Prevalence of antimicrobial resistance among bacterial pathogens isolated from cattle in different European countries: 2002–2004

Background

The project "Antibiotic resistance in bacteria of animal origin – II" (ARBAO-II) was funded by the European Union (FAIR5-QLK2-2002-01146) for the period 2003–2005, with the aim to establish a continuous monitoring of antimicrobial susceptibility among veterinary laboratories in European countries based on validated and harmonised methodologies. Available summary data of the susceptibility testing of the bacterial pathogens from the different laboratories were collected.

Method

Antimicrobial susceptibility data for several bovine pathogens were obtained over a three year period (2002–2004). Each year the participating laboratories were requested to fill in excel-file templates with national summary data on the occurrence of antimicrobial resistance from different bacterial species.A proficiency test (EQAS – external quality assurance system) for antimicrobial susceptibility testing was conducted each year to test the accuracy of antimicrobial susceptibility testing in the participating laboratories. The data from this testing demonstrated that for the species included in the EQAS the results are comparable between countries.

Results

Data from 25,241 isolates were collected from 13 European countries. For Staphylococcus aureus from bovine mastitis major differences were apparent in the occurrence of resistance between countries and between the different antimicrobial agents tested. The highest frequency of resistance was observed for penicillin. For Mannheimia haemolytica resistance to ampicillin, tetracycline and trimethoprim/sulphonamide were observed in France, the Netherlands and Portugal. All isolates of Pasteurella multocida isolated in Finland and most of those from Denmark, England (and Wales), Italy and Sweden were susceptible to the majority of the antimicrobials. Streptococcus dysgalactiae and Streptococcus uberis isolates from Sweden were fully susceptible. For the other countries some resistance was observed to tetracycline, gentamicin and erythromycin. More resistance and variation of the resistance levels between countries were observed for Escherichia coli compared to the other bacterial species investigated.

Conclusion

In general, isolates from Denmark, England (and Wales), the Netherlands, Norway, Sweden and Switzerland showed low frequencies of resistance, whereas many isolates from Belgium, France, Italy, Latvia and Spain were resistant to most antimicrobials tested. In the future, data on the prevalence of resistance should be used to develop guidelines for appropriate antimicrobial use in veterinary medicine.     

Epidemiologic cutoff values for antimicrobial agents against Aeromonas salmonicida isolates determined by frequency distributions of minimal inhibitory concentration and diameter of zone of inhibition data

OBJECTIVE: To develop epidemiologic cutoff values by use of frequency distributions for susceptibility to 4 antimicrobial agents when tested against a representative population of a major aquaculture pathogen, Aeromonas salmonicida. SAMPLE POPULATION: 217 typical and atypical A salmonicida isolates obtained from 20 states and 12 countries. PROCEDURES: Species identification of A salmonicida isolates was confirmed by detection of specific nucleotide sequences by use of a PCR assay. Minimal inhibitory concentration (MIC) and diameter of the zone of inhibition for oxytetracycline, ormetoprim-sulfadimethoxine, oxolinic acid, and florfenicol were determined for each isolate in accordance with standardized antimicrobial susceptibility testing methods that have been approved by the Clinical and Laboratory Standards Institute for bacterial isolates from aquatic animals. Susceptibility data were tabulated in a scattergram and analyzed by use of error rate bounding. RESULTS: Susceptibility tests for oxytetracycline, ormetoprim-sulfadimethoxine, and oxolinic acid revealed 2 distinct populations of bacteria. Isolates tested against florfenicol clustered into a single population. Oxolinic acid susceptibility data revealed higher MICs in the non-United States A salmonicida isolates. Slow-growing (atypical) A salmonicida isolates were generally more susceptible than typical isolates for all antimicrobials, except oxolinic acid. CONCLUSIONS AND CLINICAL RELEVANCE: Use of frequency distributions of susceptibility results to develop epidemiologic cutoff values appears to be applicable to aquatic isolates. Frequency distributions of susceptibility results for A salmonicida revealed clear divisions between isolate susceptibilities. This type of data, considered in conjunction with pharmacokinetic and efficacy data, may be useful for developing clinical breakpoints for use in aquaculture.     

Diagnosis of bacterial infections. Part 2: Bacterial cultivation,susceptibility testing and interpretation

Bacterial culture and susceptibility testing are requested frequently in equine medicine. However, there is little value in these tests unless a standardised approach for submission of specimens, pathogen identification and susceptibility testing is utilised. Additionally, appropriate interpretation must be applied when assessing the significance of the isolate and susceptibility testing results if appropriate therapies are to be prescribed. In this paper we briefly outline standard techniques used commonly in veterinary diagnostic laboratories for bacterial isolation, identification and susceptibility testing. Emphasis has been placed on the principles appropriate to ensure the correct interpretation of culture and susceptibility testing results.     

Layout proposal for a microtitre plate to be used in routine antimicrobial susceptibility testing of bacteria from infections of dogs and cats

The determination of minimum inhibitory concentrations by broth microdilution is recommended as method of choice for susceptibility testing of veterinary bacterial pathogens. Accordingly, broth microdilution is used in veterinary routine diagnostic laboratories at a progressive rate. To reduce the costs of susceptibility testing, it is reasonable to develop widely accepted uniform microtitre plate layouts that are produced in large quantities. Such microtitre plate layouts have already been developed and published for the susceptibility testing of pathogens from food-producing animals. However, a microtitre plate layout, especially designed for the testing of bacteria from dogs and cats, should be available, too. The choice of the antimicrobial agents or combinations of antimicrobial agents to be included in a suitable layout should be based on the following criteria: (1) the approval and availability of an antimicrobial agent or combination of agents, (2) known cross-resistances, and (3) availability of approved clinical breakpoints. The latter point is of particular importance for the choice of the numbers of concentrations per antimicrobial agent tested and the range of test concentrations. Taking into account these aspects, a science-based layout proposal for microtitre plates, which are suitable for routine testing of bacteria from dogs and cats, is presented and discussed.     

Prevalence of oxacillin- and multidrug-resistant staphylococci in clinical samples from dogs: 1,772 samples (2001-2005)

OBJECTIVE: To determine whether resistance to oxacillin and other antimicrobials in 3 Staphylococcus spp commonly isolated from dogs increased from 2001 to 2005. DESIGN: Retrospective case series. SAMPLE POPULATION: 1,772 clinical samples of various types obtained from dogs examined at the University of Tennessee Veterinary Teaching Hospital or at regional veterinary hospitals and submitted to the bacteriology and mycology laboratories associated with the teaching hospital. PROCEDURES: Samples were submitted by attending veterinarians to the bacteriology and mycology laboratories for routine aerobic microbial culture. Identification and antimicrobial susceptibility procedures were performed on all isolates. Susceptibility reports for each antimicrobial and Staphylococcus spp were determined from aggregate electronically archived test results. Oxacillin and multidrug resistance for Staphylococcus intermedius was analyzed by reviewing disk diffusion zone measurements. RESULTS: Oxacillin resistance increased among S. intermedius isolates during the past 5 years, and the increase was associated with multidrug resistance. In 2005, 1 in 5 Staphylococcus spp isolates from canine clinical samples was resistant to oxacillin. The most common staphylococcal species isolated were S. intermedius (n = 37), Staphylococcus schleiferi (21), and Staphylococcus aureus (4), and frequencies of oxacillin resistance in isolates of these species were 15.6%, 46.6%, and 23.5%, respectively. CONCLUSIONS AND CLINICAL RELEVANCE: Veterinarians should be aware of the potential for empiric drug treatment failures in instances where Staphylococcus spp infections are common (eg, pyoderma). Judicious use of bacterial culture and susceptibility testing is recommended.     

Investigation of falsely reported resistance of Streptococcus equi subsp. zooepidemicus isolates from horses to trimethoprim-sulfamethoxazole.

The objective of this study was to investigate the perceived increase in resistance of Streptococcus equi subsp. zooepidemicus (S. zooepidemicus) isolated from the lower respiratory tract of horses to trimethoprim-sulfamethoxazole (SXT). The recorded SXT-susceptibility results of 50 S. zooepidemicus isolates from the tracheal wash fluid of equine patients examined at Colorado State University Veterinary Teaching Hospital from each of 2 time periods (1987-1990 and 1997-2001) were compared and statistically analyzed using a cross-sectional study design. There was a statistically significant difference between the documented resistance of S. zooepidemicus isolated in the 1987-1990 time period (8%), using quantitative microbroth dilution, and the resistance reported for isolates from the 1997-2001 time period (42%), using Kirby-Bauer agar disk diffusion. Laboratory investigation revealed inadequate quality control of media and subsequent falsely reported resistance of S. zooepidemicus from 1997 to 2001 time period. This study demonstrates how minor deviations from prescribed laboratory-testing guidelines can have a major effect on antimicrobial susceptibility test results. The study also underscores the need for regular surveillance and monitoring of trends in antimicrobial susceptibility to detect and correct such problems. In addition, epidemiologists and others collecting data from laboratories should be cautioned to interact with the laboratory regarding interpretation of results of various testing methods to ensure accurate analysis and conclusions.     

Evaluation of antimicrobial susceptibility patterns in Campylobacter spp isolated from dairy cattle and farms managed organically and conventionally in the midwestern and northeastern United States

OBJECTIVE: To describe antimicrobial susceptibility patterns in Campylobacter spp isolated from dairy cattle and farms managed organically and conventionally in the midwestern and northeastern United States. DESIGN: Longitudinal study. SAMPLE POPULATION: 128 farms. PROCEDURE: Samples and data were collected every 2 months from August 2000 to October 2001. Fecal samples were collected from calves and cows. Milk samples were obtained from the bulk tank and milk line filters. Environmental samples were obtained from a water source, feed bunks of lactating cows, and cattle housing areas. Campylobacter identification and antimicrobial susceptibility testing were performed at a central laboratory by use of microbroth dilution with 2 customized antimicrobial susceptibility panels. RESULTS: 460 and 1,570 Campylobacter isolates were obtained from organic and conventional dairy farms, respectively. Most isolates from both farm types were susceptible to most antimicrobial agents tested, and antimicrobial susceptibility of conventional dairy isolates was decreased, compared with organic dairy isolates. Low proportions of isolates resistant to ampicillin (< 10%) and moderate proportions resistant (30% to 60%) to kanamycin, sulfamethoxazole, and tetracycline were observed on both farm types. The proportion of isolates resistant to tetracycline was higher for conventional than organic farms. CONCLUSIONS AND CLINICAL RELEVANCE: Campylobacter isolates from dairy cattle and farms managed organically and conventionally had similar patterns of antimicrobial resistance; the proportion of resistant isolates was higher for conventional than organic farms.     

Environmental surveillance for Salmonella enterica in a veterinary teaching hospital

OBJECTIVE: To evaluate the extent of environmental contamination with Salmonella enterica in a veterinary teaching hospital. DESIGN: Longitudinal study. SAMPLES: Environmental samples obtained from 69 representative locations within a veterinary teaching hospital by use of a commercially available electrostatic wipe. PROCEDURE: Environmental samples were obtained for bacteriologic culture, and antimicrobial susceptibility testing was performed on each environmental isolate. Environmental isolates were compared with isolates obtained from animals during the same period to investigate potential sources of environmental contamination. RESULTS: 54 S. enterica isolates were recovered from 452 (11.9%) cultured environmental samples. Five different serotypes were recovered; the most common serotypes were S. Newport and S. Agona. Within the 5 serotypes recovered, 10 distinguishable phenotypes were identified by use of serotype and antimicrobial susceptibility patterns. Of the environmental isolates, 41 of 54 (75.9%) could be matched to phenotypes of isolates obtained from animal submissions in the month prior to collection of environmental samples. CONCLUSIONS AND CLINICAL RELEVANCE: Results indicated that environments in veterinary hospitals can be frequently contaminated with S. enterica near where infected animals are managed and fecal specimens containing S. enterica are processed for culture in a diagnostic laboratory. Bacteriologic culture of environmental samples collected with electrostatic wipes is an effective means of detecting contamination in a veterinary hospital environment and may be beneficial as part of surveillance activities for other veterinary and animal-rearing facilities.     

Pulsed-field gel electrophoresis patterns and antimicrobial susceptibility phenotypes for coagulase-positive staphylococcal isolates from pustules and carriage sites in dogs with superficial bacterial folliculitis

OBJECTIVE: To determine whether coagulase-positive staphylococcal isolates that are genotypically the same strain obtained from pustules and carriage sites of individual dogs with superficial bacterial folliculitis have the same antimicrobial susceptibility phenotype. ANIMALS: 40 dogs with superficial bacterial folliculitis. PROCEDURES: Samples were obtained from 3 pustules and 3 carriage sites (ie, anus, nonlesional axillary skin, and nasal mucosa) for bacterial culture, morphologic identification, Gram staining, catalase and coagulase testing, antimicrobial susceptibility testing, speciation, and pulsed-field gel electrophoresis (PFGE). RESULTS: 223 isolates from pustules and carriage sites were included. Seventeen susceptibility phenotypes were found among isolates. One hundred twenty-eight (100%) isolates from pustules and 95 (100%) isolates from carriage sites were susceptible to cephalothin; 128 (100%) isolates from pustules and 94 (98.9%) isolates from carriage sites were susceptible to amoxicillin-clavulanic acid; 114 (89.1%) isolates from pustules and 82 (86.3%) isolates from carriage sites were susceptible to erythromycin and lincomycin hydrochloride; and 103 (80.5%) isolates from pustules and 70 (73.7%) isolates from carriage sites were susceptible to trimethoprim-sulfamethoxazole. In 37 of 39 (94.9%) dogs, isolates with the same PFGE pattern from multiple pustules had the same susceptibility phenotype. In 21 of 33 (63.6%) dogs, isolates from multiple carriage sites with the same PFGE pattern had the same susceptibility phenotype. CONCLUSIONS AND CLINICAL RELEVANCE: In dogs with superficial bacterial folliculitis, most coagulase-positive staphylococcal isolates from pustules that are genotypically the same strain will have the same susceptibility phenotype and treatment may be based on empiric antimicrobial selection or susceptibility testing of 1 lesional isolate.     

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.     

Evaluation of a rapid inoculum standardization system for antimicrobial susceptibility testing of bacterial isolates from the bovine mammary gland

A commercially available rapid inoculum standardization system (RISS) was compared to the broth inoculum standardization method (BIS) for antimicrobial susceptibility testing of bacterial isolates from the bovine mammary gland. Overall agreement between RISS and the BIS method was 95.9%. RISS bypasses the 2-8 h incubation period required by BIS, thus providing antimicrobial susceptibility test data in a more timely manner. RISS was determined to be an acceptable alternative method to the BIS method for preparation of standardized inoculum for antimicrobial susceptibility testing of bovine mammary gland isolates.     

Suggested guidelines for immunohistochemical techniques in veterinary diagnostic laboratories

This document is the consensus of the American Association of Veterinary Laboratory Diagnosticians (AAVLD) Subcommittee on Standardization of Immunohistochemistry on a set of guidelines for immunohistochemistry (IHC) testing in veterinary laboratories. Immunohistochemistry is a powerful ancillary methodology frequently used in many veterinary laboratories for both diagnostic and research purposes. However, neither standardization nor validation of IHC tests has been completely achieved in veterinary medicine. This document addresses both issues. Topics covered include antibody selection, fixation, antigen retrieval, antibody incubation, antibody dilutions, tissue and reagent controls, buffers, and detection systems. The validation of an IHC test is addressed for both infectious diseases and neoplastic processes. In addition, storage and handling of IHC reagents, interpretation, quality control and assurance, and troubleshooting are also discussed. Proper standardization and validation of IHC will improve the quality of diagnostics in veterinary laboratories.     

Antimicrobial susceptibility testing of bacteria isolated from animals: methods for in-vitro susceptibility testing and their suitability with regard to the generation of the most useful data for therapeutic applications

In-vitro susceptibility testing provides valuable informations for choosing the most suitable antimicrobial agent for the control of bacterial infections in animals. Different diffusion and dilution methods, as conducted according to various approved performance standards, can be used to determine the in-vitro susceptibility of bacterial pathogens. In the present article, problems are discussed which arise from the use of different methods and the difficulty to interpret such results. While most approved performance standards were designed for testing of bacteria from human sources, the NCCLS document M31-A2 exclusively focusses on susceptibility testing of bacteria isolated from animals and--in contrast to all other standards--includes veterinary specific breakpoints for a number of antimicrobial agents used in veterinary medicine. Therefore, performance of in-vitro susceptibility testing of veterinary pathogens should follow the recommendations given in the NCCLS document M31-A2. The microdilution method is recommended as the method of choice for susceptibility testing. The result of a microdilution test is given as the minimum inhibitory concentration (MIC). This value provides a quantitative result which precisely indicates the degree of susceptibility of the tested bacterial strain and in return gives the veterinarian a clear guidance whether therapeutic intervention with the antibiotic in question will be successful.     

Accuracy of polymerase chain reaction assays for diagnosis of feline immunodeficiency virus infection in cats

OBJECTIVE: To determine the sensitivity, specificity, and overall diagnostic accuracy of polymerase chain reaction (PCR) assays offered by commercial diagnostic laboratories for diagnosis of FIV infection in cats. DESIGN: Prospective clinical trial. ANIMALS: 124 cats. PROCEDURE: Blood was collected from cats that were neither infected with nor vaccinated against FIV, uninfected cats that were vaccinated with a licensed FIV vaccine, and cats experimentally and naturally infected with FIV representing subtypes A, B, and C. Coded blood samples were submitted to 3 laboratories in the United States and Canada offering PCR assays for diagnosis of FIV infection to veterinary practitioners. All laboratories tested fresh blood samples, and 1 laboratory also tested samples submitted as dried blood smears. The FIV infection status in all cats was confirmed by virus isolation. Sensitivity, specificity, and correct results were calculated for each PCR assay. RESULTS: Sensitivity ranged from 41% to 93%. Specificity ranged from 81% to 100% in unvaccinated cats and 44% to 95% in cats vaccinated against FIV. Correct results were obtained in 58% to 90% of 124 cats tested. All tests misidentified both uninfected and infected cats. False-positive results by all laboratories were higher in cats vaccinated against FIV than in unvaccinated cats, suggesting that vaccination interferes with the performance or interpretation of PCR assays used for diagnosis of FIV infection. CONCLUSIONS AND CLINICAL RELEVANCE: PCR assays used for diagnosis of FIV infection presently marketed to veterinary practitioners in North America vary significantly in diagnostic accuracy and did not resolve the diagnostic dilemma resulting from vaccination of cats against FIV.     

External quality assurance system for antibiotic resistance in bacteria of animal origin in Europe (ARBAO-II), 2003

Initiated in 2003 by the European Union, ARBAO-II aims to establish a monitoring of antimicrobial susceptibility among the veterinary laboratories in all European countries based on validated methodologies. This includes an external quality control system for the most important bacterial pathogens. In 2003 two trials were performed. The first on Salmonella and Escherichia coli involved 31 laboratories in 18 countries and the second on Staphylococcus and Streptococcus included 22 laboratories in 15 countries. For the E. coli strains, 92.8% of the results complied with the reference MICs, for Salmonella 93.7%, for Streptococcus 80.4% and for Staphylococcus 93.1%. Most problems were observed when testing florfenicol (79.2% correct), gentamicin (84.2%) and amoxicillin + cl (84.9%) in E. coli; streptomycin in Salmonella (62.5%); gentamicin (56.7%), lincomycin (71.4%), clindamycin (75.4%), TMP + sulfonamides (75.7%) and chloramphenicol (78.5%) in Streptococcus; erythromycin (81.5%) and oxacillin (78.2.5%) in Staphylococcus. A few laboratories caused most deviations. However, there was no correlation between good performance for one bacterial group and good performance for other groups. This study showed that most laboratories are capable of performing correct susceptibility testing for E. coli and Salmonella, even though performance of some laboratories can be improved, and that some problems exist for Staphylococcus and Streptococcus. This clearly shows the need for continuous harmonisation of methodologies within the EU.     

Overview of issues pertaining to the manufacture, distribution, and use of antimicrobials in animals and other information relevant to animal antimicrobial use data collection in the United States

This paper provides condensed literature review and contextual information concerning antimicrobial use in animals and antimicrobial use data collection techniques. Information is summarized into the following topics: (I) antimicrobial use for animal growth promotion; (II) regulatory framework for approval of veterinary antimicrobials and feed additives in the United States; (III) animal health product manufacturing and distribution networks; (IV) existing estimates of animal antimicrobial use in the United States; (V) additional sources for animal use data in the United States; (VI) recommendations from international expert groups; (VII) animal antimicrobial use surveillance systems in other nations and (VIII) human use data collection systems in the United States.     

Evaluation of the antimicrobial activity of florfenicol against bacteria isolated from bovine and porcine respiratory disease

Antimicrobial susceptibility of florfenicol (FFC) against 243 bacterial agents isolated in Korea from cattle and pigs with respiratory disease were investigated by agar diffusion and microdilution broth methods following the recommendations provided by the National Committee for Clinical Laboratory Standards. All Actinobacillus pleuropnemoniae, Pasteurella multocida, Mannheimia haemolytica and 98.6% of the Bordetella bronchiseptica isolates were susceptible to FFC, which as significantly more effective than the other antibiotics used in this study. FFC also showed high in vitro antimicrobial activities (MIC(90) < or = 1 microg/ml) against all strains tested with a minimal inhibitory concentration (MIC) determination ranging from 0.12 to 4 microg/ml. No resistant strains of A. pleuropneumoniae, P. multocida and M. haemolytica to FFC have apparently developed since the first introduction of this antibiotics for veterinary use in Korea. The results suggest that FFC is therapeutically valuable in the treatment of primary or complicating bacterial pathogens causing of the bovine and swine respiratory tract.     

Antimicrobial susceptibility of Pseudomonas aeruginosa from dogs and cats as well as Arcanobacterium pyogenes from cattle and swine as determined in the BfT-GermVet monitoring program 2004-2006

During the BfT-GermVet monitoring program, Pseudomonas (P) aeruginosa from dogs and cats (n = 99) as well as Arcanobacterium (A.) pyogenes from cattle and swine (n = 90) were examined for their antimicrobial susceptibility. In general, P. aeruginosa is known to be resistant against many antimicrobial agents whereas A. pyogenes is thought to be susceptible to most agents in-vitro. However, representative and actual minimum inhibitory concentration (MIC) values are missing for both veterinary pathogens. In the present study, MIC values were determined and categorized according to the recommendations given in the Clinical and Laboratory Standards Institute (CLSI) documents M31-A2 and M31-S1. For susceptibility testing of A. pyogenes, the CLSI methodology was slightly modified. Specific breakpoints were not available for most of the antimicrobial agents tested. P. aeruginosa isolates from infections of the skin, ear and mouth as well as the urinary and genital tract of dogs and cats were either resistant or exhibited high MIC values to most antimicrobial agents tested. However, gentamicin resistant isolates were observed in only 27% and 11% (intermediate isolates 29% and 39%), respectively. For the same bacterium/host animal/organ system combinations, enrofloxacin resistance was detected in only 24% and 11% of the isolates (intermediate isolates 49% and 61%). For A. pyogenes, resistance was most prevalent against tetracycline (33%-56%, bovine and porcine isolates) and sulfonamides (26%-40%, bovine isolates).     

In vitro susceptibility of avian Escherichia coli and Pasteurella multocida to danofloxacin and five other antimicrobials.

The in vitro susceptibility of Escherichia coli and Pasteurella multocida isolated from poultry was determined to danofloxacin, a novel fluoroquinolone, and five other commonly used antimicrobials. A total of 1737 E. coli field isolates and 107 P. multocida isolates were tested by veterinary diagnostic laboratories in Europe, Japan, South Africa, and North America during the period 1989-91. The antimicrobial susceptibility of these isolates was determined using the Sensititre broth microdilution technique. The minimum inhibitory concentrations (MIC) of danofloxacin, furaltadone, lincomycin, oxytetracycline, spectinomycin, and trimethoprim:sulfamethoxazole that prevented growth of 90% of the bacteria were 0.25 > 64, > 64, > 64, > 128, and > 16 micrograms/ml, respectively, against E. coli isolates and 0.25, 64, 64, 16, 128, and 8 micrograms/ml, respectively, against P. multocida isolates. Danofloxacin demonstrated considerable in vitro potency against these important poultry pathogens, many of which showed extensive resistance to the other antimicrobials tested.     

Bacterial isolates and antimicrobial susceptibilities in equine bacterial ulcerative keratitis (1993--2004)

REASONS FOR PERFORMING STUDY: Bacterial ulcerative keratitis is a common and often vision-threatening problem in horses. Emerging bacterial resistance to commonly used topical antibiotics has been demonstrated. Previous antibiotic use may alter the antimicrobial susceptibility of bacterial isolates. OBJECTIVES: To document aerobic bacterial isolates and associated bacterial susceptibilities from horses with ulcerative keratitis treated at the University of Tennessee between January 1993 and May 2004 and determine whether prior antibiotic therapy affected antimicrobial susceptibility of the isolates. METHODS: Medical records from horses with ulcerative keratitis and positive aerobic bacterial cultures and antimicrobial susceptibility were evaluated. Clinical history regarding antibiotic therapy prior to culture was documented. RESULTS: Fifty-one aerobic bacterial isolates from 43 horses were identified. Streptococcus equi subspecies zooepidemicus was the most commonly isolated organism, accounting for 33.3% of all isolates, followed by Pseudomonas aeruginosa (11.8%), Staphylococcus spp. (11.8%) and Gram-negative nonfermenting rods (7.8 %). No resistance was noted amongst S. equi ssp. zooepidemicus to cephalothin, chloramphenicol or ciprofloxacin. Only 64 % of S. equi ssp. zooepidemicus isolates were sensitive to bacitracin. No resistance was noted among P. aeruginosa to gentamicin, tobramycin or ciprofloxacin. Antibiotic therapy with neomycin-polymixin B-bacitracin prior to presentation and culture was documented in 11/17 horses in which S. equi ssp. zooepidemicus was isolated and in 4/6 horses in which P. aeruginosa was isolated. Three horses received topical corticosteroids prior to culture, of which 2 had polymicrobial infections. CONCLUSIONS: S. equi ssp. zooepidemicus and P. aeruginosa were the most frequently isolated bacterial organisms in equine ulcerative keratitis. No significant trends in aminoglycoside or fluoroquinolone resistance were noted among these organisms. However, the resistance of S. equi ssp. zooepidemicus to bacitracin with common use of this antibiotic suggests that previous antibiotic therapy probably affects antimicrobial resistance. POTENTIAL RELEVANCE: Therapy prior to culture may play an important role in antimicrobial susceptibility of corneal bacterial isolates. Corticosteroid use may increase the risk of polymicrobial infections of corneal ulcers, leading to a worse prognosis. Although significant fluoroquinolone resistance has not been documented in the veterinary literature, these antimicrobials should be reserved for known infected corneal ulcers and not used for prophylaxis. Empirical antibiotic therapy should not only be guided by clinical signs, but also take into consideration previous antimicrobial and corticosteroid therapy.