Impacts of L1 Promoter Variation and L2 Clavulanate Susceptibility on Ticarcillin-Clavulanate Susceptibility of Stenotrophomonas maltophilia

Characteristics of Stenotrophomonas maltophilia isolates from cystic fibrosis patients in Russia

Stenotrophomonas maltophilia is a common opportunistic microorganism and an important respiratory pathogen in cystic fibrosis (CF). The aim of this study was to determine antimicrobial resistance phenotypes, sequence-types (ST) and genetic determinants of antibiotic resistance in S. maltophilia strains recovered from CF patients in Russia. S. maltophilia isolates recovered from 170 CF patients were analyzed. Minimum inhibitory concentrations of antibacterial agents were determined using Sensititre Gram Negative GNX2F plates and the results were interpreted according to Clinical and Laboratory Standards Institute (CLSI) criteria. Whole-genome sequencing (WGS) was performed on MGISEQ-2000 platform. SPAdes software, Galaxy, ResFinder, Integrall and PubMLST were used for analysis of WGS data. S. maltophilia strains were identified from 24/170 (14%) CF patients. In total, 25 isolates were detected, two strains were isolated from the same patient. The isolates belonged to 17 different STs, including 5 new STs; ST4 was the most prevalent ST. Resistance to ceftazidime was observed in 60% of strains, to ticarcillin-clavulanate - in 32%, to levofloxacin - in 24%, to trimethoprim/sulfamethoxazole - in 12% of strains. All isolates were susceptible to minocycline. All ST4 isolates were resistant or intermediate to ceftazidime and ticarcillin-clavulanate. In two isolates, the sul1 gene was detected. In one isolate, sul1 was part of a class 1 integron. The detected integron also contained the blaGES-7 and aac(6')-Ib-cr genes. The ST4 sequence-type was the most prevalent ST among S. maltophilia strains recovered from CF patients in Russia. Antibiotic resistance genes, including sul1, blaGES-7, aac(6')-Ib-cr, were detected in single strains.

Study on Demethoxycurcumin as a Promising Approach to Reverse Methicillin-Resistance of Staphylococcus aureus

Methicillin-resistant Staphylococcus aureus (MRSA) has always been a threatening pathogen. Research on phytochemical components that can replace antibiotics with limited efficacy may be an innovative method to solve intractable MRSA infections. The present study was devoted to investigate the antibacterial activity of the natural compound demethoxycurcumin (DMC) against MRSA and explore its possible mechanism for eliminating MRSA. The minimum inhibitory concentrations (MICs) of DMC against MRSA strains was determined by the broth microdilution method, and the results showed that the MIC of DMC was 62.5 μg/mL. The synergistic effects of DMC and antibiotics were investigated by the checkerboard method and the time–kill assay. The ATP synthase inhibitors were employed to block the metabolic ability of bacteria to explore their synergistic effect on the antibacterial ability of DMC. In addition, western blot analysis and qRT-PCR were performed to detect the proteins and genes related to drug resistance and S. aureus exotoxins. As results, DMC hindered the translation of penicillin-binding protein 2a (PBP2a) and staphylococcal enterotoxin and reduced the transcription of related genes. This study provides experimental evidences that DMC has the potential to be a candidate substance for the treatment of MRSA infections.

The involvement of PacIRA system of Stenotrophomonas maltophilia in the uptake of Pseudomonas aeruginosa pyochelin and intraspecies competition for iron acquisition

BACKGROUND

Stenotrophomonas maltophilia, a species of highly genetic diversity, has emerged as an important nosocomial pathogen. S. maltophilia and Pseudomonas aeruginosa are often co-isolated from pneumonia patients. In our previous study, we have demonstrated that the pacIRA cluster present in some but not all clinical S. maltophilia isolates. Proteins encoded by pacIRA operon are an extracytoplasmic function (ECF) sigma factor, a transmembrane anti-sigma regulator, and a TonB-dependent receptor. This study aimed to elucidate PacIRA system function and its significance to S. maltophilia.

METHODS

The pacI, pacR, and pacA genes were individually or totally deleted from the chromosome of KJΔEnt, a pacIRA-positive and siderophore-null strain. Growth promotion assay was performed to examine the implication of pacIRA system in iron utilization. Gene expression was quantified by quantitative real time PCR (qRT-PCR). Growth competition assay was executed to investigate the significance of pacIRA operon to S. maltophilia.

RESULTS

PacIRA system contributed to utilize ferri-pyochelin of P. aeruginosa as iron sources for growth in an iron-depleted condition, but hardly utilized ferric citrate, hemin, ferri-stenobactin, and ferri-pyoverdine. PacIRA was founded to belong to Fur regulon and upregulated in response to iron-depleted stress. Growth competition assay demonstrated that pacIRA-positive S. maltophilia had a superiority over pacIRA-negative S. maltophilia in iron acquisition when they were co-cultured in P. aeruginosa ferri-pyochelin-supplemented medium.

CONCLUSIONS

PacIRA system of S. maltophilia is a xenosiderophore uptake implement, involving in the acquisition of pyochelin of P. aeruginosa.

Diversity of L1/L2 genes and molecular epidemiology of high-level carbapenem resistance Stenotrophomonas maltophilia isolates from animal production environment in China

Stenotrophomonas maltophilia is emerging as a significant cause of human and animal disease worldwide. A total of 3400 samples were collected from animal farms and adjacent environments in China. The bla_L1 and bla_L2 genes were identified using whole genome sequence analyses and examined by phylogenetics. Isolates were also tested for susceptibility to 18 antibiotics. We isolated 118 strains of S. maltophilia from 3400 samples. The positive rates of bla_L1 and bla_L2 genes were 75% (89/118) and 22% (26/118) and we identified 11 L1 and 6 L2 amino acid sequence variants. S. maltophilia has at least two inducible β-lactamases (L1 and L2) that can hydrolyze almost all classes of β-lactams and these genes are suspected to confer carbapenem resistance. This represents a significant public health threat especially for hospitalized patients. We conducted a molecular surveillance study on the prevalence and characteristics of the bla_L1 and bla_L2 genes of S. maltophilia.