gms | German Medical Science

As a normal inhabitant of the body, Staphylococcus aureus is frequently found in the respiratory tract, nose, and skin. Approximately 20% to 60% of the healthy population are asymptomatic nasal carriers of S. aureus [1], [2]. However, nasal colonization of methicillin-resistant S. aureus (MRSA), whether transient or persistent, poses a hazard in nosocomial environments [3]. Complicated MRSA infections result in an additional burden for both patients and healthcare settings, due to prolonging the hospital stay and increasing the mortality rate [4], [5]. Staphylococcus epidermidis is prevalent in skin and mucosa microflora, and is also associated with nosocomial infections [6]. Immunocompromised and hospitalized patients with medical devices, such as catheters and medical implants, are in serious danger of S. epidermidis colonization [7], [8]. Thus, the incidence of S. epidermidis – particularly with a resistance profile – is a great concern on many hospital wards [9]. Healthcare workers may carry either MRSA or methicillin-resistant S. epidermidis in the nasal cavity, without manifesting disease. Since MRSA transmission generally occurs by direct physical contact, carriers with inadequate hygiene may inadvertently endanger hospitalized patients [10]. Moreover, self-infection of carriers and introduction of pathogens to colleagues and community are further consequences of carriage status [2]. Findings indicate that screening and identification of asymptomatic carriers is a key measure to reduce intra-hospital transmission and subsequent risks [4]. The aim of this study was to evaluate the prevalence of nasal mucosa colonization of MRSA and methicillin-resistant S. epidermidis (MRSE) among healthcare providers.

This cross-sectional study was conducted from June to November 2017 and December 2019 at Imam Reza University Teaching Hospital in Tabriz, Iran. The study was approved by the National ethics committee (registration number IR.TBZMED.VCR.REC.1398.401).

Healthcare workers voluntarily participated in the study, and written informed consent with individual variables was obtained from each participant. Volunteers who had received antibiotic treatment for the previous 10 days were excluded from the study. A total of 102 nasal swabs were collected from participants and inoculated into tryptic soy broth (TSB) medium (Merck, Germany), then transferred to the microbiology laboratory of Imam Reza Hospital. Samples were inoculated on blood agar containing 5% sheep blood and incubated at 35°C for 24 h. The isolates were identified by conventional microbiological methods such as gram-staining, catalase test, coagulase test, and DNase test.

Staphylococcus spp. isolates were examined for antibiotic susceptibility using a modified Kirby-Bauer disk diffusion method, according to Clinical and Laboratory Standard Institute (CLSI) guidelines [11]. The antibiotic disks (Mast, UK) used for susceptibility testing comprised penicillin G (10 units), vancomycin (30 µg), gentamicin (10 µg), amikacin (30 µg), ciprofloxacin (5 µg), clindamycin (2 µg), chloramphenicol (30 µg), linezolid (30 µg), cefoxitin (30 µg), novobiocin (30 µg), and erythromycin (15 µg) [12].

Isolates with a cefoxitin-resistant profile were further subjected to PCR assay to confirm the presence of the mecA gene. DNA extraction was performed using the tissue buffer boiling method [13]. The assay was conducted in 25 µL reaction mixture with the following thermal program: initial denaturation at 95°C for 6 min, followed by 35 cycles of denaturation at 95°C for 1 min, annealing at 52°C for 30 sec, extension at 72°C for 45 sec, and a final extension of 7 min at 72°C in a thermal cycler (BIO-RAD, T100^TM Thermal Cycler). S. aureus ATCC^® 49476^TM was used as the positive control. Primers (F-AAAATCGATGGTAAAGGTTGGC and R-AGTTCTGCAGTACCGGATTTGC) were used for mecA amplification.

A total of 102 healthcare workers were screened for Staphylococcus spp. nasal colonization, of which 78 (76.47%) were female and 26 (25.49%) were male. Participants’ age ranged from 20 to 48 years. Participants were classified by their position: physician, nurse, and paramedic from intensive care units (ICUs), surgical wards and infectious wards. Of the screened population, 22 (23.4%) samples were gram-positive, catalase-, coagulase-, and DNase-positive, which were classified as S. aureus; 72 (76.6%) were coagulase-negative and novobiocin susceptible, and identified as S. epidermidis. Neither gram-negative bacteria nor Enterococci were detected.

Inhibition zone diameter was interpreted according to CLSI guidelines. Isolates were classified as resistant (R), intermediate (I), and sensitive (S). All isolates were resistant to penicillin G, and sensitive to vancomycin and linezolid. Of 22 S. aureus isolates, 7 were cefoxitin resistant; of the 72 S. epidermidis isolates, 36 presented resistance to cefoxitin. The highest resistance was observed for clindamycin, with 74.46% being resistant and 3.19% intermediate. For the remaining antimicrobials, the resistance profile was as follows: cefoxitin, 56.38% R; erythromycin, 53.2% R, 8.51% I; ciprofloxacin, 26.6% R, 5.32% I; gentamicin, 21.27% R; amikacin, 10.63% R, 1.06% I; and chloramphenicol, 2.12% R, 1.06% I.

Of the 22 S. aureus isolates, 7 were cefoxitin resistant according to the disk diffusion method. Of these, 3 isolates were positive for the mecA gene, as shown by the PCR method (Figure 1[Fig. 1]). For S. epidermidis, PCR molecular test results were positive for 35 of the 36 cefoxitin-resistant isolates, and 35 isolates harbored the mecA gene (Figure 2[Fig. 2]).

Staphylococci account for almost 30% of nosocomial infections and 50% of nosocomial septicemia [14]. Hospital staff colonized with methicillin-resistant staphylococci are high risk groups for transmitting the agent to patients. In the present study, we attempted to evaluate the nasal carriage of staphylococci among healthcare workers. Our results indicate that 23.4% of the screened population was recognized as S. aureus carriers. This prevalence is comparable to previously conducted studies from various countries, 29% in the US [15], 19.1% in Spain [16], 22.6% in Egypt [14], and 27% in Iran [17]. Higher colonization rates were reported from Nigeria, Brazil, and Saudi Arabia with 32%, 40.8%, and 43.2%, respectively [18], [19], [20]. However, the overall carriage rate of MRSA was low in this study (2 out of 75 isolates), similar to the observations from Italy [21] and Saudi Arabia [22]. In contrast, another study from Iran reported the prevalence of MRSA nasal colonization to be 32% [17], considerably higher than that of our study. On the other hand, S. epidermidis was the predominant bacterium in this study (76.6%), similar to rates reported elsewhere. The methicillin-resistant gene distribution among S. epidermidis isolates was lower than in previous studies (49.12% vs. 70.1%, 87.1%, and 96.25%) [7], [9], [23]. Our data show that the overall resistance in S. epidermidis was considerably higher compared to S. aureus isolates. This supports Najar-Peeraye et al.’s speculation that methicillin-resistant coagulase-negative Staphyloccoci show higher resistance rates than does S. aureus [6].

Of the S. aureus isolates, 7 showed cefoxitin-resistant profiles in the disk-diffusion test; however, only two isolates were positive for the mecA gene. This finding is similar to previous observations and provides evidence for the greater efficacy of PCR [24].

Analysis of antibiotic susceptibility data reveals that all isolates were susceptible to vancomycin and linezolid, which is in accordance with previous findings [6], whereas all isolates were penicillin G resistant. In a study conducted by Sadeghi et al., similarly high resistance was observed to clindamycin and erythromycin [25]. We hypothesize that this could be due to elevated consumption of these antibiotics in our region. Since these antibiotics, particularly clindamycin, are alternatives for S. aureus infections, high resistance may be a problem in healthcare settings.

It is important to point out that these organisms, particularly S. epidermidis, have significant potential to act as a reservoir and horizontally transfer antimicrobial and virulence genes [26]. For instance, S. epidermidis is known as a putative reservoir of cefoxitin- and mupirocin-resistance genes [27]. Acquisition of resistance to ß-lactams, quinolones, aminoglycosides, and glycopeptides by S. aureus contributes to further dissemination of resistant isolates and increased burden of nosocomial infections [28], [29]. Results from Bloemendaal et al.’s [30] study strongly support horizontal interspecies gene transmission. In that study, the authors indicate that S. epidermidis transferred a resistance gene to S. aureus, resulting in MRSA [30].

Self-infection of carriers is the other issue of concern. Studies indicate a correlation of skin and soft tissue infections with S. aureus nasal carriage [31], [32]. On average, 80% of patients with skin wounds were also S. aureus nasal carriers, and 65% of S. aureus strains isolated from nose and lesion had same phage type [33]. Moreover, von Eiff el al. [34] reported that the incidence of bacteremia was significantly greater in S. aureus carriers, in which 80% of bacterimic strains were identical to S. aureus isolates from nurses.

Since hospital settings and community are linked environments, it is necessary to implement control strategies for antimicrobially resistant bacteria. Screening and decolonization of healthcare providers with nasal antiseptics could be an effective strategy for controlling the transmission of infectious agents and probable subsequent infections [33].

This study has possible limitations. Many staff members did not participate in sample collection because of pain involved in sample collection, and only staff that completed the consent form were tested in this study.

The present study indicates that health professionals are at high risk of acquisition and transmission of methicillin-resistant Staphylococci. Education on standard sanitation measures, especially hand hygiene practices, remains the most important factor in controlling the spread of MRSA. Early screening and identification of colonized healthcare workers may help reduce the transfer of resistance to sensitive strains and decrease the incidence of MRSA.

The authors declare that they have no competing interests.

This study was supported by Tabriz University of Medical Sciences with grant No. 64650. All participants volunteered to participate in this study and were from the staff of Imam Reza Hospital. The second set of samples were collected from the same of staff members as in the first set. We thank all staff of DARC for their collaboration.