Methicillin-Resistant Staphylococcus epidermidis Is Part of the Skin Flora on the Hands of Both Healthy Individuals and Hospital Workers

Abstract

Staphylococcus epidermidis, a major skin flora on hands, acts as a reservoir of various antimicrobial resistance determinants including staphylococcal cassette chromosome mec (SCCmec) and contributes to multidrug resistance for S. aureus. The aim of this study was understanding the characteristics of commensal S. epidermidis on the hands of hospital workers and healthy individuals. A total of 23 hospital workers (physicians, nurses, and hospital pharmacists), 13 community pharmacists, and 24 healthy individuals (students) were studied. Commensal bacteria on hands were recovered using a glove-juice method. For methicillin-resistant S. epidermidis (MRSE), we performed SCCmec typing, pulsed-field gel electrophoresis (PFGE), and determined the antimicrobial susceptibility. The detection rates of MRSE in community pharmacists (92.3%) and students (87.5%) were higher than those in hospital workers (66.7 to 81.8%). SCCmec type IV strains were predominant in both hospital workers and students. PFGE analysis strongly suggested that the MRSE of hospital workers and students were normal inhabitants of each subject. The antimicrobial resistance rates and levels in MRSE of hospital workers were higher than those of students. Our findings showed that MRSE was frequently colonized on the hands of healthy individuals as well as hospital workers.

Staphylococci are common bacterial colonizers of the skin and mucous membranes in humans.¹⁾ Staphylococcus epidermidis, in particular, is the most frequently isolated species from human epithelia. It is classified as a coagulase-negative staphylococci and is distinguished from coagulase-positive staphylococci such as S. aureus that are highly pathogenic species. While S. epidermidis is commensal on the skin, if it breaches the skin surface and enters the bloodstream, it is considered a pathogen.²⁾ S. aureus and coagulase-negative staphylococci including S. epidermidis, comprise 30% of hospital-acquired infections and are associated with an estimated $2 billion in treatment costs annually.^1,3) S. epidermidis also forms biofilms on medical devices, such as contact lenses, catheters, and prosthetic heart valves. The detachment of bacterial cells from biofilms on these devices can lead to bacteremia, with increased morbidity and potential mortality.⁴⁾

The increasing antibiotic resistance of nosocomial isolates of S. epidermidis poses a great challenge for the management of hospital-acquired infections in general.⁵⁾ Worldwide surveillance shows that the isolation frequency of methicillin-resistant S. epidermidis (MRSE) can reach 80% in hospitals.⁶⁾ This frequency is higher than methicillin-resistant S. aureus (MRSA) (ca. 60%).⁷⁾ The mecA gene, which is located on the mobile genetic element, staphylococcal cassette chromosome mec (SCCmec), plays a key role in β-lactam resistance in staphylococci.⁸⁾ Currently, SCCmec in MRSA is divided into 11 types (I–XI) by mec gene complex and ccr gene complex.^9,10) S. epidermidis, especially MRSE, acquired various antimicrobial resistance determinants including SCCmec. Therefore, S. epidermidis acts as a reservoir of antimicrobial resistance determinants and contributes to multidrug resistance for S. aureus.¹¹⁾

We expected that the antimicrobial susceptibility of skin commensal staphylococci on the hands of hospital workers and healthy individuals to be different because antimicrobial resistance in bacteria is closely related to exposure and usage of antimicrobial agents. Furthermore, skin commensal staphylococci on the hands of hospital workers may cause infectious diseases by contact transmission. There are several surveillance studies for the nasal carriage of MRSE in hospital workers.^12–14) However, little is known about the frequency of antimicrobial-resistant staphylococci that form skin flora on the hands of hospital workers. Additionally, there are no investigations with a unified method that compare the characteristics of skin flora on hands between hospital workers and healthy individuals. In the present study, the characteristics of staphylococci on hands were determined and compared between hospital workers and healthy individuals (i.e., students). Here, we show that MRSE were frequently colonized on the hands of both healthy individuals and hospital workers.

MATERIALS AND METHODS

Subjects

A total of 23 hospital workers (9 physicians, 11 nurses, and 3 hospital pharmacists) of Tokyo Medical University Hachioji Medical Center, 13 community pharmacists of Hachioji Pharmaceutical Center, and 24 students of Tokyo University of Pharmacy and Life Sciences were studied in 2011 to 2013. We obtained written informed consent from all study subjects.

Detection and Isolation of Commensal Bacteria on Hands

Commensal bacteria on hands were recovered using the modified glove-juice technique of Larson et al.¹⁵⁾ Each participant inserted their dominant hand into a sterile surgical glove. Then 30 mL of sampling solution [1% Na₂HPO₄, 0.04% KH₂PO₄, and 0.1% Triton X-100 (Wako Pure Chemical Industries, Ltd., Osaka, Japan), pH 7.8] were added into the glove. Trained project staff obtained samples for culture by massaging the entire hand and fingers through the wall of the sterile glove for 1 min. After that, 7 mL of the sampling solution in the glove and 7 mL of the neutralizer solution [10% Tween 80 (Sigma-Aldrich Japan, Tokyo, Japan) and 3% lecithin (Wako)] were mixed. Aliquots (1 mL) of the mixture, diluted 10- and 100-fold were mixed with agar medium, and the pour cultures were incubated at 35°C for 48 h. Tryptone soya agar (Oxoid Limited, Hampshire, U.K.), mannitol salt agar (MSA; Oxoid), and MSA containing 1 µg/mL oxacillin were used for culturing total bacteria, staphylococci, and methicillin-resistant staphylococci (MRS) on hands, respectively.

Determination of Staphylococcal Species

The bacteria that were grown on MSA containing 1 µg/mL oxacillin and showed different colony morphology and color were identified and streaked onto Tryptone soya agar, then incubated at 35°C for 24 h. Staphylococcal species were determined using the PCR method.^16,17) Strains that could not be identified by the PCR method were determined by sequencing the 16S ribosomal RNA (rRNA) gene.¹⁸⁾

Detection of Antimicrobial Resistance Genes by PCR

Detection of the methicillin resistance gene (mecA), macrolides resistance genes (ermA, ermC, msrA/B, and mphC), aminoglycosides resistance gene (aacA–aphD), antiseptics efflux genes (qacA/B and smr), and SCCmec typing were performed using the PCR method.^8,19)

Antimicrobial Susceptibility Testing

Minimum inhibitory concentrations (MICs) were determined by an agar doubling-dilution method, according to the Clinical and Laboratory Standards Institute guidelines.²⁰⁾ The following antimicrobial agents were used: ampicillin (Wako), oxacillin (Sigma-Aldrich), cefotaxime (Wako), cefdinir (Sigma-Aldrich), levofloxacin (Wako), clarithromycin (Wako), spiramycin (Sigma-Aldrich), gentamicin (Wako), minocycline (Sigma-Aldrich), vancomycin (Wako), fusidic acid (Sigma-Aldrich), benzalkonium chloride (Wako), and chlorhexidine digluconate (Wako). The breakpoints of these antimicrobial agents were determined using the Clinical and Laboratory Standards Institute interpretation criteria. Undefined breakpoints were determined according to a previous study.⁸⁾

Pulsed-Field Gel Electrophoresis (PFGE)

PFGE analysis was performed as described previously.¹⁹⁾ Isolates exhibiting 100% similarity were determined to be the same pulsotypes.²¹⁾

Statistical Analysis

Differences in the average number of bacteria between hospital workers and students were compared using Student’s t-test. Differences in rates of antimicrobial resistance and the presence of various genes were compared using Fisher’s exact test. p Values of less than 0.05 were considered statistically significant.

RESULTS

Detection of MRS Colonized on Hands

Total bacterial counts from the hands of 23 hospital workers, 13 community pharmacists, and 24 students were determined (Fig. 1). Total bacterial counts in physicians, nurses, hospital pharmacists, community pharmacists, and students were 1.5±0.8×10⁵, 1.2±0.4×10⁵, 2.2±0.9×10⁵, 6.1±3.7×10⁵, and 2.0±0.6×10⁶ colony forming units (CFU)/hand (the mean±standard error of the mean (S.E.M.)), respectively. The total number of bacteria on the hands of students was significantly greater than that of physicians, nurses, and hospital pharmacists. The staphylococcal bacterial counts in physicians, nurses, hospital pharmacists, community pharmacists, and students were 1.2±0.6×10⁵, 7.7±1.8×10⁴, 2.0±0.8×10⁵, 5.3±3.3×10⁵, and 1.1±0.3×10⁶ CFU/hand, respectively. Similar to total bacterial numbers, there were fewer commensal staphylococci on the hands of hospital workers than students. Even though engaged in a similar occupation, the number of commensal staphylococci on the hands of community pharmacists was greater than that of hospital pharmacists. The counts of MRS on the hands of physicians, nurses, hospital pharmacists, community pharmacists, and students were 8.2±4.3×10³, 3.9±1.4×10⁴, 1.4±0.6×10⁵, 6.9±3.6×10⁴, and 7.3±2.9×10⁴ CFU/hand, respectively. Amazingly, these data showed the presence of numerous MRS on hands not only in hospital workers but also in students. The detection rates of MRS in physicians, nurses, hospital pharmacists, community pharmacists, and students were 77.8% (7/9), 90.9% (10/11), 66.7% (2/3), 92.3% (12/13), and 87.5% (21/24), respectively.

Fig. 1. Average Counts of Total Bacteria, Staphylococci, and Methicillin-Resistant Staphylococci Isolated from the Hands of Hospital Workers and Students

Data are expressed as the mean±S.E.M. ^a Bacteria grown on tryptone soya agar were counted as total bacteria. ^b Bacteria grown on mannitol salt agar were counted as staphylococci. ^c Bacteria grown on mannitol salt agar containing 1 µg/mL oxacillin were counted as methicillin-resistant staphylococci. ^d Hospital pharmacist. ^e Community pharmacist. * The average count is significantly higher (p<0.05) than physicians, nurses, and H-pharmacists, as determined by Welch’s t-test. ** The average count is significantly higher (p<0.05) than physicians, as determined by Welch’s t-test.

Identification of the Species and Isolation Rates for MRS

Identification of the staphylococcal species and detection of the mecA gene were performed for MRS isolates (Table 1). Zero to four MRS isolates were detected in each subject. The average number of MRS species/hand in nurses was 1.8 which was the greatest among the subjects tested. In contrast, no significant difference was found in the average number of MRS species/hand among physicians (1.3), hospital pharmacists (1.3), community pharmacists (1.2), and students (1.2). S. epidermidis was detected in 51/60 subjects (85.0%), and MRSE was the most predominant MRS on hands. The detection rates of MRSE in community pharmacists and students were higher than in hospital workers. The results showed that MRSE forms skin flora on hands, not only in hospital workers, but also in healthy individuals. However, MRSA was detected in only one (9.1%) nurse, and the detection rate was 1.7% for all MRS strains. Subsequently, we focused on MRSE which was the most detected bacterium in this study.

Table 1. Isolation Rates of Methicillin-Resistant Staphylococci from the Hands of Hospital Workers and Students

Species	No. (%) of isolates
	Physician (n=9)	Nurse (n=11)	H-Pharmacista) (n=3)	C-Pharmacistb) (n=13)	Student (n=24)	Total (n=60)
S. epidermidis	7 (77.8)	9 (81.8)	2 (66.7)	12 (92.3)	21 (87.5)	51 (85.0)
S. hominis	0	1 (9.1)	0	1 (7.7)	4 (16.7)	6 (10.0)
S. warneri	0	2 (18.2)	1 (33.3)	3 (23.1)	0	6 (10.0)
S. caprae	2 (22.2)	4 (36.4)	0	0	0	6 (10.0)
S. capitis	2 (22.2)	2 (18.2)	1 (33.3)	0	0	5 (8.3)
S. haemolyticus	1 (11.1)	0	0	0	2 (8.3)	3 (5.0)
S. saprophyticus	0	1 (9.1)	0	0	1 (4.2)	2 (3.3)
S. lugdunensis	0	0	0	0	1 (4.2)	1 (1.7)
S. aureus	0	1 (9.1)	0	0	0	1 (1.7)
NDc)	2 (22.2)	1 (9.1)	1 (33.3)	1 (7.7)	3 (12.5)	8 (13.3)

Zero to four bacteria were detected in each subject. a) Hospital pharmacist. b) Community pharmacist. c) No methicillin-resistant staphylococci was detected.

Molecular Epidemiological Analysis for MRSE Strains

The 11 MRSE strains isolated from seven physicians, 13 from nine nurses, two from two hospital pharmacists, 19 from 12 community pharmacists, and 28 from 21 students were defined as different strains even though some from the same subjects could be distinguished by biochemical characteristics and possession of antimicrobial resistance genes. SCCmec typing was conducted for these 73 MRSE strains (Table 2). The results showed that SCCmec type IV was most predominant in the strains from physicians, nurses, and hospital pharmacists. In contrast, the ratios of SCCmec types I and IV were equivalent in the strains of community pharmacists and students.

Table 2. SCCmec Types of Methicillin-Resistant Staphylococcus epidermidis Isolated from the Hands of Hospital Workers and Students

SCCmec type	No. (%) of isolates
	Physician (n=11)	Nurse (n=13)	H-Pharmacista) (n=2)	C-Pharmacistb) (n=19)	Student (n=28)	Total (n=73)
I	2 (18.2)	2 (15.4)	0	9 (47.3)	10 (35.8)	23 (31.5)
II	0	0	0	0	0	0
III	1 (9.1)	0	0	1 (5.3)	2 (7.1)	4 (5.5)
IV	7 (63.6)	11 (84.6)*	2 (100.0)	8 (42.1)	14 (50.0)	42 (57.5)
V	0	0	0	1 (5.3)	0	1 (1.4)
NTc)	1 (9.1)	0	0	0	2 (7.1)	3 (4.1)

Zero to three MRSE strains were detected in each subject. a) Hospital pharmacist. b) Community pharmacist. c) Nontypeable. * The ratio is significantly higher (p<0.05) than C-pharmacists and students, as determined by Fisher’s exact test.

Phylogenetic analyses for all MRSE strains, excluding three strains that could not be analyzed due to their low cell lysis, were conducted by PFGE (Fig. 2). We identified 64 pulsotypes and confirmed that no biases or specific pulsotypes were found between the strains of hospital workers and students. The results showed that no specific MRSE strain existed on the hands. Our data strongly suggested that these strains were normal hand flora of each subject. However, four pulsotypes (10 strains) that included multiple strains were found. Among them, only four strains of two pulsotypes were obtained from the same subjects.

Fig. 2. Molecular Epidemiological Analysis of Methicillin-Resistant Staphylococcus epidermidis (n=70) Isolated from the Hands of Hospital Workers and Students

The dashed boxes show identical pulsotypes classified by 100% similarity. The asterisks show the strains obtained from the same subjects. ^a Hospital pharmacist. ^b Community pharmacist.

Antimicrobial Susceptibility

Antimicrobial susceptibility of the 73 MRSE strains was determined and compared by subject (Table 3, Fig. 3). The antimicrobial susceptibility patterns in the strains of hospital workers were similar to each other. The patterns in the strains of community pharmacists were more similar to those of students than hospital workers. The levels of resistance to cefdinir, levofloxacin, and clarithromycin in the strains of physicians, nurses, and hospital pharmacists were higher than those of community pharmacists and students. Especially, the resistance rates of cefdinir and gentamicin in the strains of nurses were significantly higher than those of students (p<0.05). Additionally, the resistance rate of gentamicin in the strains of nurses was significantly higher than that of physicians and community pharmacists (p<0.05). Susceptibility to benzalkonium chloride, an antiseptic agent, in the strains of community pharmacists and students was higher than that of hospital workers. On the other hand, no difference was found in the susceptibilities to cefotaxime, minocycline, vancomycin, and fusidic acid in each subject.

Table 3. Antimicrobial Susceptibilities of Methicillin-Resistant Staphylococcus epidermidis Isolated from the Hands of Hospital Workers and Students

Antimicrobial agent	Physician (n=11)		Nurse (n=13)		H-Pharmacista) (n=2)		C-Pharmacistb) (n=19)		Student (n=28)		Total (n=73)
	MIC50/MIC90	R (%)	MIC50/MIC90	R (%)	MIC50/MIC90	R (%)	MIC50/MIC90	R (%)	MIC50/MIC90	R (%)	MIC50/MIC90	R (%)
Ampicillin	2/8	100	2/4	100	0.5/2	100	1/2	100	1/4	100	1/4	100
Oxacillin	4/32	100	4/32	100	4/16	100	2/32	100	2/16	100	4/32	100
Cefdinir	4/≥256	63.6	4/32	84.6*	2/32	50.0	4/8	57.9	2/4	39.3	4/16	56.2
Levofloxacin	2/4	27.3	2/8	30.8	2/2	0	0.13/2	5.3	0.13/2	7.1	0.13/4	13.7
Clarithromycin	32/≥256	63.6	≥256/≥256	69.2	≥256/≥256	100	4/≥256	36.8	≤0.06/≥256	46.4	8/≥256	52.1
Spriramycin	2/>256	36.4	≥256/≥256	53.9*	≥256/≥256	100*	4/≥256	21.1	2/8	7.1	4/≥256	26.0
Gentamicin	≤0.06/16	18.2	16/64	69.2**	≤0.06/≤0.06	0	≤0.06/8	5.3	≤0.06/16	14.3	≤0.06/16	21.9
Minocycline	≤0.06/0.25	0	0.13/0.25	0	≤0.06/≤0.06	0	≤0.06/0.25	0	≤0.06/0.5	0	≤0.06/0.25	0
Vancomycin	2/2	0	2/2	0	2/2	0	1/1	0	2/2	0	2/2	0
Fusidic acid	≤0.06/≤0.06	0	≤0.06/≤0.06	0	≤0.06/≤0.06	0	≤0.06/≤0.06	0	≤0.06/≤0.06	3.6	≤0.06/≤0.06	1.4
Benzalkonium-Clc,d)	4/8	—	4/8	—	0.5/8	—	1/4	—	1/4	—	2/8	—
Chlorhexidine-2Gluc,e)	2/2	—	2/2	—	1/2	—	1/2	—	2/2	—	2/2	—

MIC₅₀/MIC₉₀, the values indicate the MICs (µg/mL) that inhibit the growth of 50/90% of the strains; R, rate of resistant strains. The resistance breakpoints of the following antimicrobial agents were defined according to CLSI and previous study: ampicillin, ≥0.5 µg/mL; oxacillin, ≥0.5 µg/mL; cefdinir, ≥4 µg/mL; levofloxacin, ≥4 µg/mL; clarithromycin, ≥8 µg/mL; spiramycin, ≥16 µg/mL; gentamicin, ≥16 µg/mL; minocycline, ≥16 µg/mL; vancomycin, ≥16 µg/mL; fusidic acid, ≥8 µg/mL. a) Hospital pharmacist. b) Community pharmacist. c) The break points of antiseptics were not defined. d) Benzalkonium chloride. e) Chlorhexidine digluconate. * The ratio is significantly higher (p<0.05) than students, as determined by Fisher’s exact test. ** The ratio is significantly higher (p<0.05) than physicians, C-pharmacists, and students, as determined by Fisher’s exact test.

Fig. 3. Antimicrobial Susceptibility Curves for Methicillin-Resistant Staphylococcus epidermidis Isolated from the Hands of Hospital Workers and Students

Data are expressed as the percentage of bacteria susceptible to different minimum inhibitory concentrations of various antimicrobials. ^a Hospital pharmacist. ^b Community pharmacist.

Detection of Antimicrobial Resistance Determinants

Resistance genes to maclorides and aminoglycosides, and antiseptic efflux genes, were detected (Table 4). The 23S rRNA methylase gene, ermA, was found in only two strains, whereas ermC was detected in 20 strains. The macrolide efflux pump gene, msrA/B, was found in 13 strains, but in only one strain of nurses. The macrolide phosphotransferase gene, mphC, was detected in only 8.2% of all strains. The aminoglycoside acetyltransferase/phosphotransferase gene, aacA–aphD, was detected in 42.5% of all strains. The detection rate in the strains of nurses (76.9%) was significantly higher than in the strains of community pharmacists (21.1%). The multidrug efflux gene, qacA/B, conferring reduced susceptibility to antiseptics, was frequently detected in the strains of hospital workers. Among them, the detection rate in the strains of physicians was significantly higher than that of community pharmacists, while that of nurses was higher than community pharmacists and students. The smr gene, that plays a small role in the decreased susceptibility to antiseptics, was the most prevalent among the tested antimicrobial resistance genes.

Table 4. Detection Rates of Antimicrobial Resistance Determinants in Methicillin-resistant Staphylococcus epidermidis Isolated from the Hands of Hospital Workers and Students

Function	Gene	No. (%) of isolates
		Physician (n=11)	Nurse (n=13)	H-Pharmacista) (n=2)	C-Pharmacistb) (n=19)	Student (n=28)	Total (n=73)
Macrolides resistance	ermA	1 (9.1)	1 (7.7)	0	0	0	2 (2.7)
	ermC	2 (18.2)	6 (46.2)	2 (100.0)*	3 (15.8)	7 (25.0)	20 (27.4)
	msrA/B	3 (27.3)	1 (7.7)	0	4 (21.1)	5 (17.9)	13 (17.8)
	mphC	1 (9.1)	1 (7.7)	0	1 (5.3)	3 (10.7)	6 (8.2)
Aminoglycosides resistance	aacA–aphD	4 (36.4)	10 (76.9)*	0	4 (21.1)	13 (46.4)	31 (42.5)
Antiseptics efflux	qacA/B	4 (36.4)*	7 (53.8)**	1 (50.0)	1 (5.3)	3 (10.7)	16 (21.9)
	smr	6 (54.5)	5 (38.5)	1 (50.0)	7 (36.8)	14 (50.0)	33 (45.2)
NDc)		0	0	0	9 (47.4)***	8 (28.6)****	17 (23.3)

a) Hospital pharmacist. b) Community pharmacist. c) No tested antimicrobial determinants excluding mecA were detected. * The ratio is significantly higher (p<0.05) than C-pharmacists, as determined by Fisher’s exact test. ** The ratio is significantly higher (p<0.05) than C-pharmacists and students, as determined by Fisher’s exact test. *** The ratio is significantly higher (p<0.05) than physicians and nurses, as determined by Fisher’s exact test. **** The ratio is significantly higher (p<0.05) than nurses, as determined by Fisher’s exact test.

No strain without any of the tested antimicrobial resistance genes excluding mecA was found in the strains of hospital workers, whereas such strains were found in nine (47.4%) and eight (28.6%) of community pharmacists and students, respectively. These results were consistent with the antimicrobial susceptibility data.

DISCUSSION

Our findings showed that MRSE was colonized frequently on the hands of both healthy individuals and hospital workers. However, the levels of gentamicin resistance, and the rates at which aminoglycosides resistance gene, aacA–aphD, was detected in the strains of nurse (i.e., hospital workers), was higher than those of students (i.e., healthy individuals). Interestingly, antimicrobial susceptibility and the detection rates of antimicrobial resistance genes in the strains of community pharmacists were equivalent to those of students.

Detection of commensal bacteria on hands showed that the total bacterial and staphylococcal numbers were greater of students than of hospital workers. This may be because hospital workers enforce hand washing frequently. However, no significant difference in the number of MRS was found between students and hospital workers. Additionally, the detection rates of MRSE in students and hospital workers were similar. The detection rate of MRS in hospital workers was equivalent to the report of Cimiotti et al. (82–95%).²²⁾ By contrast, the detection rate of MRS in healthy individuals was significantly higher than that reported by Lee et al. (13%) (p<0.001).²³⁾ In hospitals, there is generally high selection pressure from antimicrobial use resulting in numerous patients carrying antimicrobial-resistant bacteria. Thus, most researchers and scientists presume that MRS is colonized frequently on the hands of hospital workers.²²⁾ However, our data showed that MRS is colonized frequently on the hands of both hospital workers and healthy individuals.

In MRSA, SCCmec types I, II, and III are found mainly in healthcare-associated strains, while types IV and V are found mainly in community-associated strains.²⁴⁾ Different from MRSA, SCCmec type IV is the most predominant in both healthcare- and community-associated strains of MRSE.⁶⁾ Similarly, SCCmec type IV was detected frequently in MRSE strains of both hospital workers and students in this study. The strains of community pharmacists and students showed equivalent detection rates of SCCmec types I and IV. These results show that the strains of community pharmacists are more similar to those of students than hospital workers. However, no relationship was found between the strains of community pharmacists and students by PFGE analysis. Additionally, no specific PFGE group was found in the strains of hospital workers and students. Therefore, the PFGE data suggest strongly that bacteria isolated from the hands of hospital workers and students in this study were normal inhabitants of each subject rather than transient bacteria obtained from hospitals and schools. Most strains of MRSE isolated from nasal cavities of both hospital workers and patients were classified into the sequence type (ST) 2 of multilocus sequence typing (MLST).^2,5,6) By contrast, the strains from healthy individuals showed more varied ST than those from hospital workers and patients, and did not have a specific ST. Further study is necessary to understand the origin of MRSE on the hands of each subject.

No significant difference was found in the detection rates of MRSE between hospital workers and students, although the antimicrobial susceptibilities were different. Resistance to fluoroquinolones, macrolides, and antiseptics in the strains of hospital workers was greater than that of community pharmacists and students. Supporting these results, the detection rates of macrolide resistance genes and antiseptic efflux pump genes in the strains of hospital workers were higher than those of community pharmacists and students. The higher resistance rate of gentamicin in the strains of nurses was caused by the greater presence of aacA–aphD. The ermA gene is located on transposon Tn554 and exists on the SCCmec element.²⁵⁾ The ermC gene is encoded by small multicopy plasmids.²⁶⁾ The msrA/B and mphC genes are encoded by large plasmids.^27,28) The aacA–aphD and qacA/B genes are located on the transposon and exist on the β-lactamase plasmids.²⁹⁾ Thus, these antimicrobial resistance determinants can transfer horizontally among staphylococci because they are located on mobile genetic elements.

As noted above, it is presumed that commensal bacteria on the hands of hospital workers acquired antimicrobial resistance determinants because of the widespread use of such drugs in hospitals. Because community pharmacists are less likely to come into contact with inpatients, it was expected that commensal bacteria on the hands of community pharmacists would show similar results to those of students. Supporting this prediction, no resistance determinants excluding mecA to the tested antimicrobials were found in 47.4 and 28.6% of the strains from community pharmacists and students, respectively. Overall, our data revealed that the antimicrobial resistance rates and levels in MRSE colonized on the hands of hospital workers were higher than those of healthy individuals despite the same detection rate of MRSE.

CONCLUSION

The worldwide prevalence of community-acquired MRSA was reported.³⁰⁾ Furthermore, surveillance for nasal cavity bacteria of healthy children in Japan found that the rate of MRS was 28.3%.³¹⁾ Therefore, it is presumed that dissemination of staphylococci carrying SCCmec in the community leads to colonization of MRSE on the hands of healthy individuals. There were several limitations of this study. The total number of subjects was not large enough to draw any definite conclusions. Further surveillance is needed to demonstrate exactly our data.

Acknowledgment

This work was financially supported by the Matching Fund Subsidy for the Private Schools of Japan.

Conflict of Interest

The authors declare no conflict of interest.

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