Cytotoxic activity of Staphylococcus aureus isolates from a cohort of Mexican children with cystic fibrosis

Abstract

Background: Cystic fibrosis (CF) is a genetic disease in which thick, sticky mucus is produced in the lungs (and other organs) that impairs ciliary clearance, leading to respiratory problems, increased chronic bacterial infections, and decreased lung function. Staphylococcus aureus is one of the primary bacterial pathogens colonizing the lungs of CF patients. This study aimed to characterize the genetic relatedness of S. aureus, its presence in children with CF, and its cytotoxic activity in THP1 cell-derived macrophages (THP1m). Methods: Genetic relatedness of S. aureus isolates from a cohort of 50 children with CF was determined by pulsed-field gel electrophoresis (PFGE). The VITEK 2 automated system was used to determine antimicrobial susceptibility, and methicillin-resistance S. aureus (MRSA) was determined by diffusion testing using cefoxitin disk. The presence of mecA and lukPV genes was determined by the polymerase chain reaction and cytotoxic activity of S.aureus on THP1m by CytoTox 96® assay. Results: From 51 S. aureus isolates from 50 children with CF, we identified 34pulsotypes by PFGE. Of the 50 children, 12 (24%) were colonized by more than one pulsotype, and 5/34 identified pulsotypes(14.7%) were shared between unrelated children. In addition, 3/34 pulsotypes (8.8%) were multidrug-resistant (MDR), and2/34 (5.9%) were MRSA. Notably, 30/34 pulsotypes (88.2%) exhibited cytotoxicity on THP1m cells and 14/34 (41.2%) alteredTHP1m monolayers. No isolate carried the lukPV gene. Conclusions: Although a low frequency of MRSA and MDR wasfound among clinical isolates, most of the S. aureus pulsotypes identified were cytotoxic on THP1m.

Keywords

• Staphylococcus aureus. Cytotoxicity. Macrophages. Methicillin-resistant Staphylococcus aureus (MRSA). Multidrug resistance.