Field Isolates
DIFFERENTIATING FIELD ISOLATES
FROM VACCINE STRAIN
SALMONELLA VAC E and SALMONELLA VAC T*
The attenuated
vaccinal bacteria from AviPro®
SALMONELLA VAC E or AviPro®
SALMONELLA VAC T may be
best isolated, for no more than 2–5 days post-vaccination, from
intestinal material (caecal contents, cloacal swabs, faeces) or 5 to
7 days from organs (liver, spleen). The vaccine strain has been
developed and selected using the principle of metabolic drift
mutation and is genetically stable. As a feature of attenuation it
does not survive in the environment and only
grows
on selected media (Tables 1 and 2), showing a typical growth pattern
in the presence of antibiotics. These markers allow a rapid and
simple differentiation between field isolates and the vaccine strain
using antibiotic discs on agar (Figure 1). For confirmation, the
vaccine strain can be grown on antibiotic agars containing
Rifampicin (RAM 100 µg/ml), Streptomycin (STRE 200 µg/ml) and
Erythromycin (ERY 20 and 30 µg/ml), as shown in Table 3.
Differentiating field isolates from vaccine strain
(AviPro® SALMONELLA VAC E and AviPro® SALMONELLA VAC T)
The
identification of the AviPro® Salmonella vaccine strains and their
discrimination from Salmonella field isolates is reliably done by
using the AviPro® PLATE format. This is standardised in-vitro
microdilution antimicrobial-susceptibility testing procedure which
measures antibiotic activity by determining the breakpoint of
minimal inhibitory concentrations. Vaccine-relevant concentrations
of Erythromycin, Rifampicin and Streptomycin comprise the specific
markers to identify AviPro® SALMONELLA VAC E.
Similarly,
on the same plate,
appropriate concentrations of erythromycin and rifampicin indicate
AviPro® SALMONELLA VAC T vaccines. Basically, round-bottom wells,
pre-coated with antibiotics, are filled with broth inoculum
containing a standardised number of colony-forming units of the
bacterial isolate grown on agar plates. After incubation at 35 ºC –
37 ºC for 18 – 24 hours, inhibition of bacterial growth can be
measured visually and/or by measures of a spectrophotometer to
ensure objective and unbiased interpretation of values. Thus the
results assist in controlling "take" of vaccines (these strains, as
well as field strains, will have their own typical growth patterns,
respectively).AVIPRO PLATE and field isolates
The
additional selection and concentrations of poultry-relevant
antibiotics in the AviPro® PLATE allow determination of the activity
of antibiotics against any gram-positive and gram-negative bacteria
in poultry flocks. Thus the poultry veterinarian gains information
on quantitative changes in susceptibility and resistance of
bacterial isolates to antibiotics, and obtains clear guidance for
appropriate therapeutic intervention. The overall objective of using
the AviPro® PLATE is to technically support the implementation and
establishment of microdilution testing method in poultry diagnostic
laboratories broadly following the guidelines of the standard
performance criteria issued by the Clinical and Laboratory Standards
Institute (CLSI), USA. This will contribute to the establishment of
internationally accepted standards on antimicrobial resistance
in animals and in animal-derived food.
AVIPRO PLATE
For AviPro® SALMONELLA VAC E and AviPro® SALMONELLA VAC T
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Verifies vaccine "take"
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Differentiates field isolates from vaccine strain
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Determines sensitivity and resistance of field isolates to poultry-relevant antibiotics
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Most commonly found gram-positive or gram-negative field isolates
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Standardised microdilution method broadly following international guidelines for CLSI