The incidence of antibiotic resistant bacteria in industrial and residential air
Few studies have been undertaken to assess microbial air quality in South Africa. At present not enough is known about the state of microbial air quality in the North-West Province. Past efforts to collect information on provincial air quality have been scattered, random and incomplete. However, the activities in the province provide a good indication of the potential pollutants and air quality. An international study noted a possible link between air pollution and bacterial resistance to antimicrobial chemicals. This prompted further investigation and in particular this present study. The aim of this study was to determine the diversity and levels of antibiotic resistant bacteria in the atmosphere of industrial and residential areas in Potchefstroom and to determine whether these isolates were also resistant to generally used biocides. Five sampling sites in Potchefstroom were selected based on their distance from the industrial area and general wind direction. The sites comprised of (i) highly populated residential areas, (ii) a newly developed residential area, and (iii) industrial sites. Two of the highly populated residential areas were located next to hospitals. Two other sites in different towns were included in sampling to serve as controls. One site was situated in an area (Vereeniging) known for high levels of air pollution and the other site was located in a rural area (Tzaneen). Samples were collected directly onto nutrient agar plates supplemented with either ampicillin or kanamycin. In general, it was determined that 96% of all isolates were resistant to at least 2 antibiotics, and certain isolates were resistant to as many as 10 antibiotics. The MAR index for isolates was highest for Site 1-Bult (0.55), Site 4-Miederpark (0.54) and Site V-Vereeniging (0.54). The lowest MAR indices were for Site Tz-Tzaneen (0.2) and Site 5-Mohadin (0.27). The percentage of biocide resistant isolates was generally higher in samples of industrial origin. Cluster diagrams based on inhibition zone diameter were constructed. The purpose was to establish whether there were isolates from different sites with similar antimicrobial exposure histories. Two clusters were present in the resultant dendrograms. Even though both contained isolates from industrial and residential air, one cluster contained a greater proportion of isolates from industrial air as well as residential samples that were potentially under influence of industrial air. The MICs of Zn, Cu, Cd and Hg was determined for selected isolates. It was observed that isolates that were resistant to a large number of diverse antibiotics and biocides had high MIC values for various metals. Forty five percent of all isolates were able to haemolyse sheep red blood red cells, thus exhibiting potential pathogenic properties. The largest number of pathogens were isolated from Site 4-Miederpark. Selected isolates were identified by sequencing of 16s DNA fragments and Blast searches. These isolates were identified (98-100% certainty) as various Bacillus species (including Bacillus cereus, Bacillus subtilis, Bacillus clausii), Pseudomonas, Xanthomonas, Brevibacillus and Cellulosimicrobium. The methods used in this study proved valuable tools in the isolation and identification of antimicrobial resistant bacteria and possible identification of sources of antimicrobial chemicals. It is however advised that the running of this type of project be over a period of no less than two years as seasonal fluctuations may influence results.