Phenotype, genotype, and antibiotic susceptibility of Swedish and Thai oral isolates ofStaphylococcus aureus

Abstract

ObjectiveThe present study investigated phenotypes, virulence genotypes, and antibiotic susceptibility of oral Staphylococcus aureus strains in order to get more information on whether oral infections with this bacterium are associated with certain subtypes or related to an over-growth of the S. aureus variants normally found in the oral cavity of healthy carriers.Materials and methodsA total number of 157 S. aureus strains were investigated. Sixty-two strains were isolated from Swedish adults with oral infections, 25 strains were from saliva of healthy Swedish dental students, and 45 strains were from tongue scrapings of HIV-positive subjects in Thailand, and 25 Thai strains from non-HIV controls. The isolates were tested for coagulase, nitrate, arginine, and hemolysin, and for the presence of the virulence genes: hlg, clfA, can, sdrC, sdrD, sdrE, map/eap (adhesins) and sea, seb, sec, tst, eta, etb, pvl (toxins). MIC90 and MIC50 were determined by E-test against penicillin V, oxacillin, amoxicillin, clindamycin, vancomycin, fusidic acid, and cefoxitin.ResultsWhile the hemolytic phenotype was significantly (p<0.001) more common among the Thai strains compared to Swedish strains, the virulence genes were found in a similar frequency in the S. aureus strains isolated from all four subject groups. The Panton-Valentine leukocidin (PVL) genotype was found in 73–100% of the strains. More than 10% of the strains from Swedish oral infections and from Thai HIV-positives showed low antibiotic susceptibility, most commonly for clindamycin. Only three methicillin-resistant S. aureus (MRSA) strains were identified, two from oral infections and one from a Thai HIV patient.Conclusions S. aureus is occasionally occurring in the oral cavity in both health and disease in Sweden and Thailand. It is therefore most likely that S. aureus in opportunistic oral infections originate from the oral microbiota. S. aureus should be considered in case of oral infections and complaints and the antibiotic susceptibility (including MRSA) should regularly be checked. The frequent presence of S. aureus, although in low numbers among students and staff, emphasizes the importance of standard infection control precautions and of using diagnostic test in the dental clinic.

Presence of egc-positive major clones ST 45, 30 and 22 among methicillin-resistant and methicillin-susceptible oral Staphylococcus aureus strains

“…Staphylococcus aureus isolation rates differ considerably depending on the population. In healthy adults, oral carriage rates vary from 12 to 36%, with more frequent isolation (17–48%) among students 4 , 33 . The carriage rate documented in our study (18.5%) was similar as reported by other authors 34 – 36 , and remained within a typical range for European and American adult dental patients.…”

Knowledge, attitudes and practices regarding methicillin-resistant Staphylococcus aureus (MRSA) infection control and nasal MRSA carriage rate among dental health-care professionals

“…In various studies investigating the MRSA carriage rate among DHCPs, including dental students, the rate reported varied significantly from 0% to 21% ( Table ). At a glance, the rates obtained from the first two studies differed greatly from those in the remaining studies. The results obtained from the first two studies are close to the carriage rates observed during outbreaks of MRSA infection.…”

“…The mostly likely explanation is that those institutions were experiencing an outbreak of MRSA during the survey. The last four studies showed much lower rates, ranging from 0% to 3.2%. In particular, we reported that 3.1% of dental students in the same region had MRSA colonisation during a survey from December 2014 to January 2015.…”

Low prevalence of multi-resistant bacteria in undergraduate dental students; an observational case-control multi-centre study in Europe

“…Unfortunately, reports on these topics, for different countries, are not available and would require international multi-centre studies to further explain our data in relation to previous studies. Regardless of the local MRSA prevalence within DHCPs, surface disinfection is an important step to prevent spreading MRSA within the dental clinic [ 24 , 26 ]. No previous studies report on the prevalence of ESBL and VRE in dentistry, but the current data suggest that the prevalence is not elevated amongst dental students.…”