Avian Diseases: Vol. 47, No. 3, pp. 588–593.
In Vitro Antibiotic Resistance Profiles of
Ornithobacterium rhinotracheale Strains Isolated from
Minnesota Turkeys During 1996–2002
Yashpal S. Malik,A Karen Olsen,A Kuldeep Kumar,B and Sagar M. GoyalA, 1
A
Department of Veterinary Diagnostic Medicine, University
of Minnesota, St. Paul, MN 55108
B
Department of Soils, Water, and Climate, University of
Minnesota, St. Paul, MN 55108
Received 4 November 2002
SUMMARY.
Antimicrobial resistance in nearly all human and animal pathogens is on the increase. In poultry,
Ornithobacterium rhinotracheale has been identified as a newly emerging respiratory bacterial pathogen that has
caused significant economic losses to the poultry industry. In this study, we examined in vitro antibiotic
resistance profiles of 125 isolates of O. rhinotracheale isolated from turkeys in Minnesota during 1996–2002. A
majority of isolates was sensitive to clindamycin, erythromycin, spectinomycin, and ampicillin. Resistance
against sulfachloropyridiazine decreased from 1996 to 2002, but an increase in resistance was seen against
gentamicin, ampicillin, trimethoprim sulfa, and tetracycline. The annual trend slopes for these antibiotics were
7.36%, 3.02%, 2.43%, and 1.95%, respectively. The resistance against penicillin remained constant from year to
year with a trend slope of only 0.54% per year. These results emphasize the need for continued monitoring of O.
rhinotracheale isolates for antibiotic resistance and establishment of baseline resistance pattern data for this
organism. These data can then be used to design and evaluate local epidemiological interventions.
Perfiles de resistencia a antibióticos in vitro de cepas de Ornithobacterium rhinotracheale aisladas de pavos en
Minesota durante los años 1996–2002.
La resistencia antimicrobiana en casi todos los patógenos humanos y animales se está incrementando. El
Ornithobacterium rhinotracheale se ha identificado como un nuevo patógeno bacteriano emergente de tipo
respiratorio que ha causado pérdidas económicas significantes a la industria avícola. En este estudio se
examinaron los perfiles de resistencia a antibióticos de 125 aislados de O. rhinotracheale obtenidos de pavos en
Minesota durante los años 1996 a 2002. La mayoría de los aislados fueron sensibles a la clindamicina,
eritromicina, espectinomicina y ampicilina. La resistencia contra la sulfa-cloro-piridiacina disminuyó desde el
año 1996 al 2002, pero se observó un aumento en la resistencia contra la gentamicina, ampicilina, sulfatrimetroprina y tetraciclina. Las curvas de tendencia anual para estos antibióticos fueron 7.36%, 3.02%, 2.43% y
1.95%, respectivamente. La resistencia contra la penicilina permaneció constante año tras año con una curva de
tendencia anual de sólo el 0.54%. Estos resultados enfatizan la necesidad del estudio continuo de cepas de O.
rhinotracheale en lo relacionado con la resistencia a antibióticos y el establecimiento de datos sobre los patrones
de resistencia de este organismo. Estos datos pueden ser usados para diseñar y evaluar intervenciones
epidemiológicas locales.
Abbreviations: NCCLS = National Committee for Clinical Laboratory Standards, SBA = sheep blood agar
Key words: antibiotic resistance, Ornithobacterium rhinotracheale, antibiotic resistance, surveillance,
turkeys, Minnesota, prevalence, emerging pathogen
In poultry husbandry, the control and prevention of infectious diseases is of basic economic
importance. Antibiotics are often used as feed additives for growth promotion and for
prevention of bacterial infections in chickens and turkeys (18). Unfortunately, the selection
pressure exerted by antibiotics may lead to an increase in antibiotic resistance in both the
pathogens and the fecal microflora of poultry (23). Drug resistant bacteria from poultry may
also be transmitted to humans either directly or via food. The dissemination of resistant
bacteria from turkeys to turkey farmers, slaughterers, and area residents and from chickens to
human handlers has been reported (10,17,22). The development of resistance to commonly
used antimicrobials may result in increased costs of care due to the use of alternative
antimicrobials, which are often more costly.
In recent years, Ornithobacterium rhinotracheale has become an important pathogen of
turkeys (6,7,19). This is a pleomorphic, gram negative, rod shaped bacterium causing
mortality, growth suppression, prostration, decreased feed intake, severe weight loss,
coughing, and decreased egg production in affected birds (1,2). Ornithobacterium
rhinotracheale has also been isolated from turkeys without clinical signs (15). In some cases,
mortality may reach up to 10%. In addition, condemnation at the processing plant may also
result in economic losses to the producers. This organism was first isolated from broilers with
respiratory disease in Germany in 1981. Since then, it has been reported from turkeys in South
Africa, the Netherlands, France, Israel, Belgium, Hungary, the United Kingdom, and the
United States (2,4,6,8,19,20). In late 1995, O. rhinotracheale was first isolated from market
age tom turkeys in Minnesota and Wisconsin (14).
The control of O. rhinotracheale infections is important to minimize economic losses in
poultry flocks. During recent years, O. rhinotracheale infections have become more common,
and treatment with antibiotics has become less effective (24). It is important, therefore, to
evaluate the efficacy of antimicrobial drugs in current use and to determine patterns of
antimicrobial resistance. The analysis of data over a period of time will display trends in
antimicrobial resistance, and these data should be useful in investigating the epidemiology of
drug resistance. In this study, we describe the antimicrobial resistance profiles of O.
rhinotracheale strains isolated from turkeys in Minnesota during 1996–2002.
MATERIALS AND METHODS Return to TOC
Source of samples
Tracheal swabs, lung tissues, and sinus exudate swabs from turkeys with respiratory illness
are routinely submitted to the Minnesota Veterinary Diagnostic Laboratory, St. Paul, MN, for
disease diagnosis. These samples were initially inoculated on sheep blood agar (SBA)
followed by incubation in 5% CO2 atmosphere at 37 C for 24 hr. Suspect colonies were
subjected to standard biochemical tests. Oxidase positive, catalase negative, and CO2
dependent isolates that showed no color change on triple sugar iron agar were further tested
with API-ZYM system (BioMeriuex-France, Lyon, France) for confirmation.
Antibiotic susceptibility
Since a standard protocol for antibiotic sensitivity tests for O. rhinotracheale does not exist,
the method described by the National Committee for Clinical Laboratory Standards (NCCLS)
for fastidious gram-negative organisms was followed (12). Colonies were taken directly from
an overnight blood agar culture plate and suspended in Mueller Hinton broth. The suspension
was swabbed on the surface of blood Mueller Hinton agar followed by the application of
antibiotic discs: clindamycin, erythromycin, spectinomycin, ampicillin, sulfadimethoxine,
trimethoprim sulfa, gentamicin, ceftiofur, sulfachloro-pyridiazine, enrofloxacin, penicillin,
and tetracycline. Antibiotic resistance or susceptibility was determined using the criteria for
fastidious gram-negative organisms as established by NCCLS. Antibiotics trend graphs were
plotted using sigma plot software.
RESULTS Return to TOC
During the period under report, a total of 125 samples yielded O. rhinotracheale. The
isolation rate of the organism continued to increase (from 8 to 46) from 1996 to 2000, except
for 1997 when only one isolate was obtained. During 2001 and 2002, the number of
organisms isolated was 27 and 7, respectively. As shown in Table 1 , none of the isolates
was resistant to clindamycin and only one of the 125 isolates was resistant to erythromycin.
Data on spectinomycin from 1996 to 1999 indicated that all isolates were susceptible in 1996
and 1999 but 80% of them were resistant in 1998. Resistance to ampicillin was also low (from
0% to 10%), except that 44.4% of the isolates were resistant in 2001. The trend graph showed
an increase in ampicillin resistance from 1996 to 2001 with a slope of 3.02% per year (Fig. 1
). In 2002, however, none of the isolates was resistant to ampicillin.
Complete resistance to sulfadimethoxine was seen in isolates from 1996 to 2001 with an
exception in 2002, when 85.7% of the isolates were resistant with a decreasing slope of
1.6% per year (Table 1 , Fig. 1 ). An increasing trend of resistance to gentamicin and
trimethoprim sulfa was observed with slopes of 7.36% and 2.43% per year, respectively (Fig.
1 ). Although resistance to ceftiofur increased from 1999 to 2001, none of the seven
isolates in 2002 was resistant to ceftiofur. Sulfachloropyridiazine was evaluated in 1996,
1998, and 2002 only. The isolates showed high resistance to sulfachloropyridiazine in 1996
(75.0%) but were less resistant in 1998 (20.0%) and 2002 (28.6%). The rate of resistance to
enrofloxacin remained constant from 1999 to 2001 (47.8%–59.3%) but decreased to 0.00% in
2002. The resistance to penicillin was also constant from year to year; the trend graph shows
an increase of only 0.54% per year from 1996 to 2002. A slow increase was seen in resistance
to tetracycline (25.0% in 1996 to 42.9% in 2002) with a slope of 1.95% per year (Fig. 1 ).
DISCUSSION Return to TOC
Antibiotics are commonly used to treat and prevent infectious diseases and for growth
promotion in the poultry industry. Indiscriminate use of these antibiotics, however, may lead
to antibiotic resistance in both pathogens and resident microflora. In fact, the development of
antibiotic resistance in several poultry pathogens has been well documented. Studies on
antibiotic resistance in O. rhinotracheale, however, are sparse, although this is an important
emerging respiratory pathogen of poultry. In this study, we evaluated 12 antimicrobials
against O. rhinotracheale isolated from turkeys during 1996 to 2002.
All isolates from 1999 to 2002 were susceptible to clindamycin in vitro. The results
obtained with erythromycin in this study are in agreement with earlier studies in which O.
rhinotracheale was found to be very susceptible to erythromycin in vitro (3,9,11,13).
However, these results are in contrast to those of van Veen et al. (24), in which O.
rhinotracheale was found to be the least sensitive to erythromycin. Our results on
spectinomycin are also in accordance with earlier reports, in which O. rhinotracheale isolates
were shown to be highly susceptible to spectinomycin (11,16). However, the appearance of
spectinomycin resistance in 80% of the isolates in 1998 is more in agreement with the
findings of Devriese et al. (7).
Almost solid resistance against sulfadimethoxine is in accordance with an earlier study (7)
in which most isolates of O. rhinotracheale were found to be resistant to sulfadimethoxine.
The results of resistance against trimethoprim sulfa are also in accordance with earlier studies
(9,11,21), in which most isolates of O. rhinotracheale showed consistent resistance to
trimethoprim sulfa. However, these results are in contrast to those of van Veen et al. (24) in
which all isolates of O. rhinotracheale were found to be very susceptible to this antibiotic. An
increasing trend of resistance against gentamicin in this study is similar to that reported in
earlier studies (3,9,11,13,24).
The resistance to ceftiofur increased from 1999 to 2001, which is in contrast to the findings
of van Veen et al. (24), who showed a very high rate of susceptibility to ceftiofur. However,
our results of 2002, in which all isolates were susceptible to ceftiofur, are in accordance with
van Veen et al. (24). The rate of resistance (47.00% to 59.00%) against enrofloxacin from
1999 to 2001 was similar to that reported in O. rhinotracheale from Germany and the
Netherlands (9,21). Complete susceptibility to enrofloxacin in 2002 is in accordance with
findings from France, Belgium, and Israel (3,7,24). Low and consistent resistance to penicillin
has been reported earlier (7,11,13), and the data on tetracycline resistance are also in
accordance with earlier findings (3,5,7,11,13,24).
In summary, O. rhinotracheale isolated in Minnesota between 1996 and 2002 have been
steadily becoming resistant to gentamicin, ampicillin, tetracycline, and trimethoprim sulfa.
These data on antibiotic resistance should be eventually helpful in planning strategies for the
control of O. rhinotracheale infections in turkeys.
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1
Corresponding author. Department of Veterinary Diagnostic Medicine, College of
Veterinary Medicine, University of Minnesota, 1333 Gortner Avenue, St. Paul, MN 55108
FIGURES Return to TOC
Click on thumbnail for full-sized image.
Fig. 1. Trend graph of six antibiotics against O. rhinotracheale 1996–2002. Each graph shows regression and
slope values for the antibiotic in question
TABLES Return to TOC
Table 1. Percent of antibiotic resistant O. rhinotracheale isolated from turkeys during 1996–2002.A