Abstract
Objective: To study the molecular epidemiological characteristics of Stenotrophomonas maltophilia (SMA) isolated from patients in a pediatric teaching hospital in Shanghai so as to provide data for the prevention and treatment of SMA.Methods: Non-repetitive SMA strains were isolated from patients from January 2013 to December 2014. The cloning characteristics were analyzed using multilocus sequence typing (MLST) and pulsed field gel electrophoresis (PFGE), and the drug resistance was determined using the Kirby-Bauer disk method. Virulence genes and biofilm genes were detected using polymerase chain reaction (PCR). The biofilm forming ability was analyzed using the semi-quantitative biofilm formation test.Results: A total of 104 strains were collected, primarily from the pediatric intensive care unit and thoracic surgery, and these strains were isolated from sputum sources (n = 82). A majority of the patients were male (67/104), and the age range was between 6 days and 12 years old. A total of 95 patients had 1–3 baseline diseases. All of the patients had prior use of 1–4 antimicrobial agents. A total of 59 STs were detected using the MLST analysis, of which 45 were new. The sequence types of the SMA were scattered, with no trend in the clonal spread. The PFGE showed that the 104 strains could be divided into 93 clusters, with no obvious cluster aggregations. All of the strains were susceptible to levofloxacin, trimethoprim/sulfamethoxazole, and minocycline. The positive rates of the virulence genes stmPr1, stmPr2, smf-1, and smlt3773 locus were 98.1, 86.5, 100, and 91.3%, respectively. All of the strains had biofilm formation, and most of the strains had strong biofilm formation abilities. The positive rates of the three biofilm genes rmlA, spgM, and rpfF were 83.7, 100, and 45.2%, respectively. However, the point mutations of rmlA and spgM with strong biofilm formation abilities were significantly different from those with weak biofilm formation abilities.Conclusion: Most infected patients had prior use of antibiotics and underlying diseases, and the positive rate of the virulence gene was high. The strains were susceptible to three kinds of antibiotics and had strong biofilm formation abilities. The mutations of rmlA and spgM may be related to the biofilm formation ability, and no obvious clonal transmissions were found in the same clinical department.
Highlights
Stenotrophomonas maltophilia (SMA) is a type of nonfermenting Gram-negative bacilli that widely exists in the environment
The DNA extraction kit and protease K were purchased from Tiangen Biochemistry Technology Co., Ltd., and the crystal violet and the phosphate buffer solution (PBS) buffer were purchased from Shanghai Shenggong Bioengineering Co., Ltd
The pulsed gel electrophoresis system was purchased from Bio-Rad Company, the Ultra Micro Spectrophotometer (NanoDrop2000) was purchased from Thermo Company, and the Ultraviolet Gel Imager was purchased from Shanghai Tianneng Company
Summary
Stenotrophomonas maltophilia (SMA) is a type of nonfermenting Gram-negative bacilli that widely exists in the environment. SMA is an opportunistic pathogen that colonizes in human beings, and it produces two chromosomal beta-lactamases, L1 and L2, which make SMA intrinsically resistant to many β-lactam antibiotics (Okazaki and Avison, 2008). It is nearly 100% resistant to imipenem and other carbapenem drugs. With the abuse of antibiotics, immunosuppressors, and the wide use of invasive medical equipment, the nosocomial infection rate of SMA has gradually increased (Brooke, 2012). One aim of this study is to update the status of drug resistance in Shanghai
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