Author:
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Cabrera Ortega, Roberto; Fernández Barat, Laia; Motos, Anna; López Aladid, Rubén; Vázquez, Nil; Panigada, Mauro; Álvarez Lerma, Francisco; López, Yuly; Muñoz López, Laura; Castro, Pedro; Vila Estapé, Jordi; Torres Martí, Antoni
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Notes:
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Background: Among all cases of nosocomial pneumonia, Staphylococcus aureus is the second most prevalent
pathogen (17.8%). In Europe, 29.9% of the isolates are oxacillin-resistant. The changing epidemiology of methicillinresistant Staphylococcus aureus (MRSA) nosocomial infections and the decreasing susceptibility to first-line
antibiotics leave clinicians with few therapeutic options. The objective of our study was to determine the
antimicrobial susceptibility, the associated molecular mechanisms of resistance and the epidemiological relatedness
of MRSA strains isolated from the endotracheal tubes (ETT) of intubated critically ill patients in the intensive care
unit (ICU) with nosocomial pneumonia caused by Staphylococcus aureus.
Methods: The antimicrobial susceptibility to vancomycin, linezolid, ciprofloxacin, clindamycin, erythromycin,
chloramphenicol, fusidic acid, gentamicin, quinupristin-dalfopristin, rifampicin, sulfamethoxazole/trimethoprim, and
tetracycline were measured. Resistance mechanisms were then analyzed by polymerase chain reaction and
sequencing. Molecular epidemiology was carried out by multi-locus sequence typing.
Results: S. aureus isolates were resistant to ciprofloxacin, erythromycin, gentamicin, tetracycline, clindamycin,
and fusidic acid. The most frequent mutations in quinolone-resistant S. aureus strains were S84L in the gyrA
gene, V511A in the gyrB gene, S144P in the grlA gene, and K401R/E in the grlB gene. Strains resistant to
erythromycin carried the ermC, ermA, and msrA genes; the same ermC and ermA genes were detected in
strains resistant to clindamycin. The aac(6′)-aph(2″) gene was related to gentamicin resistance, while resistance
to tetracycline was related to tetK (efflux pump). The fusB gene was detected in the strain resistant to fusidic
acid. The most frequent sequence types were ST22, ST8, and ST217, which were distributed in four clonal
complexes (CC5, CC22, CC45, and CC59). Conclusions: High levels of resistance to second-line antimicrobials threatens the treatment of nosocomial
respiratory infections due to methicillin-resistant S. aureus with decreased susceptibility to linezolid and
vancomycin. The wide genotypic diversity found reinforces the central role of ICU infection control in
preventing nosocomial transmission. |