In vitro antimicrobial susceptibility of Pasteurella haemolytica and Pasteurella multocida recovered from cattle with bovine respiratory disease complex
Karen W. Post, N. Andy Cole, Russell H. Raleigh
Abstract. The antimicrobial susceptibilities of 421 Pasteurella haemolytica and 158 P. multocida isolates
recovered from cattle with respiratory disease were determined with a microdilution minimal inhibitory con-
centration test system. Isolates were analyzed for patterns of resistance to ampicillin, ceftiofur, erythromycin,
gentamicin, penicillin, spectinomycin, sulfachlorpyridazine, sulfadimethoxine, tetracycline, and tylosin. All
isolates tested were found susceptible to ceftiofur and sulfachlorpyridazine. Pasteurella haemolytica isolates
were resistant to ampicillin, penicillin, sulfadimethoxine, tetracycline, and tylosin. Pasteurella multocida isolates
were resistant to sulfadimethoxine, tetracycline, and tylosin.
Antimicrobial susceptibility patterns are important [cfu]/ml). The adjusted culture was then diluted in Mueller-
in determining appropriate therapy against bacterial Hinton broth so that after inoculation each well contained
pathogens. Information regarding minimal inhibitory approximately 5 x 105 cfu/ml. Plates were sealed and in-
concentration (MIC) of antimicrobials to cattle isolates cubated at 37 C for 16-20 hr.
of Pasteurella species is limited to a few studies.3-6,9
Plates were read with a reflective viewer, and the MIC was
The purpose of this study was to determine the anti- recorded as the lowest concentration of antimicrobial that
microbial susceptibility patterns and MICs of P. hae-
completely inhibited all visible bacterial growth. For the sul-
fonamides, the MIC was recorded as the well where bacterial
molytica and P. multocida isolated from cattle with growth was reduced by ≥ 80% when compared with the growth
control well. The antimicrobial agents, concentrations, and
Materials and methods
criteria used to determine susceptibility, moderate suscep-
tibility, or resistance are presented in Table 1. Susceptibility
Bacterial cultures. Pasteurella haemolytica and P. mul-
interpretations were based on those described in previous
tocida isolates were selected from nasal swabs and tissue
studies or on available pharmacokinetic data1,4,6 (Halstead
specimens submitted from cattle with respiratory disease to
SL, Walker RD, Baker RE, et al.: 1989, Abstr Conf Res
the Texas Veterinary Medical Diagnostic Laboratory, Am- Workers Animal Dis #70, p. 32A). In addition, the MIC
arillo, between February and June 1989. These samples were
concentrations that inhibited 50% (MIC ) and 90% (MIC )
from cases where MIC testing was requested. The isolates
of the isolates were determined? Each lot of plates was sub-
jected to quality control using reference strains StaphylococcusMinimal inhibitory concentration testing. Antimicrobial
aureus (ATCC 29213), Streptococcusfaecalis (ATCC 29212),
powders used in the microdilution MIC procedure were am-
Pseudomonas aeruginosa (ATCC 27853), and Escherichia
picillin, a ceftiofur, b erythromycin, c gentamicin, c penicillin c
spectinomycin,c sulfachlorpyridazine, d sulfadimethoxine, c
tetracycline, a and tylosine. A standard microdilution tech-
nique was used to determine MICs.7 Antimicrobials were
Tables 2 and 3 list the range of MIC (mcg/ml) of
diluted either in phosphate-buffered saline (PBS), pH 8.0, or
each antimicrobial agent against the isolates of P. hae-
sterile water, and microtiter plates were prepared using a
molytica and P. multocida, respectively, and list the
dispenser.gEach of the Pasteurella isolates was inoculated
into 3.5 ml of Mueller-Hinton brothf and incubated 4-6 hr
cumulative MIC and MIC values of the Pasteurella
at 37 C to obtain a final concentration equal to a 0.5 Mc-
isolates. For the reference strains, the susceptibility
Farland nephelometer standard (108 colony-forming units
patterns (MIC) were within established limits.
Ninety percent of P. haemolytica isolates were mark-
edly susceptible to ceftiofur, gentamicin, and sulfa-
From the Texas Veterinary Medical Diagnostic Laboratory, 6610
chlorpyridazine. The MIC90 values for erythomycin
Amarillo Blvd. West, Amarillo, TX 79106 (Post, Raleigh), and theUS Department of Agriculture, Conservation and Production Re-
and spectinomycin were 4 µg/ml and 16 µg/ml, re-
search Laboratory, PO Drawer 10, Bushland, TX 79012 (Cole).
spectively, indicating moderate susceptibility. The
Revised for publication March 14, 1990.
MIC values for ampicillin, penicillin, sulfadimethox-
Susceptibilities of Pasteurella from cattle
Table 1. Dilution ranges of antimicrobial agents used for min-
Table 3. Antimicrobial minimal inhibitory concentration sus-
imum inhibitory concentration (MIC) testing against Pasteurella
ceptibility determinations (MIC and MIC ) of 158 Pasteurellahaemolytica and P. multocida.multocida isolates recovered from cattle.
ine, tetracycline, and tylosin were all in the resistantcategory.
Ninety percent of the P. multocida isolates indicated mine if changes in resistance are developing. This is
a marked susceptibility to ceftiofur and sulfachlorpyr- particularly important with the more newly released
idazine. Ninety percent of the isolates were moderately antimicrobial agents, i.e., ceftiofur, because resistance
susceptible to ampicillin, erythromycin, gentamicin, commonly increases in proportion to the frequency of
penicillin, and spectinomycin. As with P. haemolytica,
use. Apparently, the incidence of resistance is increas-
P. multocida was resistant to sulfadimethoxine, tet- ing among the Pasteurella species.3,5,9
Ceftiofur and sulfachlorpyridazine appear to be very
effective against both P. haemolytica and P. multocida. Discussion
However, these in vitro observations should only be
Studies involving food animal pathogens4,6 have
used as a guide for the clinician in the selection of the
demonstrated that MIC testing is preferable over the most appropriate antimicrobial agent. Resistance to
disk diffusion method for susceptibility testing because these antimicrobials may develop through increased
it provides quantitative information. The MIC value use, and continued surveillance is warranted.
can provide the necessary information for the calcu-
lation of effective dosage regimens. Sources and manufacturers
It is important to periodically monitor the antimi-
crobial susceptibilities of Pasteurella species to deter- a. American Research Products Co., S. Euclid, OH.
Table 2. Antimicrobial minimal inhibitory concentration sus-
d. E. R. Squibb and Sons, New Brunswick, NJ.
ceptibility determinations (MIC and MIC ) of 421 Pasteurella
e. Eli Lilly and Co., Indianapolis, IN. haemolytica isolates recovered from cattle.
g. Autodiluter II and SRD II semi-automaic single reagent dis-
penser, Dynatech Laboratories, Alexandria, VA.
h. American Type Culture Collection, Rockville, MD. References
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2. Carter GR, ed.: 1984, Diagnostic procedures in veterinary bac-
teriology and mycology, 4th ed., pp. 111-121. Charles C Thomas
3. Chang WH, Carter GR: 1976, Multiple drug resistance in Pas-teurella multocida and Pasteurella haemolytica from cattle and
swine. J Am Vet Med Assoc 169:710-712.
4. Fales WH, Berg JN, Morehouse LG: 1986, Use and comparison
of minimal inhibitory concentration and disk diffusion antimi-crobial susceptibility testing with bovine isolates of Pasteurellahaemolytica type 1 and Pasteurella multocida recovered from
Missouri cattle with bovine respiratory disease complex. Proc
7. National Committee for Clinical Laboratory Standards: 1985,
Annu Meet Am Assoc Vet Lab Diagn 29: 1-8.
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5. Fales WH, Selby LA, Webber JJ, et al.: 1982, Antimicrobial
that grow aerobically, vol. 5, no. 22. National Committee for
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Clinical Laboratory Standards, Villanova, PA.
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8. Prescott JF, Baggot JD: 1988, Antimicrobial therapy in veteri-
nary medicine. Blackwell Scientific Publications, Boston, MA.
6. Libal MC: 1985, Comparison of minimal inhibitory concentra-
9. Shoo MIS: 1989, Comparing different isolates of Pasteurella hae-
tion and disk-difIusion antimicrobic sensitivity testing of bacte-
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sitivity patterns. Vet Microbiol 20:73-78.
FACULTY OF HISTORY Problems in the History of Science and Technology Michaelmas Term 2005 The following seminars will be held on Wednesday at 5 p.m. (except in Week 6, when the seminar will begin at 4pm) in the History of Science and Technology Seminar Room, Modern History Faculty. They will be preceded by tea in the Faculty Common Room at 4.40 p.m. (except in Week 6, when the se
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