High prevalence and expression of antiseptic resistance genes among infectious t037/ST239 methicillin-resistant Staphylococcus aureus (MRSA) strains in North Khorasan Province, Iran.

Objectives: Staphylococcus aureus is an important infectious agent and the majority of methicillin-resistant S. aureus (MRSA) infections are of nosocomial origin. To define the level and distribution of antiseptic resistance among infectious S. aureus strains we studied MRSA and methicillin-susceptible S. aureus (MSSA) isolates collected from different infection sites in an assortment of patients. Materials and Methods: S. aureus isolates were investigated for in vitro susceptibility to antiseptic agents and detection of qacA/B, smr, vanA, and mecA genes. Results: Among the S. aureus isolates we studied, 25 and 41 were MRSA and MSSA, respectively. The mean of minimum inhibitory concentrations (MICs) for benzethonium chloride (BTC) among MRSA was statistically significantly higher than for MSSA (26 µg/ml versus 11.7 µg/ml, P=0.003) while there was no significant difference between MRSA and MSSA for benzalkonium chloride (BKC) and chlorhexidine digluconate (CHG). The qacA/B genes were carried in 68% of the MRSA and 58.2% of MSSA (P=0.601), while smr was carried in 39% of MRSA and 29.3% of MSSA strains (P=1.000). In 15 out of 25 cases, MRSA ST239 with spa types t037, t030, and t7688 was isolated from the infection site with 86.6% of them carrying a resistance gene (qacA/B or qacA/B + smr). Conclusion: The frequent presence of antiseptic resistance genes and a consequently elevated MIC against antiseptics among ST239 MRSA emphasizes the importance of mandatorily monitoring MRSA for effective infection control.

The application of randomly amplified DNA analysis in the molecular epidemiology of microorganisms.

The polymerase chain reaction (PCR) has essentially been designed to amplify specific regions within DNA molecules. This requires knowledge of the local nucleic acid sequence to design primer oligonucleotides. However, to generate DNA fingerprints, the PCR can be modified in a way that facilitates the random amplification of elements for which the precise nucleotide sequence is not known. When DNA is subjected to PCR at relatively low annealing temperatures while using relative short DNA primers of non-specific sequence, amplification is often targeted towards a larger number of domains within the template. Post-PCR analysis of these fragments, usually using electrophoretic technologies, results in strain-specific fingerprints due to small differences in primer annealing sites or the selective presence or absence of certain DNA domains among strains. These procedures are collectively called random amplification of polymorphic DNA (RAPD) analyses and have been very useful in high-speed, high-throughput screening for DNA variation among strains of a wide variety of microbial species and isolates within these species. This chapter describes the basic features of this technology, including an experimental protocol that can essentially be applied to DNA from all species of microorganisms.

Host polymorphisms in interleukin 4, complement factor H, and C-reactive protein associated with nasal carriage of Staphylococcus aureus and occurrence of boils.

BACKGROUND: Staphylococcus aureus is capable of persistently colonizing the vestibulum nasi. We hypothesized that polymorphisms in host inflammatory response genes and genetic variation in S. aureus contribute to susceptibility to S. aureus carriage and infection. METHODS: The prevalence of persistent nasal carriage of S. aureus in 3851 participants aged 61-101 years was 18% (678 of 3851 participants), whereas 73% of volunteers (2804 of 3851) were not colonized. A total of 1270 individuals had boils. Polymorphisms in TNFA (C -863T), IL4 (C -542T), CFH (Tyr402His), and CRP (C1184T, C2042T, and C2911G) were determined. Genetic similarity among 428 S. aureus isolates was determined by use of amplified fragment length polymorphism analysis (AFLP)-mediated genotyping. RESULTS: The IL4 -524 C/C host genotype was associated with an increased risk of persistent S. aureus carriage, irrespective of S. aureus AFLP genotype. The CRP haplotype 1184C; 2042C; 2911C was overrepresented in individuals who were not colonized . In individuals with boils, carriers of the CFH Tyr402 variant, and the CRP 2911 C/C genotype were overrepresented. CONCLUSION: Persistent carriage of S. aureus is influenced by genetic variation in host inflammatory response genes. As would be expected in multifactorial host-microbe interactions, these effects are limited. Interestingly, host genotype was associated with the carriage of certain S. aureus genotypes. Apparently, a close interaction between host and bacterial determinants are prerequisites for long-term colonization.