An investigation of the temporal dynamics of staphylococcus aureus nasal and oropharyngeal carriage amongst oral / dental healthcare workers
Citation:
MALONE, KEIRA MARY, An investigation of the temporal dynamics of staphylococcus aureus nasal and oropharyngeal carriage amongst oral / dental healthcare workers, Trinity College Dublin.School of Dental Sciences.ORAL BIOSCIENCES, 2017Download Item:
Abstract:
ABSTRACT
Background: Approximately 30% of humans are Staphylococcus aureus nasal carriers and oro-nasal trafficking of the organisms is frequent. Carriage of S. aureus can be persistent or transient. Healthcare workers (HCWs) have been implicated in transmission of methicillin-resistant S. aureus (MRSA) and methicillin-susceptible S. aureus (MSSA) to patients. Oro-nasal colonisation prevalence data for dental HCWs is scarce.
Aims and Objectives: To investigate the prevalence of transient and persistent oro-nasal colonisation by S. aureus of two groups of dental HCWs including (A) Dublin Dental University Hospital HCWs working at outreach multicentre facilities and (B) dental HCWs in general practices in four different locations, and to characterise S. aureus isolates recovered. To achieve these objectives, volunteers from each group were screened twice for S. aureus carriage over three months.
Methods: Ethicial permission was granted by the Tallaght Hospital/St. James's Hospital Joint Research Ethics Committee. Nasal swabs and oral rinses were taken from 79 volunteer participants (n = 39 from group A, n = 40 from group B). Presumptive S. aureus were recovered on SaSelectTM (Bio-Rad) medium and confirmed by growth on mannitol salt agar and using the Pastorex? Staph Plus kit (Bio-Rad). Twenty-four and 35 selected isolates from separate participants from the first and second collection phases, respectively, were screened for antimicrobial resistance and virulence-associated genes by DNA microarray profiling (Alere GmbH).
Results: MRSA was not detected from any of the participants. The MSSA nasal and oral carriage rate among participants during the first and second screening phases was 16.5% (13/79) and 17.7% (14/79) and 22.8% (18/79) and 21.5% (17/79), respectively. The overall S. aureus carriage rate during the first and second screening phases was 15.5%. The first phase sampling identified 13 S. aureus nasal carriers, four of which were also oral S. aureus carriers. Following the second phase screening, 19 S. aureus nasal carriers were identified, seven of which were S. aureus nasal carriers during the first sampling phase. The second screening phase identified an additional 12 nasal carriers and identified seven persistent nasal carriers, five of which retained the same S. aureus isolate CC from the first round.
Confluent growth of S. aureus from primary plating of oral swab and oral rinse samples was recorded for 21.5% (17/79) of S. aureus nasal and oral positive samples for the first round sampling with a reduced rate of 13.92% (11/79) for the second sampling round. The S. aureus cell density range recovered from S. aureus carriers yielding confluent growth from nasal swabs was 2x10⁴ - 2.8 x10⁶ colony forming units (CFU)/swab.
A total of 24 MSSA isolates from 21 participants during the first phase of sampling were investigated by DNA microarray profiling. DNA profiling detected 13 different multilocus sequence typing (MLST) clonal complexes (CCs), the most prevalent of which was CC30 (20.8%; 5/24 isolates). The most prevalent antimicrobial resistance gene detected among the 24 isolates was sdrM (91.7%; 22/24), encoding a non-specific efflux pump, and was identified in nine different CCs. Immune evasion cluster genes were detected among 87.5% (21/24) of the isolates and included scn (87.5%; 21/24), sak (75%; 18/24), chp (62.5%; 15/24) and sea (29.2%; 7/24). The most common IEC type identified was IEC type B (41.7%; 10/24), followed by D (16.7%; 4/24), IEC type A (12.5%; 3/24), IEC types C and E both detected in 8.3% (2/24). The biofilm related gene, icaA, was identified in all 24 isolates. The enterotoxin gene cluster (egc) was detected in 50% (12/24) of isolates.
Thirty-five MSSA isolates recovered from 29 participants during the second phase of screening yielded 13 different MLST CC/sequence types (STs) following DNA profiling, of which CC30 (34.3%; 12/35) was the most common. Three additional CCs (CC15, CC59 and CC97) were identified, which were not detected during the first round. The beta-lactamase resistance gene blaZ was the most prevalent antimicrobial resistance gene identified (85.7%; 30/35), detected in eight different CCs. IEC genes were detected among 85.7% (30/35) of the isolates. The most prevalent IEC type genes detected included scn (85.7%, 30/35), sak (71.4%, 25/35), chp (77.1%, 27/35) and sea (25.7%, 9/35). Similar to the first collection phase isolates, the most common IEC type for the second phase isolate collection was IEC type B (34.3%, 12/35), followed by IEC type C (20%, 7/35), IEC type A (22.9%, 8/35), IEC type D (8.6%, 3/35) and IEC type E (5.7%, 2/35). Clonal complexes CC30 and CC8 exhibited the most IEC types. The most prevalent virulence-associated gene detected was the biofilm related icaA gene, identified in all 35 isolates. The most prevalent toxin genes identified were the egc genes, detected in 19/35 (54.3%) isolates, most frequently belonging to CC30 with a total of 11/35 isolates.
Conclusion: These results indicate that there is a significant reservoir of S. aureus in dental HCWs including a subgroup that were heavily colonised. These latter individuals represent a significant health risk to both patients and fellow co-workers with the potential for onward transmission. There is no similar published data in the dental setting. Pre-employment screening may assist in identifying HCW carriers and reduce the risk of trans-contamination HCW-patient-HCW. Larger studies are warrented to investigate S. aureus carriage among dental HCWs.
Sponsor
Grant Number
Microbiology Research Unit, Division of Oral Biosciences, School of Dental Science, TCD
Author's Homepage:
http://people.tcd.ie/kemaloneDescription:
APPROVED
Author: MALONE, KEIRA MARY
Advisor:
Stassen, LeoQualification name:
Professional Doctor of Dental Surgery (D.Ch.Dent)Publisher:
Trinity College Dublin. School of Dental Sciences. Discipline of Dental ScienceType of material:
ThesisAvailability:
Full text availableMetadata
Show full item recordLicences: