidine/trisEDTA in vitro in a collection of Staphylococcus pseudintermedius (SP) from northern (NUK) and southeastern (SEUK) United Kingdom (UK) sources.

METHODS

MICs of chlorhexidine, miconazole, trisEDTA and combinations of chlorhexidine/miconazole (1:1) or chlorhexidine/trisEDTA (80:16:1 and 80:5:1) were determined for 196 canine SP isolates from NUK [49 meticillin-resistant (MRSP), 50 meticillin-susceptible (MSSP)] and fom SEUK (48 MRSP, 49 MSSP) using agar dilution.

RESULTS

TrisEDTA alone did not inhibit growth. Chlorhexidine/miconazole MICs (median = 0.5 mg/L) were lower than those of either drug alone (P < 0.05) and lower than chlorhexidine/trisEDTA MICs (median = 1 mg/L; P < 0.0005) in each bacterial type and from both regions, except for miconazole in NUK MSSP. An additive interaction was noted between chlorhexidine and miconazole or trisEDTA (80:16:1 ratio) in 79 and 43 isolates, respectively, whereas antagonism between chlorhexidine and trisEDTA was noted for three isolates. NUK isolates were more susceptible than SEUK isolates (P < 0.05), except MRSP exposed to chlorhexidine and the chlorhexidine/trisEDTA (80:16:1) combination.

CONCLUSIONS AND CLINICAL IMPORTANCE

These low MICs are likely to be exceeded by topical therapy. Evaluation of the mechanisms by which chlorhexidine combinations interact to reduce MICs is warranted, in view of increasing concerns of biocide tolerance in staphylococci.

High Prevalence of Biocide Resistance Determinants in Staphylococcus aureus Isolates from Three African Countries

We assessed the prevalence of six biocide resistance genes among 82 methicillin-resistant Staphylococcus aureus (MRSA) and 219 methicillin-susceptible S. aureus (MSSA) isolates from three African countries; the prevalence was very high for sepA (95.3%), mepA (89.4%), and norA (86.4%), intermediate for lmrS (60.8%) and qacAB (40.5%), and low for smr (3.7%). A significant association between biocide resistance genes and antibiotic resistance was observed, and a new cutoff MIC of ≥1 mg/liter for chlorhexidine nonsusceptibility was defined.