ISRAEL JOURNAL OF
VETERINARY MEDICINE
BIOCHEMICAL CHARACTERIZATION OF
STAPHYLOCOCCI ISOLATED FROM RABBITS
A.T.P. Ajuwape and E.A. Aregbesola
Vol. 56 (2) 2001
Department of Veterinary Microbiology and Parasitology,
University of Ibadan, Ibadan, Nigeria
Abstract
Coagulase activities of rabbit strains of staphylococci were tested using sterile human, rabbit and goat
plasmas. Human plasma produced the most satisfactory coagulase sensitivity while the rabbit plasma
was least sensitive. Human plasma tube coagulase gave a positive reaction within one hour, whereas
rabbit and goat tube coagulase tests took two hours to complete.
All 108 isolates of Staphylococcus aureus from clinically healthy rabbits fermented glucose, mannitol,
sucrose, dulcitol and sorbitol, 98.1% fermented maltose and trehalose; 89.8% fermented lactose while
only 46.3% fermented xylose. Urease activity was also high among the rabbit strains of staphylococci
investigated.
Introduction
In rabbits, staphylococcosis caused by Staphylococcus aureus may manifest as fatal septicaemia (1).
However if the rabbits survive, there may be clinical presentations of pneumonia (2), sore hock
(pododermatitis) with a high incidence of mastitis among the does (3, 4) and in some cases, metritis
and abortion may occur. Many litters exhibited abscesses at two to three weeks of age (4, 5). The
spread of S. aureus from rabbits to the animal technician has also been reported (2) suggesting that
close association enhances spread of staphylococcal strains among livestock and animal attendants
through contact or aerosol. In Nigeria S. (pyogenes) aureus was reported from cases of rabbit
bacteruria (6).
Not much information is available on characterization of rabbit strains of staphlococci in Nigeria
except for the serological characterization of a few isolates (7). However, most of the earlier research
was centered on man, goats and cattle (7-14). This is worthy of note against the backdrop of
information (15) that characteristics of staphylococci isolates from certain hosts vary between
geographical regions and strains derived from different animal species also differ from each other.
This paper reports the epidemiological incidence, coagulase activities and biochemical properties of
staphylococci isolated from clinically healthy rabbits in Ibadan, because of recent increase observed in
rabbit keeping in this part of the country.
Materials and Methods
Materials and Methods
Animals:
One hundred and eight clinically healthy rabbits: 39 rabbits from Teaching and Research Farm,
University of Ibadan comprising 35 females and 4 males were sampled, while 69 rabbits comprising 23
females and 46 males were sampled from Ajibode village via Ibadan. The rabbits were between 6
weeks and 24 months of age. The animals were raised under intensive management in hutches and fed
commercially prepared pellets produced by Pfizer ® Nig. Ltd. and forages (Aspilia and/or Talinum spp.)
The breeds sampled were predominantly New Zealand White, while some Chinchilla and their crosses
were sampled. The epidemiological survey was carried out to determine the staphylococcal nasal
carriage (16).
Bacteriology:
Nasal swabs obtained from the clinically healthy rabbits were inoculated on 7 percent human blood
agar (Oxoid Columbia blood agar CM331) and MacConkey agar No. 2 (Oxoid CM 109) plates and
were incubated aerobically at 370C for 24 hours. Gram positive, cluster forming, catalase positive and
oxidase negative cocci were characterized as staphylococci according to standard methods (17).
Coagulase activity:
Each isolate was tested for production of coagulase by slide coagulase (18, 19) and tube coagulase (20)
using sterile human plasma. The tube coagulase method was repeated for each isolate using sterile
rabbit and goat plasmas respectively. Oxford Staphylococcus (NCTC 6571) and sterile human plasma
in nutrient broth were employed as positive and negative controls (8).
Haemolysis:
Each staphylococcus isolate was inoculated on 7% human blood agar and incubated aerobically for 18
hours after which the plates were examined for haemolysis.
Biochemical reactions:
The isolates were examined biochemically by a standard method (17, 21) using the following sugars:
glucose, mannitol, maltose, lactose sucrose, dulcitol, sorbitol, xylose, and trehalose. Urease production
was tested for each isolate on Christensen urea agar (Oxoid CM53) (17, 21).
Results
All the animals were positive for staphylococci. The coagulase activities of the 108 staphylococci
isolated from the clinically healthy rabbits are shown in Table 1. All the isolates were positive by both
tube and slide coagulase tests using sterile human plasma. Only 14 (12.9%) of the isolates showed
beta-haemolysis on blood agar, 88 (81.5%) were positive by the rabbit plasma tube coagulase test, and
105 (97.2%) were positive with the goat plasma tube coagulase test. The coagulation of human plasma
by these rabbit strains of staphylococci occurred within one hour whereas rabbit and goat plasmas were
coagulated by the same isolates within 2 hours.
All 108 isolates examined produced acid from glucose within 18-24 hours at 370C. Also all the
isolates fermented mannitol, sucrose, dulcitol, and sorbitol, while 106(98.1%) fermented maltose,
97(89.8%) fermented lactose, 50(46.3%) fermented xylose and 106(89.1%) fermented trehalose (Table
2), and 92 (85.2%) produced urease.
All 108 strains investigated were Staphylococcus aureus.
Discussion
The high incidence of coagulase positive staphylococci recorded in this investigation portends
a serious potential threat to the growing rabbitries in this part of the world, and it is even of public
healthy concern against the backdrop of possibility of transmission to man and the high correlation that
exists between coagulase production and staphylococcal pathogenecity (2,22). Furthermore, the current
increase in rabbit keeping as a source of food, cash income and high nutritive value of rabbit meat that
is high in protein and low in fat, which interestingly, is unsaturated (23), will be endangered. Also
rabbit plasma used in commercial quantities in several laboratories for coagulase testing (8,10,24) will
also be adversely affected. This is because natural barriers may be compromised through injury,
medical or managemental stress or immunosuppression with resultant life-threatening disease (25) will
cause severe economic loss.
The incidence of beta-haemolysis (12.9%) correlates with the findings of others who gave the
percentage and incidence of beta haemolysin production in coagulase positive human associated strains
of Staphylococcus aureus to be 10.8% and 11.8% respectively (26,27).
Human plasma appears to give the best indication of coagulase activity of staphylococci
isolated in this study and is similar to earlier works in cattle (13,14) and goats (8,10). Human plasma
was coagulated by these rabbit strains of staphylococci within one hour, similar to an earlier report
(10). Differentiation of Staphylococcus aureus is usually based on the presence of ‘free’ or ‘bound’
coagulase (25). Rabbit strains of staphylococci appear to produce both ‘free’ and ‘bound’ coagulase as
observed from the results of slide and tube coagulase tests using human plasma, though slide coagulase
test is generally regarded as less sensitive than tube coagulase.
More ‘bound’ coagulase was found in caprine strains of staphylococci (8), while the cattle strains
produced more ‘free’ coagulase (14).
The high sensitivity of human plasma was closely followed by goat plasma (97.2%). This confirms
earlier reports (8,10,14), while the sensitivity of rabbit plasma was lowest (81.5%). A similar pattern
was recorded in cattle in which cattle plasma showed the least sensitivity by tube coagulase for isolates
from cattle (14). Thus the plasma of animal species from which staphylococci are isolated may not be
best for testing their coagulase activities. The tube coagulase test has been used in rapid blood cultures
to identify staphylococcus to a great advantage over immunological and thermonuclease methods (28).
This is confirmed by the high predictive values of 100%, 97.2% and 81.5% observed in this study with
human, goat and rabbit plasma respectively.
The complete fermentation obtained respectively for glucose, mannitol, sucrose, dulcitol, sorbitol
conforms to previous reports (11,13). The 89.8% positive reactions obtained from fermentation of
lactose by rabbit strains of staphylococci is higher than that reported in caprine strains (11). However,
46.3% xylose fermentation is lower than that reported in caprine (11), but similar to that reported in
cattle strains (13,14). The 85.2% urease activities of the rabbit strains of Staphylococcus aureus are
similar to 97.7% recorded earlier in cattle strains (13) but higher than 48% reported in cattle strains
(11).
Acknowledgements
We are grateful for the provision of the reagents used for this work by University of Ibadan Senate
Research Grant Code SRG/FVM/93-94/010A. We are also indebted to Mrs. O.O. Orioke, Department
of Veterinary Microbiology and Parasitology, University of Ibadan for technical support.
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