Methicillin resistant staphylococci (MRS) commonly found in clinical samples or associated environment pose a major health challenge globally. The carriage rate of MRS in human population is high, especially in India but research on airborne distribution of MRS is scanty. The present study aimed to evaluate the prevalence of MRS in indoor and outdoor environment of residential houses. Air samples were collected using impactor air sampler. The total counts of viable bacteria, staphylococci, and MRS along with the particles of various sizes were determined from indoor and outdoor environment of 14 residential houses. MRS bacteria were identified as methicillin resistant
Bioaerosols and particulate matter of indoor and outdoor environment have a direct effect on the human health [
Methicillin resistant staphylococci (MRS) including
In previous studies in India, carriage rate of MRS and involvement of MRSA in nosocomial infection was found higher than USA [
A total of 14 residential houses located in 7 different colonies (2 houses from each colony) were selected for indoor and outdoor bacterial aerosol sampling from Gwalior, Central India (longitude 78°13′E, latitude 26°13′N). Those houses were selected from the city that had no adverse health issues and the inhabitants were neither healthcare worker nor hospitalized within the past 1 year. Air samples for microbiological analysis were collected using Reuter Centrifugal Sampler (Biotest, Germany) at a height of 1.5 meters from the surface to simulate human breathing zone.
The head of air sampler was disinfected with alcohol swabs before each air sampling and the sampler was turned on for 2 min prior to sampling to allow the alcohol to evaporate. Sterile media strips containing microbial content test agar (MCA) supplemented with cycloheximide (100
Airborne particulate matter concentrations of six different sizes (aerodynamic diameter 0.3
Five representative colonies of mannitol fermenting and nonfermenting bacteria from MSA containing methicillin from each house (indoor and outdoor) were cultured on brain heart infusion (BHI) agar. Presumptive MRSA were further screened for coagulase and thermonuclease production. A part of colony was emulsified in normal saline then mixed with rabbit plasma; clumping indicated positive result [
The bacterial colonies were grown in LB broth for 18 h. One mL of broth was centrifuged and the pellet was processed for DNA extraction using genomic DNA extraction kit as per the manufacturer instructions (MBI Fermentas, Vilnius, Lithuania). The amount and purity of the DNA were measured by spectrophotometer (NanoDrop-1000, Australia). A multiplex PCR was performed as described elsewhere, using the primers targeting a
All the MRS isolates were subjected to antibiotic susceptibility testing by disc diffusion method according to Clinical Laboratory Standards Institute guidelines [
The statistical analysis was carried out using SigmaPlot 2000. Indoor and outdoor total bacterial count and staphylococcal and MRS count were compared using paired
The total bacterial concentrations inside the residential homes varied in the range of 5650 to 12425 CFU/m3 (
Bacterial concentrations from inside and outside of residential houses at Gwalior.
Total bacteria |
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Methicillin resistant |
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(CFU/m3) | (CFU/m3) | (CFU/m3) | |||||||
Indoor | Outdoor | In/out | Indoor | Outdoor | In/out | Indoor | Outdoor | In/out | |
House 1 | 7088 | 5875 | 1.2 | 2050 | 1075 | 1.9 | 825 | 181.25 | 4.55 |
House 2 | 6275 | 5913 | 1.06 | 1575 | 1038 | 1.52 | 193.75 | 163.25 | 1.17 |
House 3 | 5650 | 4025 | 1.4 | 1475 | 1150 | 1.28 | 356.25 | 131.25 | 2.71 |
House 4 | 6925 | 1768 | 3.92 | 1225 | 700 | 1.75 | 275 | 87.5 | 3.14 |
House 5 | 7775 | 10175 | 0.76 | 1975 | 1713 | 1.15 | 662.5 | 400 | 1.66 |
House 6 | 7438 | 3950 | 1.88 | 1313 | 1100 | 1.19 | 275 | 212.5 | 1.29 |
House 7 | 12425 | 11013 | 1.13 | 3213 | 2350 | 1.37 | 881.25 | 618.75 | 1.42 |
House 8 | 11950 | 8900 | 1.34 | 2925 | 2313 | 1.26 | 1175 | 806 | 1.46 |
House 9 | 11275 | 13350 | 0.84 | 3050 | 3600 | 0.85 | 475 | 525 | 0.9 |
House 10 | 7375 | 8625 | 0.86 | 2568 | 3050 | 0.84 | 462.5 | 400 | 1.16 |
House 11 | 7413 | 6938 | 1.06 | 2825 | 2813 | 1 | 237.5 | 262.5 | 0.9 |
House 12 | 8725 | 6775 | 1.29 | 3475 | 1375 | 2.53 | 162.5 | 212.5 | 0.76 |
House 13 | 7175 | 6325 | 1.13 | 2575 | 3050 | 0.84 | 462.5 | 394 | 1.17 |
House 14 | 10413 | 10075 | 1.03 | 4125 | 3712.5 | 1.11 | 312.5 | 187.5 | 1.66 |
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Average | 8421.5 ± 2184.5 | 7407.64 ± 3142.4 | 1.35 | 2454.92 ± 880.96 | 2074.25 ± 1037 | 1.18 | 495.68 ± 299.47 | 338.04 ± 208.01 | 1.71 |
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The average concentration of airborne MRS was significantly higher inside the residential houses than outdoor environment (Table
Under indoor conditions, a significant positive correlation of total bacteria was found with particle size of 10
Correlation between bacteria and particle size.
Correlation (Spearman |
Particle size (number/m3) | ||||||
---|---|---|---|---|---|---|---|
0.3 |
0.5 |
1 |
5 |
10 |
25 | ||
Indoor | Total bacteria | −0.2967 | 0.09451 | 0.2352 | 0.6 |
0.736 |
0.4664 |
Staphylococci | −0.2923 | 0.1516 | 0.244 | 0.4989 | 0.7319 |
0.5919 |
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MRS | −0.207 | −0.2885 | 0.3216 | 0.4912 | 0.5352 |
0.6891 |
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Outdoor | Total bacteria | −0.5297 | 0.2264 | 0.7363 |
0.8374 |
0.7934 |
0.644 |
Staphylococci | −0.4224 | 0.6008 |
0.7217 |
0.677 |
0.5985 |
0.33 | |
MRS | −0.4361 | 0.1718 | 0.5176 | 0.7753 |
0.8261 |
0.6542 |
The viable bacteria in air tend to aggregate and exist on large particles [
The presumptive MRS strains selected from methicillin containing MSA strips were found to be PCR positive for staphylococci specific 16S rDNA gene. Out of them, 94% strains were found positive for
Flow diagram for isolation of MRS bioaerosols from residential houses. (F) Multiplex PCR for the detection of
A total of 87.4% of
MRS infections, including MRSA, occur most frequently among persons in hospitals and healthcare facilities who are at high risk or have weakened immune systems. Now CA-MRSA (USA300) has started replacing traditional MRSA (healthcare associated) in hospitals on a large scale and become dangerous epidemic strain worldwide [
MRS are well known as nasal colonizer in normal community and the colonization of virulent MRSA is significantly high [
Thus, the study confirmed that airborne MRS are commonly present in indoor and outdoor environment of the residential houses. Their concentration is significantly higher inside the houses as compared to the outdoor environment. Molecular surveillance, antibiotic stewardship programme, and infection control policies can help to manage increasing MRS burden in developing countries.
The authors declare that there is no conflict of interests regarding the publication of this paper.
The authors thank Director, DRDE, Gwalior for providing necessary facilities and financial support for the work. P. Kumar thanks Council of Scientific & Industrial Research (CSIR), New Delhi, for providing Senior Research Fellowship.