Date Published: April 10, 2017
Publisher: Springer Netherlands
Author(s): Anna Lenart-Boroń, Katarzyna Wolny-Koładka, Katarzyna Juraszek, Andrzej Kasprowicz.
Bacteria of the genus Staphylococcus were isolated from air sampled from living spaces in Kraków (Poland). In total, 55 strains belonging to the genus Staphylococcus were isolated from 45 sites, and 13 species of coagulase-negative staphylococci were identified. The species composition of studied airborne microbiota contains Staphylococcus species that are rarely infectious to humans. Most commonly isolated species comprised S. hominis and S. warneri. The disk-diffusion tests showed that the collected isolates were most frequently resistant to erythromycin. The PCR technique was employed to search for genes conferring the resistance in staphylococci to antibiotics from the group of macrolides, lincosamides and streptogramins. The analyzed Staphylococcus isolates possessed simultaneously 4 different resistance genes. The molecular analysis with the use of specific primers allowed to determine the most prevalent gene which is mphC, responsible for the resistance to macrolides and for the enzymatic inactivation of the drug by phosphotransferase. The second most often detected gene was msrA1, which confers the resistance of staphylococci to macrolides and is responsible for active pumping of antimicrobial particles out of bacterial cells.
Nowadays, people spend increasingly more time indoors but these places often do not meet the indoor air quality standards. Indoor environment is frequently conquered by pathogenic and drug-resistant microorganisms, hazardous to the health and life of residents (Górny and Dutkiewicz 2002). The major source of airborne microbiological contamination in living spaces is usually people emitting microorganisms during processes such as talking, coughing, sneezing and desquamation. Another important factor affecting the composition of airborne microflora is the process of microbial migration from the outdoor environment, which is of a particular importance during summer and autumn when buildings are naturally ventilated (Butarewicz 2005). Significant internal sources of bioaerosols include also pets, whose hair may constitute a factor of pathogen transmission (Jo and Kang 2006). Pathogenic microorganisms in flats may also dwell in surface linings and construction materials, such as wallpaper, insulating materials, plasterboards and many others. Microbiological air pollution is also favored by the increasing presence of air conditioners, fans and heating systems that are ideal place for dwelling, proliferation and subsequent spreading of microorganisms (Gąska-Jędruch and Dudzińska 2009).
Two species: S. hominis and S. warneri prevailed among collected isolates (Table 2). Staphylococcus aureus, which is potentially most dangerous pathogenic staphylococcal species, was absent in the studied material. A total of 55 strains of coagulase-negative Staphylococcus spp., belonging to 13 species, were isolated from the air of 45 randomly selected flats in Kraków.Table 2Share of individual staphylococci species in the isolated materialNoSpeciesNumber of isolates/percentage1S. hominis10/182S. warneri9/163S. cohnii subsp. cohnii7/134S. sciuri6/115S. haemolyticus4/86S. epidermidis3/57S. saprophyticus3/58S. xylosus3/59S. auricularis3/510S. capitis2/411S. lugdunensis2/412S. lentus2/413S. simulans1/2Total55/100
The results of our study indicate that most of airborne staphylococci isolated from the studied flats possibly poses no threat to their healthy residents. Nevertheless, the presence of potentially pathogenic strains—although in small numbers—can cause infections particularly in elderly, children and in immunocompromised people (Gąska-Jędruch and Dudzińska 2009). The most numerous species in the analyzed material was S. hominis (18%), which is usually isolated from human skin armpits, arms, legs and trunk. S. hominis usually does not cause serious infections in humans, but it is an opportunistic pathogen that can contribute to infections of hospitalized patients weakened by long-term pharmacological treatment (Jiang et al. 2012). On the other hand, studies conducted by Pastuszka et al. (2000) in flats of Upper Silesia (Poland) showed that the main bacterial species isolated from indoor air was S. epidermidis, which was present in 76% of studied flats constituting 14% of the total amount of bacteria. In our study, S. epidermidis isolates constituted only 5% of all Staphylococcus species. The second most frequently isolated species in the presented research was S. warneri (16%), which is a component of the human epithelium and mucous membrane microflora, but in some cases can be the cause of bacteriemia in long-term hospitalized patients (Campoccia et al. 2010). Another species among the identified staphylococci was S. cohnii subsp. cohnii (13%), which may cause pneumonia, acute cholecystitis, endocarditis, bacteriemia and urinary tract infections. S. cohnii subsp. cohnii is mostly isolated in hospitals (Hu et al. 2014). The last most frequently observed staphylococci were the species defined as the one resistant to novobiocin—S. sciuri (11%). It is regarded as a typical animal-related species, isolated from skin and mucous membranes, as well as from food products of animal origin. In humans, it can be present in nasopharynx, on skin and in urogenital system. Clinicians are increasingly interested in this species, as it has been recognized as one of the etiological factors of diseases such as endocarditis, peritonitis, septic shock, urinary tract infections and endophthalmitis (Dakić et al. 2005).
The group of analyzed airborne staphylococci isolated from flats in Kraków was dominated by S. hominis and S. warneri species. In this group, the resistance to erythromycin and tetracycline was most frequently detected; however, 31% of strains were susceptible to all tested antimicrobial agents including cefoxitin, ciprofloxacin, erythromycin, gentamycin, clindamycin, tetracycline and trimethoprim/sulfamethoxazole. A large variation was found in the prevalence and composition of antibiotic resistance-determining genes among the tested strains. The most common antibiotic resistance genes were mphC and msrA1, conferring the resistance to macrolides. The resulting antimicrobial resistance profile gives grounds to conclude that in the case of staphylococci infection, the use of antibiotics from basic antibiogram will be effective in therapy.