Evaluation of Methods for Sampling of Staphylococcus aureus and Other Staphylococcus Species from Indoor Surfaces

Abstract

Objectives Methicillin-resistant Staphylococcus aureus (MRSA) is an increasing public and occupational health concern. As transmission of MRSA can occur via contact with fomites, it is crucial to have sensitive methods for sampling of bacteria. The overall aim of this study was to obtain knowledge about methods and strategies for quantitative sampling Staphylococcus species on surfaces. Methods The study was designed as a comparative sampling experiment with different samplers [dipslide (two agar types), swabs (three brands, used wet and dry, and elution from swabs or plate diluted)] on smooth stainless steel surfaces spiked with MRSA and methicillin-sensitive S. aureus (MSSA). Furthermore, bacteria sampled from indoor surfaces with frequent or infrequent contact with hands were quantified and identified using matrix-assisted laser desorption-ionization time-of-flight (MALDI-TOF) mass spectrometry (MS). Results Pre-moistened swabs in combination with dilution plating and dipslides were more sensitive than dry swabs. For recovery of MRSA and MSSA from surfaces with eSwabs, at least 0.3–100 CFU MRSA cm−2 and 5.3–8.6 CFU MSSA cm−2 should be present. The sensitivities of pre-moistened eSwabs were approximately 10-fold higher than those of dipslides and pre-moistened viscose and cotton swabs. The variation in concentrations of Staphylococcus species in replicate sampling of adjacent squares on indoor surfaces was higher for surfaces frequently touched by hands than for surfaces infrequently touched. In total 16 different Staphylococcus species were identified, and S. aureus was found only in 2 of 66 surface samples. A considerable overlap was found between species in replicate sampling within an environment and between the air and surfaces within an environment. Conclusions Pre-moistened eSwabs in combination with dilution plating were found to be the best method for surface sampling of MSSA and MRSA. The method can be used for assessing the risk of exposure and transmission of MRSA from environmental surfaces. To obtain a reliable measure of concentrations and the presence of Staphylococccus species a higher number of samples should be taken from surfaces with hand contact than from surfaces dominated by sedimented bacteria.

Airborne bacterial species in indoor air and association with physical factors

“…Many of the found species have previously been found in quite different environments. The bacteria found in high concentrations, P. yeei, B. megatarium, and M. luteus, have previously been found on indoor surfaces (32,33), but also as airborne bacteria in totally other environments such as wastewater treatment plants (34), pigeon coops (35), and on workers' clothes (36). We have found many different Bacillus species and a high species richness of Bacillus has also been found in air samples from different occupational settings (35,37) as well as on indoor surfaces (32).…”

“…The bacteria found in high concentrations, P. yeei, B. megatarium, and M. luteus, have previously been found on indoor surfaces (32,33), but also as airborne bacteria in totally other environments such as wastewater treatment plants (34), pigeon coops (35), and on workers' clothes (36). We have found many different Bacillus species and a high species richness of Bacillus has also been found in air samples from different occupational settings (35,37) as well as on indoor surfaces (32). When considering the bacteria at the genus level the genera Kocuria, Micrococcus, Bacillus, and Paenibacillus were among the dominating, and these genera were also dominating in indoor air in Hong Kong and China (reviewed in (20)).…”

Airborne bacterial species in indoor air and association with physical factors

“…Many of the found species have previously been found in quite different environments. The bacteria found in high concentrations, P. yeei, B. megatarium, and M. luteus, have previously been found on indoor surfaces 33,34 , but also as airborne bacteria in totally other environments such as wastewater treatment plants 35 , pigeon coops 36 , and on workers' clothes 37 . We have found many different Bacillus species, and a high species richness of Bacillus has also been found in air samples from different occupational settings 36,38 as well as on indoor surfaces 33 .…”

“…The bacteria found in high concentrations, P. yeei, B. megatarium, and M. luteus, have previously been found on indoor surfaces 33,34 , but also as airborne bacteria in totally other environments such as wastewater treatment plants 35 , pigeon coops 36 , and on workers' clothes 37 . We have found many different Bacillus species, and a high species richness of Bacillus has also been found in air samples from different occupational settings 36,38 as well as on indoor surfaces 33 . When considering the bacteria at the genus level the genera Kocuria, Micrococcus, Bacillus, and Paenibacillus were among the dominating, and these genera were also dominating in indoor air in Hong Kong and China (reviewed in 20 ).…”

Review of pork and pork products as a source for transmission of methicillin-resistant Staphylococcus aureus

“…In general, S. aureus can survive on stainless steel surfaces, possibly leading to recontamination in the long term. In experimental studies, S. aureus at contamination levels of 5 log CFU/100 cm 2 -7 log CFU/100 cm 2 was detected on dry stainless steel surfaces for at least 96 h. Even at a low contamination level of 3 log CFU/100 cm 2 , S. aureus can still be found within 48 h [70]. In a study in Colombia, Gutierrez et al [71] found MRSA in three pork processing facilities and two institutional kitchens.…”