Variability of laboratory identification and antibiotic susceptibility reporting of pseudomonas spp. isolates from dogs with chronic otitis externa

Variability of laboratory identification and antibiotic
susceptibility reporting of Pseudomonas spp. isolates
from dogs with chronic otitis externa
Anthea E. Schick*, John C. Angus†
Agreement in susceptibility to individual antibiotics
and Kimberly S. Coyner*
was observed in 13 of 16 (81%) occasions for amikacin
and gentamicin, 10 of 16 (63%) occasions for ticarcillin,
*Dermatology Clinic for Animals, Gilbert, Arizona, USA and nine of 16 (56%) for enrofloxacin. These results
†Southern Arizona Veterinary Specialty and Emergency Center, indicate that Pseudomonas spp. were identified by all
three laboratories chosen for this study in 83% of the
Correspondence: Anthea E. Schick, 86 West Juniper Dr., Gilbert, AZ time. Moreover, antibiotic susceptibility patterns and
85233, USA. E-mail: antheaschick@gmail.com.
MIC values reported to veterinarians may not agree
between laboratories. Veterinarians should interpret
bacterial culture and susceptibility results with multi-
What is known about the topic of this paper
ple caveats including variability between laboratories.
• Pseudomonas otitis is an important secondary cause of
• Veterinarians rely on correct identification and consistent
antimicrobial susceptibility of Pseudomonas for soundtreatment of Pseudomonas otitis.
What this paper adds to the field of veterinary
dermatology
Introduction
• This study demonstrates interlaboratory variability in identi- fication of Pseudomonas and variability in susceptible Canine otitis externa is a common condition encountered versus resistant classification to various antimicrobials in small animal medicine. Common organisms isolated that may affect selection of therapy.
from dogs with otitis externa include Staphylococcus spp.,Pseudomonas spp., Proteus spp., Streptococcus spp.,Escherichia coli, Klebsiella spp., Bacteroides spp., Pas-teurella spp. and Malassezia spp.1,2 The recommended Abstract
management of canine otitis externa consists of identi- The purpose of this study was to evaluate interlabo-
fying and treating the predisposing factors and primary ratory variation in isolation and antibiotic susceptibility
disease, ear cleaning, topical therapy and, if indicated, sys- pattern of Pseudomonas spp. as reported to veteri-
temic antimicrobial medication.3 Culture and antimicrobial narians for cases of canine chronic bacterial otitis
susceptibility testing are recommended in severe or chronic externa. Twenty-six dogs with unilateral or bilateral
cases of otitis externa, when rod-shaped bacteria are bacterial otitis externa from multiple referral practices
present, when inflammatory cells are present on cytology, were included in this prospective study. Triplicate
or in cases that fail to respond to antimicrobials chosen samples collected simultaneously from the same loca-
empirically.4–6 Pseudomonas aeruginosa is an aerobic, tion in the external ear canal were randomly sub-
gram-negative bacillus, which is associated with chronic mitted to three laboratories for culture and susceptibility
otitis externa and otitis media and often displays resist- testing. Pseudomonas spp. were isolated from 18 of 34
ance to multiple antimicrobial drugs.1,7 Because of this (53%) ears. All three laboratories agreed on the pres-
resistance, veterinarians may focus on susceptibility ence of Pseudomonas spp. in 15 (83.3%) ears sampled.
patterns of Pseudomonas spp. when multiple organisms However, two laboratories agreed on two (11.1%)
are isolated. Accurate bacterial identification and consistent occasions, and on one occasion (5.5%) Pseudomonas
antibiotic susceptibility reporting are important for proper spp. were identified in only one laboratory. Minimum
antimicrobial drug choice by veterinarians.
inhibitory concentration (MIC) susceptibilities to 11
Several studies have evaluated the microbial isolates and antibiotics were compared between laboratories B
antimicrobial susceptibility patterns of dogs with otitis.1,8,9 and C. Using laboratory-defined susceptibility of
One study found that Pseudomonas spp. isolated from sensitive (S), intermediate (I) and resistant (R), none
the horizontal ear canal had different susceptibility profiles of the 16 Pseudomonas spp. with MIC data reported
from Pseudomonas spp. isolated from the middle ear in 75% had identical patterns of antibiotic susceptibility.
of the time.1 A study comparing samples taken from thesame location in the ear canal and submitted to the samecommercial laboratory found that 70% of the P. aeruginosa This study was presented at the North American Veterinary cases had different susceptibility profiles suggesting that there may be multiple strains of Pseudomonas spp. inhabiting 2007 The Authors. Journal compilation 2007 ESVD and ACVD. 18; 120–126

Pseudomonas susceptibility between laboratories
the ear canal of dogs with Pseudomonas otitis.8 Another study All three laboratories followed the guidelines set by the Clinical and comparing bacterial isolates and their antimicrobial sus- Laboratory Standards Institute (CLSI), formerly the National Committee ceptibility patterns from parallel cultures submitted to the same laboratory found that 11% of P. aeruginosa isolateshad different susceptibility patterns and that cytopathology Bacterial culture and antimicrobial susceptibility
agreed with the culture results in 68% of the time.9 These methods
All samples were received by the laboratories within 24 h of collection.
studies raise the question of the reproducibility of cultureand susceptibility testing in canine Pseudomonas otitis.
Many veterinarians utilize the culture and antimicrobial Samples were plated on blood agar and MacConkey’s agar, cultured susceptibility reports from laboratories to select antimicrobial at 37 °C overnight with carbon dioxide enhancement and observed for drugs for both topical and systemic therapy of otitis. Incon- growth the following day. Following incubation, microbes were iden- sistencies in identification and antimicrobial susceptibility tified by colonial morphology, size and zones of haemolysis, pigment patterns of Pseudomonas spp. between laboratories can production, growth inhibition and differences in reactions. Once a affect antibiotic choice and, subsequently, treatment outcome pure culture was obtained, a sterile cotton tip swab was touched tothree to five colonies and suspended in saline solution to a uniform of dogs with Pseudomonas otitis. The purpose of this study turbidity of 0.5 McFarland. The Trek Sensititre® (TREK Diagnostic was to determine whether reports of Pseudomonas spp.
Systems, Inc., Cleveland, OH, USA) automated machine was used to identification and antimicrobial susceptibility patterns from measure the minimum inhibitory concentration (MIC). A 50-µL loop clinical cases of otitis externa were consistent between two was used to inoculate Mueller–Hinton broth, then equal volumes of major commercial laboratories and one academic laboratory.
the culture were manually pipetted into each of the 96-well agarplate of serially diluted antibiotics. Turbidity of samples was readby Sensititre ARIS® (TREK Diagnostic Systems, Inc.) machine for Materials and methods
Study population
Cases were selected from a population of client-owned dogs presented Samples were plated and identified as for laboratory A. Once a pure to a private veterinary dermatology referral practice with multiple culture was obtained, a sterile cotton tip swab was touched to one to locations in the south-western and western USA. Dogs with chronic two colonies and suspended in saline solution to a uniform turbidity otitis externa, defined as persistent or intermittent unilateral or bilateral of 0.1 McFarland. VITEK® (VITEK bioMerieux, Inc., Durham, NC, otitis of at least 6 months duration, were selected for the study. Bacterial USA) automated machine was used to measure MIC. A uniform otitis was diagnosed by clinical assessment and cytological criteria volume of the culture was machine-pipetted and added to serial characterized by greater than 10 bacteria per 1000× magnification dilutions of the antibiotics being tested. The samples were incubated present in a minimum of five fields.11 Dogs with rod-shaped bacteria for 2–24 h, with samples automatically read for turbidity of growth at found on cytological evaluation were included in the study. The pres- 15-min intervals. A growth curve for the isolate was calculated for each ence or absence of leucocytes was also noted. Cytological evidence antibiotic. The algorithm stored in the VITEK® (VITEK bioMerieux, Inc.) of a concurrent Malassezia otitis did not exclude a dog from the study.
system analysis program calculated the organisms’ MIC for each of Additionally, dogs that had been receiving treatment with systemic or topical antibiotics at the time of evaluation were not excluded, asthe goal of the study was to compare bacterial culture results and antimicrobial susceptibility patterns between different microbiology Samples were plated on Columbia blood, MacConkey’s, and laboratories under typical clinical practice circumstances.
Columbia colistin Nalidixic acid agar plates, incubated at 37 °Covernight and observed for growth the following day. Following Sample collection and randomization for bacterial
incubation, microbes were identified as for laboratory A. Once a pureculture was obtained, a sterile cotton tip swab was touched to one culture and antimicrobial susceptibility
colony and suspended in saline solution to a uniform turbidity of Samples for otic cultures were obtained by passing a gas-sterilized 0.5 McFarland. The Trek Sensititre® automated machine was used disposable ear cone into the external canal and visualizing the junction to measure MIC. A uniform volume of the culture 10 µL of solution of the vertical and horizontal ear canal. Three sterile minitip cul- was manually pipetted into each of the 96-well Mueller–Hinton turette swabs (Mini-tip Culturette, Becton-Dickinson, Cockeysville, agar plate of serially diluted antibiotics. Turbidity of samples was read MD, USA) were passed simultaneously through the ear cone, forming by Sensitouch® (TREK Diagnostic Systems, Inc., Cleveland, OH, USA) a three-prong cluster emerging from the end of the cone tip. The three culturettes were rotated and rubbed together to equally distribute theexudate on each culturette. Thereafter, each swab was placed into a Statistical analyses
separate sterile culture transport tube (Mini-tip Culturette, Becton-Dickinson) for aerobic bacterial culture and antibiotic susceptibility.
Sign test was used to investigate distributions of MIC values Samples were randomly assigned to one of three laboratories by between laboratories B and C for four antibiotics considered effective labelling each sample A, B, and C. Using a die, laboratory A (Antech in treating Pseudomonas otitis, including amikacin, enrofloxacin, genta- Microbiology Laboratory, Irvine, CA, USA) was assigned the values of micin and ticarcillin. Since laboratory B failed to report MIC data for 1 and 4, laboratory B (IDEXX Reference Laboratory, West Sacra- ticarcillin in one sample, this sample was not included in the comparison.
mento, CA, USA) the values of 2 and 5, and laboratory C (Veterinary Differences were considered significant at P < 0.05.
Diagnostic Laboratory, College of Veterinary Medicine, University ofIllinois, Urbana, IL, USA) the values of 3 and 6. A die was rolled for the first sample and the sample was sent to the laboratory correspondingwith the value on the die. That laboratory was then eliminated as a Twenty-six dogs were found to have bacterial otitis externa choice, and the die was rolled until a number representing one of the with rod-shaped bacteria present on cytology and were two remaining labs was obtained. The third sample was sent to the included in the study. Eighteen dogs had one ear sampled remaining laboratory. Samples submitted to laboratories A and B weretransported by the standard courier service provided by each labora- for culture and antimicrobial susceptibility and eight dogs tory. Samples submitted to laboratory C were sent next day by air by had both ears sampled, resulting in a total of 34 ears tested. Triplicate samples were collected from all 34 ears 2007 The Authors. Journal compilation 2007 ESVD and ACVD.
Schick et al.
resulting in a total of 102 samples submitted for bacterial MIC susceptibility results for the 16 cases for laboratories B and C are shown in Table 1. Both laboratories performeda full range of MICs. Dilutions of antimicrobials tested and Bacterial culture results
the MIC breakpoint for resistance for laboratories B and C Pseudomonas aeruginosa or Pseudomonas spp. were isolated by at least one of the three laboratories in culture Direct comparison of reported specific MIC results samples from 18 of 34 (53%) ears and in 50 of 102 (49%) was only possible between laboratories B and C. Since the total samples. Laboratory A isolated Pseudomonas spp. in majority of the antibiotics included on the panels from 16 of the 34 ear samples, while laboratories B and C each both laboratories are ineffective for Pseudomonas spp.,13 isolated Pseudomonas spp. from 17 ears. Bacteria other only the antibiotics that have been reported to be effective than Pseudomonas spp. were isolated from 16 ear samples.
in treating Pseudomonas spp. otitis were used in the All three laboratories agreed on isolating Pseudomonas comparison tests. The distributions for MIC values for spp. in samples collected from 15 of the 18 (83.3%) ears.
amikacin and enrofloxacin were not significantly different In two occasions (11.1%), Pseudomonas spp. were iso- between laboratory B and laboratory C (P = 0.21 and lated by only two laboratories and, in one occasion (5.5%), P = 0.61, respectively). The MIC values for gentamicin by only one laboratory. Pseudomonas aeruginosa was and ticarcillin reported by laboratory B were significantly consistently identified by the laboratories with the excep- higher than the MIC values reported by laboratory C tion of three occasions where the species was not reported (P = 0.023 and P = 0.001, respectively).
Discussion
Antimicrobial susceptibility patterns
Although the tube dilution testing with MIC results was
Veterinarians frequently rely on culture and susceptibility requested on the submission form sent to all laboratories, testing from otic swabs to select antibiotic therapy for some isolates were tested using the Kirby–Bauer (KB) bacterial otitis externa. Repeatability and reliability of disk diffusion method for determining antimicrobial sus- laboratory results are desirable to minimize administra- ceptibility. Laboratory A reported KB results for five of the tion of inappropriate antibiotics. This study demonstrated 16 Pseudomonas spp. Isolates, while laboratories B and C inconsistency between laboratories in isolation of Pseu- reported MIC data for all 17 Pseudomonas spp. isolates.
domonas spp. and in antimicrobial susceptibility patterns Because of the differences between the KB and the MIC for Pseudomonas spp. reported for otic swabs submitted methods of susceptibility testing,13,14 KB data were not from clinical cases. When one laboratory isolated Pseu- included in the comparison of antimicrobial susceptibility domonas spp., at least one of the other laboratories failed pattern. As a result, laboratory A susceptibility data were to isolate Pseudomonas spp. in 16.7% of cases. As Pseu- not analysed because of the small number of isolates domonas otitis can be one of the most challenging types of otitis often associated with antibiotic resistance,3 failure MIC data for 11 antibiotics common to the antimicrobial to consistently isolate Pseudomonas spp. by laboratories panels of laboratories B and C were compared including may lead to inappropriate therapy decisions and more amikacin, amoxycillin/clavulanic acid, ampicillin, first- prolonged disease course for affected animals.
generation cephalosporin (cefalexin and cephalothin), One possible reason for failure of all three laboratories third-generation cephalosporin (ceftiofur), chloramphenicol, to consistently isolate Pseudomonas spp. in this study enrofloxacin, gentamicin, tetracycline, ticarcillin and tri- is the presence of very small numbers of organisms in methoprim/sulfamethoxazole. Using laboratories B and the samples submitted for culture. All dogs included in the C’s reported antimicrobial susceptibility of sensitive (S), present study had active, chronic otitis with abundant otic intermediate (I) and resistant (R), none of the 16 Pseu- exudate. All dogs with positive cultures for Pseudomonas domonas spp. Isolates, in which MIC data were provided spp. had numerous bacterial rods present on cytology, for all tested antimicrobials from both laboratories, had making the possibility of inadequate samples less likely.
the same antibiotic susceptibility patterns. For amoxycillin/ Also, rotating and rubbing the culturettes together should clavulanic acid and first-generation cephalosporin, both have distributed organisms among the three culturettes.
laboratories reported resistance for all 16 isolates. The Other possible reasons for failure of all laboratories to iso- laboratories agreed on resistance to chloramphenicol late Pseudomonas include variation in sample processing, for 14 of the 16 (88%) Pseudomonas spp. isolates. For variation in culture technique, and error inherent to culture ampicillin, ceftiofur, and tetracycline, both laboratories methods. All laboratories received the samples within the agreed on resistance for 13 (81%) isolates. Resistance same time period and used similar culturing techniques, to trimethoprim/sulfamethoxazole was reported by both using both blood agar and MacConkey’s agar to grow the laboratories in 11 of the 16 (69%) tested isolates. For initial cultures. As different laboratories have different amikacin and gentamicin, the laboratories agreed that the laboratory technicians, there could have been differences cultured Pseudomonas spp. isolates were susceptible in in plating techniques or identification of Pseudomonas Laboratory B reported KB data for ticarcillin susceptibility Laboratory A reported KB susceptibility data for five of in one occasion and these data were not included in the the16 isolates despite the specific request by the sub- comparison. Both laboratories agreed on whether the mitting veterinarian for MIC determination. A previous study Pseudomonas spp. isolates were resistant or susceptible examining the differences between these two testing to ticarcillin and enrofloxacin in nine of 15 (60%) occasions.
methods showed that for susceptibility of Pseudomonas 2007 The Authors. Journal compilation 2007 ESVD and ACVD.
2007 The Authors. Journal compilation 2007 ESVD and ACVD.
Table 1. Susceptibility results based on minimal inhibitory concentration of 11 antibiotics tested against Pseudomonas spp. isolates sampled from the ear canals of dogs with chronic otitis externa
R ≥ 32
R ≥ 16
R ≥ 8
R ≥ 16
R ≥ 32
R ≥ 256
R ≥ 320
S ≤ 0.25
R > 16
R ≥ 320
R ≥ 320
R ≥ 32
R ≥ 32
R ≥ 8
R ≥ 2
R ≥ 16
R ≥ 256
S ≤ 0.25
R ≥ 2
Pseudomonas
R ≥ 256
R ≥ 2
R ≥ 16
susceptibility between laboratories
R ≥ 2
Minimum inhibitory concentration (MIC) expressed in µg mL−1; S, sensitive (MIC lower than the breakpoint for the drug); I, intermediate (MIC close to or equal to the breakpoint for the drug); R, resistant (MIC greater than the breakpoint for the drug); S ≤ indicates that no smaller dilution was tested, R > and R ≥ indicates that no higher dilution was tested; S or R indicates that a discrete endpoint was achieved; values in bold indicate disagreement in laboratory-defined susceptibility status; *Kirby–Bauer disk diffusion method was used.

Schick et al.
Table 2. Dilutions of antimicrobials tested and minimum inhibitory
submitted sample but only one strain selected by the concentration breakpoints for resistance for laboratories B and C laboratory for susceptibility testing. Additionally, hetero-resistance may exist among a single strain. The term heteroresistant is most commonly used for vancomycin- 2, 4, 8, 16, 32, 64
4, 8, 16, 32, 64
resistant Staphylococci spp. and refers to variability in 8/4, 16/8, 32/16
antibiotic susceptibility among subpopulations of a single 0.25, 0.5, 1, 2, 4, 8, 16, 32 0.5, 1, 2, 4, 8, 16
isolate.16 A heteroresistant isolate contains two popula- 0.25, 0.5, 1, 2, 4
tions of cells, one that is susceptible to a certain antibiotic Cefalexin/cephalothin 2, 4, 8, 16, 32
2, 4, 8, 16
and a minority population that is resistant.16 If only a few 2, 4, 8, 16, 32
colonies are chosen for MIC evaluation, the laboratory 0.25, 0.5, 1, 2
0.5, 1, 2, 4
may report resistance patterns of only one subpopulation.
0.5, 1, 2, 4, 8, 16
1, 2, 4, 8, 16
Significant difference in distribution of MIC values 1, 2, 4, 8, 16
reported by laboratories B and C was shown for gentamicin 16, 32, 64, 128, 256
8, 16, 32, 64
10, 20, 40, 80, 160, 320*
and ticarcillin, but not for amikacin and enrofloxacin. For gentamicin and ticarcillin, MIC values from laboratory Bwere higher than those from laboratory C and explained All values in ug mL−1; values in bold indicate breakpoint for resistance.
Laboratory B: IDEXX Reference Laboratory, West Sacramento, CA, the disparate laboratory-defined susceptibility results (i.e.
sensitive, intermediate, resistant) for both antibiotics. For Laboratory C: Veterinary Diagnostic Laboratory, College of Veterinary enrofloxacin, MIC values from laboratory B were also Medicine, University of Illinois, Urbana, IL, USA.
generally higher than those from laboratory C and explained *Trimethoprim/sulfamethoxazole expressed as combined five of the seven disparate laboratory-defined susceptibility trimethoprim + sulfamethoxazole fractions.
results. The finding of quantitative differences in MIC report-ing suggests that when given duplicate samples from thesame ear Pseudomonas spp. susceptibility and MIC patterns spp. to enrofloxacin, KB and MIC results agreed only one may differ between laboratories for some antimicrobials.
third of the time.13 A second study found that KB results Differences in MIC values between laboratories B and tended to yield a more conservative clinical interpretation C may have been due to different MIC testing methods.
than MIC results; meaning KB method may underestimate Laboratory B used the Vitek® automated machine, whereas susceptibility.14 Veterinarians should know which tech- laboratory C used the Trek Sensititre® automated machine nique their laboratory employed, as well as understand the to measure MIC values. A study published in 1987 com- differences in methodology and how this methodology paring seven commonly used antimicrobial susceptibility influences the interpretation of antimicrobial susceptibility.
methods to test 150 isolates of P. aeruginosa found no Susceptibility patterns were compared between labo- significant differences between the Sensititre® and the ratories B and C for 16 Pseudomonas spp. isolates. Of the Vitek® methods for aminoglycosides;17 however, fluoro- relevant antibiotic choices for treating Pseudomonas quinolones and ticarcillin were not tested.
otitis, which typically include amikacin, enrofloxacin, genta- Results from this study demonstrate variability between micin, and ticarcillin, complete agreement between the two major commercial laboratories and an academic labo- two laboratories for these four antibiotics was found ratory in isolation of Pseudomonas spp. Moreover, sub- only in three (19%) occasions. Both laboratories reported sequent antimicrobial susceptibility data for the isolates susceptibility to amikacin and gentamicin for 81% of the were occasionally discrepant between two of the labora- Pseudomonas spp. isolates, whereas the agreement for tories. Veterinarians need to be aware of possible laboratory ticarcillin was 60% and for enrofloxacin 56%.
variability in the isolation of Pseudomonas spp. from otic The variability in the report of enrofloxacin susceptibility cultures as well as differences in antimicrobial susceptibility between laboratories B and C could be partially explained reporting that may result from variability in MIC determina- by differences in using CLSI-recommended enrofloxacin tions and possible differences in antibiotic breakpoints used.
breakpoint values for evaluating susceptibility patternsof Pseudomonas spp. isolates. In this study, laboratory B Acknowledgements
used an MIC breakpoint for enrofloxacin of 2 µg mL−1,whereas laboratory C used 4 µg mL−1. CLSI changed The authors would like to thank David J. Schaeffer, from the breakpoint for enrofloxacin from 2 to 4 µg mL−1 in University of Illinois at Urbana-Champaign, College of 1999.12 Of the seven ears sampled that resulted in con- Veterinary Medicine for statistical analysis, Tom Lewis, flicting susceptibility data from laboratories B and C, four Helen Power, and Amy Shumaker, for their help with this of them may have agreed that laboratory B used the study as well as Bayer Animal Health for funding.
higher MIC breakpoint. A Pseudomonas organism that is‘resistant’ using a breakpoint of 2 µg mL−1, the drug con- References
centration achieved using the low end of the dose rangefor enrofloxacin, may be ‘sensitive’ using a breakpoint of 1. Cole LK, Kwochka KW, Kowalski JJ et al. Microbial flora and anti- 4 µg mL−1, the approximate drug concentration achiev- microbial susceptibility patterns of isolated pathogens fromthe horizontal ear canal and middle ear in dogs with otitis media.
able using the highest oral dose of 20 mg kg−1.15 Journal of the American Veterinary Medical Association 1998; Other potential causes for the discrepant results in the antibiotic susceptibility patterns include the presence of 2. Paterson S. A review of 200 cases of otitis externa in the dog.
multiple strains of the same species of bacteria within the Veterinary Dermatology 2003; 14: 249 (Abstract).
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3. Nuttall T. Treating Pseudomonas Otitis. In: Hillier A, Foster AP, 10. Rosychuk RAW. Therapeutics for otitis externa. In: Harrison BA, Kwochka KW, eds. Advances in Veterinary Dermatology, Vol. 5.
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Forum, Harrisburg, PA: American Academy of Veterinary Derma- 4. Scott DW, Miller WH, Griffin CE. Muller and Kirk’s Small Animal Dermatology, 6th edn. Philadelphia, PA: W.B. Saunders Co, 2001; 11. Ginel PJ, Lucena R, Rodriquez JC, Ortega J. A semiquantitative cytological evaluation of normal and pathological samples from 5. Hall JA. Medical management of otitis externa: an alternative the external ear canal of dogs and cats. Veterinary Dermatology approach. In: Harrison BA, ed. Proceedings of North American Veterinary Dermatology Forum, Harrisburg, PA: American Acad- 12. Clinical and Laboratory Standards Institute (CLSI) website. Micro- emy of Veterinary Dermatology, 2005; 147 – 51.
biology laboratory guideline information. A 6. Cole LK. Diagnostic tests and techniques for otitis. In: Harrison BA, ed. Proceedings of the North American Veterinary Derma- 13. Cole LK, Schwassmann M. Antibiotic use in chronic otitis tology Forum, Harrisburg, PA: American Academy of Veterinary externa. In: Thoday KL, Foil CS, Bond R, eds. Advances in Veterinary Dermatology, Vol. 4. Oxford: Blackwell Publishing, 7. Seol B, Naglic T, Madic J et al. In vitro antimicrobial susceptibility of 183 Pseudomonas aeruginosa strains isolated from dogs to 14. DeBoer D, Verbrugge MJ, Hartmann FA. Antimicrobial suscepti- selected antipseudomonas agents. Journal of Veterinary Medi- bility patterns in fluoroquinolone-susceptible and fluoroquinolone- nonsusceptible isolates of Pseudomonas aeruginosa from the ear 8. Griffin CE. Otitis diagnosis, methods for determining secondary canal of dogs. Veterinary Dermatology 2005; 16: 195 (Abstract).
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9. Graham-Mize CA, Rosser EJ. Comparison of microbial isolates 17. taneck JL, Glenn S, DiPerson JR, Leist PA. Wide variability in and susceptibility patterns from the external ear canal of dogs Pseudomonas aeruginosa aminoglycoside results among seven with otitis externa. Journal of the American Animal Hospital susceptibility testing procedures. Journal of Clinical Microbiology Résumé
Le but de cette étude était d’évaluer la variabilité interlaboratoire pour l’isolement et les anti- biogrammes en rapport avec Pseudomonas spp. Retrouvé dans les cas d’otite canine chronique. Vingt sixchiens à otite externe bactérienne, uni ou bilatérale, de diverses clientèles référées, ont été inclus dans cetteétude prospective. Les prélèvements ont été réalisés en triple, et soumis au hasard à trois laboratoires pourculture et antibiogramme. Pseudomonas spp. A été isolé de 18 sur 34 (53%) oreilles. Les trois laboratoiresétaient d’accord sur la présence de Pseudomonas spp. dans 15 (83.3%) oreilles. En revanche, deux labo-ratoires étaient en accord dans 2 cas (11.1%) et dans un cas (5.5%) Pseudomonas spp. a été identifié parun seul laboratoire. Les concentrations minimales inhibitrices (MIC) à 11 antibiotiques ont été comparéesentre les laboratoires B et C. En se basant sur les sensibilités définies comme sensible (S), intermédiaire(I) et résistant (R), aucune des 16 souches de Pseudomonas spp. présentaient des sensibilités identiques.
Un accord sur la sensibilité aux antibiotiques individuels a été observée dans 13 sur 16 (81%) cas pourl’amikacine et la gentamicine, 10 de 16 (63%) cas pour la ticarcilline, et 9 de 16 (56%) cas pour l’enro-floxacine. Ces résultats indiquent que Pseudomonas spp. A été identifié par les trois laboratoires choisispour cette étude dans 83% des cas. En outre, les sensibilités antibiotiques et les valeurs de MIC donnéesaux vétérinaires ne sont pas toujours les mêmes en fonction des laboratoires. Les vétérinaires doivent doncinterpréter avec précaution les résultats des antibiogrammes et des cultures bactériologiques réalisés enpratique.
El propósito de este estudio fue evaluar la variación interlaboratorial en el aislamiento y suscep- tibilidad a antibióticos de Pseudomonas spp. en casos de otitis bacteriana externa crónica canina. Veintiseisperros con otitis externa unilateral o bilateral procedentes de diversas clínicas de referencia se incluyeronen este estudio prospectivo. Muestras triplicadas recogidas simultaneamente de la misma localización enel canal auditivo externo se remitieron a tres laboratorios de forma aleatoria para la realización del cultivo ysusceptibilidad. Pseudomonas spp. se aisló de 18 de 34 oídos (53%). Todos los laboratorios coincidieronen la presencia de Pseudomonas en 15 (83.3%) de los oídos cultivados. Sin embargo sólo dos laboratorioscoincidieron en 2 ocasiones (11.1%), y en una ocasión (5.5%) Pseudomonas spp. se aisló unicamente enuno de los laboratorios. La susceptibilidad a la concentración inhibitoria mínima (MIC) para once antibióticosse comparó entre los laboratorios B y C. Utilizando parametros de susceptibilidad definidos por el laboratoriocomo sensible (S), intermedio (I) o resistente (R), ninguna de las 16 Pseudomonas spp. con datos de MICdocumentados presentaron un perfil idéntico de susceptibilidad a antibióticos. Una coincidencia en lasusceptibilidad a antibióticos individuales se observó en 13 de 16 (81%) de los casos para amikacina ygentamicina, 10 de 16 (63%) para ticarcilina, y 9 de 16 para enrofloxacina. Estos resultados indican que Pseu-domonas spp. se identificó en los 3 laboratorios en un 83% de los casos. Más aún, los perfiles de sensibilidadantibiótica y valores de MIC indicados a los veterinarios pueden ser diferentes entre laboratorios. Losveterinarios clínicos deben interpretar los resultados del cultivo y la susceptibilidad con ciertos interrogantes,incluidos la variación entre laboratorios.
2007 The Authors. Journal compilation 2007 ESVD and ACVD.
Schick et al.
Zusammenfassung
Das Ziel dieser Studie war es, eine Variation zwischen den Laboratorien bei der Isolierung von Pseudomonas spp. und Erstellung eines Antibiogramms, welches bei Fällen von chronischerbakterieller Otitis externa bei Hunden an die Tierärzte gesendet wird, zu evaluieren. SechsundzwanzigHunde aus mehreren Überweisungspraxen mit uni- oder bilateraler bakterieller Otitis externa wurden indieser prospektiven Studie inkludiert. Die Proben wurden gleichzeitig in dreifacher Ausführung von derselbenStelle im äußeren Gehörgang entnommen und wahllos an drei Laboratorien für Bakterienkultur undErstellung eines Antibiogramms geschickt. Pseudomonas spp. wurde von 18 der 34 (53%) Ohren isoliert.
Alle drei Laboratorien stimmten im Bezug auf ein Vorhandensein von Pseudomonas spp. in 15 (83,3%) derkultivierten Ohren überein. Allerdings stimmten nur zwei Laboratorien in 2 (11,1%) Fällen überein, währendPseudomonas spp. einmal nur von einem Labor identifiziert wurde. Die minimale inhibitorische Konzentra-tion (MIC) für elf Antibiotika wurde zwischen den Laboratorien B und C verglichen. Bei Verwendung der vonden Laboratorien definierten Empfindlichkeiten als sensitiv (S), intermediär (I) und resistent (R) zeigte keinerder 16 Pseudomonas spp. mit vorhandenen MIC Daten ein identisches Muster im Bezug auf die anti-biotische Empfindlichkeit. Eine Übereinstimmung für individuelle Antibiotika wurde bei 13 der 16 (81%) Fällefür Amikacin und Gentamycin, bei 10 der 16 (63%) Fälle für Ticarcillin, und bei 9 der 16 (56%) Fälle für Enro-floxacin beobachtet. Diese Ergebnisse weisen darauf hin, dass Pseudomonas spp. in 83% der Fälle von allendrei Laboratorien, die für diese Studie ausgewählt worden waren, identifiziert wurde. Außerdem kann esvorkommen, dass die Ergebnisse der Antibiogramme und die MIC Daten, die an die Tierärzte weitergegebenwerden zwischen den Labors nicht übereinstimmen. Tierärzte sollten die Ergebnisse von Bakterienkulturund Antibiogrammen mit viel Vorsicht interpretieren und die Variabilität zwischen Labors beachten.
2007 The Authors. Journal compilation 2007 ESVD and ACVD.

Source: http://asaplab.com.au/April_2010_files/variability%20in%20lab%20reporting%20pseudomonas.pdf