Introduction
Staphylococcus aureus (S. aureus) is one of the most common bacteria causing nosocomial infection.1 Although Staphylococcus species is an asymptomatic colonizer but may causes skin and soft tissue infections, wound infections, ventilator-associated pneumonias, community-acquired pneumonia, necrotizing pneumonia, necrotizing fasciitis, and sepsis.2
Nasal carriage of Staphylococcus aureus among heathcare workers is becoming an alarming problem. In hospital environment, healthcare workers and asymptomatically colonized patients are the major source of MRSA. Carrier levels of 25% have been reported among healthcare workers(HCW’s).3
The increasing prevalence of methicillin resistance among Staphylococci is an emerging problem not because of resistance to methicillin but also resistance to macrolide-lincosamide-streptogramin B(MLSB) antibiotics. Clindamycin is preferred agent of MLSB but due to its extensive use, number of Staphylococcal strains resistance to this drug have been isolated.4, 5 Due to modification of target site mediated by erm genes; Constitutive or Inducible Resistance to Clindamycin in presence of Erythromycin have been found.6, 5 Clindamycin resistance among S. aureus isolates appears to be susceptible to clindamycin in the absence of erythromycin disk or when not placed at a recommended distance during routine antimicrobial susceptibility testing. In vivo treatment of such cases with clindamycin drug may select constitutive erm mutants resulting in no cure.
Materials and Methods
A cross-sectional prospective study was carried out in the Department of Microbiology, Government Medical College, Amritsar, Punjab for 11 months from January 2019 to November 2019. A total of 100 nursing staff, doctors and residents participated in the study. Nasal samples were collected by rotating sterile cotton swabs inside anterior nares of HCW’s. These nasal swabs were inoculated on Mannitol salt agar and blood agar and incubated at 37°C for 24 h. S. aureus was identified by standard microbiological procedures.7 Antimicrobial susceptibility testing was performed by the Kirby-Bauer disk diffusion method and interpreted as per the CLSI recommendations.8 The Antibiotics used in the study were Ampicillin(10µg), Gentamycin(10µg), Amikacin(30µg), Ciprofloxacin(5µg), Teicoplanin(30µg), Linezolid(30µg). All cultured plates were aerobically incubated at 37°C for 24 hours before the zone sizes were recorded. A disk diffusion method with cefoxitin (30µg) was used to detect Methicillin Resistant Staphylococcus Aureus strains.9 MRSA ATCC 43300 and MSSA ATCC 25923 were used as a control strains.8 Inducible clindamycin resitance was detected by D-test. Quality control was performed by S. aureus ATCC 25923.10
Results
Out of the 100 nasal swab samples examined, 46 were culture positive. Out of the 46 culture positive, 18 were found to be S. aureus.
18 S. aureus isolates were screened for the presence of Methicillin Resistance; 33.3% were found to be MRSA and 66.6% were MSSA as shown in Fig 1.
The results of antimicrobial susceptibility test of the S. aureus isolated from healthcare workers are given in Figure 2.
Both MRSA and MSSA showed maximum resistance to Ampicillin, Erythromycin Ciprofloxacin and Clindamycin. All the isolates show 100% susceptibility to Teicoplanin and Vancomycin.
Eighteen S. aureus isolates (6 MRSA and 12 MSSA) tested for ICR by D-test, 6 (33.33%) yielded inducible resistance. Inducible clindamycin resistance was found to be notably higher among MRSA than MSSA isolates.
Discussion
Determination of colonization prevalence provides a useful estimate of the potential for development of S. aureus infections.11, 12 In the present study, the prevalence of S. aureus nasal colonization among healthcare workers was 18% which is similar to the findings by Radhakrishna M et al(17.5%).13 These findings are also similar to study carried out in tertiary care hospital in Assam where prevalence was found to be 22.22%.14 However, study conducted in Gauhati Medical College, and in Burdwan Medical College nasal colonization was found to be 36% and 34.80% respectively.15, 16
Surveillance of HCW’s for MRSA carriage is essential specially in critical care areas as they pose a threat to infection control practices.17 Different studies have described a higher prevalence of MRSA colonization among persons of low socio-economic status in the general community, may be associated with crowding, limited access to healthcare, or barriers to maintaining adequate hygiene.18 The carriage rate of MRSA in present study was 6% which is similar to study carried out in Delhi by Goyal R et al (6.6%). Another study carried out in Rajajinagar, Banglore by Malini J et al, MRSA carriage rate was found to be 8%.19 A study from Nigeria by Fadeyi A et al reported 38.9% carriage rate.20
The overall prevalence ICR was 33.3%; with 66.6% of MRSA and 16.6% of MSSA. Similar study by Mahmoud AM et al found overall prevalence of ICR 29.4; with 43.5% of MRSA and 20.9% of MSSA.21 In contrast, Patel et al found the overall prevalence was 52%, with 50% of MRSA and 60% of MSSA isolates exhibiting ICR.4 These findings with our current results indicate the significant occurrence of ICR between MRSA and MSSA. Therefore, antimicrobial susceptibility data of ICR isolates should be evaluated routinely in each infection caused by S. aureus before starting the treatment.
Conclusion
Increasing incidence of MRSA and Inducible Clindamycin resistance among HCW’s is a cause of concern leaving few therapeutic options. Regular implementation of infection control practices, including screening of nasal carriages are necessary to prevent spread of MRSA. It is also advisable to perform routine nasal decolonization of healthcare workers using mupirocin ointment to prevent transmission of these organisms.
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