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spa typing

Registry Details

Area Health Science
Lab name Nosocomial Infections Laboratory
Lab location Kenepuru Science Centre, Porirua
Test name spa typing
Organisms Staphylococcus aureus, including methicillin-resistant S. aureus (MRSA)
Requested for surveillance no
Notice required no
Routine turnaround time 6 working days for reference specimens
Culture requirements Pure culture
Media requirements A slope of any medium that supports the growth of the organism
Pre-transport requirements Ambient temperature
Transport requirements Ambient temperature
Unacceptable sample types Clinical specimens will not be accepted. Single methicillin-susceptible S. aureus isolates, that are not connected to any other isolates or situation, will not be typed.
How results reported The spa type will be reported. For MRSA, the MRSA strain will also be reported if the isolate belongs to a recognised MRSA strain.
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Details

spa typing is a sequence-based typing method which targets the polymorphic X region of the staphylococcal protein A gene (spa). This region of the spa gene consists of a variable number of 21 to 27-bp repeats with differing nucleotide sequences. The region is subject to spontaneous mutations, as well as loss and gain of repeats. The variation in the number and sequences of the repeats is the basis of spa typing.

spa typing has been shown to be a robust, reproducible and highly discriminatory typing system, capable of providing both short-term epidemiological and longer-term clonal lineage information. In addition, as it is sequence-based, the results produced in different labs are easily comparable.

ESR uses the Ridom system of spa typing nomenclature. Access is free to the Ridom Spa Server(external link). In the Ridom system, each repeat sequence is assigned a unique identifier (eg, r08), and the combination and order of repeats (eg, r08-r16-r02-r16-r02-r25-r17-r24) corresponds to a unique spa type (eg, t019). In this example of spa type t019, there are eight repeats, and one of the repeats, r16, occurs twice. Closely related spa types can be identified and clustered using the BURP (based on repeat pattern) algorithm.

When reporting results, we will report the spa type, and, in the case of MRSA isolates, the MRSA strain (eg, WSPP MRSA) if the spa typing indicates that the MRSA isolate belongs to a named strain. When we report the results for a batch of S. aureus isolates that have been referred for comparison, we will report each isolate's spa type and also include an indication of the relatedness, based on BURP analysis, of the different spa types of the isolates.

We will continue to offer and use DNA macrorestriction analysis using pulsed-field gel electrophoresis (PFGE) to type S. aureus when spa typing alone is not sufficient to definitely identify strains, especially MRSA strains, and when further discrimination is required. In general, PFGE typing is considered more discriminatory than spa typing. However, it is more costly, has a longer turnaround time, and inter-laboratory comparison can be difficult.

Description of common MRSA strains, including their spa types [PDF, 131 KB]