18 days post-op, have pseudomonas aeruginosa on incision. How do I know the infection isn't on the inside? (photo)

So im 18 days post op last week my incition still hadnt closed they swabbed and i just got call to say i have pseudomonas aeruginosa. The incision is now closed fine redness around it but closed. I said im worried il lose my implant and he said dont worry its just on incision not on inside how do they know its not on inside? .Said take course of anti biotics then i see him 15th june hes saying hes not concerned at all can it just be on incision as insides would of closed wouldnt they now anyway? xx