Growth inhibitory effect of selected medicinal plants from Southern Ethiopia on the mycelial phase of Histoplasma capsulatum var. farciminosum.

BACKGROUND: Epizootic lymphangitis is an infectious and chronically debilitating disease of the equines. Histoplasma capsulatum var. farciminosum, a thermally dimorphic fungi, is the causative agent for the disease. In Ethiopia, the disease significantly affects carthorses, posing threats to animal welfare, and resulting in substantial economic losses. Limited availability of widely accessible antifungals in addition to the chronic nature of the disease is the major challenge against management of epizootic lymphangitis. This study aimed to assess the in vitro efficacy of specific local medicinal plant extracts against the mycelial phase development of H. capsulatum var. farciminosum in southern Ethiopia. The leaves of Xanthium strumarium, Kanda (Family Rubiaceae), Croton macrostachyus (Bisana in Amharic), and Centella Asiatica (Echere waye as a local name in Zeyissegna) that are traditionally used for the treatment of different skin ailments were collected and extracted for the in vitro trial. RESULTS: The study revealed that methanol extracts of Xanthium strumarium, Kanda, Croton macrostachyus, and Centella Asiatica, at minimum inhibitory concentrations of 1.25 mg/ml, 2.5 mg/ml, 2.5 mg/ml, and 5 mg/ml, respectively, inhibited the growth of H. capsulatum var. farciminosum. CONCLUSION: This in vitro finding could serve as significant preliminary data in the exploration of effective alternative treatment options for epizootic lymphangitis. This study provides a crucial foundation for further research aimed at determining the chemical components and in vivo effectiveness of these plant extracts against both the mycelial and yeast forms of Histoplasma capsulatum var. farciminosum.

Comparison of five basal compositions of selective chocolate agar media for isolation of Taylorella equigenitalis.

The gold standard method to isolate and identify Taylorella equigenitalis, the contagious agent of equine metritis, is the culture method according to the World Organisation for Animal Health Terrestrial Manual. No selective T. equigenitalis chocolate agar medium has been developed since the 1980s and the existing media show limited performances due to the fastidious nature of T. equigenitalis and the presence of interfering bacteria in the genital tract of equines. Here, the growth rates of 6 T. equigenitalis strains and 7 non-T. equigenitalis strains were compared on Timoney's selective medium formulated with 5 different basal agars (Columbia, Eugon, Blood, Mueller-Hinton and Tryptose Blood) provided by 2 to 4 suppliers per basal agar. The impact of glucose and/or Vitox supplementation was also investigated. Overall, the performance of selective T. equigenitalis media could be improved by substituting Eugon or Columbia agar with Blood, Mueller-Hinton or Tryptose Blood agar. It is nevertheless essential to validate the basal agar/supplier pair using a panel of T. equigenitalis strains. Furthermore, our findings confirm the need to supplement the selective media with a mixture of amino acids, nucleotides, and organic, mineral and vitamin compounds, translated here by Vitox supplementation.

Leptospiral antibody prevalence and surgical treatment outcome in horses with Equine Recurrent Uveitis (ERU) in Switzerland.

OBJECTIVE: To evaluate leptospiral antibody prevalence in 65 horses with ERU and compare outcome in 36 surgically treated eyes (2010-2015). PROCEDURES: Retrospective data analysis of horses with ERU (n = 65). C-value calculation with microagglutination assay titer (MAT) results for Leptospira spp. Evaluation of follow-up data after pars plana vitrectomy (PPV, n = 21 eyes) and suprachoroidal cyclosporine device implantation (SCDI, n = 15 eyes). Differences between groups were statistically analyzed using Fishers exact test, significance set at P < .05. RESULTS: Positive leptospiral titers were found in 28/65 blood, 31/65 aqueous humor (AH), and 19/20 vitreal (post-PPV) samples. The most common intraocular serovars were Leptospira interrogans grippotyphosa, pomona, and bratislava. Intraocular antibody production was suspected in samples of 22 horses (c-values > 1). Mean follow-up of surgical cases was 3.8 years (PPV) and 3.4 years (SCDI). PPV was performed in 21 eyes with positive, SCDI in 15 eyes with negative leptospiral test results. Uveitis recurred less often after PPV (2/21) compared to SCDI (6/15, P = .04). Retinal detachment occurred after PPV only (5/21, SCDI 0/15, P = .06), whereas only SCDI-treated eyes were enucleated (PPV 0/21, SCDI 3/15, P = .06). Blindness or visual impairment was equally likely to occur in both treatment groups after surgery (PPV 7/21, SCDI 7/15, P = .5). CONCLUSIONS: Leptospiral antibody prevalence is high in horses with ERU in Switzerland. Recurrence of uveitis is uncommon following PPV in the present study; an increased risk of retinal detachment exists. Enucleation is more often warranted in horses after SCDI in this study due to a higher uveitis recurrence.

Differences in isolation rate and antimicrobial susceptibility of bacteria isolated from foals with sepsis at admission and after ≥48 hours of hospitalization.

BACKGROUND: Antimicrobial treatment protocols for foals with sepsis that do not improve clinically often are adjusted based on bacteriological and antimicrobial susceptibility testing results from samples collected at hospital admission. OBJECTIVES: To evaluate whether hospitalization for ≥48 hours affects bacteriological and antimicrobial susceptibility testing results. ANIMALS: Two-hundred sixty-seven foals <30 days of age admitted to a neonatal intensive care unit and diagnosed with sepsis. METHODS: Medical records were reviewed retrospectively to identify foals with sepsis and positive bacteriological cultures. Results from samples collected at hospital admission were compared to those collected ≥48 hours after admission. Logistic regression for clustered data and exact logistic regression were used for statistical analysis. RESULTS: Three-hundred fifty-three unique bacterial isolates were obtained from 231 foals at hospital admission and 92 unique bacterial isolates were obtained from 57 foals after ≥48 hours of hospitalization. Relative isolation frequency after ≥48 hours of hospitalization increased for Acinetobacter spp., 0.6% versus 3.3% (odds ratio [OR], 7.63; 95% confidence interval [CI], 1.28-45.45); Enterococcus spp., 4.8% versus 19.6% (OR, 5.37; 95% CI, 2.64-10.90); Klebsiella spp., 5.1% versus 10.9% (OR, 2.27; 95% CI, 1.05-4.89); Pseudomonas spp., 3.0% versus 7.6% (OR, 3.49; 95% CI, 3.49-240.50); and Serratia spp., 3.0% versus 5.4% (OR, 20.23; 95% CI, 2.20-186.14). Bacteria isolated after ≥48 hours of hospitalization were less susceptible to all tested antimicrobial drugs, except for imipenem. CONCLUSIONS AND CLINICAL IMPORTANCE: Decreased antimicrobial susceptibility of bacteria isolated after ≥48 hours of hospitalization provides a rationale for repeated bacteriological culture and susceptibility testing in hospitalized foals with sepsis.

An evaluation of serum gentamicin concentrations and bacterial susceptibility to gentamicin in equine practice.

BACKGROUND: Therapeutic drug monitoring and minimum inhibitory concentration (MIC) data allow more informed use of gentamicin. HYPOTHESIS/OBJECTIVES: To measure peak and trough serum gentamicin concentrations in horses after a 6.6 mg/kg dose of gentamicin given IV and the MIC of gentamicin of bacteria for which gentamicin might be selected. METHODS: Retrospective analysis of hospital records. Peak and trough plasma gentamicin concentrations were measured after 6.6 mg/kg gentamicin IV in 339 hospitalized horses. The MIC of gentamicin was measured for 503 isolates from ambulatory practice and 33 from hospital practice. The distribution of gentamicin concentrations and MIC results were compared to current recommendations for MIC breakpoints. RESULTS: The median serum gentamicin concentration at 60 minutes after administration (C60min ) was 21.4 µg/mL with a distribution indicating that bacteria with MIC ≥2 µg/mL were unlikely to be exposed to sufficient gentamicin for effective killing. Approximately 90% of isolates from ambulatory practice and 36% of hospital isolates had MICs at or below breakpoints for susceptibility with most of the remainder unlikely to be responsive, even to higher IV doses. CONCLUSIONS AND CLINICAL IMPORTANCE: Gentamicin at a dosage of 6.6 mg/kg IV is likely to be effective against the majority of infections encountered in ambulatory practice, but less effective in an equine hospital. Because there was a dichotomy of most bacteria as being clearly susceptible or clearly resistant to gentamicin, it appears unlikely that higher doses would have been more efficacious, especially in the hospitalized population in our study.

Septic keratitis in dogs, cats, and horses in Switzerland: associated bacteria and antibiotic susceptibility.

OBJECTIVE: To evaluate the most common bacterial pathogens associated with septic keratitis in veterinary patients from Switzerland. The second objective was to analyze antibiotic susceptibility test results of the identified bacterial pathogens. The third objective was to evaluate potential breed predispositions to septic keratitis. PROCEDURES: Two hundred and fifty-five cultures and antibiotic susceptibility reports from dogs, cats, and horses with septic keratitis that were presented to the University of Zurich Veterinary Medical Teaching Hospital between 2009 and 2013 were reviewed. Odds ratios for the risk of having a septic keratitis were estimated for all dog and cat breeds compared to the general nonbrachycephalic hospital population. RESULTS: Ninety-six, 29, and 31 positive cultures were obtained from 89 canine, 28 feline, and 29 equine eyes, respectively. Repeat sampling accounted for the differences in numbers. Negative culture results were obtained in 50, 31, and 18 cases. Staphylococci and streptococci accounted for 66% of the isolates in dogs and 80% of the isolates in cats and horses. Staphylococcus spp. had a higher percentage of fluoroquinolone-resistant isolates compared to previous reports. Brachycephalic breeds had elevated odds ratios for the presence of septic keratitis. CONCLUSION: Identified bacterial pathogens and their prevalence as well as the elevated odds ratios for septic keratitis in brachycephalics are roughly consistent with previous studies. Based on systemic breakpoint data, resistance to commonly used topical antibiotics, including the second-generation fluoroquinolones, was found.

In vitro susceptibility of Borrelia burgdorferi isolates to three antibiotics commonly used for treating equine Lyme disease.

BACKGROUND: Lyme disease in humans is predominantly treated with tetracycline, macrolides or beta lactam antibiotics that have low minimum inhibitory concentrations (MIC) against Borrelia burgdorferi. Horses with Lyme disease may require long-term treatment making frequent intravenous or intramuscular treatment difficult and when administered orally those drugs may have either a high incidence of side effects or have poor bioavailability. The aim of the present study was to determine the in vitro susceptibility of three B. burgdorferi isolates to three antibiotics of different classes that are commonly used in practice for treating Borrelia infections in horses. RESULTS: Broth microdilution assays were used to determine minimum inhibitory concentration of three antibiotics (ceftiofur sodium, minocycline and metronidazole), for three Borrelia burgdorferi isolates. Barbour-Stoner-Kelly (BSK K + R) medium with a final inoculum of 106 Borrelia cells/mL and incubation periods of 72 h were used in the determination of MICs. Observed MICs indicated that all isolates had similar susceptibility to each drug but susceptibility to the tested antimicrobial agents varied; ceftiofur sodium (MIC = 0.08 µg/ml), minocycline hydrochloride (MIC = 0.8 µg/ml) and metronidazole (MIC = 50 µg/ml). CONCLUSIONS: The MIC against B. burgorferi varied among the three antibiotics with ceftiofur having the lowest MIC and metronidazole the highest MIC. The MIC values observed for ceftiofur in the study fall within the range of reported serum and tissue concentrations for the drug metabolite following ceftiofur sodium administration as crystalline-free acid. Minocycline and metronidazole treatments, as currently used in equine practice, could fall short of attaining MIC concentrations for B. burgdorferi.

The antimicrobial activity of bupivacaine, lidocaine and mepivacaine against equine pathogens: An investigation of 40 bacterial isolates.

Lameness is the most commonly reported health problem in horses, and lameness investigations which include local anaesthetic injections are routinely performed by equine practitioners. Through this process, bacteria can enter the tissues perforated by the needle and may cause local infections at the injection site. The objective of this in vitro study was to investigate if local anaesthetics at concentrations available in commercially available solutions could inhibit growth and/or kill bacteria that could be inoculated into the synovial space or soft tissues during injection. This study evaluated the antimicrobial activity of the local anaesthetics bupivacaine, lidocaine and mepivacaine against 40 equine clinical bacterial isolates of the Actinobacillus, Corynebacterium, Enterobacter, Escherichia, Pseudomonas, Rhodococcus, Staphylococcus and Streptococcus genera. Minimum inhibitory and minimum bactericidal concentrations (MICs and MBCs) were determined by the broth microdilution method. Clinically applied concentrations of bupivacaine, lidocaine, and mepivacaine inhibited visual growth of 93%, 93%, and 80% of isolates tested, respectively. For the majority (80%) of the inhibited isolates, the concentrations were also bactericidal. The tested local anaesthetics possessed antimicrobial activity against equine pathogens at concentrations that are routinely applied in clinical cases. However, this antimicrobial activity should not discourage antiseptic preparation prior to local anaesthetic injections.

Biofilms of Candida spp. from the ocular conjunctiva of horses with reduced azole susceptibility: a complicating factor for the treatment of keratomycosis?

OBJECTIVES: This study aimed to assess the biofilm-forming ability of Candida spp. from the ocular conjunctiva of horses and to investigate the antifungal susceptibility of these biofilms. PROCEDURES: Initially, the biofilm-forming ability of 15 strains was assessed by crystal violet staining, which reveals the fungal biomass adhered to the polystyrene plates, and scanning electron microscopy. Then, the minimum inhibitory concentrations (MICs) of amphotericin B, fluconazole, itraconazole, and caspofungin were initially determined against strains in planktonic form. Afterward, antifungal susceptibility of mature biofilms was evaluated by exposing them to 10 × MIC and 50 × MIC of the tested drugs, followed by the assessment of their metabolic activity, using the oxidoreduction indicator XTT. Results were analyzed through ANOVA and Tukey's post-test, and P-values below 5% led to significant conclusions. RESULTS: Eight strains produced biofilms and were classified as strong (1/15), moderate (3/15) and weak (4/15) producers, according to the amount of crystal violet retained by the adhered fungal biomass. Biofilm metabolic activity of one C. tropicalis did not decrease after exposure to the tested antifungals, while biofilm metabolic activity of five strains was reduced by amphotericin B, but not the other drugs. One C. parapsilosis sensu stricto and one C. glabrata showed significant reduction in biofilm metabolic activity after exposure to fluconazole, itraconazole, and caspofungin, but not amphotericin B. CONCLUSIONS: The results demonstrate that Candida from the ocular conjunctiva of horses can pose as a risk to animal health as they are capable of forming biofilms, which are commonly involved in fungal keratitis.

Zoonotic necrotizing myositis caused by Streptococcus equi subsp. zooepidemicus in a farmer.

BACKGROUND: Streptococcus equi subsp. zooepidemicus is a beta-hemolytic group C streptococcus mainly causing infections in domesticated animals. Here we describe the first case of zoonotic necrotizing myositis caused by this bacterium. CASE PRESENTATION: The patient was a 73-year-old, previously healthy farmer with two asymptomatic Shetland ponies in his stable. After close contact with the ponies while feeding them, he rapidly developed erythema of his left thigh and sepsis with multiple organ failure. The clinical course was severe and complicated, requiring repetitive surgical excision of necrotic muscle, treatment with vasopressors, mechanical ventilation and continuous venovenous hemofiltration, along with adjunctive hyperbaric oxygen therapy. The patient was discharged from hospital at day 30, without obvious sequelae. The streptococcal isolate was identified as Streptococcus equi by MALDI-ToF MS, and was later assigned subspecies identification as S. equi subsp. zooepidemicus. Multilocus sequence typing identified the strain as a novel sequence type (ST 364), closely related to types previously identified in horses and cattle. A focused proteomic analysis revealed that the ST 364 expressed putative virulence factors similar to that of Streptococcus pyogenes, including homologues of the M protein, streptodornases, interleukin 8-protease and proteins involved in the biosynthesis of streptolysin S. CONCLUSION: This case illustrates the zoonotic potential of S. equi subsp. zooepidemicus and the importance of early clinical recognition, rapid and radical surgical therapy, appropriate antibiotics and adequate supportive measures when necrotizing soft tissue infection is suspected. The expression of Streptococcus pyogenes-like putative virulence determinants in ST 364 might partially explain the fulminant clinical picture.

Fighting Off Wound Pathogens in Horses with Honeybee Lactic Acid Bacteria.

In the global perspective of antibiotic resistance, it is urgent to find potent topical antibiotics for the use in human and animal infection. Healing of equine wounds, particularly in the limbs, is difficult due to hydrostatic factors and exposure to environmental contaminants, which can lead to heavy bio-burden/biofilm formation and sometimes to infection. Therefore, antibiotics are often prescribed. Recent studies have shown that honeybee-specific lactic acid bacteria (LAB), involved in honey production, and inhibit human wound pathogens. The aim of this pilot study was to investigate the effects on the healing of hard-to-heal equine wounds after treatment with these LAB symbionts viable in a heather honey formulation. For this, we included ten horses with wound duration of >1 year, investigated the wound microbiota, and treated wounds with the novel honeybee LAB formulation. We identified the microbiota using MALDI-TOF mass spectrometry and DNA sequencing. In addition, the antimicrobial properties of the honeybee LAB formulation were tested against all wound isolates in vitro. Our results indicate a diverse wound microbiota including fifty-three bacterial species that showed 90 % colonization by at least one species of Staphylococcus. Treatment with the formulation promoted wound healing in all cases already after the first application and the wounds were either completely healed (n = 3) in less than 20 days or healing was in progress. Furthermore, the honeybee LAB formulation inhibited all pathogens when tested in vitro. Consequently, this new treatment option presents as a powerful candidate for the topical treatment of hard-to-heal wounds in horses.

Micafungin alone and in combination therapy with deferasirox against Pythium insidiosum.

This study evaluated the in vitro and in vivo activity of micafungin alone and in combination with the iron chelator deferasirox against Pythium insidiosum. Micafungin showed a poor in vitro activity when it was used alone, but synergistic interactions were observed for 88.2% of the strains when the drug was combined with deferasirox. Smaller lesions were observed in infected rabbits receiving the combination therapy, although it favored disease dissemination to the lungs. The present results show that micafungin alone is ineffective against P. insidiosum, and the combination micafungin-deferasirox might have deleterious effects for the host.

Development of ELISA test for determination of the level of antibodies against Rhodococcus equi in equine serum and colostrum.

Rhodococcus equi infection occurs worldwide and is one of the major causes of losing foals in the first six months of life. The application of serological tests in the diagnostics of rhodococcosis is limited, however they play a crucial role in immunological studies. The objective of this study was to develop and standardize ELISA test for the determination of the level of antibodies against Rhodococcus equi in equine serum and colostrum.Bacterial cell lysate was used as antigen. The test was standardized on 175 sera obtained from adult horses kept on rhodococcosis-free and endemic farms. Positive and negative control sera were used. The test detected IgG antibodies mainly against VapA protein, which was confirmed by Western blot analysis. The test was easy to perform, did not require inactivation of sera and had low well-to-well variation. The shelf life of antigen-coated ELISA plates was 21 days.The test allowed to reveal significant increase of R. equi-specific antibodies in both serum and colostrum in response to the vaccination (p<0.001). Therefore it can be applied to the evaluation of efficacy of immunization. Moreover, no statistically significant difference in the baseline antibody level in adult horses from rhodococcosis-free and endemic farm was revealed (α=0.05).

In vitro potential of equine DEFA1 and eCATH1 as alternative antimicrobial drugs in rhodococcosis treatment.

Rhodococcus equi, the causal agent of rhodococcosis, is a severe pathogen of foals but also of immunodeficient humans, causing bronchopneumonia. The pathogen is often found together with Klebsiella pneumoniae or Streptococcus zooepidemicus in foals. Of great concern is the fact that some R. equi strains are already resistant to commonly used antibiotics. In the present study, we evaluated the in vitro potential of two equine antimicrobial peptides (AMPs), eCATH1 and DEFA1, as new drugs against R. equi and its associated pathogens. The peptides led to growth inhibition and death of R. equi and S. zooepidemicus at low micromolar concentrations. Moreover, eCATH1 was able to inhibit growth of K. pneumoniae. Both peptides caused rapid disruption of the R. equi membrane, leading to cell lysis. Interestingly, eCATH1 had a synergic effect together with rifampin. Furthermore, eCATH1 was not cytotoxic against mammalian cells at bacteriolytic concentrations and maintained its high killing activity even at physiological salt concentrations. Our data suggest that equine AMPs, especially eCATH1, may be promising candidates for alternative drugs to control R. equi in mono- and coinfections.

Diagnosis, treatment, control, and prevention of infections caused by Rhodococcus equi in foals.

Rhodococcus equi, a gram-positive facultative intracellular pathogen, is one of the most common causes of pneumonia in foals. Although R. equi can be cultured from the environment of virtually all horse farms, the clinical disease in foals is endemic at some farms, sporadic at others, and unrecognized at many. On farms where the disease is endemic, costs associated with morbidity and mortality attributable to R. equi may be very high. The purpose of this consensus statement is to provide recommendations regarding the diagnosis, treatment, control, and prevention of infections caused by R. equi in foals.

Changes in faecal bacteria and metabolic parameters in foals during the first six weeks of life.

Many foals develop diarrhoea within the first two weeks of life which has been suggested to coincide with postpartum oestrus in their dams. To analyse the pathogenesis of this diarrhoea we have determined faecal bacteria in foals and their dams (n=30 each), and serum IGF-1 and γ-globulins for 6 weeks after birth. In addition, effects of ß-carotene supplementation to mares (group 1: 1000 mg/day, n=15, group 2: control, n=15) on diarrhoea in foals were studied. Diarrhoea occurred in 92 and 79% of foals in groups 1 and 2, respectively, but was not correlated with oestrus in mares. Beta-carotene supplementation was without effect on foal diarrhoea. In mares, bacterial flora remained stable. The percentage of foals with cultures positive for E. coli was low at birth but increased within one day, the percentage positive for Enterococcus sp. was low for 10 days and for Streptococcus sp. and Staphylococcus sp. was low for 2-4 weeks. By 4 weeks of age, bacterial flora in foals resembled an adult pattern. Concentration of serum IGF-1 was low at birth (group 1: 149 ± 11, group 2: 166 ± 17ng/ml), increased after day 1 (day 7 group 1: 384 ± 30, group 2: 372 ± 36) but at no time differed between groups. Serum γ-globulin concentration in foals was low before colostrum intake and highest on day 1 (p<0.001 over time). In conclusion, neonatal diarrhoea in foals does not coincide with postpartum oestrus in their dams but with changes in intestinal bacteria and is not influenced by ß-carotene supplementation given to mares.

Determination of the prevalence of antimicrobial resistance to macrolide antimicrobials or rifampin in Rhodococcus equi isolates and treatment outcome in foals infected with antimicrobial-resistant isolates of R equi.

OBJECTIVE: To determine the prevalence of antimicrobial resistance to macrolide antimicrobials or rifampin in Rhodococcus equi isolates and to describe treatment outcome in foals infected with antimicrobial-resistant isolates of R equi. DESIGN: Cross-sectional study. SAMPLE POPULATION: 38 isolates classified as resistant to macrolide antimicrobials or rifampin received from 9 veterinary diagnostic laboratories between January 1997 and December 2008. PROCEDURES: For each isolate, the minimum inhibitory concentration of macrolide antimicrobials (ie, azithromycin, erythromycin, and clarithromycin) and rifampin was determined by use of a concentration-gradient test. Prevalence of R equi isolates from Florida and Texas resistant to macrolide antimicrobials or rifampin was determined. Outcome of antimicrobial treatment in foals infected with antimicrobial-resistant isolates of R equi was determined. RESULTS: Only 24 of 38 (63.2%) isolates were resistant to >or= 1 antimicrobial. Two isolates were resistant only to rifampin, whereas 22 isolates were resistant to azithromycin, erythromycin, clarithromycin, and rifampin. The overall prevalence of antimicrobial-resistant isolates in submissions received from Florida and Texas was 3.7% (12/328). The survival proportion of foals infected with resistant R equi isolates (2/8 [25.0%]) was significantly less, compared with the survival proportion in foals that received the same antimicrobial treatment from which antimicrobial-susceptible isolates were cultured (55/79 [69.6%]). Odds of nonsurvival for foals infected with resistant R equi isolates were 6.9 (95% confidence interval, 1.3 to 37) times the odds for foals infected with susceptible isolates. CONCLUSIONS AND CLINICAL RELEVANCE: Interpretation of the results emphasized the importance of microbiological culture and antimicrobial susceptibility testing in foals with pneumonia caused by R equi.

In vitro antimicrobial activity of gallium maltolate against virulent Rhodococcus equi.

The objective of this study was to determine the in vitro antimicrobial activity of gallium maltolate (GaM) against Rhodococcus equi. A total of 98 virulent bacterial isolates from equine clinical cases were examined, of which 19 isolates were known to be resistant to macrolides and rifampin. Isolates were cultured with various concentrations of GaM and minimal inhibitory concentration (MIC) values were determined after 24 and 48 h. Both the MIC(50) and the MIC(90) after 24h of growth were 558 ng/mL (8 µM) and after 48 h of growth were 2230 ng/mL (32 µM). There were no apparent differences between MICs of macrolide-resistant and macrolide-susceptible isolates.

Association of Stenotrophomonas maltophilia infection with lower airway disease in the horse: a retrospective case series.

Stenotrophomonas maltophilia is being reported with increasing frequency as a human nosocomial pathogen, especially among immuno-compromised patients. To the authors' knowledge, this pathogen has not previously been associated with lower airway disease in the horse. In this paper the clinical findings, laboratory diagnosis and response to treatment of seven cases of respiratory infection with S. maltophilia in horses, presented at three equine referral hospitals in Denmark in 2007, are described. In all cases there was a clinical history of chronic coughing and abundant mucopurulent exudate was observed in the lower trachea on endoscopy. On culture of tracheal aspirate, grey, slow-growing colonies, identified as S. maltophilia by both API 20NE identification and 16s ribosomal DNA sequencing, were identified. All isolates had a similar antibiotic susceptibility pattern characterised by resistance to all penicillins and cephalosporins, and to imipenem, gentamicin, amikacin and rifampicin. Ribotyping and pulsed-field gel electrophoresis of the S. maltophilia isolates from different patients indicated that they were either indistinguishable or closely related. This study indicates that S. maltophilia can be associated with chronic lower airway disease in the horse and provides useful initial insights into the diagnosis, therapy and epidemiology of this novel condition.