A 26-year-old woman has been undergoing treatment for community-acquired pneumonia for 10 days. It is known that her husband had been treated for drug addiction. Sequential intravenous administration of Amoksiklav (Amoxicillin + Clavunate) Levofloxacin combination and vancomycin in the prescribed dosage was ineffective. Within the last two days the patient’s dyspnea and intoxication acutely exacerbated, bilateral pulmonary infiltrates are observed. What is the most likely cause of the medication ineffectiveness?