ISRAEL JOURNAL OF
VETERINARY MEDICINE
THE BACTERIAL FLORA OF THE UPPER
RESPIRATORY TRACT OF NORMAL RABBITS
T. P. Ajuwape and E. A. Aregbesola
Vol. 57 (2) 2002
Department of Veterinary Microbiology and Parasitology, University of
Ibadan, Ibadan, Nigeria.
Abstract
The nasal bacterial flora of 108 apparently healthy rabbits housed in Ibadan rabbitaries
was examined. All 108 isolates of Staphylococcus aureus were coagulase positive. Other
notable bacteria isolated were Klebsiella pneumonia 10%; Micrococcus luteus 9%;
Escherichia coli 6%; Streptococcus zooepidemicus 4% and Pseudomonas aeruginosa 1%.
Introduction
The lower respiratory tract in health is normally sterile. In contrast, a unique variety of
microorganisms, which are predominantly aerobes colonize the upper respiratory tract (1,2).
Most studies on the bacterial flora of the respiratory tract of domestic animals in Nigeria have
been focused on pneumonic lungs of goats, sheep and cattle (3,4,5). Ojo has isolated
Staphylococcus albus (saprophyticus) from the normal nasopharynx, trachea and lungs of
goats in Nigeria (6), and also found Pasteurella haemolytica, Klebsiella aerogenes,
Pseudomonas aeruginosa and coliforms in their normal respiratory tracts. Other reports have
identified Staphylococcus aureus in respiratory diseases of rabbits (7,8).
This paper deals with the description of the incidence of nasal bacterial flora in apparently
healthy rabbits. An earlier communication described the biochemical characteristics of the
staphylococci isolated from these rabbits (9).
Materials and Methods
One hundred and eight clinically healthy rabbits: 39 rabbits from the Teaching and Research
Farm, University of Ibadan comprising of 35 females and 4 males were sampled by inserting
sterile swab 3-4cm into the nasal passage. An additional 69 rabbits comprising 23 femals and
46 males were sampled from Ajibode village via Ibadan. These rabbits were betwen 6 weeks
and 24 months, while the majority of the sampled animals were adults. The animals were
raised under intensive management in all-wire hutches. The hutches and equipment were
cleansed every two days and complete cleaning was done between litters with detergent and
water followed by disinfectant (Izal®). Feed and water were provided separately in concrete
bowls; and they were fed commercially-prepared pellets marketed by Pfizer® Nigeria Ltd and
forage (Aspilia and / or Talinium spp.). The breeds sampled were predominantly New
Zealand white along with some Chinchilla and their crosses.
The nasal swab were inoculated on 7 percent human agar (Oxoid Columbia blood agar
CM331) and MacConkey agar No. 2 (Oxoid CM109). Each swab was cultured on blood agar
in duplicate and the plates were incubated aerobically and anaerobically at 37 oC for 24 hours
while the MacConkey agar plates were incubated aerobically only. Mycoplasma culture was
not done. Full identification of the pure cultures was carried out according to standard
techniques (10).
Results
The anaerobic incubation of the duplicate blood agar plate did not result in isolation of
additional bacteria. All the rabbits tested were carriers of coagulase positive Staphylococcus
aureus as previously reported in an earlier communication (9). Other bacteria isolated were
Klebsiella pneumoniae 10%, Micrococcus luteus 9%, Escherichia coli 6%, Streptococcus
zooepidemicus 4% and Pseudomonas aeruginosa 1%. Interestingly no pasteurellae were
found. (Tables 1 and 2).
Table 1: Bacteria isolated from upper respiratory tract of healthy rabbits In Ibadan, Nigeria.
Location
Teaching and
Research Farm
University
of Ibadan
Ajibode Farm
Bacteria
No of
Animals
sampled
Frequency
Incidence %
Staphylococcus
aureus
39
39
100
Klebsiella
pneumoniae
39
0
0
Escherichia coli
39
1
2.6
Streptococcus
zooepidemicus
39
1
2.6
Pseudomonas
aeruginosa
39
0
0
Micrococcus
luteus
39
3
7.7
Pasteurella
species
39
0
0
Staphylococcus
aureus
69
69
100
Klebsiella
pneumoniae
69
11
15.9
Escherichia coli
69
5
7.3
Streptococcus
zooepidemicus
69
3
4.4
Pseudomonas
aeruginosa
69
1
1.5
Micrococcus
luteus
69
7
10.5
Pasteurella
species
69
0
0
Table 2: Bacteria isolated from upper respiratory tract of healthy rabbits
*Bacteria
No of Animals samled Frequency
Incidence
%
Staphylococcus aureus
108
108
100
Klebsiella pneumoniae
108
11
10.2
Micrococcus luteus
108
10
9.3
Escherichia coli
108
6
5.6
Streptococcus zooepidemicus
108
4
3.7
Pseudomonas aeruginosa
108
11
0.9
Pasteurella species
108
0
0
* Some bacteria occurred as multiple infections in rabbits
+ All isolates were coagulase positive.
Discussion
The bacteria isolated from the clinically healthy nares of rabbits doffer in some cases from
those isolated from the nasopharynx of healthy goats (6). In this study they were
predominantly aerobes, as reported by others (2, 4). Despite a lack of published information
on the nasal bacterial flora of normal rabbits in this part of the world, the 100% incidence of
coagulase positive Staphylococcus aureus reported here is similar to unpublished data from
Ibadan. In a similar study in goats the predominance of Staphyloccous aureus of 73.7% was
recorded (3); while Ojo reported on a 10% incidence of this organism in healthy goats in
Nigeria (6). As stated by Ajuwape and Aregbesola (9) the high incidence of these potentially
pathogenic coagulase positive staphylococci in rabbits is of public health significance
because of the high correlation that exists between coagulase production and pathogenicity
(11,12). Furthermore, research findings on the association of staphylococci with disease have
shown a zoonotic association with opportunities for reciprocal transmission between man and
domestic animals especially when natural barriers are compromised (14, 15). Also there is an
observable increase in the incidence of this bacterium against the backdrop of 10% incidence
reported by Ojo and 73.7% reported by Obi et al. though in goats vis-a-vis 100% incidence
now recorded in rabbits (6,3). Renquist and Soave reported that Staphylococcus aureus of
the same phage types were isolated from the nasal cavity of the rabbit and from the nasal
cavity of the animal attendants caring for them (7).
The incidence of enterobacteriaceae group: Klebsiella pneumoniae (10%) and Escherichia
coli (6%) in the clinically healthy nares of rabbit in the absence of clinical enteritis is note
worthy. While Klebsiella are commonly found saprophytes in soil and respiratory tract of
healthy animals (12). The 6% incidence recorded in this study is higher than that earlier
recorded (6) when no Klebsiella were found in the respiratory tracts of healthy goats. This
higher incidence may be related to coprophagy (13). The above findings, not surprisingly,
suggest that the natural barriers of these rabbits are able to keep the normal flora in check
because the bacteria have been incriminated in lung abscesses, chronic pneumonias and
emphysema, notably in cattle (5).
The reported 4% incidence of Streptococcus zooepidemicus is lower than 10% recorded from
healthy goats while the 1% incidence of Pseudomonas aeruginosa in this work is similar to
that recorded (6). Micrococcus species are usually commensals and are non-pathogenic
(12). It is worthy of note that no pasteurella species was found in the nares, it suggests that
they may not be the carriage site of this organism.
Acnowledgements
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 of the Department of Veterinary Microbiology and Parasitology, University of Ibadan
for technical support.
LINKS TO OTHER ARTICLES IN THIS ISSUE
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