Weilong Shang

Molecular and phenotypic evidence for the spread of three major methicillin-resistant Staphylococcus aureus clones associated with two characteristic antimicrobial resistance profiles in China

OBJECTIVES The distribution of methicillin-resistant Staphylococcus aureus (MRSA) clones is dynamic and geographically unique. To understand the changing epidemiology of MRSA infections in China, we performed a prospective, multicity surveillance study with molecular typing and phenotypic analysis to determine the association of major prevalent clones with their antimicrobial resistance profiles. METHODS A total of 517 S. aureus isolates collected between January 2009 and March 2012 from six cities in China were subjected to antibiogram analysis and molecular typing, including staphylococcal cassette chromosome mec typing, multilocus sequence typing, staphylococcal protein A gene typing and PFGE typing. RESULTS Among the isolates collected, 309 were characterized as MRSA, with a prevalence of 59.8%. Three major clones were found to be prevalent in China: ST239-MRSA-III-t030, ST239-MRSA-III-t037 and ST5-MRSA-II-t002. These three clones were associated with two characteristic resistance profiles, namely, gentamicin/ciprofloxacin/rifampicin/levofloxacin for the first clone and gentamicin/ciprofloxacin/clindamycin/erythromycin/tetracycline/levofloxacin/trimethoprim/sulfamethoxazole for the latter two. Several geographically unique minor clones were also identified. CONCLUSIONS The predominant MRSA clones in China were associated with characteristic antimicrobial resistance profiles. Antibiotics for treating patients with MRSA infections can be selected based on the strain typing data.

Cell wall thickening is associated with adaptive resistance to amikacin in methicillin-resistant Staphylococcus aureus clinical isolates

OBJECTIVES Methicillin-resistant Staphylococcus aureus (MRSA) infection is increasing and causing global concern. The mechanism of MRSA resistance to amikacin is poorly understood. We report on the first matched-pair study to reveal that the phenotypic cell wall thickening of MRSA is associated with adaptive resistance to amikacin. METHODS Two MRSA strains (CY001 and CY002) were isolated from blood and synovial fluid samples, respectively, from a 12-year-old male patient with osteomyelitis. The strains were subjected to a matched-pair study, including antimicrobial agent susceptibility determination, molecular typing, morphological observation and in vitro resistance induction. RESULTS Both strains are Panton-Valentine leucocidin-positive, multilocus sequence type 59, staphylococcal cassette chromosome mec type IV and spa type 437 MRSA with identical PFGE profiles. The drug susceptibility spectra of the two isolates are similar. However, CY001 is resistant to amikacin (CY001-AMI(R); MIC = 64 mg/L), contrary to the susceptible CY002 (CY002-AMI(S); MIC = 8 mg/L). CY001-AMI(R) may have developed adaptive resistance, because it lacks aminoglycoside-modifying enzymes and has an altered growth curve. Interestingly, CY001-AMI(R) has a thicker cell wall (36.43 ± 4.25 nm) than CY002-AMI(S) (18.15 ± 3.74 nm) in the presence of amikacin at its MIC. The thickened cell wall can also be observed in an in vitro-induced strain (CY002-AMI(R)) in the presence of amikacin at its MIC (36.78 ± 3.41 nm); this strain was obtained by gradually increasing the amount of amikacin. However, the cell wall-thickened strains cultured in the presence of amikacin are still susceptible to vancomycin. CONCLUSIONS Cell wall thickening is associated with adaptive resistance in MRSA and alternative antibiotics can be used to treat patients when adaptive resistance to amikacin has developed.

Genetic polymorphisms of molecules involved in host immune response to dengue virus infection

The dengue virus (DENV) belongs to the flavivirus family. Each of the four distinct serotypes of this virus is capable of causing human disease, especially in tropical and subtropical areas. The majority of people infected with DENV manifest asymptomatic or dengue fever with flu-like self-limited symptoms. However, a small portion of patients emerge with severe manifestations referred to as dengue hemorrhagic fever, which has a high mortality rate if not treated promptly. The host immune system, which plays important roles throughout the whole process of DENV infection, has been confirmed to have double-edged effects on DENV infection. Recently, much attention has been paid to the genetic heterogeneity of molecules involved in the host immune response to DENV infection. This heterogeneity has been proved to be the determining factor for DENV disease orientation. The present review discusses the primary functions and single nucleotide polymorphisms of some critical molecules in the human DENV immunological defense, especially the polymorphism locus associated with the DENV pathogenesis and disease susceptibility.

Dengue virus-like particles: construction and application

Virus-like particles (VLPs) are shell-like viruses that lack virus-specific genetic materials. Many viral-structured proteins can assemble into VLPs, which mimic the overall structure of virus particles and can elicit strong immune responses in a host. Dengue viruses (DENVs), from the genus Flavivirus, are transmitted to humans through the bites of an infected Aedes mosquito. DENVs cause several diseases that prevailed mainly in tropical and subtropical areas. However, effective treatment measures and preventive strategies for dengue diseases are still lacking. The present minireview summarized the assembly and maturation of DENVs, the strategies and effective factors for dengue VLP construction, and the application of DENV VLPs.

Staphylococcus aureus ST121: a globally disseminated hypervirulent clone.

Staphylococcus aureus is a leading cause of bacterial infections in hospitals and communities worldwide. With the development of typing methods, several pandemic clones have been well characterized, including the extensively spreading hospital-associated meticillin-resistant S. aureus (HA-MRSA) clone ST239 and the emerging hypervirulent community-associated (CA) MRSA clone USA300. The multilocus sequence typing method was set up based on seven housekeeping genes; S. aureus groups were defined by the sharing of alleles at ≥ 5 of the seven loci. In many cases, the predicted founder of a group would also be the most prevalent ST within the group. As a predicted founder of major S. aureus groups, approximately 90 % of ST121 strains was meticillin-susceptible S. aureus (MSSA). The majority of ST121 strains carry accessory gene regulator type IV, whereas staphylococcal protein A gene types for ST121 are exceptionally diverse. More than 90 % of S. aureus ST121 strains have Panton-Valentine leukocidin; other enterotoxins, haemolysins, leukocidins and exfoliative toxins also contribute to the high virulence of ST121 strains. Patients suffering from S. aureus ST121 infections often need longer hospitalization and prolonged antimicrobial therapy. In this review, we tried to summarize the epidemiology of the S. aureus clone ST121 and focused on the molecular types, toxin carriage and disease spectrum of this globally disseminated clone.

Panton-Valentine Leukocidin (PVL)-Positive Health Care-Associated Methicillin-Resistant Staphylococcus aureus Isolates Are Associated with Skin and Soft Tissue Infections and Colonized Mainly by Infective PVL-Encoding Bacteriophages

ABSTRACT The emergence of Panton-Valentine leukocidin (PVL)-positive methicillin-resistant Staphylococcus aureus (MRSA) is a public health concern worldwide. PVL is associated with community-associated MRSA and is linked to skin and soft tissue infections (SSTIs). However, PVL genes have also been detected in health care-associated (HA) MRSA isolates. The diseases associated with PVL-positive HA-MRSA isolates and the distributions of PVL-encoding bacteriophages in HA-MRSA have not been determined. In this study, a total of 259 HA-MRSA strains isolated between 2009 and 2012 in China from inpatients with SSTIs, pneumonia, and bacteremia were selected for molecular typing, including staphylococcal cassette chromosome mec typing, multilocus sequence typing, and staphylococcal protein A gene typing. The PVL genes and PVL bacteriophages in the MRSA isolates were characterized by PCR. Among the tested MRSA isolates, 28.6% (74/259) were PVL positive. The high prevalence of PVL-carrying HA-MRSA was observed to be associated with SSTIs but not with pneumonia or bacteremia. The PVL-positive HA-MRSA isolates were colonized mainly by infective PVL phages, namely, Φ7247PVL, ΦSLT, and ΦSa2958. The distribution of PVL-carrying bacteriophages differed geographically. Our study highlights the potential risk of the emergence of multidrug-resistant HA-MRSA strains with increased virulence.

First report of a sequence type 239 vancomycin-intermediate Staphylococcus aureus isolate in Mainland China.

Methicillin-resistant Staphylococcus aureus (MRSA) is an important pathogen that causes a wide range of both hospital- and community-acquired infections. The high prevalence of MRSA and the extensive use of vancomycin in Mainland China may lead to the emergence of vancomycin-intermediate S. aureus (VISA) isolates. In this case, we report a VISA isolate from a 34-year-old male patient with steam burn. The isolate was determined to be sequence type 239 staphylococcal cassette chromosome mec type III, the most prevalent MRSA clone in Mainland China.

Superficial vimentin mediates DENV-2 infection of vascular endothelial cells.

Damage to vascular endothelial cells (VECs) is a critical hallmark of hemorrhagic diseases caused by dengue virus (DENV). However, the precise molecular event involved in DENV binding and infection of VECs has yet to be clarified. In this study, vimentin (55 kDa) was identified to be involved in DENV-2 adsorption into VECs. This protein is located on the surface of VECs and interacts with DENV-2 envelope protein domain III (EDIII). The expression level of the superficial vimentin on VECs was not affected by viral infection or siRNA interference, indicating that the protein exists in a particular mode. Furthermore, the rod domain of the vimentin protein mainly functions in DENV-2 adsorption into VECs. Molecular docking results predicted several residues in vimentin rod and DENV EDIII; these residues may be responsible for cell–virus interactions. We propose that the superficial vimentin could be a novel molecule involved in DENV binding and infection of VECs. DENV EDIII directly interacts with the rod domain of vimentin on the VEC surface and thus mediates the infection.

Complete Genome Sequence of Staphylococcus aureus XN108, an ST239-MRSA-SCCmec III Strain with Intermediate Vancomycin Resistance Isolated in Mainland China

ABSTRACT ST239-MRSA-SCCmec III (ST239, sequence type 239; MRSA, methicillin-resistant Staphylococcus aureus; SCCmec III, staphylococcal cassette chromosome mec type III) is the most predominant clone of hospital-acquired methicillin-resistant S. aureus in mainland China. We report here the complete genome sequence of XN108, the first vancomycin-intermediate S. aureus strain isolated from a steam-burned patient with a wound infection.

Comparative Fitness and Determinants for the Characteristic Drug Resistance of ST239-MRSA-III-t030 and ST239-MRSA-III-t037 Strains Isolated in China.

Sequence type (ST) 239 with SCCmec type III methicillin-resistant Staphylococcus aureus (ST239-MRSA-III) is the most predominant multidrug-resistant clone in China. The subclone ST239-MRSA-III-t037 has been gradually replaced with ST239-MRSA-III-t030 since 2000. Subclones are characterized by drug resistance profiles. However, the mechanisms of the clonal dynamics and determinants of distinct drug resistance remain poorly understood. In the present study, 12 ST239-MRSA-III-t030 and 12 ST239-MRSA-III-t037 strains were collected from Chongqing, Guangzhou, and Shanghai; these strains were selected and investigated in terms of t030/t037 strain pairs. Independent growth curve assay revealed that the ST239-MRSA-III-t030 strains grew more rapidly, with significantly shorter doubling times, than the ST239-MRSA-III-t037 strains (p < 0.001). The ST239-MRSA-III-t037 strains exhibited slightly to moderately higher (3-13%) fitness cost than the ST239-MRSA-III-t030 strains in a competition assay in vitro. The ST239-MRSA-III-t037 strains yielded lower bacterial loads in the kidneys of the infected mice than the ST239-MRSA-III-t030 rivals in a coinfection assay (p < 0.05). The ST239-MRSA-III-t030 strains were resistant to rifampicin but susceptible to trimethoprim/sulfamethoxazole (SXT). In contrast, the ST239-MRSA-III-t037 strains were susceptible to rifampicin but resistant to SXT. The genetic determinants of the resistance to rifampicin and SXT in the MRSA strains were determined. Our results suggest that the relatively low fitness cost and characteristic drug resistance phenotype can help explain the current predominance of these ST239-MRSA-III-t030 strains in Chinese hospitals.