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

Towards a Harmonized Terminology: A Glossary for Biocide Susceptibility Testing

Disinfection is a key strategy to reduce the burden of infections. The contact of bacteria to biocides-the active substances of disinfectants-has been linked to bacterial adaptation and the development of antimicrobial resistance. Currently, there is no scientific consensus on whether the excessive use of biocides contributes to the emergence and spread of multidrug resistant bacteria. The comprehensive analysis of available data remains a challenge because neither uniform test procedures nor standardized interpretive criteria nor harmonized terms are available to describe altered bacterial susceptibility to biocides. In our review, we investigated the variety of criteria and the diversity of terms applied to interpret findings in original studies performing biocide susceptibility testing (BST) of field isolates. An additional analysis of reviews summarizing the knowledge of individual studies on altered biocide susceptibility provided insights into currently available broader concepts for data interpretation. Both approaches pointed out the urgent need for standardization. We, therefore, propose that the well-established and approved concepts for interpretation of antimicrobial susceptibility testing data should serve as a role model to evaluate biocide resistance mechanisms on a single cell level. Furthermore, we emphasize the adaptations necessary to acknowledge the specific needs for the evaluation of BST data. Our approach might help to increase scientific awareness and acceptance.

The nose is not enough: Multi-site sampling is best for MRSP detection in dogs and households

BACKGROUND

Following recovery from meticillin-resistant Staphylococcus pseudintermedius (MRSP) infection of any type, dogs may continue to carry MRSP asymptomatically on skin and mucosae, contributing to the spread of this multidrug-resistant, veterinary hospital-associated pathogen with zoonotic potential to others and into the environment.

OBJECTIVES

This study determined which canine anatomic and household environmental sites are most sensitive for sampling to identify carriage and contamination.

METHODS AND MATERIALS

Fifty-one dogs and 22 households, MRSP-positive on at least one tested site, were sampled on 132 and 40 occasions over time, respectively. Dogs were swabbed at six sites (mouth, nose, conjunctiva, skin, prepuce/vulva, perianal area); household environments were sampled using contact plates (mannitol salt agar [MSA] and MSA + 6 mg/L oxacillin [MS+]) on five sites. MRSP was isolated after enrichment, grown on MSA/MS+ and was confirmed by PCR. Generalized estimating equations were used for calculation of sensitivity (95% confidence interval) for each site/combination.

RESULTS

Each anatomical and environmental site yielded MRSP at least once. MRSP was isolated from only a single site in 27.3% of dogs, with the buccal mucosa showing the highest sensitivity (63.8%). Multi-site sampling of a minimum of four canine anatomical or four environmental sites, respectively, was needed to achieve >95% sensitivity.

CONCLUSIONS AND CLINICAL RELEVANCE

The canine buccal mucosa should be included in MRSP sampling protocols, ideally in addition to at least three other anatomical sites. Likewise, environment sampling should be of multiple household sites in cases where it is used as a part of clinical case management.

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.

The promising anti-virulence activity of candesartan, domperidone, and miconazole on Staphylococcus aureus

Staphylococcus aureus is a primary cause of hospital and community-acquired infections. With the emergence of multidrug-resistant S. aureus strains, there is a need for new drugs discovery. Due to the poor supply of new antimicrobials, targeting virulence of S. aureus may generate weaker selection for resistant strains, anti-virulence agents disarm the pathogen instead of killing it. In this study, the ability of the FDA-approved drugs domperidone, candesartan, and miconazole as inhibitors of S. aureus virulence was investigated. The effect of tested drugs was evaluated against biofilm formation, lipase, protease, hemolysin, and staphyloxanthin production by using phenotypic and genotypic methods. At sub-inhibitory concentrations, candesartan, domperidone, and miconazole showed a significant inhibition of hemolysin (75.8-96%), staphyloxanthin (81.2-85%), lipase (50-65%), protease (40-64%), and biofilm formation (71.4-90%). Domperidone and candesartan have similar activity and were more powerful than miconazole against S. aureus virulence. The hemolysins and lipase inhibition were the greatest under the domperidone effect. Candesartan showed a remarkable reduction in staphyloxanthin production. The highest inhibitory effect of proteolytic activity was obtained with domperidone and candesartan. Biofilm was significantly reduced by miconazole. Expression levels of crtM, sigB, sarA, agrA, hla, fnbA, and icaA genes were significantly reduced under candesartan (68.98-82.7%), domperidone (62.6-77.2%), and miconazole (32.96-52.6%) at sub-MIC concentrations. Candesartan showed the highest inhibition activity against crtM, sigB, sarA, agrA, hla, and icaA expression followed by domperidone then miconazole. Domperidone showed the highest downregulation activity against fnbA gene. In conclusion, candesartan, domperidone, and miconazole could serve as anti-virulence agents for attenuation of S. aureus pathogenicity.

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.

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.

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.