Abstract: The present invention provides bacterial and fungal ABC transporter proteins, immunogenic fragments thereof, neutralising agents specific thereto and binding agents specific thereto for therapeutic and diagnostic use, together with diagnostic test methods, methods of same and kits for performing same. Also provided are immunodominant conserved antigens from gram positive staphylococci, together with neutralising and binding agents specific thereto for use in therapy and diagnosis, and methods of same. Also provided are Staphylococcal holomogues of IstA and IstB and immunogenic fragments thereof, and their uses in methods of treatment and diagnosis of the human or animal body.