Abstract

      Background and Objective: Agr is the most important regulatory system for the expression of Staphylococcus aureus virulence factors in different conditions. Agr acts as a quorum sensing system in this bacterium which is activated by increased cell concentration during the transition from logarithmic growth phase to stationary phase. Its role is to upregulate the secretory virulence factors such as alpha-hemolysin and inhibit the transcription of surface proteins including protein A-encoding gene. The aim of this study was to assess the relationship between the agr system expression and some virulence factors of Staphylococcus aureus in Brain-heart infusion (BHI) culture medium.

     Methods: The expression level of agrA and RNAIII genes from the agr locus along with the expression of hla, spa and mecA genes in BHI broth were assessed in different growth phases using Real time-PCR. Also, gyrB was used as an internal control in this study.

     Results: The growth curve of the five tested isolates in BHI broth at 24 hours showed that all the isolates had relatively similar growth patterns. AgrA gene expression in the stationary phase was decreased by 0.89-fold compared with the logarithmic phase. Although the expression of RNAIII gene increased by 3-fold, hla expression decreased by 0.47-fold.

     Conclusion: An inactive agr system is observed in the BHI broth medium. BHI broth medium contains high amounts of suitable nutrients for the growth of Staphylococcus aureus, thus the bacteria do not require the activity of the agr system for the regulation of the virulence genes in these conditions.

    

ABSTRACT
         Background and Objectives: Klebsiella pneumoniae is one of the most important nosocomial pathogens. Its capsular polysaccharide is considered as the first and most important virulence factor of this bacterium. This study aimed to investigate the presence of capsular serotypes K1 and K2 in K. pneumoniae isolates to examine the virulence potency of the isolates.
         Methods: Overall, 65 capsulated K. pneumoniae isolates were collected from patients with urinary tract infections in Rasht, Iran. The isolates were examined using biochemical tests and CPS gene amplification using PCR. Mucoid phenotype of the isolates was determined by the string test. The presence of K1 and K2 genes was evaluated by PCR using specific primers for the genes.
         Results: Of 65 K. pneumoniae isolates, seven (10.77%) were positive for the presence of the K1 gene and four (6.15%) were positive for the presence of the K2 gene. In addition, six serotype K1 isolates (27.27%), four serotype K2 isolates (18.18%), and 12 non-K1/K2 serotype isolates (54.54%) had hypermucoviscosity phenotypes.
          Conclusion: Our results confirm the presence of the capsular serotypes in K. pneumoniae isolates, with a relatively high prevalence for the capsular serotype K1. This study clarifies the importance of rapid diagnosis and suitable treatment of infections caused by K. pneumoniae in prevention of complicated infections.
         Keywords: Klebsiella pneumoniae, Virulence factors, Capsular polysaccharide.

ABSTRACT
         Background and Objectives: Silver nanoparticles (AgNPs) have physical and surface properties that could threaten human and environmental health. AgNPs are classified as ‘very toxic’ to eukaryotic organisms and are less toxic to bacteria. The aim of the present study was to study the effects of different sub-minimum inhibitory concentrations (MICs) of AgNPs on some virulence factors of Staphylococcus aureus as a pathogenic bacterial model.
         Methods: Tube double serial dilution method was used to determine MIC of AgNPs against standard strain and ten field isolates of S. aureus. Tube cultures of isolates in LB broth were supplemented with different concentrations of AgNPs and were incubated at 37 °C with constant shaking under aerobic conditions. Samples from each tube were streaked on blood agar plates and assay for hemolysins, coagulase and DNase production were performed.
         Results: The MIC of AgNPs against all examined isolates was determined as 50 µg/mL. The results showed that 1/2, 1/4 and 1/8 MIC of AgNPs had no negative effect on DNase and coagulase production but inhibited alpha- and beta-hemolysin production in most isolates (64-91%). In addition, production of delta-hemolysin was inhibited by 1/2 MIC of AgNPs.
         Conclusion: The effects of sub-MIC of AgNPs on bacterial growth appear at 4-8 hours post-exposure and then the bacteria follow a normal growth trend. This toxic effect may affect ecosystems species.
         Keywords: Silver particles, Minimum inhibitory concentration, Virulence factors, Staphylococcus aureus.

ABSTRACT
             Background and objectives: Urinary tract infections (UTIs) are one of the most common infectious diseases caused by bacteria. The primary etiologic agent of UTIs is Escherichia coli. Uropathogenic E.coli (UPEC) strains have a number of specific virulence factors, which can worsen UTIs. This study was performed to detect fim, pap, sfa and afa genes among E.coli strains isolated from UTIs.
             Methods: A total of 100 E. coli isolates from patients with UTI was collected between June and December 2015 from Mosavi and Sayyad Shirazi hospitals in Gorgan, Iran. All bacterial isolates were identified via standard biochemical testing and Gram straining. Presence of the genes was assessed by polymerase chain reaction.
             Results: The frequency of the fim, pap, sfa and afa genes was 100%, 79%, 69% and 8%, respectively. All isolates contained at least one virulence gene. Prevalence of multiple adhesion genes was 6% for all genes and 65% for three genes (fim, pap and sfa) together. In addition, the frequency of the fim gene was significantly higher than that of the other genes (P<0.0001).
             Conclusion: The results of this study indicate the high prevalence of virulence factors that can enhance pathogenicity of E. coli. Therefore, these factors could be used as diagnostic markers or vaccine targets.
             Keywords: Virulence factors, Urinary tract infection, Uropathogenic Escherichia coli.