Detecção de genes de virulência e caracterização genética de Staphylococcus aureus resistentes à meticilina isolados de infecções mamárias humanas

Abstract

Several microorganisms can cause infections in the breast, however, Staphylococcus aureus is the most frequent pathogen, being present in about 40 to 50% of cases. Infections caused by S. aureus can become more serious due to the different virulence genes that it can carry. The present study aimed to verify the prevalence of methicillin-resistant S. aureus (MRSA) in breast infections of patients treated at a University Hospital, as well as to detect virulence-related genes and to genetically characterize these isolates. The investigation was carried out between 2017 and 2019 and 75 patients were included. The epidemiological data of the patients were obtained through the records in their medical records. The isolates were subjected to susceptibility tests and molecular tests to type the SCCmec, the gene that encodes protein A, and to determine the genetic relationship between the isolates. Forty-three MRSA were identified. The isolates were susceptible to most of the tested antimicrobials, with the exception of ampicillin, ciprofloxacin, levofloxacin, and erythromycin. SCCmec IV was detected in all isolates with a prevalence of subtype IVa (90.6%). The genes encoding the PVL toxin were detected in all isolates, as well as the clfA and clfB genes. A high frequency of hemolysins was observed in the isolates, 93% positive for the hla, hld and hlg-2 genes. The fnbB gene was detected in 81.3% and cna in 37.2% of the isolates.The 43 isolates showed only three genetically distinct pulsotypes (A-C), 40 of which belong to pulsotype A, that presented four subtypes (A1-A4). Isolates of this pulsotype presented ST8 and six types of spa: t008, t1405, t1451, and t1767, with t008 being prevalent (36 isolates). The genetic profile of pulsotype A was compatible with the named USA300 clone. This is the first study to describe the spread of the USA300 PVL-positive clone in breast infections in Brazil. The presence of PVL and hemolysins in breast infections is a cause for concern and may contribute to the worsening of the infection. No apparent epidemiological relationship has been identified among the patients, thus, some hospitals/maternity hospitals may be serving as sources for the dissemination of these isolates to the community