Genetic analysis of methicillin-susceptible Staphylococcus aureus clinical isolates: High prevalence of multidrug-resistant ST239 with strong biofilm-production ability.

BACKGROUND: The distributions of methicillin-susceptible Staphylococcus aureus (MSSA) are divers geographically with different genetic backgrounds. Data related to molecular characteristics of MSSA compare to methicillin-resistant Staphylococcus aureus (MRSA) is sparse. METHODS: In this cross-sectional study, antimicrobial susceptibility testing, virulence genes analysis, biofilm formation, accessory gene regulator (agr) typing, and multilocus sequence typing (MLST) characterized on 75 MSSA isolates. RESULTS: Multidrug-resistance MSSA was found to be 84%. Forty-eight (64%) isolates were toxinogenic with 34 and 14 isolates carrying pvl and tst representing 45.3% and 18.7%. The most common SE genes were sed (20%), sec (16%), and sea (16%). Fifty-five (73.3%) isolates were confirmed as biofilm producer with a markedly high prevalence of fnbA (93.3%), fnbB (86.7%), icaA (65.3%), icaD (53.3%), can (24%), ebp (10.7%), and bap (1.3%). A total of 3 agr types (I, 73.3%; III, 16%; II, 10.7%) and 4 clonal complexes (CCs) and sequence types (STs), namely CC8/ST293 (45.3%), CC/ST22 (28%), CC/ST30 (16%), and CC/ST5 (10.7%) were detected in this study. All the high and low-level mupirocin resistance strains belonged to ST239 and ST22 strains, respectively. All the fusidic acid-resistant isolates carried fusC and belonged to ST30. CONCLUSIONS: These findings indicated that ST239 with strong biofilm production ability is the most common type in MSSA strains isolated from patients. It seems that the antimicrobial resistance profiles, toxin, and biofilm formation were closely associated with specific STs. Further studies are required to identify and control of these clonal lineages in our area.

Immunopotentiating properties of chimeric OprF-OprI-PopB protein against Pseudomonas aeruginosa PAO1 in the infected burned rat model.

Objectives: Pseudomonas aeruginosa, as an opportunistic pathogen, is known to cause nosocomial infections among patients suffering from burn injuries and also cystic fibrosis patients. The objective of our research was to develop a novel vaccine against P. aeruginosa. Materials and Methods: A recombinant P. aeruginosa subunit vaccine based on the outer membrane proteins, including the OprF-OprI region and its major protein in the type III secretion system, PopB (called FIB protein) was formulated. To induce a robust immune response, our preferred regions were conjugated to a carrier protein, GMCSF (Granulocyte-macrophage colony-stimulating factor). FIB protein's immunogenicity with and without adjuvant was evaluated in vaccinated rats and also burned rat models, which were subcutaneously challenged by the PAO1 strain of P. aeruginosa. Results: Antibody levels were increased in sera of rats in this study. Assessment of the resident memory CD4+ T cells in splenocytes from vaccinated rats demonstrated that the FIB conjugated with GMCSF could cause higher responses in comparison with other groups. Moreover, immunization with the FIB plus adjuvant protein could improve interferon-gamma (IFN-γ) production, interleukin 17A (IL-17A), and IL-4, contributing to elicit humoral and cellular immune responses and decreased post-infection bacterial loads after PA challenge, pathology, and inflammatory cell infiltration. Conclusion: These observations demonstrated that FIB conjugated with GMCSF can be a putative vaccine candidate against P. aeruginosa in burnt rat models.

Molecular investigation of methicillin-resistant staphylococcus aureus isolates from blood: USA600 emerges as the major type.

INTRODUCTION: The widespread emergence of methicillin-resistant Staphylococcus aureus is turning into a real worry in public health. The goals of the present study were to identify resistance and virulence encoding genes and molecular characteristics of methicillin-resistant S. aureus bloodstream isolates. METHODOLOGY: A cross-sectional study was conducted on 84 S. aureus bloodstream isolates during a 10-month period. To evaluate antibiotic susceptibility of the isolates, we used Kirby-Bauer disk diffusion method. In addition, the prevalence of antimicrobial resistance and toxins genes was assessed using polymerase chain reaction. Isolates were typed according to polymorphisms seven housekeeping genes by MLST. RESULTS: All the isolates were resistant to methicillin. The most prevalent resistance gene was mecA gene (100%) followed by tetM (57.1%), aac (6΄)-Ie/aph (2˝) (53.6%), ant (4΄)-Ia (46.4%), ermA (45.2%), msrA (35.7%), msrB (33.3%), aph (3΄)-IIIa (33.3%), ermB (31%), ermC (16.7%), and mupA (14.3%) genes. The presence of toxin encoding genes tst, pvl, eta, and etb were detected in 25%, 14.3%, 3.6% and 3.6%, respectively. The isolates were classified into five different sequence types: ST45 (29.8%), ST239 (27.4%), ST858 (21.4%), ST22 (17.8%), and ST59 (3.6%). All the high-level mupirocin-resistant (HLMUPR) strains belonged to ST239, while the low-level mupirocin resistant (LLMUPR) strains belonged to ST22 (13%) and ST239 (6%). CONCLUSIONS: To the best of our knowledge, the present study is the first report of ST59 in MRSA bloodstream isolates in Iran. Our data demonstrated the need for thorough epidemiological monitoring to detect emergence and dissemination of MDR- MRSA types in our hospitals.