Carriage frequency, phenotypic, and genotypic characteristics of methicillin-resistant Staphylococcus aureus isolated from dental health-care personnel, patients, and environment

Abstract

There is limited data on methicillin-resistant Staphylococcus aureus (MRSA) carriage in dental clinics. 1300 specimens from patients, health personnel, and environmental surfaces of a dental clinic in Egypt were tested for MRSA. Antibiotic susceptibility, biofilm formation, Staphylococcal protein A (spa) typing, SCCmec typing, and PCR-based assays were used to detect mecA, mecC, vanA, Panton-Valentine Leukocidin toxin (PVL), and toxic shock syndrome toxin-1 (tst) genes. Among 34 mecA-positive MRSA isolates, five (14.7%) were PVL-positive, seventeen (50%) were tst-positive, ten (29.4%) were vanA-positive, while none harboured mecC. MRSA hand carriage rates in patients, nurses, and dentists were 9.8%, 6.6%, and 5%. The respective nasal colonization rates were 11.1%, 6.7%, and 9.7%. 1.3% of the environmental isolates were MRSA-positive. Strong and moderate biofilm-forming isolates represented 23.5% and 29.4% of MRSA isolates. 24 MRSA isolates (70.6%) were multi-resistant and 18 (52.9%) harboured SCCmec IV. Among eight spa types, t223 (26.5%), t267 (23.5%), and t14339 (23.5%) were predominant. We noted an alarming genetic relatedness between 7 (20.6%) MRSA isolates and the epidemic EMRSA-15 clone, as well as a combined occurrence of tst and PVL in 3 (8.8%) isolates. Results suggest high MRSA pathogenicity in dental wards highlighting the need for more efficient surveillance/infection control strategies.

Figure 1

Population structure of the tested MRSA isolates (n = 34) based on BURP analysis. This analysis was performed using the Based Upon Repeat Pattern (BURP) algorithm of the Ridom StaphType software (Ridom GmbH, Würzburg, Germany) at a cost setting of ≤ 5 and excluding spa-types with 5 or fewer repeats. Each dot represents a different spa type, with the diameter of the dot being proportional to the quantity of the corresponding spa type. Clusters of linked spa types correspond to spa clonal complexes (spa-CCs). The predict founder of a cluster (which was used for defining the cluster) is shown in blue, while the others in black. Near the lines of connection, the mutations involved in the transition from a spa type to the next one are reported in detail. All DNA changes are meant to occur from the founder to the periphery. Legend: numbers along the lines refer to the repeat sequence involved in the mutation; +indicates the acquisition of a repeat sequence; - indicates the loss of a repeat sequence; within circles the numbers of the strains of each CC appear between brackets. In summary, the analysis identified a single clonal complex (spa-CC223) comprising spa types t223, t14339, t3689, and t8506; n = 20 isolates, and accounted for 58.8% of all tested MRSA isolates, as well as 3 singletons (t267, t084, and t1339; n = 12 isolates, 35.2%), while excluded 2 isolates (t380, 5.8%) from the clustering, as they consisted of four repeat units only.

Figure 2

Biofilm-forming abilities of the tested MRSA isolates in relation to the specimen source.