Comparison of molecular characteristics between infective and colonizing strains in children with invasive Staphylococcus aureus infection / 中华实用儿科临床杂志

ABSTRACT

Objective:To study the molecular biological characteristics of isolates from the infection site and isolates colonizing in anterior nares of children with invasive Staphylococcus aureus (SA) infection, and to analyze the concordance between the two types of strains from different sources. Methods:A total of 45 strains were collected from children with invasive SA infection treated in the Pediatric Ward of Sichuan Provincial Maternal and Child Health Care Hospital from January 2019 to August 2019, and 28 colonization isolates were obtained from the anterior nares of these patients.The susceptibility test was carried out by broth dilution method.The drug resistance genes mecA and blaZ and the virulence gene panton-valentine leucocidin( pvl) were detected by PCR.The homology of infective and colonizing isolates was detected by pulsed-field gel electrophoresis(PFGE)typing technique. Results:Colonization of SA was found in the nasal vestibule of 62.2% (28/45 cases) of patients with invasive SA infection.A total of 40.0% (18/45 strains) of the infective isolates and 32.1% (9/28 strains) of the colonizing isolates were Methicillin-resistant SA (MRSA), and the difference was not statistically significant( P>0.05). The resistance of infective isolates to Clindamycin, Azithromycin and Erythromycin was stronger than that of colonizing isolates, the difference of drug resistance rate was statistically significant( χ2=7.114, 7.820, 5.359, all P<0.05). There were no differences in the carrying rates of the drug resistance gene blaZ and the virulence gene pvl between the infective and colonizing bacteria( P>0.05). Phenotypically, Methicillin-susceptible SA (MSSA)was more susceptible to concordant colonization than MRSA[16.7%(3/18 cases) vs.48.1%(13/27 cases), χ2=4.671, P<0.05]. PFGE indicated that patients with invasive MSSA infection were significantly more likely to have a concordant MSSA colonization isolate in their anterior nares, compared with patients with invasive MRSA infection[59.3%(16/27 strains) vs.27.8%(5/18 strains), χ2=4.301, P<0.05]. Conclusions:The infective and colonizing strains of invasive SA show no difference in their resistance to some anti-biotics, but they carry almost the same number of drug resistance and virulence genes.Compared with those with MRSA infection, patients with MSSA infection are more likely to have concordant colonizing isolates.It is of potential clinical significance to screen the colonizing SA strains in patients with invasive SA infection.