Pneumonia Caused by Community-Acquired Methicillin-Resistant Staphylococcus aureus Positive for Exfoliative Toxin A and Secondary to Allergic Bronchopulmonary Aspergillosis

Abstract

Community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) causes severe pneumonia. Previous reports found that CA-MRSA producing the Panton-Valentine leukocidin (PVL) or toxic shock syndrome toxin-1 (TSST-1) triggered severe necrotizing pneumonia. However, other toxins and genetic factors responsible for CA-MRSA pneumonia are rarely analyzed in Japan. In this study, we performed whole-genome sequencing (WGS) to analyze the clinical features of CA-MRSA genetically. As a result, we identified a strain with a rare sequence-type of MRSA. Herein, we present a case of CA-MRSA pneumonia in a 64-year-old woman. Her condition improved rapidly with vancomycin therapy. Draft WGS led to identifying the genotype and virulence factors and showed that the strain was a rare sequence-type of MRSA with the following characteristics: staphylococcal cassette chromosome mec (SCCmec) type IV, sequence type 121, exfoliative toxin A-positive, and specific staphylococcal protein A type t5110. To the best of our knowledge, a strain with this profile has not been previously reported. Our findings provide new insights into CA-MRSA pneumonia and its genetic and clinical features. Therefore, we recommend accumulating genetic profiles of CA-MRSA pneumonia to identify genetic features and the clinical characteristics of the patients.

Keywords: community-acquired methicillin-resistant staphylococcus aureus; community-acquired pneumonia; exfoliative toxin a; sequence type 121; whole-genome sequencing.

Figure 1. Chest X-ray.

Chest X-ray films obtained six months before admission (a) and on admission to our hospital (b). Chest radiograph showed consolidations in the bilateral lower lung fields.

Figure 2. Chest computed tomography.

(a-c) Chest CT revealed bronchiectasis with bronchial wall thickening and mucoid impaction in the bilateral lung fields. (d-f) After six months, CT revealed bronchial wall thickening and consolidations (red arrowheads) in the left upper lobe and bilateral lower lobes.

Figure 3. Treatment and clinical course of the patient.

The patient received IV administration of ceftriaxone (2 g/day) and oral administration of levofloxacin (500 mg/day) in the outpatient clinic. She was hospitalized the following day and received an IV administration of sulbactam/ampicillin (3 g, three times for one day). In addition, IV vancomycin (0.5 g, twice daily) was administered for five days, with subsequent minocycline (200 mg/day) treatment for eight days. The WBC count and C-reactive protein concentrations over time are shown. Chest CT findings before admission (day 0) and after treatment (day 18) revealed an improvement in the consolidations of the bilateral lower lobes. CRP: C-reactive protein; CTRX: Ceftriaxone; LVFX: Levofloxacin; MINO: Minocycline; MRSA: Methicillin-resistant Staphylococcus aureus; SBT/ABPC: Sulbactam/Ampicillin; VCM: Vancomycin.