The best strategy (and incidentally, the optimal one) is to...
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×...kill the queens in an order that allows you to progress from one side of the room to the other without having to move backwards (so you don't end up with roaches attacking you from the rear).
As a further hint...
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×...being efficient is also a good idea since you get fewer roaches to deal with. Thus, you should aim for an order that allows you to reduce the number of spawn events you get.
A final hint:
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× The internal floorspace measures (roughly) 33*27 squares. The spawn cycle is 30.
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Resident Medic/Mycologist