Table of Contents  
Year : 2016  |  Volume : 9  |  Issue : 4  |  Page : 479-483  

Methicillin and mupirocin resistance in nasal colonizers coagulase-negative Staphylococcus among health care workers

1 Department of Microbiology, Mayo Institute of Medical Sciences, Barabanki, Uttar Pradesh, India
2 Department of Microbiology, Hind Institute of Medical Sciences, Barabanki, Uttar Pradesh, India
3 Department of Physiology, Mayo Institute of Medical Sciences, Barabanki, Uttar Pradesh, India

Date of Web Publication12-Jul-2016

Correspondence Address:
Loveleena Agarwal
Department of Microbiology, Mayo Institute of Medical Sciences, Barabanki, Uttar Pradesh
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/0975-2870.186070

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Objective: Coagulase-negative Staphylococcus (CoNS) is a harmless commensal flora of human body but may cause infections related to medical device implant, blood stream infections, and infections of newborns. Health care workers (HCWs) colonizing methicillin-resistant CoNS (MRCoNS) may help in transmission of the microorganism and thus leads to the development of infection. The purpose of this study was to determine the prevalence of methicillin and mupirocin resistance in CoNS as nasal colonizer among HCWs and its antimicrobial susceptibility pattern.
Materials and Methods: Nasal swabs collected from 210 HCWs of various categories such as doctor, nurse, nursing student, nursing orderlies, technician, and others working in the hospital were taken in equal representation. Methicillin resistance among the CoNS isolates was identified using cefoxitin 30 μg disc. Antimicrobial susceptibility profile of the isolates was also determined for several antibiotics. Mupirocin resistance was determined by epsilometer test using E-strip.
Results: Of 210 nonduplicate nasal swabs collected from HCWs, 69 (32.8%) CoNS, and 16 (7.6%) MRCoNS isolates were obtained. A higher carrier rate of CoNS was found among nursing students (53%) with 50% MRCoNS as compared to other categories of HCWs. MRCoNS strains were significantly associated (P < 0.05) with resistance to most of the antibiotics with 100% resistance to penicillin and a higher resistance to rifampin (88%), clindamycin (69%), septran (63%), and erythromycin (56%). All CoNS isolates were uniformly susceptible to linezolid. Mupirocin resistance detected using E-strip showed 3 (1.4%) MRCoNS isolates had high-level resistance.
Conclusion: MRCoNS showed a significant association of resistance to other antibiotics, thus methicillin and mupirocin resistance in CoNS must be detected in HCWs as a routine protocol of hospital infection control policy to limit nosocomial infections.

Keywords: Coagulase-negative Staphylococcus, methicillin-resistant coagulase-negative Staphylococcus, mupirocin-resistant coagulase-negative Staphylococcus

How to cite this article:
Agarwal L, Singh AK, Agarwal A, Agarwal A. Methicillin and mupirocin resistance in nasal colonizers coagulase-negative Staphylococcus among health care workers. Med J DY Patil Univ 2016;9:479-83

How to cite this URL:
Agarwal L, Singh AK, Agarwal A, Agarwal A. Methicillin and mupirocin resistance in nasal colonizers coagulase-negative Staphylococcus among health care workers. Med J DY Patil Univ [serial online] 2016 [cited 2023 Sep 30];9:479-83. Available from:

  Introduction Top

Coagulase-negative Staphylococcus (CoNS) until recently was considered as a harmless commensal flora of human body but now is emerging as an important cause of nosocomial as well as community acquired infections. CoNS is the leading cause of medical implant device-related infections, nosocomial blood-stream infections, and account substantially for infections in the preterm and low-birth-weight newborns.[1],[2],[3],[4] It is also associated with native valve endocarditis, mediastinitis, postcataract endophthalmitis, and keratitis.[5],[6],[7],[8] The incidence of infections caused by this group of organisms is mostly under-reported because of the difficulty in identifying its pathogenic role; even by using molecular techniques, colonization, and infection cannot be differentiated.[9]

Host susceptibility is important in determining infection by CoNS as the bacteria possess a few virulence factors. The major risk factors associated with CoNS infections are prolonged hospitalization, exposure to invasive medical procedure, foreign bodies in place, and immunocompromised status of the patients.[10],[11]

Besides, various virulence factors as biofilm formation, methicillin resistance has contributed to the emergence of CoNS as a common cause of nosocomial infections.[12] Methicillin resistance in CoNS may not only lead to treatment failure but also spread this resistance to Staphylococcus aureus which may pose a challenge to clinicians.

Indiscriminate use of mupirocin, a topical antibiotic that is used for eradication of staphylococcal nasal colonization to prevent healthcare-associated methicillin-resistant staphylococcal infections has already led to the emergence of its resistance. CoNS on nasal mucosal surfaces, when exposed to repeated or prolonged treatment with mupirocin ointment, may become a reservoir of high-level resistance determinants and then pass on this resistance to S. aureus. The genetic transfer events are most likely to occur at anatomical sites colonized by both CoNS and coagulase positive staphylococci such as the normal nasal mucosa.[13]

Health care workers (HCWs) who come in contact with the patients directly or indirectly are prone to colonization while working in the hospital may become reservoir or victims of drug-resistant hospital strains, and when they come in contact with the patients they spread the bacteria to the patients they take care of. Nasal carriage among HCWs is the most important source of nosocomial infections by Staphylococcus.[14] Numerous studies have been done on nasal carriage of S. aureus and MRSA among HCWs but studies on nasal carriage of CoNS in HCWs are few. Thus, this study was undertaken to determine the nasal carriage of methicillin and mupirocin-resistant CoNS among HCWs, and its antimicrobial susceptibility pattern.

  Materials and Methods Top

Two hundred and ten HCWs of various categories such as doctor, nurse, nursing student, nursing orderlies, technician, and others (including pharmacists, receptionists, and security guards) working in Mayo Institute of Medical Sciences, Barabanki, Uttar Pradesh taken in equal representation were included in the study. Nonduplicate nasal swabs were collected from HCWs except those who were on antibiotics within last 1 week or hospitalized within the previous 1 year. Epidemiological data were collected and recorded at the time of nasal swabs collection by interviewing the participants. Approval from the Institutional Ethical Committee was taken before the start of the study. All participants gave written informed consent before specimen collection.

For sample collection, sterile cotton swab with transport tube was used. Swab was inserted approximately 2 cm into the nares, rotated against the anterior nasal mucosa for 3 s and using the same swab repeated for other nares. Swabs were then labeled and transported to the microbiology laboratory in the transport tube where they were cultured on 5% sheep blood agar and mannitol salt agar. The plates were then incubated for 18-24 h at 37°C, and on the basis of colony morphology, Gram-stain, catalase, dimethyl sulfoxide oxidase, and coagulase tests isolates were identified as CoNS.

Methicillin resistance was detected using cefoxitin 30 µg disc while performing antibiotic susceptibility testing (Hi-Media Labs, India), and a zone of inhibition of size <21 mm was considered as resistant. In vitro antibiotic susceptibility test was done by Kirby–Bauer disc diffusion method and various antibiotic discs used were penicillin (10 units), ciprofloxacin (5 µg), clindamycin (2 µg), erythromycin (15 µg), levofloxacin (5 µg), linezolid (30 µg), rifampin (5 µg), tetracycline (30 µg), and co-trimoxazole (1.25/23.75 µg). S. aureus ATCC 29213 was used as the reference strain for the standardization of antibiotic susceptibility testing. Diameters of the zone of inhibition were measured, and interpretation for determining sensitive, intermediate, or resistant was done according to standard CLSI guidelines.[15]

Resistance to mupirocin was determined by epsilometer test using HiComb mupirocin E-strip performed similar to antimicrobial susceptibility test. Minimum inhibitory concentrations >512 μg/ml were considered as high-level mupirocin-resistant (MuH), whereas 8-256 μg/ml were considered as low-level mupirocin-resistant.

  Results Top

Of 210 nonduplicate nasal swabs collected from HCWs, 69 (32.8%) CoNS isolates were obtained. Antibiotic susceptibility test of these isolates using cefoxitin 30 µg disc showed that 16 (7.6%) isolates were methicillin-resistant CoNS (MRCoNS). The distribution of CoNS, methicillin sensitive CoNS (MSCoNS), and MRCoNS isolates among HCWs on the basis of the source is documented in [Table 1]. A higher carrier rate of CoNS was found among nursing students (53%) with 50% MRCoNS as compared to other categories of HCWs.
Table 1: Distribution of isolates on the basis of source

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Antibiotic susceptibility pattern of MRCoNS and MSCoNS strains to various antibiotics primarily effective against Gram-positive organisms is depicted in [Table 2]. MRCoNS strains were significantly associated (P< 0.05) with resistance to most of the antibiotics with 100% resistance to penicillin, and a higher resistance to rifampin (88%), clindamycin (69%), co-trimoxazole (63%), and erythromycin (56%). All CoNS isolates were uniformly susceptible to linezolid.
Table 2: Antibiotic resistance pattern of methicillin-sensitive coagulates negative Staphylococcus and methicillin-resistant coagulates negative Staphylococcus isolates

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Mupirocin resistance detected using E-strip showed 3 (1.4%) MRCoNS isolates were resistant to the drug. All the mupirocin-resistant isolates fell in the category of MuH. All these MuH strains were isolated from the nursing students. None of the MSCoNS isolates were found to be mupirocin-resistant.

  Discussion Top

Advancement in medical sciences with development and the use of medical implants and devices has prolonged the human life span on one hand. While, on the other hand, it led CoNS, commensal bacteria to become one of the major cause of nosocomial infections, and an important etiological agent of serious life-threatening infections of blood stream, central nervous system shunts prosthetic joints, and preterm babies. HCWs play a key role in the epidemiology and pathogenesis of nosocomial infections by harboring the resistant strains of bacteria which may spread in the hospitals.

In our study, nasal carriage of CoNS among HCWs was found to be 32.8% which is much less as compared to that reported by Kaur and Narayan (52.14%)[16] and Akhtar (73.3%)[17] but comparable to that found by Al-Abdli and Baiu (36.4%)[18] and Kumar et al. (39.3%).[19]

CoNS have a remarkable tendency to accumulate antibiotic resistance determinants such as to penicillin, clindamycin, macrolide, tetracycline, and methicillin and, more recently, mupirocin (MUP), and vancomycin. This leads to the formation of multidrug-resistant strains which reduce the options for the treatment of infections caused by such organisms. Methicillin resistance was found among 7.6% CoNS isolates which are higher as reported by Akhtar (2.1%)[17] and much lower than 18-60% reported elsewhere.[20],[21] Only 1.4% isolates in this study were resistant to mupirocin and in other studies conducted in India, Mupirocin-resistant CoNS (MupRCoNS) was found to be 16% and 10.3% elsewhere in the world.[22],[23] Differences in the prevalence of CoNS, MRCoNS, and MupRCoNS can be attributed to the variation in the methodology of detection used in the laboratories, knowledge, practices, and policies of the institution.

Authors of different studies across the globe have used different antibiotics to determine the antibiotic susceptibility pattern of CoNS and found that MRCoNS were multidrug-resistant and recommend performing antibiotic sensitivity test before treatment of infections caused by these species. In this study, MRCoNS is significantly associated with resistance to other antibiotics such as penicillin, rifampin, clindamycin, septran erythromycin, and ciprofloxacin. Rahman et al.[24] studied the CoNS clinical isolates and found in decreasing order the percentage of isolates resistant to oxacillin (45%), followed by gentamicin (40%), cefuroxime (31%), ceftriaxone (30%), ciprofloxacin (22%), and none resistant to imipenem and vancomycin and Shah et al.[25] found >50% of the clinical CoNS isolates were resistant to cephalosporins, aminoglycosides, quinolones, and no organisms resistant to vancomycin.

Higher carriage rate for CoNS, MRCoNS, and MupRCoNS seen in nursing students and housekeeping staff may be partially explained by long hours spent in the hospital on the day-to-day basis, direct patient contact, and partially be related to their personal hygiene.

  Conclusion Top

This study showed a significant number of CoNS and MRCoNS associated with the HCWs which may transmit the microorganisms to the coworkers and the patients leading to development of infections. As MRCoNS showed a higher resistance to other antibiotics, methicillin and mupirocin resistance in CoNS must be detected in HCWs as routine protocol of hospital infection control policy to limit nosocomial infection. It is also advisable to perform routine nasal decolonization of the HCWs using mupirocin ointment to prevent the transmission of microorganisms which may lead to infections. In case of development of mupirocin resistance, other decolonization options should be considered.

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Conflicts of interest

There are no conflicts of interest.

  References Top

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