Molecular epidemiology and risk factors of Stenotrophomonas maltophilia infections in a Chinese teaching hospital

Abstract

Background: Stenotrophomonas maltophilia (S. maltophilia) is an important opportunistic pathogen that can be isolated in hospitals. With the abuse of broad spectrum antibiotics and invasive surgical devices, the rate of S. maltophilia infection is increasing every year. This study was an epidemiological analysis of the clinical and molecular characteristics of S. maltophilia infection in a Chinese teaching hospital. The goal was to obtain a comprehensive understanding of the status of S. maltophilia infection to provide strong epidemiological data for the prevention and treatment of S. maltophilia infection.

Results: A total of 93 isolates from Renji Hospital affiliated with the Shanghai Jiaotong University School of Medicine were included, in which 62 isolates were from male patients. In addition, 81 isolates were isolated from sputum samples. A total of 86 patients had underlying diseases. All patients received antibiotics. Multilocus sequence typing (MLST) analysis indicated that 61 different sequence types (STs) were found (including 45 novel STs), and MLST did not show significantly dominant STs. Pulsed field gel electrophoresis (PFGE) results showed that 93 isolates could be divided into 73 clusters, and they also showed weak genetic linkages between isolates. The resistant rates to trimethoprim/sulfamethoxazole (TMP/SMX) and levofloxacin were 9.7 and 4.3%, respectively, and all isolates were susceptible to minocycline. Four virulence gene's loci Stmpr1, Stmpr2, Smf-1, and Smlt3773 were positive in 79.6, 91.4, 94.6, and 52.7% of the isolates, respectively. Three biofilm genes rmlA, spgM, and rpfF were positive in 82.8, 92.5, and 64.5% of the isolates, respectively. Mean biofilm forming level of OD₄₉₂ was 0.54 ± 0.49. We did not find any significant difference between different genders and different age-groups. We retrospectively analyzed data from patients in the intensive care unit (ICU) and the control group. The independent risk factors of those who were infected in the ICU included immunosuppression and the increased antibiotic usage.

Conclusions: Most of the patients had prior medical usage histories and baseline diseases. The positive rate of virulence genes was high, the drug resistance rate of S. maltophilia was low, and the biofilm formation ability was strong. The increased use of antibiotics was an independent risk factor for S. maltophilia infection, which should receive more attention. No obvious clonal transmissions were found in the same departments.

Keywords: Biofilm; Epidemiology; MLST; Stenotrophomonas maltophilia.

Fig. 1

The distribution of S. maltophilia in the different departments. The pie graph shows the distribution of the wards, among the top three wards. Blue, red, and yellow represent the ICU, neurosurgery, and emergency internal medicine ward, respectively

Fig. 2

The MLST results of 93 S. maltophilia isolates. This is a neighbor-joining tree analysis for the concatenated data for all seven loci of the 93 isolates. The tree was rooted with the corresponding concatenate

Fig. 3

Biofilm formation abilities of S. maltophilia in the different genders and ages. Histogram illustrating the ability of biofilm formation. There are no differences in different genders and ages. The number of isolates that formed strong biofilms, however, was significantly greater than the weak and moderate ones

Fig. 4

The point mutation of spgM in bacterial isolates with different biofilm formation abilities. The spgM gene mutations in isolates with strong biofilm formation abilities are significantly different from that with the weak ones. The mutated portions of the DNA bases are shown in the red box