Biology Reference
In-Depth Information
18. Following the appropriate incubation time, count the
S. aureus
colonies on each
plate (
see
Note 25
) and multiply by the dilution factor (in this case by five) to
determine the
S. aureus
recovered per nose (see
Note 27
).
4. Notes
1. A leather gardening glove should be worn on the grabbing hand when handling
cotton rats. The animals should be pinned under a gloved hand and the rat then
grabbed by its scruff for control. Cotton rats are very skittish and will attempt
to escape, so open the cage lid only as far as needed to grab a single rat. Do not
grab a cotton rat by its tail as the tail will deglove
(14)
.
2. Frozen stocks of
S. aureus
are stored in TSB at -70 °C. Most wild-type
S. aureus
strains examined successfully colonize the cotton rat nares (
see
Table 2
).
3. Make an additional two or three animal doses (2-3 mL) than required to allow
for extra volume and to titer the actual dose of
S. aureus
instilled per animal.
Table 2
Cotton Rat Nasal Colonization by Various
Staphylococcus aureus
strains
S. aureus
strain
Animals colonized Mean colonization
per nose
ATCC 49521 (MSSA, Type 5 capsule)
5/5
>10000
ATCC 12605 (MSSA, Type 8 capsule)
5/5
5418
Sa113 (MSSA)
15/15
6011
SH1000 (MSSA)
5/5
2553
Newman (MSSA)
5/5
4021
SA5 StrR (Streptomycin resistant
a
)
1/5
100
MBT 5040 (MRSA)
41/41
5262
MBT 5040 LysoR (Lysostaphin resistant
b
)
1/5
200
MRSA 12/12 (MRSA, StrR
c
)
5/5
567
Col (MRSA, StrR
c
)
5/5
3825
BK 2352 (MRSA)
5/5
3481
BK 2454 (MRSA)
5/5
2323
SA 3865 (mupirocin resistant)
5/5
268
NRS 79 (VISA)
5/5
2574
All animals instilled with
5×10
8
colony-forming units (CFUs) of
S. aureus
and killed
∼
6-7 days post-instillation.
MSSA, methicillin-sensitive
S. aureus
; MRSA, methicillin-resistant
S. aureus
; StrR, strep-
tomycin resistant; VISA, vancomycin intermediate susceptibility.
a
A streptomycin-resistant variant isolated by serial passage on streptomycin agar.
b
See reference
(21)
.
c
Naturally streptomycin resistant.
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