Influence of hospital size on antimicrobial resistance and advantages of restricting antimicrobial use based on cumulative antibiograms in dogs with Staphylococcus pseudintermedius infections in Japan.

BACKGROUND: Antimicrobial resistance in Staphylococcus pseudintermedius (SP) and the prevalence of meticillin-resistant SP (MRSP) is increasing in dogs worldwide.
OBJECTIVES: To evaluate the influence of hospital size on antimicrobial resistance of SP and whether restricted use of antimicrobials based on antibiograms could reduce the identification of antimicrobial resistance in SP from infected dogs. METHODS AND MATERIALS: In Study 1, a total of 2,294 SP isolates from dogs with pyoderma (n = 1,858, 52 hospitals) or otitis externa (OE; n = 436, 44 hospitals) taken between 2017 and 2019 were analysed. Clinics were categorised into small, medium and large based on numbers of practicing veterinary surgeons. In Study 2, a cumulative antibiogram was constructed for 12 antimicrobials from one large veterinary clinic from 2017 to 2018. Referring to this antibiogram, the clinic introduced strict antimicrobial selection criteria to treat dogs with pyoderma and OE, starting in 2018.
RESULTS: MRSP was identified in 981 dogs (42.8%). In large clinics, the isolation rate of MRSP was 51.1% (404 of 791), which was significantly higher (P < 0.01) than in small clinics with less than two veterinary practitioners (34.0%, 154 of 453). In the antibiogram study, the susceptibility rates of oxacillin (MPIPC, 61.5%), cefpodoxime (CPDX, 55.8%) and minocycline (MINO, 55.8%) were significantly higher in 2019 (n = 52) than in 2017 to 2018 (n = 54; MPIPC, 37.0%; CPDX, 33.3%; MINO, 20.4%; P < 0.05). CONCLUSIONS AND CLINICAL RELEVANCE: Hospital size could affect the isolation rate of MRSP in dogs. Restricted use of antimicrobials for over a year based on cumulative antibiograms could reduce the resistance rate of multiple antimicrobials in SP isolated from dogs with pyoderma and OE.

Introduction

Canine pyoderma and otitis externa (OE) are among the most common diseases encountered in veterinary practice. , , , , , Staphylococcus pseudintermedius (SP) is a commensal and common bacterial pathogen in dogs with pyoderma and OE. , , In recent years, SP has gained considerable attention because of the emergence of antimicrobial resistance of SP and meticillin‐resistant SP (MRSP) in dogs worldwide. , , MRSP expresses the penicillin‐binding protein 2a, encoded by the mecA gene, and shows low affinity to all β‐lactam antimicrobials, including cephalosporins and carbapenems. In Japan, the isolation of MRSP in dogs was not reported until 2000. , Since then, MRSP has been reported in dogs with pyoderma or OE in several regions in Japan; however, the isolation rates of MRSP have varied greatly depending on the research areas and institutions. , , , , ,

Because MRSP isolates often are resistant not only to β‐lactams, but also to several other classes of antimicrobial drugs, the treatment of MRSP infection in dogs has been a challenge in veterinary medicine. The recommendations for MRSP infections in small animals by the Clinical Consensus Guidelines of the World Association for Veterinary Dermatology state that restriction policies for certain antimicrobial drugs might help to mitigate the progressive development and dissemination of multidrug‐resistant staphylococci. Recent studies in Japan revealed that the restricted use of antimicrobials for over a period of approximately two years, especially the use of third‐generation cephalosporins and fluoroquinolones, was effective in reducing antimicrobial resistance rates in the Staphylococcus intermedius group, including MR strains, and Escherichia coli isolated from diseased dogs in an animal hospital.

A cumulative antibiogram is a periodic summary of the test results of the antimicrobial susceptibility of specific micro‐organisms to batteries of antimicrobial drugs during a specific period of time (e.g. 12 months). Cumulative antibiograms are used to select appropriate empirical antimicrobial treatments and monitor the trends of antimicrobial resistance. In humans, the use of hospital cumulative antibiograms to guide the choice of empirical antimicrobial therapy has been identified as a key strategy to prevent and control the spread of antimicrobial‐resistant micro‐organisms in hospitals. ,

The influence of hospital size on meticillin resistance or the antimicrobial susceptibility pattern is unclear in SP isolated from dogs with pyoderma and OE. Moreover, only a few studies have evaluated the usefulness of antibiograms to establish the criteria for antimicrobial restriction in small animal practices. One objective of this study was to investigate the antimicrobial resistance pattern of SP in infected dogs from animal hospitals in Japan categorized into three different sizes based on numbers of practicing veterinary surgeons. The other objective was to evaluate whether the restricted use of antimicrobials based on cumulative antibiograms could reduce the frequency of resistance of several types of antimicrobials in clinical SP isolates from dogs with pyoderma and OE.

Materials and methods

Ethics

This study was conducted in compliance with applicable animal welfare regulations relating to the care and use of animals for scientific purposes. The study was conducted in accordance with good clinical practice guidelines, and informed consent was obtained from the owner of each participating dog.

Study design

This study analysed the antimicrobial resistance patterns of SP isolates from lesions of dogs with pyoderma or OE in different animal hospitals (Study 1), and evaluated the usefulness of restricting antimicrobial use based on an antibiogram for SP infections in dogs (Study 2).

Study 1: Analysis of antimicrobial resistance patterns of SP isolates from different animal hospitals

Bacterial samples and animal hospitals

Samples of SP were obtained from 2,294 dogs with pyoderma or OE that were treated in our affiliated veterinary clinics between 1 January 2017 and 31 December 2019. These samples were collected initially for bacterial culture and susceptibility testing by a commercial diagnostic bacteriology laboratory service. The samples were stored in Luria–Bertani broth (Sigma‐Aldrich Corp.; St Louis, MO, USA) with 10% glycerol at –80°C until further use. Pyoderma or OE had been confirmed by the attending veterinary surgeons based on clinical signs, cytological findings and bacterial culture. There were 1,858 SP isolates from pyoderma from 52 veterinary clinics and 436 from OE from 44 veterinary clinics in 17 cities (Hokkaido, Miyagi, Fukushima, Tokyo, Kanagawa, Chiba, Saitama, Ibaraki, Shizuoka, Aichi, Gifu, Nara, Kyoto, Osaka, Hyogo, Okayama and Hiroshima). The veterinary clinics were categorized into three sizes: large clinics with >10, medium clinics with three to nine, and small clinics with two or fewer practising veterinary surgeons.

Species identification

Each swab (Seed Swab TechnoAmenity Inc.; Kyoto, Japan) was inoculated onto 5% sheep blood agar (Eiken Chemical Co., Ltd; Tokyo, Japan) and/or mannitol salt agar (Eiken Chemical Co., Ltd) and incubated aerobically at 37°C for 18–24 h. Identification of SP was determined by colony morphology, the ability to grow on mannitol salt agar, Gram‐stain characteristics, coagulase reaction and multiplex‐polymerase chain reaction (multiplex‐PCR), which was performed with thermonuclease genes using a primer pair reported previously. Crude DNA for PCR was extracted with achromopeptidase (Wako Chemical Co. Ltd.; Osaka, Japan), as described previously.

Antimicrobial susceptibility testing and identification of MRSP

Antimicrobial susceptibility analyses were carried out on SP isolates by the disk diffusion susceptibility test using the KB disk (Eiken Chemical Co., Ltd.) according to the Clinical and Laboratory Standards Institute (CLSI) guidelines. , , The following commonly used drug classes in Japan were tested: oxacillin (MPIPC, 1 μg/disk), clavulanic acid‐amoxicillin (AMPC/CVA, 20 μg/10 μg/disk), cefalexin (CEX; 30 μg/disk), cefpodoxime (CPDX; 10 μg/disk), enrofloxacin (ERFX; 5 μg/disk), gentamicin (GM; 10 μg/disk), trimethoprim‐sulfamethoxazole (ST; 23.75 μg‐1.25 μg/disk), clindamycin (CLDM; 2 μg/disk), doxycycline (DOXY; 30 μg/disk), minocycline (MINO; 30 μg/disk), chloramphenicol (CP; 30 μg/disk) and fosfomycin (FOM; 50 μg/disk). In the disk diffusion testing, the interpretative criteria for susceptible (S), intermediate (I) or resistant (R), were taken from: the CLSI VET08 for MPIPC, CPDX and DOXY; the CLSI M100‐S30 for AMPC/CVA, ERFX, GM, ST, CLDM, MINO and CP; and the KB disk standard of Staphylococcus spp. for CEX and FOM. MRSP was identified with MPIPC disk (1 μg/disk) diffusion testing according to CLSI guidelines.

Study 2: Evaluation of the usefulness of restricting antimicrobials use with an antibiogram for SP infections in dogs

A cumulative antibiogram was constructed for all isolates collected from one large clinic (Tokyo) between 1 January 2017 and 31 September 2018 for 12 antimicrobial agents, including MPIPC, AMPC/CVA, CPDX, ERFX, GM, ST, CLDM, DOXY, MINO, CP and FOM according to the CLSI guidelines. The methods for disk diffusion testing were as described above. The CLSI guidelines recommend compiling the antibiogram at least annually, including only the first isolate per case in the period analysed, as well as only organisms for which ≥30 isolates were tested in the period analysed. The susceptibility rate of each antimicrobial was calculated based on the number of susceptible isolates, not including intermediate isolates. Based on the results of an antibiogram from 2017 to 2018, veterinary clinics introduced strict antimicrobial prescribing criteria starting on 1 November 2018 for the treatment of dogs with pyoderma or OE. Furthermore, the clinics preferred topical antimicrobial treatments, such as 0.5–2% chlorhexidine lotion or shampoo, and antimicrobial ear drops or cleaner, over systemic antimicrobial treatment. Following the restricted use of antimicrobials for over a year, a cumulative antibiogram was reconstructed using the susceptibility test data between 1 January 2019 and 31 December 2019.

Statistical analysis

Antimicrobial susceptibility patterns from different clinic sizes were analysed using a logistic regression equation. The susceptibility patterns before and after antimicrobial restriction with an antibiogram in a large veterinary clinic were analysed using the Chi‐square test. STATVIEW software (v.5.0, Hulinks; Tokyo, Japan) was used for both statistical analyses. A P‐value < 0.05 was considered statistically significant.

Results

Study 1

Tables 1 and 2 show the antimicrobial susceptibility testing results of SP isolated from dogs with pyoderma or OE in veterinary clinics of different sizes. The isolation rate of MRSP with the MPIPC disk diffusion test in large clinics was 51.1% (404 of 791), which was significantly higher (P < 0.01) than that in the small (34.0%, 154 of 453) and medium clinics (40.3%, 423 of 1,050; Table 3). Each susceptibility rate of AMPC/CVA, CEX, CPDX, ERFX, GM, ST, CLDM, MINO and CP in pyoderma, and that of CEX, CPDX, ERFX, ST, CLDM, CP and FOM in OE, was significantly higher in small clinics than in large clinics (P < 0.05; Table 3). Each susceptibility rate of MPIPC, AMPC/CVA, CEX, CPDX, ERFX, GM, ST CLDM, DOXY, MINO and CP in pyoderma, and that of MPIPC, AMPC/CVA, CEX, CPDX and ERFX in OE, was significantly higher in medium clinics than in large clinics (P < 0.05; Table 3). No antimicrobials used in both small and medium clinics had significantly lower susceptibility than those used in large clinics. There were no significant differences in the susceptibility rates of all tested antimicrobials in pyoderma between small and medium clinics. The susceptibility rates of CPDX and CLDM in OE were significantly higher in small clinics than in medium and large clinics (P < 0.05; Table 3).

Table 1

Antimicrobial susceptibility test results of Staphylococcus pseudintermedius isolated from dogs with pyoderma according to veterinary clinic size

Number of SP isolates (%)	Small (n = 356)			Medium (n = 886)
	R	I	S	R	I	S
MPIPC	124 (34.8%)	0 (0.0%)	232 (65.2%)	358 (40.4%)	0 (0.0%)	528 (59.6%)
AMPC/CVA	44 (12.4%)	0 (0.0%)	312 (87.6%)	126 (14.2%)	0 (0.0%)	760 (85.8%)
CEX	79 (22.2%)	19 (5.3%)	258 (72.5%)	217 (24.5%)	39 (4.4%)	630 (71.1%)
CPDX	111 (32.9%)	22 (6.5%)	204 (60.5%)	298 (34.3%)	83 (9.6%)	487 (56.1%)
ERFX	204 (57.3%)	21 (5.9%)	131 (36.8%)	521 (58.8%)	43 (4.9%)	322 (36.3%)
GM	120 (35.6%)	30 (8.9%)	187 (55.5%)	314 (36.2%)	72 (8.3%)	482 (55.5%)
ST	140 (40.7%)	19 (5.5%)	185 (53.8%)	307 (43.5%)	41 (5.8%)	358 (50.7%)
CLDM	182 (52.9%)	32 (9.3%)	130 (37.8%)	403 (57.1%)	63 (8.9%)	240 (34.0%)
DOXY	204 (60.5%)	28 (8.3%)	105 (31.2%)	548 (63.1%)	48 (5.5%)	272 (31.3%)
MINO	41 (12.2%)	120 (35.6%)	176 (52.2%)	87 (9.8%)	355 (40.2%)	442 (50.0%)
CP	98 (29.1%)	38 (11.3%)	201 (59.6%)	238 (27.4%)	131 (15.1%)	499 (57.5%)
FOM	17 (5.0%)	26 (7.7%)	294 (87.2%)	83 (9.6%)	52 (6.0%)	733 (84.4%)

SP, Staphylococcus pseudintermedius; MPIPC, oxacillin; AMPC/CVA, clavulanic acid‐amoxicillin; CEX, cefalexin; CPDX, cefpodoxime; ERFX, enrofloxacin; GM, gentamycin; ST, trimethoprim‐sulfamethoxazole; CLDM, clindamycin; DOXY, doxycycline; MINO, minocycline; CP, chloramphenicol; FOM, fosfomycin.

Table 2

Antimicrobial susceptibility test results of Staphylococcus pseudintermedius isolated from dogs with otitis externa according to veterinary clinic size

Number of SP isolates (%)	Small (n = 97)			Medium (n = 164)
	R	I	S	R	I	S
MPIPC	30 (30.9%)	0 (0.0%)	67 (69.1%)	65 (39.6%)	0 (0.0%)	99 (60.4%)
AMPC/CVA	15 (15.5%)	0 (0.0%)	82 (84.5%)	24 (14.6%)	0 (0.0%)	140 (85.4%)
CEX	16 (16.5%)	4 (4.1%)	77 (79.4%)	38 (23.2%)	14 (8.5%)	112 (68.3%)
CPDX	21 (21.6%)	9 (9.3%)	67 (69.1%)	61 (37.2%)	16 (9.8%)	87 (53%)
ERFX	60 (61.9%)	7 (7.2%)	30 (30.9%)	112 (68.3%)	12 (7.3%)	40 (24.4%)
GM	35 (36.1%)	12 (12.4%)	50 (51.5%)	74 (45.1%)	21 (12.8%)	69 (42.1%)
ST	41 (42.3%)	6 (6.2%)	50 (51.5%)	83 (51.6%)	9 (5.6%)	69 (42.9%)
CLDM	46 (56.1%)	5 (6.1%)	31 (37.8%)	103 (70.5%)	10 (6.8%)	33 (22.6%)
DOXY	66 (68.0%)	8 (8.2%)	23 (23.7%)	105 (64%)	8 (4.9%)	51 (31.1%)
MINO	14 (20.0%)	27 (38.6%)	29 (41.4%)	20 (19.8%)	28 (27.7%)	53 (52.5%)
CP	23 (23.7%)	17 (17.5%)	57 (58.8%)	68 (41.5%)	18 (11.0%)	78 (47.6%)
FOM	7 (7.2%)	7 (7.2%)	83 (85.6%)	16 (9.8%)	16 (9.8%)	132 (80.5%)

SP, Staphylococcus pseudintermedius; MPIPC, oxacillin; AMPC/CVA, clavulanic acid‐amoxicillin; CEX, cefalexin; CPDX, cefpodoxime; ERFX, enrofloxacin; GM, gentamycin; ST, trimethoprim‐sulfamethoxazole; CLDM, clindamycin; DOXY, doxycycline; MINO, minocycline; CP, chloramphenicol; FOM, fosfomyci.

Table 3

Comparisons between small, medium and large clinics for antimicrobial susceptibility rates in Staphylococcus pseudintermedius isolated from dogs affected with pyoderma or otitis externa

	Pyoderma
	Small (versus Large)			Medium (versus Small)			Medium (versus Large)
	OR	95% CI	P‐value	OR	95% CI	P‐value	OR	95% CI	P‐value
MPIPC	1.86	1.42–2.44	<0.001*	0.79	0.61–1.02	0.07	1.47	1.19–1.8	<0.001*
AMPC/CVA	2.03	1.41–2.96	<0.001*	0.85	0.58–1.22	0.39	1.73	1.32–2.26	<0.001*
CEX	1.75	1.32–2.33	<0.001*	0.93	0.71–1.23	0.63	1.64	1.32–2.03	<0.001*
CPDX	1.87	1.42–2.45	<0.001*	0.83	0.64–1.08	0.16	1.55	1.26–1.92	<0.001*
ERFX	1.86	1.4–2.47	<0.001*	0.98	0.76–1.27	0.88	1.82	1.45–2.3	<0.001*
GM	1.56	1.19–2.04	<0.001*	1	0.78–1.29	0.99	1.56	1.27–1.93	<0.001*
ST	1.44	1.1–1.89	0.01*	0.88	0.68–1.14	0.35	1.27	1.01–1.59	0.04*
CLDM	1.94	1.45–2.61	<0.001*	0.85	0.65–1.11	0.23	1.65	1.28–2.12	<0.001*
DOXY	1.28	0.95–1.72	0.10	1.01	0.77–1.33	0.95	1.29	1.02–1.63	0.03*
MINO	1.75	1.34–2.3	<0.001*	0.91	0.71–1.18	0.49	1.6	1.3–1.98	<0.001*
CP	1.73	1.32–2.27	<0.001*	0.91	0.71–1.18	0.5	1.59	1.29–1.96	<0.001*
FOM	1.42	0.97–2.1	0.07	0.79	0.54–1.14	0.22	1.13	0.85–1.49	0.40

MPIPC, oxacillin; AMPC/CVA, clavulanic acid‐amoxicillin; CEX, cefalexin; CPDX, cefpodoxime; ERFX, enrofloxacin; GM, gentamycin; ST, trimethoprim‐sulfamethoxazole; CLDM, clindamycin; DOXY, doxycycline; MINO, minocycline; CP, chloramphenicol; FOM, fosfomyci; OR; odds ratio, CI; confidence interval.

P < 0.05.

Study 2

From 2017 to 2018, 54 SP isolates were collected from dogs with pyoderma (n = 30) and OE (n = 24). The resulting cumulative antibiogram from 2017 to 2018 showed the following susceptibility rates (in ascending order): DOXY (14.8%), CLDM (16.7%), ERFX (18.5%), MINO (20.4%), ST (31.5%), CPDX (33.3%), MPIPC (37.0%), GM (40.7%), CEX (50.0%), CP (50.0%), FOM (57.4%) and AMPC/CVA (66.7%).

Based on these results, the large veterinary clinic introduced strict antimicrobial prescribing criteria to treat dogs with pyoderma and OE, which included the following: (i) systemic treatments with fluoroquinolones and β‐lactam antimicrobials, including first‐ and third‐generation cephalosporins should be used only when life‐threatening infection is expected; (ii) CP and FOM could be used for empirical treatment; and (iii) ST, CLDM, DOXY and MINO should be used according to the results of susceptibility tests. Following the restricted use of antimicrobials, a cumulative antibiogram was reconstructed using the susceptibility test data between 1 January and 31 December 2019. A total of 52 SP strains were isolated from dogs with pyoderma (n = 30) and OE (n = 22). Although the frequency of susceptibility was higher for all antimicrobials in 2019 compared to 2017 to 2018, with the exception of ST, these differences were significant only for MPIPC (61.5%, P = 0.02), CPDX (55.8%, P = 0.03) and MINO (55.8%, P = 0.001), as shown in Table 4.

Table 4

Results of antibiograms from Staphylococcus pseudintermedius isolated from dogs affected with pyoderma and otitis externa before (2017–2018) and after (2019) the restriction of antimicrobial use

Number of SP isolates (%)	2017–2018		2019		P‐value
	n	%	n	%
Total	54	100.0	52	100.0
MPIPC	20	37.0	32	61.5	0.02*
AMPC/CVA	36	66.7	41	78.8	0.23
CEX	27	50.0	35	67.3	0.11
CPDX	18	33.3	29	55.8	0.03*
ERFX	10	18.5	15	28.8	0.31
GM	22	40.7	30	57.7	0.10
ST	17	31.5	14	26.9	0.76
CLDM	9	16.7	15	28.8	0.21
DOXY	8	14.8	15	28.8	0.13
MINO	11	20.4	29	55.8	0.001*
CP	27	50.0	30	57.7	0.34
FOM	31	57.4	32	61.5	0.63

SP, Staphylococcus pseudintermedius; MPIPC, oxacillin; AMPC/CVA, clavulanic acid‐amoxicillin; CEX, cefalexin; CPDX, cefpodoxime; ERFX, enrofloxacin; GM, gentamycin; ST, trimethoprim‐sulfamethoxazole; CLDM, clindamycin; DOXY, doxycycline; MINO, minocycline; CP, chloramphenicol; FOM, fosfomycin

P < 0.05.

Discussion

This study investigated the influence of hospital size (number of practising veterinary surgeons) on the antimicrobial resistance of SP, and determined whether the restricted use of antimicrobials with antibiograms could reduce the antimicrobial resistance of SP in infected dogs. Study 1 included a total of 2,294 SP isolates from 17 cities in Japan. Previous Japanese studies analysed 31 to 282 strains of SP in dogs. , , , , , To the best of the authors’ knowledge, the present study used the largest number of SP strains isolated from dogs with pyoderma and OE in Japan. Previous reports revealed that the antimicrobial susceptibility patterns of MRSP differed between North America and Europe, which indicates differences in the susceptibility patterns between different MRSP clones across different countries. Although the present study revealed that the isolation rate of MRSP was 42.8% in total, the isolation rates of MRSP varied greatly (11.4–69.1%) depending on the research year (2007–2014), area and institution (private clinic or referral clinic) according to previous Japanese studies. , , , , ,

Two studies performed in referral clinics showed higher isolation rates of MRSP in dogs with pyoderma (2007–2009: 66.5%; 2010: 57%) , than those in a study performed in 11 animal hospitals (2009: 11.4%). Our study showed that the susceptibility rates of several classes of antimicrobials in SP isolated from dogs with pyoderma or OE were significantly lower in large veterinary clinics than in small and medium clinics. Furthermore, the isolation rate of MRSP was significantly higher in large clinics than in small and medium clinics. These findings indicate that the number of practising veterinary surgeons in a clinic could influence the antimicrobial resistance of SP in dogs.

A significant correlation between antimicrobial resistance and consumption of antimicrobials for S. aureus has been reported. Although the present study did not confirm the antimicrobial consumption in each clinic, or the medical history in each case, it was presumed that large veterinary clinics or referral clinics would use larger amounts of antimicrobials and have a larger number of recurrent cases than smaller clinics.

It has been reported that patterns of antimicrobial use could influence the antimicrobial resistance of S. aureus in humans. , For appropriate antimicrobial use, two guidelines were created independently in North America and the European Union in 2013 to 2014 for the antimicrobial treatment of canine skin diseases. , , However, these guidelines are not relevant to particular countries. There are no guidelines on the antimicrobial treatment of pyoderma and OE in dogs in Japan. The Guideline Committee of the Japanese Society of Veterinary Dermatology stated that it was difficult to propose a guideline for Japanese practitioners in 2017, because evidence for the practice was quite limited. The lack of guidelines leads to an inconsistent selection of antimicrobials by veterinary practitioners, which may contribute to an increase in resistant strains, especially in large veterinary clinics.

In Study 2, the restricted, antibiogram‐based use of antimicrobials significantly improved the susceptibility rate of MPIPC (37.0–61.5%) and CPDX (33.3–55.8%). We restricted the systemic use of fluoroquinolones and β‐lactam antimicrobials, including first‐ and third‐generation cephalosporins, as well as AMPC/CVA, which showed the highest susceptibility rate (66.7%) before restriction in this study. The susceptibility to MPIPC was low (37.0%) from 2017 to 2018, indicating a high prevalence of MRSP. For S. aureus, it has been reported that the use of fluoroquinolones and β‐lactam antimicrobials is a risk factor for meticillin resistance. A previous study indicated the importance of fluoroquinolones in promoting the survival and spread of multidrug‐resistant MRSP. Furthermore, the restriction of antimicrobials – mainly, third‐generation cephalosporins and fluoroquinolones – reduced the isolation rate of the MR S. intermedius group from 41.5% to 9.3%.

These findings suggest that the restriction of fluoroquinolones and β‐lactam antimicrobials for over a year could be useful in reducing the meticillin resistance rate of SP in dogs. The susceptibility rate of ERFX increased slightly from 18.5% to 28.8% and was not significantly changed in the present study. In a previous study, from 2016, the use of fluoroquinolones in the treatment of S. intermedius infections in dogs and cats was restricted; subsequently, the resistance rate of ERFX was significantly decreased in 2017 (39.0%) and 2018 (22.2%) compared to that in 2015 (59.4%). In the present study, the resistance rate of ERFX in SP isolates before the restriction was 81.5% (2017 to 2018), which was higher than that reported previously. Although further studies are needed to confirm the change in fluoroquinolone resistance after antimicrobial use restriction, the high resistance rate of ERFX and short duration of antimicrobial restriction could influence the recovery of fluoroquinolone resistance in SP.

Cumulative antibiograms help establish the criteria for empirical systemic treatment with antimicrobials in each hospital. However, in the treatment of canine OE, topical antimicrobial therapy is commonly used in small animal practices. The large hospital enrolled in this study usually has chronic severe or referral cases of canine OE that require systemic antimicrobial treatment. Therefore, our study analysed and established antibiograms for both pyoderma and OE. The antimicrobials that show a high susceptibility rate (>80%) in antibiograms are commonly recommended for empirical use. However, there were no antimicrobials with a susceptibility rate >80% in the present study. Therefore, we recommend the use of topical antiseptic therapy, especially chlorhexidine lotion or shampoo products for pyoderma, and antimicrobial ear drops or cleaner for OE, before systemic antimicrobial treatment, as much as possible. Previous reports showed that a twice‐weekly chlorhexidine shampoo combined with daily chlorhexidine spray was as effective as oral AMPC/CVA for treatment in dogs with pyoderma, including MRSP infection. A Japanese study revealed that the minimal inhibitory concentration (MIC) for chlorhexidine remained low, and that there were no significant differences in the MIC of chlorhexidine between mecA‐positive and mecA‐negative SP isolated from dogs with pyoderma. After the restriction of systemic antimicrobial treatment and the recommendation of topical treatment, MINO revealed a significant elevation in susceptibility rate (from 20.4% to 55.8%), while other classes of antimicrobials did not show a significant decrease in susceptibility rates in the present study. Although this study did not investigate the detailed use of each antimicrobial, topical treatment with antiseptics may be used as an alternative to antimicrobial use in veterinary clinics to prevent the resistance of SP, if systemic antimicrobials with susceptible rates >80% cannot be used based on the results of antibiograms in dogs.

Conclusions

In summary, antimicrobial resistance, including meticillin resistance in SP, may be influenced by the number of veterinary practitioners in the clinic. The restricted use of antimicrobials for over a year, based on antibiograms, reduced the rate of antimicrobial resistance of SP strains, including MRSP isolated from dogs with pyoderma and OE. Although the number of dogs is gradually decreasing in Japan, the estimated sale of antimicrobials has been increasing in recent years. It is important to select and restrict antimicrobials and to create antibiograms regularly at each veterinary clinic to prevent future antimicrobial resistance in dogs.