Genetic Diversity and Ecological Success of Staphylococcus aureus Strains Colonizing Humans

Abstract

The genetic determinants and phenotypic traits which make a Staphylococcus aureus strain a successful colonizer are largely unknown. The genetic diversity and population structure of 133 S. aureus isolates from healthy, generally risk-free adult carriers were investigated using four different typing methods: multilocus sequence typing (MLST), amplified fragment length polymorphism analysis (AFLP), double-locus sequence typing (DLST), and spa typing were compared. Carriage isolates displayed great genetic diversity which could only be revealed fully by DLST. Results of AFLP and MLST were highly concordant in the delineation of genotypic clusters of closely related isolates, roughly equivalent to clonal complexes. spa typing and DLST provided considerably less phylogenetic information. The resolution of spa typing was similar to that of AFLP and inferior to that of DLST. AFLP proved to be the most universal method, combining a phylogeny-building capacity similar to that of MLST with a much higher resolution. However, it had a lower reproducibility than sequencing-based MLST, DLST, and spa typing. We found two cases of methicillin-resistant S. aureus colonization, both of which were most likely associated with employment at a health service. Of 21 genotypic clusters detected, 2 were most prevalent: cluster 45 and cluster 30 each colonized 24% of the carrier population. The number of bacteria found in nasal samples varied significantly among the clusters, but the most prevalent clusters were not particularly numerous in the nasal samples. We did not find much evidence that genotypic clusters were associated with different carrier characteristics, such as age, sex, medical conditions, or antibiotic use. This may provide empirical support for the idea that genetic clusters in bacteria are maintained in the absence of adaptation to different niches. Alternatively, carrier characteristics other than those evaluated here or factors other than human hosts may exert selective pressure maintaining genotypic clusters.

Age- and Gender-Associated Staphylococcus aureus spa Types Found among Nasal Carriers in a General Population: the Tromsø Staph and Skin Study

“…As many as 86.1% of the spa types were found in fewer than four individuals, and 65.5% of the spa types were observed only in single individuals. This large diversity is consistent with previous findings for both community and clinical strains (19,29,31). Still, the three most successful strains comprised 21.0% and the three largest spa CCs (spa CC012, spa CC065, and spa CC084) 62.4% of the 1,113 S. aureus nasal isolates from healthy colonized individuals in the baseline screening.…”

“…The presence of more than one spa type in nasal carriers was described previously (3,29), suggesting that single-colony sampling excludes the possibility of considering the influence of different cocolonizers. However, results from a recent study on nasal carriage indicated that strain replacement was more common than cocolonization during a 9-month period (28).…”

“…In vivo abundance of bacteria in terms of numbers of CFU could be an important factor in successful colonization, as it has been demonstrated that CFU count depends on the bacterial genotype. Sakwinska et al (29) found a lower CFU count for MLST CC15 (including spa type t084) than for CC30, including t012. However, the CFU count for CC45 was marginally lower than that for CC15, indicating that the same effect should have been observed for this lineage as well, which was not the case.…”

“…The population structure of S. aureus of nonclinical origin has been thoroughly investigated in children (age 1 to 19 years) and elderly adults (Ͼ55 years) (18); however, only smaller studies including a younger adult population have been performed (29), leaving a gap in our understanding of S. aureus diversity and population structure. We wished to find the most successful S. aureus clones and compare their respective distribution in a population-based study, the Tromsø Staph and Skin Study, which included 4,026 healthy men and women aged 30 to 87 years.…”

Dissemination of Resistance and Virulence Determinants in Methicillin-Resistant Staphylococcus aureus During Colonization and Disease: A Review

“…Similarly, it was also observed that persistent carriage was more common in children than adults and the pattern of carriage was observe to change in most individuals between the ages of 10 and 20 years. A number of studies have revealed that quite a large number of the human populations are at great risk of S. aureus infection with some persistently colonized while others intermittently colonized (Oliveira et al, 2002;Sakwinska et al, 2009). For instance, investigation of pig farm dominated areas for nasal colonization of MRSA between farm owners, veterinarians and their non-exposed families as well as 462 pupils revealed that 86% of farmers sampled where exposed and only 4.3% of their family members were observed to carry MRSA with similar spa types belonging to that of clonal complex CC398 found in Pigs.…”