Antimicrobial resistance in bacteria from horses: Epidemiology of antimicrobial resistance

Antimicrobial resistance poses a significant threat to the continued successful use of antimicrobial agents for the treatment of bacterial infections. While the epidemiology of antimicrobial resistance in bacteria from man has been studied extensively, less work has been undertaken in companion animals, particularly horses. Methicillin‐resistant Staphylococcus aureus has been identified as a cause of infections, with a low prevalence of nasal carriage by horses in the community but higher for hospitalised horses. Molecular characterisation has shown methicillin‐resistant Staphylococcus aureus strains either to be predominantly of types associated with horses or of sequence type ST398. Antimicrobial‐resistant Escherichia coli (including multidrug‐resistant and extended spectrum β‐lactamase‐producing isolates) have caused infections and been documented in faecal carriage by horses, with many significant resistance mechanisms identified. More sporadic reports and molecular characterisation exist for resistance in other bacteria such as enterococci, Salmonella, Acinetobacter and Pseudomonas species. Limited work has been undertaken evaluating risk factors and much of the epidemiology of antimicrobial resistance in bacteria from horses remains to be determined.     

Airborne Gram‐Negative Bacterial Flora in Animal Houses

The concentration and the species composition of airborne gram‐negative bacteria were studied in four cattle houses, one pig house and one poultry barn. On average only between 0.02 and 5.2 % of the total number of culturable aerobic bacteria were identified as gram‐negative bacteria. Obligate anaerobic gram‐negative bacteria were not isolated at all. In the airborne gram‐negative bacterial flora the following bacterial families dominated: the Enterobacteriaceae, the Pseudomonadaceae and the Neisseriaceae. Within the family of the Enterobacteriaceae the species Escherichia coli and Enterobacter agglomerans were predominant. In animal houses using straw as bedding material Ent. agglomerans was most frequent, whereas in animal houses without litter E. coli was mainly found. Airborne Neisseriaceae were isolated very frequently in cow barns with Acinetobacter lowffii as the primary species. Airborne Pseudomonadaceae were found in high concentrations during periods of high air humidity. The results presented may also give some indications on the origin and sources of airborne endotoxins in animal housing.     

Seasonal effects on the aerobic bacterial and fungal conjunctival flora of normal thoroughbred brood mares in Florida

Objective To evaluate seasonal effects on the presence or absence of fungal and aerobic bacterial flora of the conjunctival fornix of normal Florida Thoroughbred horses. Sample population Both eyes of 100 horses. Procedure Horses with normal anterior segment ophthalmic examinations from three farms in north central Florida were included. Each animal had the ventral conjunctival fornix of each eye swabbed with sterile culturettes. Samples were taken in October, January, April, and July (1999–2000). Aerobic and fungal cultures were plated. Bacterial cultures were reviewed at 24 and 48 h. Fungal cultures were reviewed weekly for 4 weeks. Logistic regression analysis with season as a factor and age of the horse as a covariate was performed. Statistical significance was set at P < 0.01. Results Horses ranged from 3 to 24 years of age, with a median age of 9 years. Twenty‐four genera of bacteria and 35 genera of fungi were recovered. Corynebacterium sp., Staphylococcus sp., Bacillus sp. and Moraxella sp. were the bacteria most frequently isolated. Mold species, dematiaceous mold species, Chrysosporium sp., Cladosporium sp., and Aspergillus sp. were the most frequently recovered fungi. Season did not have a significant effect on the presence of microorganisms isolated for individual horses adjusted for age. Younger horses had an increased incidence of gram‐negative rods and fungal isolates. The number of bacteria and fungi isolated are not uniform across seasons. Conclusion There were no significant differences between the number or type of organisms cultured during the sampling seasons in normal Florida horses. A large range of normal bacterial and fungal flora were isolated from these horses. The number of bacteria and fungi isolated are not uniform across seasons. The likelihood of detecting an organism depends on the horses’ age.     

Methicillin-resistant Staphylococcus aureus in a population of horses in Australia

Objective To evaluate if methicillin‐resistant Staphylococcus aureus (MRSA) is present in the horse population in Australia. Design A two‐part retrospective study of laboratory submissions of microbial culture results from horses. Methods Part A: medical records of 216 horses that had MRSA screening performed on nasal swabs collected over a 30‐day period at admission to the Scone Equine Hospital Clovelly Intensive Care Unit were retrieved. Part B: laboratory records from 2004 to 2009 of culture submissions to the Scone Veterinary Laboratory were reviewed and cultures that grew MRSA were identified. The MRSA isolates from Parts A and B were genotyped over an 18‐month period. Results MRSA screening of 216 horses identified eight (3.7%) positive samples. MRSA was isolated from cultures of 80 (0.002%) clinical bacteriology samples over a 6‐year period. Genotypic analysis was performed on 36 isolates. All MRSA characterised had the same pulse field gel electrophoresis pattern (type 1), with eight closely related subtypes identified (subtypes A–F and H) and 66% of isolates classified as subtype D, which multilocus sequence and staphylococcal cassette chromosome mec typing analysis identified as ST612‐MRSA‐IVa, a clonal complex (CC) 8 S. aureus strain. Antimicrobial resistance to more than two classes of antimicrobials was common. Conclusions MRSA was present in a population of horses in Australia. Genotypic analysis of the isolates identified the MRSA strain as CC8 S. aureus. Further research needs to be undertaken to evaluate MRSA infection and colonisation of horses and personnel in Australia.     

P‐74 Evaluation of the in vivo effects of Tris‐EDTA and chlorhexidine digluconate 0.15% solution in chronic bacterial otitis externa: 11 cases

The objectives of this study were to evaluate in vivo tolerance, and antimicrobial and clinical activities of a topical otic preparation containing EDTA tromethamine (Tris) and chlorhexidine digluconate 0.15% solution (Otodine^®) in dogs with chronic bacterial otitis externa. Eleven dogs were included. The affected ears were filled with the solution once daily during a 2‐week period. Dogs were evaluated on days 0, 14 and 28. Three clinical parameters (exudate, erythema, pain) and three cytologic parameters (Malassezia, cocci, rods) were scored (0–4 scale) by otoscopic and cytological examinations of otic exudate. Bacterial cultures were performed at each time point. If there were bacteria on cytological examination on day 14, the dogs were treated with the original product, with the addition of enrofloxacin (5%) applied 10 min after the original product, for a further 2 weeks. All 11 cases yielded isolates of resistant gram‐negative bacteria; gram‐positive bacteria were also isolated from six of 11 dogs. On day 14, six of 11 dogs were negative on culture examination; on day 28, 10 of 11 were negative and only one case had a positive culture. On day 14, clinical and microbial scores (cytology) were reduced by 54.6 and 71.1%, respectively, and by 85.7 and 94% on day 28. All cases reported good tolerance of the treatment. The results show that this ear solution was helpful in the management of chronic bacterial otitis externa in dogs and was well tolerated. There seems to be a synergistic effect of the combination of Tris‐EDTA/chlorhexidine digluconate 0.15% solution, and an antimicrobial agent (enrofloxacin) against resistant gram‐positive and gram‐negative bacteria. Funding: Self‐funded.     

Isolation of obligate anaerobic bacteria from ulcerative keratitis in domestic animals

Objective To determine the frequency of obligate anaerobic bacterial isolation from corneal samples of domestic animals with ulcerative keratitis and to characterize the historical, clinical, cytological, and microbiological features of culture‐positive cases. Animals studied Three hundred and thirty domestic animals with ulcerative keratitis. Procedures Anaerobic bacteriologic culture and Gram stain were performed on corneal samples from consecutive animals examined with suspect septic ulcerative keratitis. Additional corneal diagnostics included: aerobic bacteriologic culture for all species; fungal culture for ungulates; Mycoplasma culture and virus isolation or feline herpesvirus‐1 (FHV‐1) polymerase chain reaction (PCR) for cats. Historical, clinical, and cytological findings were correlated with microbiologic data. Results Anaerobic bacteria were isolated from 13.0% of corneal samples (dogs: 14.0%; horses: 12.9%; cats: 7.9%; alpacas: 18.8%). The most frequent isolates were Clostridium, Peptostreptococcus, Actinomyces, Fusobacterium, and Bacteroides species. The majority of these infections were mixed anaerobic and aerobic bacteria, unless antimicrobial therapy had been administered prior to presentation. The clinical appearance of anaerobic bacterial culture‐positive cases was highly variable. Ocular trauma, pre‐existing corneal disease, previous corneal surgery, and chronic dermatological disease were significantly (P ≤ 0.05) correlated with positive anaerobic cultures in one or more species. Conclusions The results of the present study demonstrate that obligate anaerobic bacteria are present within the intralesional flora of ulcerative keratitis in domestic animals. In most species evaluated, these bacteria were identified infrequently. Anaerobic bacterial infection of the cornea most frequently occurs in association with other ocular pathogens and previous corneal abnormalities.     

Prevalence of ocular microorganisms in hospitalized and stabled horses

Microorganisms from normal eyes of hospitalized and stabled horses were identified, and the frequency of isolation was compared between the 2 groups. Using standard techniques, swab specimens from both eyes of 22 hospitalized horses and both eyes of 18 stabled horses were cultured for aerobic bacteria and fungi. Ninety-six aerobic bacteria and 57 fungi were isolated. The predominant bacterial isolates were gram-positive organisms, most of which belonged to the genera Corynebacterium, Bacillus, Staphylococcus, and Streptomyces. Gram-negative organisms comprised less than one-fourth of the bacterial isolates, with the genera Neisseria, Moraxella, and Acinetobacter being the most commonly isolated. Environmental fungi Cladosporium and Alternaria accounted for half of all fungal isolates. In only 5 horses were fungi isolated without accompanying isolation of bacteria. The frequency of isolation of fungi was higher (P less than 0.01) in stabled horses. For bacteria, the frequency of isolation was higher (P less than 0.08) in male horses. Results of susceptibility testing were recorded as the percentage of all isolates susceptible to a given antimicrobic drug. Bacterial isolates were highly susceptible (greater than or equal to 90%) to neomycin, polymixin B, gentamicin, and chloramphenicol. Overall, filamentous fungi had highest susceptibility to natamycin (97%). Miconazole was highly efficacious (100% susceptibility) against Fusarium and Aspergillus.     

Detection of methicillin‐resistant Staphylococcus aureus (MRSA) in the microbial flora from the conjunctiva of healthy donkeys from Sicily (Italy)

Objective To describe the bacterial flora present in the normal conjunctiva of donkeys from Sicily (Italy). Animals studied A total of 46 healthy donkeys housed in 3 locations within the territory of Palermo (Sicily, Italy) were studied. Donkeys ranged from 2 to 13 years of age, with a median age of 6 years. Procedures Forty‐six conjunctival swabs were obtained from both eyes of each animal, and specimens were cultured for aerobic bacteria. Furthermore, the antimicrobial activity of methicillin (1 μg) and oxacillin (5 μg) on Staphylococcus spp. isolates was evaluated, and a specific PCR assay, which allows the detection of mecA gene specific for methicillin‐resistant Staphylococcus aureus (MRSA) strains, was performed. Results Forty of 46 (86.9%) donkeys were positive for bacteria. Eighty bacterial isolates, representing 9 bacteria genera, were successfully cultured. The most frequently recovered bacterial genus was Staphylococcus (52/80 isolates; 65%). Several strains (20/80 isolates; 25%) belonging to the Enterobacteriaceae family were also isolated, among which the most frequently isolated genus was Enterobacter (eight isolates). Of the 52 Staphylococcus spp. isolates, 14 (26.9%) strains were oxacillin/methicillin resistant. The mecA gene was detected in 6/52 (11.5%) strains. Conclusions This study contributes to the knowledge about normal ocular flora and MRSA occurrence in donkey farms in Sicily.     

Orbital abscess bacterial isolates and in vitro antimicrobial susceptibility patterns in dogs and cats

Objective To determine bacterial populations, in vitro antimicrobial susceptibility patterns, and sources of microorganisms for dogs and cats with orbital abscess. Animals studied In total, 34 dogs and 7 cats with orbital abscess participated in the study. Procedure Medical records of dogs and cats with a clinical diagnosis of orbital abscess, confirmed by cytologic or histopathologic evaluation of orbital specimens, were reviewed from the years 1990 to 2007. Animal signalment, presumptive source of microorganisms and mechanism of orbital introduction, bacterial isolates, and aerobic bacterial in vitro antimicrobial susceptibility test results were recorded. Percentages of susceptible aerobic bacterial isolates were compared among antimicrobials. Results Twenty dogs and five cats had positive culture results. The most frequent bacterial genera isolated from dogs were Staphylococcus, Escherichia, Bacteroides, Clostridium and Pasteurella. The most frequent bacterial genera isolated from cats were Pasteurella and Bacteroides. Aerobic bacterial isolates from dogs had the highest percentage of susceptibility to amikacin, ceftiofur, gentamicin, imipenem, ticarcillin and trimethoprim–sulfamethoxazole. Aerobic bacterial isolates from dogs had the lowest percentage of susceptibility to ampicillin, clindamycin, erythromycin and penicillin. Antimicrobial resistance was uncommon among feline aerobic bacterial isolates. The most commonly identified routes of orbital bacteria introduction were extension from adjacent anatomical structures, penetrating exogenous trauma, and foreign bodies. Conclusions Mixed aerobic and anaerobic bacterial infections of the orbit occur commonly in dogs and cats. On the basis of aerobic and anaerobic bacterial isolates and in vitro susceptibility testing of aerobic bacterial isolates, cephalosporins, extended‐spectrum penicillins, potentiated‐penicillins and carbapenems are recommended for initial antimicrobial therapy of orbital abscess in dogs and cats.     

Ulcerative keratitis in thoroughbred racehorses in Japan from 1997 to 2008

Objective To describe the number of cases, etiologies, healing times, and results of microbial culture and susceptibility testing of corneal ulcers in thoroughbred racehorses in Japan. Procedure Retrospective study of the medical records of racehorses belonging to the Japan Racing Association (JRA) from 1997 to 2008. Results A total of 2846 horses suffered ulcerative keratitis. These horses accounted for 90.5% of all the corneal problems and 54.9% of the entire number of horses with ocular diseases. Running in races was the cause in 64.3% of the cases. The mean healing time of the ulcers developed in races was 5.5 ± 9.6 days, which was shorter than that of the ulcers unrelated to racing (8.6 ± 11.7 days). In horses presented for examination by the next day after the race, healing was even more rapid (4.1 ± 7.5 days) than in horses presented later (12.4 ± 14.7 days). Microbial culture was performed on 74 samples of 58 horses. Forty‐four bacterial and four fungal organisms were isolated from 35 samples of 29 horses. Pseudomonas aeruginosa (10) and Streptococcus equi subspecies zooepidemicus (5) were the bacteria most frequently isolated. There was no tendency of increasing antibiotic resistance of these organisms. Conclusions Ulcerative keratitis is the most frequent corneal and ocular disease of the racehorse in Japan. Careful observation of the eyes after racing is necessary as early diagnosis and treatment of corneal ulcers speeds healing. Many antibiotic have efficacy against the bacterial isolates, however, potent antibiotics should be reserved for the most severe corneal ulcers.     

Cross-sectional study of antimicrobial-resistant bacteria in horses. Part 1: Prevalence of antimicrobial-resistant Escherichia coli and methicillin-resistant Staphylococcus aureus

Reasons for performing study: The increasing prevalence of antimicrobial‐resistant bacteria such as methicillin‐resistant Staphylococcus aureus (MRSA) and antimicrobial‐resistant Escherichia coli represents a significant problem. However, the carriage of such bacteria by horses in the UK has not been well characterised. Objectives: To estimate the prevalence of nasal carriage of MRSA and faecal carriage of antimicrobial‐resistant E. coli amongst horses in the general equine community of the mainland UK. Methods: A cross‐sectional study of horses recruited by 65 randomly selected equine veterinary practices was conducted, with nasal swabs and faecal samples collected. Faecal samples were cultured for antimicrobial‐resistant E. coli. Nasal swabs were cultured for staphylococcal species; methicillin‐resistant isolates identified as S. aureus were characterised by SCCmec and spa gene typing. Multilevel logistic regression models were used to calculate prevalence estimates with adjustment for clustering at practice and premises levels. Spatial variation in risk of antimicrobial resistance was also examined. Results: In total, 650 faecal samples and 678 nasal swabs were collected from 692 horses located on 525 premises. The prevalence of faecal carriage of E. coli with resistance to any antimicrobial was 69.5% (95% CI 65.9–73.1%) and the prevalence of extended‐spectrum β‐lactamase (ESBL)‐producing E. coli was 6.3% (95% CI 4.1–9.6%). The prevalence of nasal carriage of MRSA was 0.6% (95% CI 0.2–1.5%). Spatial analysis indicated variation across the UK for risk of carriage of resistant and multidrug‐resistant (resistant to more than 3 antimicrobial classes) E. coli. Conclusions and potential relevance: Carriage of MRSA by horses in the community appears rare, but the prevalence of antimicrobial‐resistant E. coli (including ESBL‐producing E. coli) is higher. A high prevalence of antimicrobial‐resistant bacteria could have significant health implications for the horse population of the UK.     

Effects of Machine‐milking on the Bacterial Flora of Teat Duct and Mammary Gland of Ewes

In total, 308 paired‐samples of teat duct material and milk, were collected before and 50–70 min after machine‐milking, from 30 ewes. Samples were processed bacteriologically. For analysis of results, we compared changes in bacterial isolation following milking, for duct and milk samples; statistical significance was assessed by the Sign Test. Bacteria were isolated from 18 (6%) duct and 19 (6%) milk samples collected before the milking procedure; respective figures after it, were 81 (26%) and 33 (11%). In 77 (25%) cases, bacteriological findings in the two duct samples of each pair were different; in seven cases bacteria were isolated only before, whilst in 70 cases bacteria were isolated only after milking (P < 0.005); respective results for milk samples were 26 (8%): 6 and 20 cases (P = 0.693). The majority of bacterial isolates were staphylococci, accounting for 63% of 99 isolates. The milking procedure predisposes to entrance of bacteria into the teat duct; however, increased bacterial isolation from the teat did not result to increased mammary infections, likely as a consequence of defence mechanisms present in healthy teats.     

Blood thiamine levels in clinically normal goats and goats with suspected polioencephalomalacia

Abstract

AIMS: To identify and describe culture and antimicrobial resistance (AMR) patterns in bacteria isolated from canine urinary samples submitted to a New Zealand veterinary diagnostic laboratory.

METHODS: Records from a veterinary diagnostic laboratory were examined for bacterial isolates cultured from canine urine samples between January 2005 and December 2012. Culture and susceptibility results were compiled with information on the age, sex and breed of dog. Repeat submissions were removed. Susceptibility was assessed using results of the Kirby-Bauer disk diffusion method, for a standard panel including amoxicillin-clavulanic acid (AMC), cefovecin (from 2010–2012), cephalothin, clindamycin, enrofloxacin and trimethoprim-sulphonamide (TMS).

RESULTS: A total of 5,786 urine samples were submitted for analysis, and 3,135 bacterial isolates were cultured from 2,184 samples. Of these 3,135 isolates, 1,104 (35.2%) were Escherichia coli, 442 (14.1%) were Staphylococcus spp., 357 (11.4%) Proteus mirabilis and 276 (8.8%) were Enterococcus spp. The frequency of culture-positive samples increased with increasing age in both female and male dogs (p<0.001). The percentage of E. coli isolates resistant to AMC and cephalothin increased between 2005 and 2012 (p<0.001), as did resistance to enrofloxacin (p=0.022), but there was no change in resistance to TMS (p=0.696). Enrofloxacin was the antimicrobial with the least resistance shown by the four most common bacteria isolated during the course of the study.

CONCLUSIONS AND CLINICAL RELEVANCE: The results of this study provide important regional information regarding the prevalence of bacterial uropathogens and their susceptibility patterns. There was an increase in resistance to some commonly used antimicrobials in the treatment of urinary tract infections. Having access to regional antimicrobial susceptibility results is crucial when forming guidelines for the use of antimicrobials for the treatment of urinary tract infections. Given changes in practising habits and antimicrobial usage over time, ongoing monitoring and surveillance of resistance in pathogens is needed.     

Trends in fluoroquinolone resistance of bacteria isolated from canine urinary tracts.

Fluoroquinolone (FQ) antimicrobial agents are used extensively in human and veterinary medicine. Widespread use of any antimicrobial agent can apply selective pressure on populations of bacteria, which may result in an increase in the prevalence of antimicrobial-resistant isolates. Antimicrobial-susceptibility data on bacteria isolated from the canine urinary tract by the University of Missouri-Columbia Veterinary Medical Diagnostic Laboratory, Columbia, MO, were used to determine whether there has been an increase in the prevalence of FQ-resistant bacteria over time. Between January 1992 and December 2001, minimum inhibitory concentrations of either ciprofloxacin (1992-1998) or enrofloxacin (1998-2001) were determined for 1,478 bacterial isolates from the canine urinary tract. The predominant bacterial species isolated were Escherichia coli (547 isolates), Proteus mirabilis (156), and Staphylococcus intermedius (147). In all, there were 13 bacterial species with more than 25 isolates each. A significant increase in the overall proportion of resistant bacterial isolates was documented from 1992 to 2001 (Cochran-Armitage test for trend, P < 0.0001). The same increase in resistant isolates was documented when either ciprofloxacin or enrofloxacin was analyzed separately (P < 0.0001 and P < 0.0002, respectively). No difference was detected in rates of bacterial FQ resistance with regard to the sex of the dog from which the bacteria were isolated. The frequency with which some bacterial species were isolated differed with the sex of the infected dog. Proteus mirabilis was found more often in females (P < 0.0001), whereas beta hemolytic Streptococcus spp., were found more often in males (P = 0.0003). Although the overall efficacy of FQ antimicrobials remained high with greater than 80% of isolates being susceptible, the data demonstrated an increase in the proportion of resistant bacteria isolated from the urinary tract of the dog.     

Cross-sectional study of antimicrobial-resistant bacteria in horses. Part 2: Risk factors for faecal carriage of antimicrobial-resistant Escherichia coli in horses

Reasons for performing study: The increasing prevalence of antimicrobial resistant bacteria such as antimicrobial‐resistant and extended spectrum β‐lactamase (ESBL)‐producing Escherichia coli represents a significant problem for human and veterinary medicine. Despite this, the risk factors for faecal carriage of such bacteria by horses in the UK, particularly those in the wider community, have not been well described. Objectives: To characterise the risk factors for faecal carriage of antimicrobial‐resistant E. coli amongst horses in the mainland UK. Methods: A cross‐sectional study of horses recruited by 65 randomly selected equine veterinary practices was conducted, with a faecal sample collected and self‐administered questionnaire completed by the horse owner. Faecal samples were cultured for antimicrobial‐resistant E. coli, with isolates confirmed as E. coli having their antimicrobial resistance profile determined. Multilevel, multivariable logistic regression models were used to investigate risk factors for the carriage of antimicrobial‐resistant E. coli in the sample population. Results: Faecal samples and completed questionnaires were obtained for 627 horses located on 475 premises. Recent hospitalisation, contact with specific types of nonequid animals, the type of premises, the surrounding land use, the reason for veterinary treatment received in the last 6 months and antimicrobial treatment in the previous 10 days were identified as risk factors for many of the antimicrobial‐resistance outcomes considered. Being stabled on the same yard as a recently hospitalised horse was identified as a risk factor for increased risk of carriage of ESBL‐producing E. coli. Conclusions and potential relevance: Increasing antimicrobial resistance may have significant health implications for the horse population of Great Britain. This form of epidemiological investigation highlights potential risk factors that may be controlled to limit the extent of the problem.     

Antimicrobial Susceptibilities of Aerobic Isolates from Respiratory Samples of Young New Zealand Horses

Background

Decreased efficacy of antimicrobials and increased prevalence of multidrug resistance (MDR) is of concern worldwide.

Objectives

To describe and analyze bacterial culture and antimicrobial susceptibilities from respiratory samples submitted from young horses (4 weeks to 3 years old).

Animals

Samples from 289 horses were submitted to a commercial laboratory.

Methods

A retrospective database search of submissions made to a New Zealand veterinary laboratory between April 2004 and July 2014. The results of in vitro susceptibility testing by Kirby‐Bauer disc diffusion were described and tabulated for the major bacterial species isolated. Multiple correspondence analysis (MCA) was used to describe the clustering of MDR isolates and selected demographic variables.

Results

Overall, 774 bacterial isolates were cultured from 237 horses, the majority of these isolates were gram‐positive (67.6%; 95% CI 64.3–70.9%). Streptococcus spp. were the most common genus of bacteria isolated and were 40.1% (95% CI 36.6–43.5%) of the isolates cultured. Susceptibility of Streptococcus spp. to penicillin, gentamicin, and ceftiofur was >85%. Overall, gram‐negative susceptibility to ceftiofur, tetracycline, and TMPS was <75%. MDR was defined as resistance to 3 or more antimicrobials, and was found in 39.2% of horses (93/237; 95% CI 33.0–45.5%).

Conclusions and clinical importance

Culture and susceptibility results have highlighted that MDR is an emerging problem for young horses in New Zealand (NZ), where a bacterial respiratory infection is suspected. This should be considered when prescribing antimicrobials, and emphasizes the need for submission of samples for culture and susceptibility.     

Comparison of the bacterial and fungal flora in the pharynx of normal horses and horses affected with pharyngitis

A total of 43 horses were used for the study of the pharyngeal bacterial flora. The median value of the number of bacteria in the group of 19 normal horses was 3.8 × 10⁴ cfu/g of secretions. This value was 6.4 × 10⁴cfu/g in horses with grade I pharyngitis, 1.3 × 10⁵ cfu/g in horses with grade II pharyngitis and 3.5 × 10⁶ cfu/g in horses affected with grades III and IV pharyngitis. Corynebacterium spp, coagulase-negative staphylococci, Nocardia spp, Moraxella spp and Enterobacter spp were the most frequently encountered bacteria in the normal animals as well as in horses affected with pharyngitis of grades I or II. Moraxella spp were isolated in 87.5% of the horses with pharyngitis of grades III and IV, followed by Streptococcus zooepidemicus, Pseudomonas aeruginosa, coagulase-negative staphylococci and Enterobacter spp. No fastidious bacteria, nor strict anaerobes were isolated from any of the 43 horses. None of the microorganisms were found in 100% of the animals and the majority of the isolates were opportunistic bacteria. These results demonstrate that the isolation of Moraxella spp and S. zooepidemicus in large numbers is frequent in horses with lymphoid follicular hyperplasia grades III and IV. Fungi were isolated in small numbers from two or three horses in each group.     

Airway microbial culture and susceptibility patterns in dogs and cats with respiratory disease of varying severity

Objective – To compare airway microbiological culture and susceptibility results in 2 groups of dogs and cats: 1 with respiratory failure requiring positive pressure ventilation (PPV) and 1 with respiratory disease. Design – Retrospective study. Setting – University teaching hospital. Animals – Fifty‐two dogs and cats requiring PPV that had an airway microbiologic culture submitted from October 1, 2003 to October 31, 2008 were included. One hundred and four airway microbiologic cultures from dogs and cats with respiratory disease not requiring PPV were randomly sampled for comparison. Interventions – None. Measurements and Main Results – Patients with respiratory failure were more likely to have a gram‐negative enteric isolate identified (P<0.001), while patients with respiratory disease were more likely to have a gram‐negative nonenteric isolate (P<0.001) or anaerobic isolate (P<0.001) identified. Aerobic bacterial isolates from patients with respiratory failure were less likely to be susceptible to ampicillin (P=0.006), amoxicillin/clavulonate (P<0.001), chloramphenicol (P=0.004), enrofloxacin (P<0.001), ticarcillin/clavulonate (P=0.004), and the combination of ampicillin with enrofloxacin (P<0.001) than were aerobic bacterial isolates from patients with respiratory disease. Conclusions – Canine and feline patients with respiratory failure severe enough to require PPV exhibit a different pattern of bacterial isolates cultured from their airways when compared with isolates from patients with respiratory disease that has not resulted in ventilator dependence. These isolates are more likely to be resistant to commonly used antimicrobials/antimicrobial combinations than patients in the respiratory disease group. These findings suggest that in canine and feline patients with infectious lower respiratory tract disease, consideration of the severity of the pulmonary insult may allow for better prediction of likely isolates and their antimicrobial susceptibilities. Further prospective studies with a standardized collection technique are warranted.     

Identification and antimicrobial susceptibility patterns of bacteria causing otitis externa in dogs

Bacterial agents are considered important pathogens causing external otitis in dogs. It is essential to carry out bacterial culture and antimicrobial susceptibility test in the case of otitis externa, particularly for chronic or recurring cases. Sterile swab samples were obtained from terminal part of vertical ear canals of 74 dogs with otitis externa for cytology, bacterial culture and antimicrobial susceptibility test. Cytologic smears were stained using Gram and Giemsa staining methods. Aerobic bacterial culture performed on blood agar and MacConkey agar. Among total number of 92 isolated bacteria, 68 were Staphylococcus intermedius. Other isolated bacteria included: Pseudomonas aeruginosa, Proteus mirabilis, Escherichia coli, Pasteurella canis, and six other species of coagulase-negative Staphylococcus. Antimicrobial susceptibility test were performed for all isolated bacteria using 14 antibiotics. Based on the results of this study, all isolated Staphylococcus spp. were sensitive to amikacin, enrofloxacin, and rifampin, and had low resistance to gentamicin, cephalothin and ceftriaxone. More than half of gram-positive isolates were resistant to penicillin and ampicillin. Generally, all isolated gram-negative bacteria, were sensitive to amikacin and enrofloxacin, and had low resistance to ceftriaxone and gentamicin. They were highly resistant to penicillin, eythromycin, and cephalothin. Regarding the results of this study, in cases of uncomplicated otitis externa, it is possible to select antimicrobial drugs merely based on cytology, but it is recommended to perform bacterial culture and antimicrobial susceptibility test. However, in complicated or refractory cases, antimicrobials should be selected based on bacterial culture and antimicrobial susceptibility test.     

Misuse of Antimicrobials and Selection of Methicillin‐Resistant Staphylococcus pseudintermedius Strains in Breeding Kennels: Genetic Characterization of Bacteria After a Two‐year Interval

Methicillin‐resistant Staphylococcus pseudintermedius (MRSP) strains have been isolated from dogs with increasing frequency; prolonged or excessive use of antimicrobials is associated with the selection of MRSP, and misuse of antimicrobials is frequent in breeding kennels. This study was carried out in two breeding kennels (A and B) in which we had isolated MRSP in 2008: the aim was to assess colonization of previously positive bitches and of other bitches sharing the same environment and to assess the genetic profile of both the old and the new strains [spa typing, staphylococcal cassette chromosome mec (SCCmec) typing and Pulsed‐field Gel Electrophoresis (PFGE)]. Six animals from Kennel A (two from 2008) and eight from Kennel B (one from 2008) were tested: 16 MRSP strains were isolated only from bitches housed in Kennel B. Old and new isolates were mecA positive, resulted spa type t02 and carried SSCmec II–III. PGFE showed that all isolates were related and belonged to the main clone lineage dominating in Europe, ST71‐J‐t02‐II–III. Kennels A and B differ in the use of antimicrobials, which has been reduced over time in Kennel A, while has remained excessive in Kennel B, where many agents belonging to different classes (third‐generation cephalosporins, fluoroquinolones, macrolids) are administered to dogs, without veterinary supervision, especially around parturition. Misuse of antimicrobials is the key factor for the selection of MRSP strains in healthy dogs and for their persistence over time. Dog breeders should be aware that infections caused by multiresistant bacteria have very limited therapeutical options and represent a huge challenge for animal health.