Antibiotic resistance, biofilm formation, and molecular epidemiology of Staphylococcus aureus in a tertiary hospital in Xiangyang, China

Abstract

Staphylococcus aureus is a common clinical pathogen that causes various human infections. The aim of this study was to investigate the antibiotic susceptibility pattern, molecular epidemiological characteristics, and biofilm formation ability of S. aureus isolates from clinical specimens in Xiangyang and to analyze the correlation among them. A total of 111 non-duplicate S. aureus isolates were collected from the Affiliated Hospital of Hubei University of Arts and Science. All isolates were tested for antibacterial susceptibility. Methicillin-resistant S. aureus (MRSA) was identified by the mecA gene PCR amplification. All isolates were analyzed to determine their biofilm-forming ability using the microplate method. The biofilm-related gene was determined using PCR. SCCmec, MLST, and spa types of MRSA strains were performed to ascertain the molecular characteristics. Among the 111 S. aureus isolates, 45 (40.5%) and 66 (59.5%) were MRSA and MSSA, respectively. The resistance of MRSA strains to the tested antibiotics was significantly stronger than that of MSSA strains. All isolates were able to produce biofilm with levels ranging from strong (28.9%, 18.2%), moderate (62.2%, 62.1%), to weak (8.9%, 19.7%). Strong biofilm formation was observed in MRSA strains than in MSSA strains, based on percentages. There were dynamic changes in molecular epidemic characteristics of MRSA isolates in Xiangyang. SCCmecIVa-ST22-t309, SCCmecIVa-ST59-t437, and SCCmecIVa-ST5-t2460 were currently the main epidemic clones in this region. SCCmecIVa-ST5-t2460 and SCCmecIVa/III-ST22-t309 have stronger antibiotic resistance than SCCmecIVa-ST59-t437 strains, with resistance to 6 ~ 8 detected non-β-lactam antibiotics. The molecular epidemic and resistance attributes of S. aureus should be timely monitored, and effective measures should be adopted to control the clinical infection and spread of the bacteria.

Keywords: Staphylococcus aureus; Antimicrobial susceptibility; Biofilm; Multilocus sequence typing; SCCmec typing.

Fig. 1

The distribution of specimen sources

Fig. 2

Distribution of MRSA and MSSA in different specimens. BAL, bronchoalveolar lavage fluid; MRSA, methicillin-resistant S. aureus; MSSA, methicillin-susceptible S. aureus

Fig. 3

Distribution of MRSA and MSSA strains in different departments (n > 3) (double asterisk indicates statistically significant in two different departments by Fisher’s exact test; “a,” “b,” “c,” and “d” indicate the four groups with each including two different departments). CCM Department, Critical Care Medicine Department; OO Department, Ophthalmology Otorhinolaryngology Department

Fig. 4

Biofilm-related gene carrying of MRSA and MSSA strains (double asterisk indicates significant level by Pearson chi-squared test, P < 0.01)

Fig. 5

Molecular typing results of 45 methicillin-resistant Staphylococcus aureus (MRSA) isolates. SCCmec, staphylococcal cassette chromosome mec; MLST, multilocus sequence typing; ST, sequence type; spa, staphylococcal protein A