Susceptibility of Pseudomonas isolates from the ears and skin of dogs to enrofloxacin, marbofloxacin, and ciprofloxacin

Antibiotic Susceptibility Profile of Pseudomonas aeruginosa Canine Isolates from a Multicentric Study in Romania

Treating infections caused by Pseudomonas aeruginosa is increasingly difficult due to high antibiotic resistance, materialized through the presence of multiple resistance strains, as well as due to rapid development of resistance throughout treatment. The present survey was conducted to investigate the antibiotic susceptibility profile of Pseudomonas aeruginosa pathogens in two University Veterinary hospitals from different geographical regions of Romania (i.e., Southwest Timișoara county and Northeast Iași county) involved in superficial canine infections. A total of 142 swab specimens were collected from dogs with superficial infections (superficial skin infections, otitis externa, and perianal abscess) to assess the presence of Pseudomonas aeruginosa, based on phenotypic and molecular characterization. According to their confirmed morphological and molecular features, 58 samples (40.84%; 58/142) were positive for Pseudomonas aeruginosa (according to their confirmed morphological and molecular features). Antibiotic susceptibility testing for 12 antibiotics was conducted using the Kirby–Bauer disc diffusion method. Drug resistance was observed in the case of all tested antibiotics. The susceptibility rate of P. aeruginosa strains that were tested in this study was in the following order: ceftazidime (53.44%; 31/58), followed by aztreonam (51.72%; 30/58), amikacin (44.82%; 26/58), azithromycin (41.37%; 24/58), gentamicin (37.93%; 22/58), cefepime (36.20%; 21/58), meropenem (25.86%; 13/58), piperacillin-tazobactam (25.86%; 13/58), imipenem (22.41%; 13/158), ciprofloxacin (17.24%; 10/58), tobramycin (8.62; 5/58), and polymyxin B (1.72; 1/58). The results highlight the importance of antibiotic susceptibility testing in Pseudomonas aeruginosa isolates from dogs with superficial infections to use an adequate treatment plan to manage the skin condition and other pathologies (otitis externa and perianal abscesses).

Occurrence, antimicrobial susceptibility, and pathogenic factors of Pseudomonas aeruginosa in canine clinical samples

Background and Aim:

Pseudomonas aeruginosa is a relevant opportunistic and difficult to treat pathogen due to its widespread environmental diffusion, intrinsic resistance to many classes of antimicrobials, high ability to acquire additional resistance mechanisms, and wide range of pathogenic factors. The present study aimed to investigate the prevalence of P. aeruginosa in canine clinical samples, the antimicrobial susceptibility against antipseudomonal antibiotics, and the presence of extracellular pathogenic factors of the isolates, as well as their ability to produce biofilm.

Materials and Methods:

Overall, 300 clinical specimens from dogs with pyoderma or abscesses (n=58), otitis (n=59), and suspected bladder infection (n=183) were analyzed by standard bacteriological methods. P. aeruginosa isolates were tested for their antimicrobial susceptibility by disk and gradient diffusion methods to determine the minimum inhibitory concentrations. The ability of the isolates to produce biofilm was investigated by a microtiter plate assay, while virulence genes coding for elastase (lasB), exotoxin A (toxA), alkaline protease (aprA), hemolytic phospholipase C (plcH), and exoenzyme S (ExoS) were detected by polymerase chain reaction method.

Results:

A total of 24 isolates of P. aeruginosa were found in clinical specimens (urine n=3, skin/soft tissue n=6, and ear canal n=15). No resistance was found to ceftazidime, gentamicin, aztreonam, and imipenem (IMI), while low levels of resistance were found to enrofloxacin (ENR) (4.2%) and piperacillin-tazobactam (8.3%). However, 41.7% and 29.2% of the isolates showed intermediate susceptibility to ENR and IMI, respectively. Disk and gradient diffusion methods showed high concordance. The majority of the isolates revealed a weak (33.3%) or intermediate (45.8%) ability to form biofilm, while the strong biofilm producers (20.8%) derived exclusively from the ear canal samples. All isolates (100%) were positive for lasB, aprA, and plcH genes, while exoS and toxA were amplified in 21 (87.5%) and 22 (91.7%) isolates, respectively.

Conclusion:

In the present study, P. aeruginosa isolates from canine clinical samples were characterized by low levels of antimicrobial resistance against antipseudomonal drugs. However, the high presence of isolates with intermediate susceptibility for some categories of antibiotics, including carbapenems which are not authorized for veterinary use, could represent an early warning signal. Moreover, the presence of isolates with strong ability to produce biofilm represents a challenge for the interpretation of the antimicrobial susceptibility profile. In addition, the high prevalence of the extracellular pathogenic factors was indicative of the potential virulence of the isolates.

Antimicrobial resistance and novel mutations detected in the gyrA and parC genes of Pseudomonas aeruginosa strains isolated from companion dogs

Background

Fluoroquinolone agents, such as enrofloxacin and marbofloxacin, are commonly used for pseudomonal infection in veterinary medicine. However, the rate of resistance to fluoroquinolones is rapidly increasing, according to multiple studies in various countries. Point mutations in the quinolone resistance-determining region (QRDR) are closely related to the increased fluoroquinolone resistance of Pseudomonas aeruginosa. The aim of this study was to investigate current antimicrobial susceptibility and fluoroquinolone resistance in P. aeruginosa strains isolated from dogs. The presence of point mutations in the QRDR was confirmed by gyrA and parC polymerase chain reaction and nucleotide sequencing analysis.

Results

A total of 84 nonduplicated P. aeruginosa strains were obtained from 228 healthy dogs (healthy group) and 260 dogs with clinical signs (infected group). Among these isolates, 38 strains from the healthy group were detected in several sample types, whereas 46 strains from the infected group were obtained mostly from dogs’ ears with otitis externa (41/260, 15.8%). All strains were resistant to nalidixic acid, while some were also resistant to enrofloxacin (23/84, 27.4%), marbofloxacin (17/84, 20.2%), levofloxacin (12/84, 14.3%), or ciprofloxacin (11/84, 13.1%). Enrofloxacin resistance was significantly higher in strains from the infected group than in those from the healthy group (p < 0.05). Among the 23 fluoroquinolone-resistant strains, 8 and 4 different mutations were detected in the gyrA and parC genes, respectively. Mutations in gyrA were significantly common in the infected group (p < 0.05). Hotspots for the gyrA and parC mutations were Thr83 (34.8%, 8/23) and Pro116 (91.3%, 21/23), respectively. Double and triple mutations were also found in 5 of the strains.

Conclusion

Novel mutations in the gyrA and parC genes were first found in P. aeruginosa isolated from companion dogs in South Korea. These findings suggest that it is important to encourage prudent use of fluoroquinolone antibiotics in canine pseudomonal infection treatment.

Antimicrobial resistance patterns of bacteria isolated from dogs with otitis

Antimicrobial-resistant bacteria in dogs can be transmitted to humans and close contact between dogs and people might foster dissemination of resistance determinants. The aim of our study was to describe the antimicrobial resistance (AMR) pattern of the major causative agents of canine otitis - one of the most common diseases in dogs - isolated in France. Data collected between 2012 and 2016 by the French national surveillance network for AMR, referred to as RESAPATH, were analysed. Resistance trends were investigated using non-linear analysis (generalised additive models). A total of 7021 antibiograms were analysed. The four major causative agents of canine otitis in France were coagulase-positive staphylococci, Pseudomonas aeruginosa, Proteus mirabilis and streptococci. Since 2013, resistance to fluoroquinolones has been on the decrease in both P. aeruginosa and Staphylococcus pseudintermedius isolates. For P. aeruginosa, 19.4% of isolates were resistant to both enrofloxacin and gentamicin. The levels of multidrug resistance (acquired resistance to at least one antibiotic in three or more antibiotic classes) ranged between 11.9% for P. mirabilis and 16.0% for S. pseudintermedius. These results are essential to guide prudent use of antibiotics in veterinary medicine. They will also help in designing efficient control strategies and in measuring their effectiveness.

In vitro antimicrobial activity of narasin and monensin in combination with adjuvants against pathogens associated with canine otitis externa

BACKGROUND

The emergence of antimicrobial resistance represents a serious human and animal health risk. Good antimicrobial stewardship is essential to prolong the lifespan of existing antibiotics, and new strategies are required to combat infections in man and animals.

HYPOTHESIS/OBJECTIVES

To determine the in vitro interaction of ionophores (narasin or monensin) with antimicrobial adjuvants (N-acetylcysteine (NAC), Tris-EDTA or disodium EDTA) against bacterial strains representing pathogens associated with canine otitis externa (OE).

ANIMAL/ISOLATES

American Type Culture Collection (ATCC) strains Staphylococcus aureus 29213, Pseudomonas aeruginosa 27853 and P. aeruginosa biofilm producer PAO1, and a clinical isolate of Proteus mirabilis from a case of canine OE were tested.

METHODS AND MATERIALS

A 2D microdilution checkerboard method was used, allowing calculation of fractional inhibitory concentration index (FICI), dose reduction index (DRI) and plotting of isobolograms.

RESULTS

The combination of narasin with either Tris-EDTA or disodium EDTA produced additive effects (FICI = 0.75) against P. aeruginosa ATCC 27853 and P. aeruginosa biofilm producer ATCC PAO1. An additive effect (FICI = 0.53-0.75) was found against S. aureus ATCC 29213 when narasin or monensin were combined with NAC. The highest DRI (32-fold) was found with monensin/NAC where the MIC of monensin was reduced from 4 to 0.125 μg/mL.

CONCLUSIONS AND CLINICAL IMPORTANCE

The combination of narasin with Tris-EDTA or disodium EDTA is a promising strategy to inhibit the intrinsic resistance elements of Gram-negative bacteria. These novel combinations potentially could be useful as a multimodal approach to treat mixed infections in canine OE.

Antimicrobial resistance in bacteria isolated from diseased horses in France

BACKGROUND

Horses are one of the potential reservoirs of antimicrobial resistance (AMR) determinants that could be transferred to human subjects.

OBJECTIVE

To describe the AMR patterns of major bacteria isolated from diseased horses in France.

STUDY DESIGN

Retrospective observational study.

METHODS

Data collected between 2012 and 2016 by RESAPATH, the French national surveillance network for AMR, were analysed. Only antimicrobials relevant in veterinary and human medicine for the isolated bacteria were considered. Mono- and multidrug resistance were calculated. The resistance proportions of major equine diseases were assessed and compared. Where data permitted, resistance trends were investigated using nonlinear analysis (generalised additive models).

RESULTS

A total of 12,695 antibiograms were analysed. The five most frequently isolated bacteria were Streptococcus spp., Escherichia coli, Pseudomonas spp., Staphylococcus aureus, Pantoea spp. and Klebsiella spp. The highest proportions of resistance to gentamicin were found for S. aureus (22.1%) and Pseudomonas spp. (26.9%). Klebsiella spp. and E. coli had the highest proportions of resistance to trimethoprim-sulfamethoxazole (15.5 and 26.2%, respectively). Proportions of resistance to tetracycline were among the highest for all the bacteria considered. Resistance to third-generation cephalosporins was below 10% for all Enterobacteriaceae. The highest proportions of multidrug resistance (22.5%) were found among S. aureus isolates, which is worrying given their zoonotic potential. From 2012 to 2016, resistance proportions decreased in Pseudomonas spp. isolates, but remained the same for S. aureus. For Streptococcus spp. and E. coli, resistance proportions to trimethoprim-sulfamethoxazole increased.

MAIN LIMITATIONS

Since antibiograms are not systematic analyses, any selection bias could impact the results.

CONCLUSIONS

Such studies are essential to estimate the magnitude of the potential threat of AMR to public health, to design efficient control strategies and to measure their effectiveness. These findings may also guide the initial empirical treatment of horse diseases.

Determination of minimum inhibitory concentrations for silver sulfadiazine and other topical antimicrobial agents against strains of Pseudomonas aeruginosa isolated from canine otitis externa

BACKGROUND

Otitis externa is a common presenting complaint in practice. Ear infections by Pseudomonas aeruginosa are particularly problematic due to the organism's high level of resistance and ability to damage the tympanum. Treatment should be based on susceptibility testing although minimum inhibitory concentrations (MICs) are not available for all treatment options. Silver sulfadiazine has been used in cases of recurrent P. aeruginosa otitis, although a MIC for silver sulfadiazine as a single agent has not been established.

OBJECTIVES

To describe susceptibility patterns of P. aeruginosa isolated from canine otitis externa and determine the MIC for silver sulfadiazine and other topical antimicrobials.

ANIMALS

Thirty-six P. aeruginosa isolates were collected from client-owned dogs, suffering from otitis externa.

METHODS AND MATERIALS

Susceptibility patterns were established using disc diffusion susceptibility testing against 17 antimicrobial agents. For determination of the MIC, selected strains were tested against increasing concentrations of marbofloxacin, enrofloxacin, gentamicin, polymyxin B and silver sulfadiazine using broth microdilution.

RESULTS

For nine of 17 antimicrobial agents, complete resistance was seen in all isolates tested via disk diffusion susceptibility testing. Approximately 94% and 96% of isolates were susceptible to gentamicin and imipenem, respectively. These findings were consistent with broth dilution, where all strains were susceptible to gentamicin. Resistance was higher against polymyxin B and the fluoroquinolones. Silver sulfadiazine was effective in vitro with a MIC ranging from 1 to 64 μg/mL.

CONCLUSIONS AND CLINICAL SIGNIFICANCE

As the MIC of silver sulfadiazine was lower than the concentration in a 1% preparation, such a product potentially represents a treatment option for dogs with P. aeruginosa otitis.

In vitro antimicrobial activity of monensin against common clinical isolates associated with canine otitis externa

Antimicrobial resistance and antimicrobial stewardship are of ever-increasing importance in veterinary medicine. Multidrug-resistant infections of the canine skin and ear continue to emerge, but the use of antibiotic classes of critical importance to human medicine may not represent good antimicrobial stewardship. Repurposing of old drugs that are not used in human medicine is one approach that addresses both these issues. In this study, the minimal inhibitory concentration (MIC) of monensin for 111 bacterial and yeast canine otitis isolates was determined using microdilution methodology according to Clinical Laboratory Standards Institute (CLSI) guidelines. Monensin was effective against all Gram-positive bacteria including the multidrug-resistant staphylococcal strains with MICs ranging from 1 to 4 μg/ml, but lacked antimicrobial activity against Gram-negative bacteria and yeast isolates. Monensin has potential to be incorporated as one of the main components in an otic formulation.

A study to evaluate the primary causes associated with Pseudomonas otitis in 60 dogs

OBJECTIVES

To evaluate the primary causes, age of onset and time from diagnosis of otitis to development of Pseudomonas otitis in each case.

MATERIALS AND METHODS

Data from clinical records of 60 dogs were extracted to address the study objectives. Pseudomonas otitis was diagnosed by clinical signs and positive culture.

RESULTS

In total, 57 purebred dogs and three crossbreed dogs were included: 32 dogs had unilateral and 28 bilateral disease. Underlying primary causes of otitis were allergy (42), masses (8), endocrine disease (7) and autoimmune disease (3). The mean age of onset of otitis (and subsequent time to development of Pseudomonas otitis) in dogs with allergic otitis was 40 months (28 months), with endocrine disease was 56 months (19 months) and masses 99 months (10 months).

CLINICAL SIGNIFICANCE

The most common primary causes of otitis in dogs with Pseudomonas infections are, in decreasing frequency: allergies, masses, endocrine disease and autoimmune disease. Secondary infections with Pseudomonas developed more quickly if there was a mass or autoimmune disease, as compared with allergies and endocrinopathies.

Public health risk of antimicrobial resistance transfer from companion animals

Antimicrobials are important tools for the therapy of infectious bacterial diseases in companion animals. Loss of efficacy of antimicrobial substances can seriously compromise animal health and welfare. A need for the development of new antimicrobials for the therapy of multiresistant infections, particularly those caused by Gram-negative bacteria, has been acknowledged in human medicine and a future corresponding need in veterinary medicine is expected. A unique aspect related to antimicrobial resistance and risk of resistance transfer in companion animals is their close contact with humans. This creates opportunities for interspecies transmission of resistant bacteria. Yet, the current knowledge of this field is limited and no risk assessment is performed when approving new veterinary antimicrobials. The objective of this review is to summarize the current knowledge on the use and indications for antimicrobials in companion animals, drug-resistant bacteria of concern among companion animals, risk factors for colonization of companion animals with resistant bacteria and transmission of antimicrobial resistance (bacteria and/or resistance determinants) between animals and humans. The major antimicrobial resistance microbiological hazards originating from companion animals that directly or indirectly may cause adverse health effects in humans are MRSA, methicillin-resistant Staphylococcus pseudintermedius, VRE, ESBL- or carbapenemase-producing Enterobacteriaceae and Gram-negative bacteria. In the face of the previously recognized microbiological hazards, a risk assessment tool could be applied in applications for marketing authorization for medicinal products for companion animals. This would allow the approval of new veterinary medicinal antimicrobials for which risk levels are estimated as acceptable for public health.

Topical ear treatment - options, indications and limitations of current therapy

Topical otic products form an integral part of the overall management of otitis externa. With an ever increasing array of ear drops and cleaners to choose from, appropriate selection of therapy can be difficult. The investigation of all cases of otitis externa should consider primary and secondary causes and predisposing and perpetuating factors. This article considers topical therapy under these same broad headings and discusses, through literature review, the various properties of the components of the ear cleaning solutions and drops.

Antimicrobial resistance in companion animals

Antimicrobial resistance (AMR) is an emerging problem in companion animals, because of difficult-to-treat infections, possible pressure to use antimicrobials that are important in human medicine, and potential zoonotic transmission. The extent and importance of AMR in companion animals are poorly understood, in part because of limited surveillance; however, it is clear that resistance is problematic in many pathogens and commensals, including staphylococci, enterococci, Escherichia coli and Salmonella.