Characterization and Control of the Microbial Community Affiliated with Copper or Aluminum Heat Exchangers of HVAC Systems

Abstract

Microbial growth in heating ventilation and air-conditioning (HVAC) systems with the subsequent contamination of indoor air is of increasing concern. Microbes and the subsequent biofilms grow easily within heat exchangers. A comparative study where heat exchangers fabricated from antimicrobial copper were evaluated for their ability to limit microbial growth was conducted using a full-scale HVAC system under conditions of normal flow rates using single-pass outside air. Resident bacterial and fungal populations were quantitatively assessed by removing triplicate sets of coupons from each exchanger commencing the fourth week after their installation for the next 30 weeks. The intrinsic biofilm associated with each coupon was extracted and characterized using selective and differential media. The predominant organisms isolated from aluminum exchangers were species of Methylobacterium of which at least three colony morphologies and 11 distinct PFGE patterns we found; of the few bacteria isolated from the copper exchangers, the majority were species of Bacillus. The concentrations and type of bacteria recovered from the control, aluminum, exchangers were found to be dependent on the type of plating media used and were 11,411–47,257 CFU cm−2 per coupon surface. The concentration of fungi was found to average 378 CFU cm−2. Significantly lower concentrations of bacteria, 3 CFU cm−2, and fungi, 1 CFU cm−2, were recovered from copper exchangers regardless of the plating media used. Commonly used aluminum heat exchangers developed stable, mixed, bacterial/fungal biofilms in excess of 47,000 organisms per cm2 within 4 weeks of operation, whereas the antimicrobial properties of metallic copper were able to limit the microbial load affiliated with the copper heat exchangers to levels 99.97 % lower during the same time period.

Ecological succession of the microbial communities of an air-conditioning cooling coil in the tropics

“…Lastly, the time lapse used to investigate the coil succession might be short. However, previous studies have shown that biofilm does form over this time period on the same scale that we measured (Schmidt et al., ).…”

“…Water samples also contained Agaricomycetes (Fungi), but at a lower abundance (18% on average across all water samples), and the bacteria Sphingomonas (18.1%), Methylobacterium (5.3%), and Streptophyta (6.2%). Sphingomonas and Methylobacterium are ubiquitous in the environment and were previously found to be easily isolated from air‐conditioning systems (Hugenholtz and Fuerst, ; Schmidt et al., ; Simmons et al., ). Their prevalence and the variation in Agaricomycetes abundance were the main factors differentiating air from condensed water samples (SIMPER analysis).…”

Characterizing the bacterial communities in retail stores in the United States

“…If the four outlying sites with high Methylobacterium abundance are removed, the average relative abundance decreases to 6.8%. Methylobacterium is ubiquitous in nature (Gallego et al., ) and has been observed in biofilms on HVAC heat exchangers (Hugenholtz et al., ; Schmidt et al., ), residences (Martin et al., ) and even in the human eye (Dong et al., ). However, classification of the Methylobacterium sequences through the Ribosomal Database Project (Cole et al., ) indicates that the Methylobacterium detected in this study were actually Streptophyta (more specifically from a chloroplast 16S rRNA gene in the Cyanobacteria phylum).…”

Skin squames contribute to ammonia and volatile fatty acid production from bacteria colonizing in air-cooling units with odor complaints

“…Our findings imply that these methods did not work because they cannot stop the skin squama and the odor‐causing bacteria entering the units. Schmidt et al also reported the difficulty in completely inhibiting microbial growth even when using copper fins instead of aluminum fins in AC units. The 2 Staphylococcus spp.…”