Honey bee larvae are infected by spores from the bacteria
Beekeepers have been urged to be vigilant after an outbreak of a deadly disease which infects colonies.
The Scottish Government said four hives in three apiaries would have to be destroyed after American Foulbrood (AFB) was found in the Perthshire area.
AFB was discovered during investigations into European Foulbrood (EFB), which was confirmed last month.
A government spokesman said that unlike EFB, hives with AFB could not be treated with antibiotics.
A surveillance zone has been put in place around the infected sites and inspections are taking place.
So far 1,093 hives have been examined for European Foulbrood, with 61 testing positive. Of those 40 hives have had to be destroyed.
The Scottish Government said its animal health contingency plan had been activated but that there was no risk to public health.
American Foulbrood bacteria spores germinate in the gut of bee larvae and can prove highly destructive to bee colonies.