75 research outputs found
Characterization and Control of the Microbial Community Affiliated with Copper or Aluminum Heat Exchangers of HVAC Systems
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 30Â 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 11,411â47,257Â CFUÂ cmâ2Â per coupon surface. The concentration of fungi was found to average 378Â CFUÂ cmâ2. Significantly lower concentrations of bacteria, 3Â CFUÂ cmâ2, and fungi, 1Â CFUÂ cmâ2, 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 cm2Â within 4Â 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 99.97Â % lower during the same time period
Shaping the growth behaviour of biofilms initiated from bacterial aggregates
Bacterial biofilms are usually assumed to originate from individual cells
deposited on a surface. However, many biofilm-forming bacteria tend to
aggregate in the planktonic phase so that it is possible that many natural and
infectious biofilms originate wholly or partially from pre-formed cell
aggregates. Here, we use agent-based computer simulations to investigate the
role of pre-formed aggregates in biofilm development. Focusing on the initial
shape the aggregate forms on the surface, we find that the degree of spreading
of an aggregate on a surface can play an important role in determining its
eventual fate during biofilm development. Specifically, initially spread
aggregates perform better when competition with surrounding unaggregated
bacterial cells is low, while initially rounded aggregates perform better when
competition with surrounding unaggregated cells is high. These contrasting
outcomes are governed by a trade-off between aggregate surface area and height.
Our results provide new insight into biofilm formation and development, and
reveal new factors that may be at play in the social evolution of biofilm
communities
- âŠ