The study of genotype and virulence differences of hospital-acquired methicillin-resistant staphylococcus aureus and community-acquired methicillin-resistant staphylococcus aureus

Abstract

Objective To investigate the differences of genotyping and virulence of hospital-acquired methicillin-resistant staphylococcus aureus (HA-MRSA) and community-acquired methicillin-resistant staphylococcus aureus (CA-MRSA). Methods A total of 83 non-repetitive clinical specimens were collected in this study. All samples were classified into HA-MRSA and CA-MRSA according to the definition of the USA Centers for Disease Control and Prevention (CDC). Multiple polyemeras chain reaction (PCR) was used for SCCmec typing, and spa typing was conducted by means of PCR plus DNA sequencing. Panton-valentine leucocidin (PVL), phenol-soluble modulins α (PSMa), phenol-soluble modulins mec (PSM-mec), exfoliative toxin A (ETA), exfoliative toxin B (ETB), toxic shock syndrome toxin (TSST), α-toxin (hla), δ-toxin (hld) were also detected by conventional PCR. Results The SCCmec type Ⅰ, Ⅱ, Ⅲ, Ⅳa and unclassified type accounted for 1.2%, 3.6%, 65.1%, 28.9% and 1.2%, respectively. 82.1% of the 39 strains of HA-MRSA were identified as SCCmec Ⅲ. While for the 44 strains of CA-MRSA, SCCmec Ⅲ and Ⅳa each accounted for 50%. The proportions of SCCmec Ⅲ and Ⅳa in HA-MRSA and CA-MRSA showed significant differences (χ2=9.343, 20.253, both P<0.05); There were 15 types of spa, t437, t062, t015 accounted for 39.8%, 21.7% and 10.8% respectively. Among the strains of HA-MRSA, the spa type t437 and t062 accounted for 28.2% and 23.1%, respectively, while for the spa type of CA-MRSA, t437 and t062 accounted for 50% and 20.5%, respectively. There was significant difference of t437 type between HA-MRSA and CA-MRSA (χ2=4.100, P=0.043). The positive rates of PSM-a, hla and hld were all 100%, and the positive rates of PVL, ETA, ETB, TSST and PSM-mec were 24.3%, 4.8%, 1.2%, 10.8% and 4.8%, respectively. The proportions of PVL positive HA-MRSA and CA-MRSA were 10.3% and 36.4%, respectively, which was significantly different (χ2=7.705, P=0.006), while PSM-mec positive HA-MRSA and CA-MRSA were 10.3% and 0%, respectively. Conclusions The strains of SCCmec Ⅳa and spa t437 are detected in HA-MRSA, suggesting that the more virulent CA-MRSA genotypes coexist with the traditional HA-MRSA genotypes in the hospital-acquired infections, which brings new challenges for the prevention and control of hospital infection. Key words: Community-acquired infections; Genotype; Virulence; Methicillin-resistant staphylococcus aureus; Hospital-acquired