La susceptibilidad bacteriana de 40 cepas aisladas de Pseudomonas aeruginosa a seis agentes antimicrobianos ceftiofur (CFT), colistin (COL), danofloxacin (DNF), enrofloxacin (ENF), gentamicin, (GEN), y trimethoprim:sulphamethoxazole (TMS) (razón 1:19) fue determinado para concentración inhibitoria mínima (CIM) usando el método del agar-dilución. Todas las cepas fueron aisladas de criaderos de visones (Mustela vison) de casos de neumonía hemorrágica y fueron recolectadas durante los últimos catorce años. La CIM que previno el crecimiento del 90% de las bacterias fue en mg/ml: 100 para CFT, 100 para COL, 1,57 para DNF y ENF, 12,5 para GEN y > 100 para las TMS. Las fluoroquinolonas mostraron actividad más alta en nuestras de cepas que los clásicos antibióticos usados contra Pseudomonas aeruginosa. Basado en los valores de CIM obtenidos y teniendo en cuenta la forma de administración de estas drogas (mezcla en el alimento o suministro de agua), consideramos que podrían ser útiles para el tratamiento de esta enfermedad.Bacterial susceptibility of 40 isolates of Pseudomonas aeruginosa to six antimicrobial agents ceftiofur (CFT), colistin (COL), danofloxacin (DNF), enrofloxacin (ENF), gentamicin (GEN), and trimethoprim:sulphamethoxazole (TMS) (ratio 1:19) were determined for the minimal inhibitory concentration (MIC) using the agar-dilution method. All strains were from ranch-raised mink (Mustela vison) origin, were considered clinically important (mostly with Pneumonia infection) and were collected during the past fourteen years. The MIC that prevented the growth of 90 % of the bacteria were in mg/ml, 100 for CFT, 100 for COL, 1.57 for DNF and ENF, 12.5 for GEN and > 100 for TMS. The fluoroquinolones showed higher activity in our strains than the classical antibiotics used against Pseudomonas aeruginosa. Based on the MIC values obtained and taking into account the administration form (mixed into the feed or water supply) of these drugs, we consider that they might be useful for treatment on this illness.Facultad de Ciencias Veterinaria

Copes, Julio Alberto

Martino, Pablo Eduardo

Pantozzi, Florencia Laura

Stanchi, Néstor Oscar

Analecta Veterinaria

SEDICI - Repositorio de la UNLP

32 ANALECTA VETERINARIA 2000; 20, 1: 32-35                                                ISSN 1514-2590
F.L.Pantozzi y col.
Comunicación breve
Dirección para correspondencia:
F.Pantozzi. Laboratorio de Investigaciones y Diagnóstico Bacteriológicos (LADIB). Facultad de Ciencias
Veterinarias. Universidad Nacional de La Plata CC 296 (B1900AVW) La Plata, Argentina. Tel/Fax: (0221)
4257980. CC 296 La Plata (B1900AVW). Argentina E-mail: fpantozzi@fcv.medvet.unlp.edu.ar
Fecha de recepción: 10/09/99 Fecha de aprobación: 18/05/00
ANTIMICROBIAL SUSCEPTIBILITY OF Pseudomonas aeruginosa
ISOLATED FROM DISEASED MINKS
F.L. Pantozzi1, J.A. Copes2, P. Martino3,4, N. Stanchi1,3
1Laboratorio de Diagnóstico e Investigaciones Bacteriológicas
2 CÆtedra de Tecnología y Sanidad de Alimentos
3 CÆtedra de Microbiología. Facultad de Ciencias Veterinarias.
Universidad Nacional de La Plata
4 Comisión de Investigaciones Científicas. Provincia de Buenos Aires
ABSTRACT: Bacterial susceptibility of 40 isolates of Pseudomonas aeruginosa to six antimi-
crobial agents ceftiofur (CFT), colistin (COL), danofloxacin (DNF), enrofloxacin (ENF), gentami-
cin (GEN), and trimethoprim:sulphamethoxazole (TMS) (ratio 1:19) were determined for the
minimal inhibitory concentration (MIC) using the agar-dilution method. All strains were from
ranch-raised mink (Mustela vison) origin, were considered clinically important (mostly with
Pneumonia infection) and were collected during the past fourteen years. The MIC that pre-
vented the growth of 90 % of the bacteria were in µg/ml, 100 for CFT, 100 for COL, 1.57 for DNF
and ENF, 12.5 for GEN and > 100 for TMS. The fluoroquinolones showed higher activity in our
strains than the classical antibiotics used against Pseudomonas aeruginosa. Based on the
MIC values obtained and taking into account the administration form (mixed into the feed or
water supply) of these drugs, we consider that they might be useful for treatment on this
illness.
Key Words: vison, antibiotics, Pseudomonas aeruginosa
SUSCEPTIBILIDAD ANTIMICROBIANA DE Pseudomonas aeruginosa
AISLADAS DE VISONES ENFERMOS
RESUMEN: La susceptibilidad bacteriana de 40 cepas aisladas de Pseudomonas aeruginosa
a seis agentes antimicrobianos ceftiofur (CFT), colistin (COL), danofloxacin (DNF), enrofloxacin
(ENF), gentamicin, (GEN), y trimethoprim:sulphamethoxazole (TMS) (razón 1:19) fue determina-
do para concentración inhibitoria mínima (CIM) usando el mØtodo del agar-dilución. Todas las
cepas fueron aisladas de criaderos de visones (Mustela vison) de casos de neumonía hemorrÆ-
gica y fueron recolectadas durante los œltimos catorce aæos. La CIM que previno el crecimiento
del 90% de las bacterias fue en µg/ml: 100 para CFT, 100 para COL, 1,57 para DNF y ENF,
12,5 para GEN y > 100 para las TMS. Las fluoroquinolonas mostraron actividad mÆs alta en
nuestras de cepas que los clÆsicos antibióticos usados contra Pseudomonas aeruginosa. Ba-
sado en los valores de CIM obtenidos y teniendo en cuenta la forma de administración de
estas drogas (mezcla en el alimento o suministro de agua), consideramos que podrían ser
œtiles para el tratamiento de esta enfermedad.
Palabras Clave: visón, antibióticos, Pseudomonas aeruginosa
33ISSN 1514-2590 ANALECTA VETERINARIA 2000; 20, 1: 32 -35
Antimicrobianos y Pseudomonas en visones
MINIMAL INHIBITORY CONCENTRATION (µg/ml) 
DRUGS
 
>100
 
100  
 
 50
 
25
 
12.5
 
 6.3
 
3.15
 
1.57
 
0.78
 
0.39
 
ENF (enrofloxacin) 
 
 
   2
 
     
  12
 
  25
 
      1
 
DNF (danofloxacin) 
 
 
    2
 
     
    8
 
  22
 
      8
 
COL (colistin) 
 
       5
 
    
   32
 
3     
 
   
GEN (gentamicin) 
 
       2
 
   
     3
 
     1
 
16
 
   16
 
     2
 
 
CFT (ceftiofur) 
 
 
   10
 
   25
 
   5
 
      
TMS (trimethoprim-
sulphametoxazole)
 
     35
 
     5
 
        
 
INTRODUCTION
Pseudomonas aeruginosa is known world-
wide to produce severe acute pneumonia in mink
(Mustela vison) and is considered to be an impor-
tant cause of economic loss in fur-bearing ranches.
Hundreds of animals (up to the 80 % of the farm)
may die within 12-24 hours (1, 2, 3, 4, 5). Never-
theless, its antimicrobial sensitivity status in mink
has not been clearly defined.
Many different treatments have been pro-
posed for control of Pseudomonas aeruginosa
(chlorination of the water supply, disinfection with
formalin of mittens and cages, drugs) but the dis-
ease is prevented well only by vaccination with
autogenous formalinized vaccine (5, 6, 7).
Theres no effective therapy for the disease
but it would be possible to alleviate the condition
by prompt and frequent administration of effec-
tive antibiotics.
In this survey, antibiotic susceptibility of 40
strains of Pseudomonas aeruginosa isolated from
fatal pneumonic and septicemic cases in mink has
been conducted.
MATERIAL AND METHODS
Collection of bacterial strains: Forty isolates
of Pseudomonas aeruginosa were obtained from
the Laboratorio de Investigaciones y Diagnóstico
Bacteriológico (LADIB), Universidad Nacional de
La Plata. Mostly of the specimens had been iso-
lated from ranch-raised mink between 4 and 6
months old with sporadic or epizootic pneumonia
infection (n = 31); the rest (n = 9) were from mink
kits (1-4 week-old) with septicaemia (8). The strains
were collected from different ranches (n = 7) of the
southeastern region of the country, between April
1981 and May 1995. They had been stored at -
70”C in trypteine soy broth with 20 % glycerine
and/or lyophilized. All strains were characterized
biochemically, and identification was carried out
according to Lennette et al. (9) and Holt (10) (mainly
with standard methods including serotyping (5)
with a commercial Pseudomonas aeruginosa anti-
sera test (Difco Lab., Detroit USA) following the
manufacturers instructions). Serotypes 1, 4 and
6 were the most commonly found among our
strains (5). Pseudomonas aeruginosa ATCC (Ameri-
can Type Culture Collection) 27853 was used as
reference strain.
Drugs used in this study were: ceftiofur (CFT,
Upjhon Lab., USA), colistin (COL Argentia Lab.,
Argentina), danofloxacin (DNF, Pfizer Lab., Argen-
tina), enrofloxacin (ENF, Bayer Lab., Argentina),
gentamicin (GEN, Sigma Lab., USA), and
trimethoprim: sulphamethoxazole (ratio 1:19)
(TMS, Sigma Lab., USA).
Drug susceptibility testing was carried out
by the agar-dilution method (NCCLS) (11). Each
strain was grown on tripteine soy broth (Britania
Lab., Argentina) at 37”C for 18 h. A broth culture
of each strain was diluted to 106 colony-forming
units/ml and spotted onto Mueller Hinton agar
(Britania Lab., Argentina) supplemented with
Cl2Ca 50 mg/l and Cl2Mg 25 mg/l, containing
serial 2 fold dilutions of each drug by a multiplanter
(Sakuma Seisakusho, Tokyo, Japan). Final con-
centrations of antibiotics tested ranged from 0.05
to 100 µg/ml. The minimal inhibitory concentra-
tion (MIC) was determined after aerobic incuba-
tion at 37°C for 18 h and was considered the low-
est antimicrobial concentration that produced no
visible bacterial growth.
RESULTS
The organisms were highly susceptible to
DNF and ENF for each, (MIC 50: 0.78); (MIC 90:
1.57) (Table 1). COL and GEN showed low values
to MIC 50 but high for MIC 90. The least-effective
drugs were CFT and TMS.
The resistance pattern was homogeneous
among the most recent and oldest isolations (1981-
1995). Moreover, no particular association was
observed between serotyping or case status (sep-
ticaemia, pneumonia epizootics) of the strains and
their antimicrobial susceptibilities.
Table 1. Minimal Inhibitory Concentration (µg/ml)
of 40 strains of Pseudomonas aeruginosa isolated
from 40 mink.
Tabla 1. Concentración inhibitoria mínima (µg/ml) de 40 cepas
de Pseudomonas aeruginosa aisladas de 40 visones.
34 ANALECTA VETERINARIA 2000; 20, 1: 32-35                                                ISSN 1514-2590
F.L.Pantozzi y col.
DISCUSSION
Literature on susceptibility of Pseudomonas
aeruginosa isolates from mink is scarce. Chemo-
therapy with antibiotics is a commonly-used
method for the control of mink pneumonia. How-
ever, treatment of this illness with these drugs is
not effective owing possibly to its short incubation
period which lasts 18-20 hours and the difficult
to inject hundreds of animals at the same time
during an epizootic (12, 13). Stress of handling
and possible spread of the organism on mink-han-
dling gloves are also possible reasons for poor re-
sults (14). When many mink are to be treated , the
medication should be incorporated in the feed or
water.
In The Netherlands and Denmark, the iso-
lated Pseudomonas aeruginosa strains were highly
resistant to most common antibiotics and chemo-
therapeutic drugs, therefore the disease couldnt
be controlled satisfactorily by medication (4, 6).
Despite the fact that many isolates were re-
ported as being antibiotic-susceptible in vitro, re-
sponse to treatment in field outbreaks was often
ineffective. This was widely documented with sul-
fathiazole, the drug of choice in the past (12, 15,
16, 17), polimixin B and streptomycin (18), sulfa-
diazine-trimethoprim (4) and neomycin and dihy-
drostreptomycin (19).
Moreover, streptomycin and sulfonamides
are not recommended for treating mink because
of their toxicity and adverse local or systemic re-
actions in these animals (20, 21, 22).
Many ranchers rely on sulfathiazole to treat
affected animals despite the fact that some of the
Pseudomonas aeruginosa isolates are not suscep-
tible to sulfathiazole using in vitro disc diffusion
testing methods. Strains of P. aeruginosa virulent
for mink vary in their susceptibility to sulfathiaz-
ole (15).
Long & Gorham (14) reported that most of
the isolates have been susceptible to gentamicin
but resistant to other antibiotics tested; neverthe-
less treatment with gentamicin by injection was
variable and often not satisfactory.
In our study DNF and ENF were active in
vitro against most of the strains suggesting that
these drugs could be appropriate choices for ini-
tial treatment of infections. These 2 drugs have
the additional advantage of oral administration
and the post antibiotic effect (17, 23).
Seven strains were recovered from kits with
general infection. Septicaemia is the most impor-
tant cause of death among kits between 0-4 weeks-
old of our ranches (8).
Two isolates showed values of MIC 100 and
>100 µg/ml for all the drugs used in this survey.
Although studies of multiresistant mechanisms
were not realized, we suspected that this resistant
mechanisms is due to impermeability .
In spite of the use of fluoroquinolones might
be recommended administered in food or water
for prevention and treatment on this illness, the
only way of the correct use of antibiotics is the
isolation of each strain in the outbreak and the
choise of antibiotic of best performance with mi-
nor risk if generation of resistance in this type of
bacteria. Moreover, it this pattern of antimicrobial
susceptibility of Pseudomonas aeruginosa may be
unique to our farms, and further studies from other
countries are needed to determine general recom-
mendations.
REFERENCES
1.Jorgensen, M., 1985. Mink Production. Published by
The Danish Fur Breeders Association/
Scientifur.Denmark.
2.Kull, K.E., 1982. 11th.FAO/SIDA International
Course in Veterinary Pathology. Uppsala,Sweden. Vol-
ume XI:1-9.
3.Washington,  JA, and Sutter, VL.,1985. Dilution sus-
ceptibility test agar and macro-broth dilution proce-
dures. Lennette E.H., Ballows, A., Hausler, W.J..1985.
Manual of Clinical Microbiology 4th Edition Washing-
ton DC, American Society of Microbiology.
4.Jorgensen, M., 1989. Smitson lungebetaendelse hos
mink. Dansk Veterinaertidsskrift.17:997-1000.
5.Martino,  P.E.,  Martino,  J.J. and Villar,  J.A., 1991.
A note on diseases on mink. Journal of Vet.Med.
Zentralblatt fur Veterinarmedizin B 38:227-230.
6.Haagsma, J., 1980. Disease problems in mink and
blue fox in The Netherlands. Bull.Off.Int.Epiz.9-
10:1081-1088.
7.Nordstoga,  K., 1992. Fur Animal Health: current sta-
tus. Norwegian Journal of Agricultural Sciences.
Suppl.No.9:363-377.
8.Martino, P.E. and Villar, J.R., 1990. A survey on peri-
natal mortality in young mink. Veterinary Research
Communications.14:199-205.
9.Lennette, E.H., Ballows, A.,  and Hausler, W.J., 1985.
Manual of Clinical Microbiology.4th Edition Washing-
ton DC, American Society of Microbiology.
10.Holt, J.G.,1986. Bergeys Manual of Systematic Bac-
teriology, Vol.2. Baltimore: Wilkins & Wilkins Co.
11.National Comittee for Clinical Laboratory Standards.
Method for dilution antimicrobial susceptibility test for
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Antimicrobianos y Pseudomonas en visones
bacteria that grow aerobically. M7-72. Villanova, Pa.,
1988.
12.Hansen,  M., 1974. Smitsom lugbetaaendelse hos
mink. Dansk Pelsdyravel.5:188-189.
13.Hartsough, G.R. and Gorham,  J.R., 1969. Sanita-
tion and Health.Section V. The Blue Book of Fur Farm-
ing. 1969 Edition
14.Long, G.G. and Gorham, J.R., 1981. Pseudomonas
pneumonia of mink. JAVMA. 11: 1343-1344.
15.Hunter, D.B., and Prescott, J.F., 1984. Effect of sul-
fathiazole treatment of Pseudomonas pneumonia in
mink. Fur Rancher.6: 8-10.
16.Schwartz,  M.,  1985. Facts od understanding
Haemorrhagic Pneumonia Blue Book of Fur Farm-
ing.1985 Edition.68-79.
17.Kumar, A, Hay, N.B., Maier, G.A., and Dyke, J.W.
1992. Post antibiotic effect of Ceftazidime, Ciprofloxacin,
Imipenem, Piperacillin and Tobramicyn for Pseudomo-
nas cepacia. J Antimicrob Chemother 1992  Nov:30(5):
597- 602.
18.Danilov, E.P., 1985. Epidemiological state and prob-
lems of Veterinary Science in Fur Farming. In: Biology
and Pathology of farm bred fur-bearing
animals.Published by U.S.Department of Agriculture.
Washington. pp.38-41.
19.Beckenhauer, W.B., 1960. Pseudomoniasis infection
in mink. Vet.Med. 11:55-56.
20.Farrel, R.K., Leader, W., and Gorham, J.R., 1958.
An outbreak of Haemorrhagic Pneumonia in mink.
Cornell Vet. 48:378.
21.Hartsough, G.R., 1974. Current disease problems
in the USA and current research in mink. 9th. Train-
ing Course and Conference. York, UK. 9-19.
22.Budd, J., Pridham, T.J., and Karstad, L.H.A., 1966.
Common diseases of fur-bearing animals. Can Vet J
2:25-30.
23.Howard, B.N., Pinney, R.J., and Smith,  J.T., 1993.
Post antibiotic effect of Ofloxacin on Escherichia coli,
Klebsiella pneumoniae, Staphylococcus aureus and
Streptococcus pyogenes. Chemotherapy 1993 Jul-Aug:
39(4): 265-71.


English

Antimicrobial susceptibility of Pseudomonas aeruginosa isolated from diseased minks

Servicio de Difusión de la Creación Intelectual

32 ANALECTA VETERINARIA 2000; 20, 1: 32-35                                                ISSN 1514-2590F.L.Pantozzi y col.Comunicación breveDirección para correspondencia:F.Pantozzi. Laboratorio de Investigaciones y Diagnóstico Bacteriológicos (LADIB). Facultad de CienciasVeterinarias. Universidad Nacional de La Plata CC 296 (B1900AVW) La Plata, Argentina. Tel/Fax: (0221)4257980. CC 296 La Plata (B1900AVW). Argentina E-mail: fpantozzi@fcv.medvet.unlp.edu.arFecha de recepción: 10/09/99 Fecha de aprobación: 18/05/00ANTIMICROBIAL SUSCEPTIBILITY OF Pseudomonas aeruginosaISOLATED FROM DISEASED MINKSF.L. Pantozzi1, J.A. Copes2, P. Martino3,4, N. Stanchi1,31Laboratorio de Diagnóstico e Investigaciones Bacteriológicas2 CÆtedra de Tecnología y Sanidad de Alimentos3 CÆtedra de Microbiología. Facultad de Ciencias Veterinarias.Universidad Nacional de La Plata4 Comisión de Investigaciones Científicas. Provincia de Buenos AiresABSTRACT: Bacterial susceptibility of 40 isolates of Pseudomonas aeruginosa to six antimi-crobial agents ceftiofur (CFT), colistin (COL), danofloxacin (DNF), enrofloxacin (ENF), gentami-cin (GEN), and trimethoprim:sulphamethoxazole (TMS) (ratio 1:19) were determined for theminimal inhibitory concentration (MIC) using the agar-dilution method. All strains were fromranch-raised mink (Mustela vison) origin, were considered clinically important (mostly withPneumonia infection) and were collected during the past fourteen years. The MIC that pre-vented the growth of 90 % of the bacteria were in µg/ml, 100 for CFT, 100 for COL, 1.57 for DNFand ENF, 12.5 for GEN and > 100 for TMS. The fluoroquinolones showed higher activity in ourstrains than the classical antibiotics used against Pseudomonas aeruginosa. Based on theMIC values obtained and taking into account the administration form (mixed into the feed orwater supply) of these drugs, we consider that they might be useful for treatment on thisillness.Key Words: vison, antibiotics, Pseudomonas aeruginosaSUSCEPTIBILIDAD ANTIMICROBIANA DE Pseudomonas aeruginosaAISLADAS DE VISONES ENFERMOSRESUMEN: La susceptibilidad bacteriana de 40 cepas aisladas de Pseudomonas aeruginosaa seis agentes antimicrobianos ceftiofur (CFT), colistin (COL), danofloxacin (DNF), enrofloxacin(ENF), gentamicin, (GEN), y trimethoprim:sulphamethoxazole (TMS) (razón 1:19) fue determina-do para concentración inhibitoria mínima (CIM) usando el mØtodo del agar-dilución. Todas lascepas fueron aisladas de criaderos de visones (Mustela vison) de casos de neumonía hemorrÆ-gica y fueron recolectadas durante los œltimos catorce aæos. La CIM que previno el crecimientodel 90% de las bacterias fue en µg/ml: 100 para CFT, 100 para COL, 1,57 para DNF y ENF,12,5 para GEN y > 100 para las TMS. Las fluoroquinolonas mostraron actividad mÆs alta ennuestras de cepas que los clÆsicos antibióticos usados contra Pseudomonas aeruginosa. Ba-sado en los valores de CIM obtenidos y teniendo en cuenta la forma de administración deestas drogas (mezcla en el alimento o suministro de agua), consideramos que podrían serœtiles para el tratamiento de esta enfermedad.Palabras Clave: visón, antibióticos, Pseudomonas aeruginosa33ISSN 1514-2590 ANALECTA VETERINARIA 2000; 20, 1: 32 -35Antimicrobianos y Pseudomonas en visonesMINIMAL INHIBITORY CONCENTRATION (µg/ml) DRUGS >100 100    50 25 12.5  6.3 3.15 1.57 0.78 0.39 ENF (enrofloxacin)      2        12   25       1 DNF (danofloxacin)       2          8   22       8 COL (colistin)         5        32 3         GEN (gentamicin)         2         3      1 16    16      2  CFT (ceftiofur)      10    25    5       TMS (trimethoprim-sulphametoxazole)      35      5          INTRODUCTIONPseudomonas aeruginosa is known world-wide to produce severe acute pneumonia in mink(Mustela vison) and is considered to be an impor-tant cause of economic loss in fur-bearing ranches.Hundreds of animals (up to the 80 % of the farm)may die within 12-24 hours (1, 2, 3, 4, 5). Never-theless, its antimicrobial sensitivity status in minkhas not been clearly defined.Many different treatments have been pro-posed for control of Pseudomonas aeruginosa(chlorination of the water supply, disinfection withformalin of mittens and cages, drugs) but the dis-ease is prevented well only by vaccination withautogenous formalinized vaccine (5, 6, 7).Theres no effective therapy for the diseasebut it would be possible to alleviate the conditionby prompt and frequent administration of effec-tive antibiotics.In this survey, antibiotic susceptibility of 40strains of Pseudomonas aeruginosa isolated fromfatal pneumonic and septicemic cases in mink hasbeen conducted.MATERIAL AND METHODSCollection of bacterial strains: Forty isolatesof Pseudomonas aeruginosa were obtained fromthe Laboratorio de Investigaciones y DiagnósticoBacteriológico (LADIB), Universidad Nacional deLa Plata. Mostly of the specimens had been iso-lated from ranch-raised mink between 4 and 6months old with sporadic or epizootic pneumoniainfection (n = 31); the rest (n = 9) were from minkkits (1-4 week-old) with septicaemia (8). The strainswere collected from different ranches (n = 7) of thesoutheastern region of the country, between April1981 and May 1995. They had been stored at -70”C in trypteine soy broth with 20 % glycerineand/or lyophilized. All strains were characterizedbiochemically, and identification was carried outaccording to Lennette et al. (9) and Holt (10) (mainlywith standard methods including serotyping (5)with a commercial Pseudomonas aeruginosa anti-sera test (Difco Lab., Detroit USA) following themanufacturers instructions). Serotypes 1, 4 and6 were the most commonly found among ourstrains (5). Pseudomonas aeruginosa ATCC (Ameri-can Type Culture Collection) 27853 was used asreference strain.Drugs used in this study were: ceftiofur (CFT,Upjhon Lab., USA), colistin (COL Argentia Lab.,Argentina), danofloxacin (DNF, Pfizer Lab., Argen-tina), enrofloxacin (ENF, Bayer Lab., Argentina),gentamicin (GEN, Sigma Lab., USA), andtrimethoprim: sulphamethoxazole (ratio 1:19)(TMS, Sigma Lab., USA).Drug susceptibility testing was carried outby the agar-dilution method (NCCLS) (11). Eachstrain was grown on tripteine soy broth (BritaniaLab., Argentina) at 37”C for 18 h. A broth cultureof each strain was diluted to 106 colony-formingunits/ml and spotted onto Mueller Hinton agar(Britania Lab., Argentina) supplemented withCl2Ca 50 mg/l and Cl2Mg 25 mg/l, containingserial 2 fold dilutions of each drug by a multiplanter(Sakuma Seisakusho, Tokyo, Japan). Final con-centrations of antibiotics tested ranged from 0.05to 100 µg/ml. The minimal inhibitory concentra-tion (MIC) was determined after aerobic incuba-tion at 37°C for 18 h and was considered the low-est antimicrobial concentration that produced novisible bacterial growth.RESULTSThe organisms were highly susceptible toDNF and ENF for each, (MIC 50: 0.78); (MIC 90:1.57) (Table 1). COL and GEN showed low valuesto MIC 50 but high for MIC 90. The least-effectivedrugs were CFT and TMS.The resistance pattern was homogeneousamong the most recent and oldest isolations (1981-1995). Moreover, no particular association wasobserved between serotyping or case status (sep-ticaemia, pneumonia epizootics) of the strains andtheir antimicrobial susceptibilities.Table 1. Minimal Inhibitory Concentration (µg/ml)of 40 strains of Pseudomonas aeruginosa isolatedfrom 40 mink.Tabla 1. Concentración inhibitoria mínima (µg/ml) de 40 cepasde Pseudomonas aeruginosa aisladas de 40 visones.34 ANALECTA VETERINARIA 2000; 20, 1: 32-35                                                ISSN 1514-2590F.L.Pantozzi y col.DISCUSSIONLiterature on susceptibility of Pseudomonasaeruginosa isolates from mink is scarce. Chemo-therapy with antibiotics is a commonly-usedmethod for the control of mink pneumonia. How-ever, treatment of this illness with these drugs isnot effective owing possibly to its short incubationperiod which lasts 18-20 hours and the difficultto inject hundreds of animals at the same timeduring an epizootic (12, 13). Stress of handlingand possible spread of the organism on mink-han-dling gloves are also possible reasons for poor re-sults (14). When many mink are to be treated , themedication should be incorporated in the feed orwater.In The Netherlands and Denmark, the iso-lated Pseudomonas aeruginosa strains were highlyresistant to most common antibiotics and chemo-therapeutic drugs, therefore the disease couldntbe controlled satisfactorily by medication (4, 6).Despite the fact that many isolates were re-ported as being antibiotic-susceptible in vitro, re-sponse to treatment in field outbreaks was oftenineffective. This was widely documented with sul-fathiazole, the drug of choice in the past (12, 15,16, 17), polimixin B and streptomycin (18), sulfa-diazine-trimethoprim (4) and neomycin and dihy-drostreptomycin (19).Moreover, streptomycin and sulfonamidesare not recommended for treating mink becauseof their toxicity and adverse local or systemic re-actions in these animals (20, 21, 22).Many ranchers rely on sulfathiazole to treataffected animals despite the fact that some of thePseudomonas aeruginosa isolates are not suscep-tible to sulfathiazole using in vitro disc diffusiontesting methods. Strains of P. aeruginosa virulentfor mink vary in their susceptibility to sulfathiaz-ole (15).Long & Gorham (14) reported that most ofthe isolates have been susceptible to gentamicinbut resistant to other antibiotics tested; neverthe-less treatment with gentamicin by injection wasvariable and often not satisfactory.In our study DNF and ENF were active invitro against most of the strains suggesting thatthese drugs could be appropriate choices for ini-tial treatment of infections. These 2 drugs havethe additional advantage of oral administrationand the post antibiotic effect (17, 23).Seven strains were recovered from kits withgeneral infection. Septicaemia is the most impor-tant cause of death among kits between 0-4 weeks-old of our ranches (8).Two isolates showed values of MIC 100 and>100 µg/ml for all the drugs used in this survey.Although studies of multiresistant mechanismswere not realized, we suspected that this resistantmechanisms is due to impermeability .In spite of the use of fluoroquinolones mightbe recommended administered in food or waterfor prevention and treatment on this illness, theonly way of the correct use of antibiotics is theisolation of each strain in the outbreak and thechoise of antibiotic of best performance with mi-nor risk if generation of resistance in this type ofbacteria. Moreover, it this pattern of antimicrobialsusceptibility of Pseudomonas aeruginosa may beunique to our farms, and further studies from othercountries are needed to determine general recom-mendations.REFERENCES1.Jorgensen, M., 1985. Mink Production. Published byThe Danish Fur Breeders Association/Scientifur.Denmark.2.Kull, K.E., 1982. 11th.FAO/SIDA InternationalCourse in Veterinary Pathology. Uppsala,Sweden. Vol-ume XI:1-9.3.Washington,  JA, and Sutter, VL.,1985. Dilution sus-ceptibility test agar and macro-broth dilution proce-dures. Lennette E.H., Ballows, A., Hausler, W.J..1985.Manual of Clinical Microbiology 4th Edition Washing-ton DC, American Society of Microbiology.4.Jorgensen, M., 1989. Smitson lungebetaendelse hosmink. Dansk Veterinaertidsskrift.17:997-1000.5.Martino,  P.E.,  Martino,  J.J. and Villar,  J.A., 1991.A note on diseases on mink. Journal of Vet.Med.Zentralblatt fur Veterinarmedizin B 38:227-230.6.Haagsma, J., 1980. Disease problems in mink andblue fox in The Netherlands. Bull.Off.Int.Epiz.9-10:1081-1088.7.Nordstoga,  K., 1992. Fur Animal Health: current sta-tus. Norwegian Journal of Agricultural Sciences.Suppl.No.9:363-377.8.Martino, P.E. and Villar, J.R., 1990. A survey on peri-natal mortality in young mink. Veterinary ResearchCommunications.14:199-205.9.Lennette, E.H., Ballows, A.,  and Hausler, W.J., 1985.Manual of Clinical Microbiology.4th Edition Washing-ton DC, American Society of Microbiology.10.Holt, J.G.,1986. Bergeys Manual of Systematic Bac-teriology, Vol.2. Baltimore: Wilkins & Wilkins Co.11.National Comittee for Clinical Laboratory Standards.Method for dilution antimicrobial susceptibility test for35ISSN 1514-2590 ANALECTA VETERINARIA 2000; 20, 1: 32 -35Antimicrobianos y Pseudomonas en visonesbacteria that grow aerobically. M7-72. Villanova, Pa.,1988.12.Hansen,  M., 1974. Smitsom lugbetaaendelse hosmink. Dansk Pelsdyravel.5:188-189.13.Hartsough, G.R. and Gorham,  J.R., 1969. Sanita-tion and Health.Section V. The Blue Book of Fur Farm-ing. 1969 Edition14.Long, G.G. and Gorham, J.R., 1981. Pseudomonaspneumonia of mink. JAVMA. 11: 1343-1344.15.Hunter, D.B., and Prescott, J.F., 1984. Effect of sul-fathiazole treatment of Pseudomonas pneumonia inmink. Fur Rancher.6: 8-10.16.Schwartz,  M.,  1985. Facts od understandingHaemorrhagic Pneumonia Blue Book of Fur Farm-ing.1985 Edition.68-79.17.Kumar, A, Hay, N.B., Maier, G.A., and Dyke, J.W.1992. Post antibiotic effect of Ceftazidime, Ciprofloxacin,Imipenem, Piperacillin and Tobramicyn for Pseudomo-nas cepacia. J Antimicrob Chemother 1992  Nov:30(5):597- 602.18.Danilov, E.P., 1985. Epidemiological state and prob-lems of Veterinary Science in Fur Farming. In: Biologyand Pathology of farm bred fur-bearinganimals.Published by U.S.Department of Agriculture.Washington. pp.38-41.19.Beckenhauer, W.B., 1960. Pseudomoniasis infectionin mink. Vet.Med. 11:55-56.20.Farrel, R.K., Leader, W., and Gorham, J.R., 1958.An outbreak of Haemorrhagic Pneumonia in mink.Cornell Vet. 48:378.21.Hartsough, G.R., 1974. Current disease problemsin the USA and current research in mink. 9th. Train-ing Course and Conference. York, UK. 9-19.22.Budd, J., Pridham, T.J., and Karstad, L.H.A., 1966.Common diseases of fur-bearing animals. Can Vet J2:25-30.23.Howard, B.N., Pinney, R.J., and Smith,  J.T., 1993.Post antibiotic effect of Ofloxacin on Escherichia coli,Klebsiella pneumoniae, Staphylococcus aureus andStreptococcus pyogenes. Chemotherapy 1993 Jul-Aug:39(4): 265-71.

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Antimicrobial susceptibility of Pseudomonas aeruginosa isolated from diseased minks

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