Microorganisms have been found to remain viable in inanimate surfaces from days to even years (1). The longer a microorganism persists on a surface, the longer the contaminated surface may be a source of transmission and thus endanger a susceptible patient or healthcare worker of becoming the target of infection.

The two main environmental factors that influence how long microorganisms can survive on inanimate surfaces are relative humidity (RH) and  temperature.

By Y tambe - Y tambe's file, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=9999296
Gram positive cocci (violet) and Gram negative rods (pink)

The influence of these two factors on the viability of the microorganisms varies singnificantly and this is especially noted for bacterial organisms depending if they are Gram-positive or Gram-negative.

S. aureus, for example, can persist longer at low humidity (2), while Enterococcus faecalis survival decreased at 25% RH compared to 0% RH (3). The survival of Gram-negative bacteria including Pseudomonas spp., Enterobacter spp. and Klebsiella spp. is higher at higher relative humidity and low temperature (4). Constant temperatures > 24°C appear universally to decrease airborne bacterial survival (4).

The reason for the difference in bacterial behavior is the difference in the bacterial cell wall, which allows Gram-positive organisms to tolerate dry conditions better than Gram-negative organisms.

 

Environmental survival of bacteria is not affected by antibiotic resistance status, as there is no observable difference in survival between multi-resistant and susceptible strains of bacteria (5).

In addition many bacteria in the presence of low humidity can form biofilms that restrain water and nutrients and protects the microorganisms against environmental harsh influences (6, 7). Once formed, biofilms are an important factor of persistence of microorganisms on inanimate surfaces.

Sand Biofilm 4

Fungi and viruses can also be influenced by  relative humidity and environmental temperature, but it is worth noting that viruses, as a whole, are very sensitive to  environmental humidity. Viruses with lipid envelops, such as most respiratory viruses including Influenza virus, Para-Influenza virus, Corona virus, Respiratory syncytial virus, Herpes simplex virus, Measles virus, Rubella virus, and Varicella zoster virus, will tend to survive longer at lower relative humidity (20–30% RH). Conversely to enveloped viruses, non-lipid enveloped viruses such as Adenovirus, Enterovirus, and Rhinoviruses tend to survive longer at higher relative humidity (70–90% RH) (8).

Viruses are also significantly affected by the environmental temperature, as the viral genome (viral DNA or RNA) is sensitive to the surrounding temperature. Higher temperatures impact viral proteins and enzymes, as well as the viral genome. In general, DNA viruses are more stable than RNA viruses; yet, high temperature also will affect DNA integrity. For most viruses, such as Astrovirus, Adenovirus, Poliovirus, Herpes simplex virus, and Hepatitis A virus, low temperature is associated with a longer persistence (1).

Inconsistent results are reported for the influence of type of materials, especially for viral survival. For example, while some authors reported that the type of material did not affect the persistence of Echovirus, Adenovirus, Para-Influenza virus, Rotavirus, Respiratory syncytial virus, Poliovirus, or Norovirus, others investigators found that virus persistence was favoured on non-porous surfaces for Influenza virus on formica and gloves for Respiratory syncytial virus, and on hand pieces of telephones for Feline calicivirus (1).

A number of other factors may influence the survival of microorganisms on surfaces. Clearly, the material character of a surface itself, the surface’s faecal or other biological contamination, and the bio-inoculum will all impact the survival time of the microorganisms ( 8,1).

References cited in this article

  1. Kramer A, Schwebke I, Kampf G. How long do nosocomial pathogens persist on inanimate surfaces? A systematic review. BMC Infect Dis 2006;6:130-7.
  2. McDade JJ,   Hall LB. Survival of Staphylococcus aureus in the environment. II. Effect of elevated temperature on surface-exposed staphylococci. Am J Hyg 1964;80:184-91
  3. Robine E, Derangere D, Robin D. Survival of a Pseudomonas fluorescens and Enterococcus faecalis aerosol on inert surfaces. Int J Food Microbiol 2000;55:229-34
  4. Tang JW. The effect of environmental parameters on the survival of airborne infectious agents. Interface 2009;6 (Suppl 6):S737-S74
  5. Neely AN, Maley MP. Survival of enterococci and staphylococci on hospital fabric and plas-tic. J Clin Microbiol 2000;38:724-6
  6. Donlan RM. Biofilms: microbial life on surfaces. Emerg Inf Dis 2002;8:881–90.
  7. Flemming HC, Wingender J. The biofilm matrix. Nature rev 2010; 8(9): 623–33
  8. Lai MYY, Cheng PKC, Lim WWL. Survival of severe acute respiratory syndrome Corona-virus. Clin Infs Dis 2005;41:e67–71;

 

Image references

Gram’s stain organisms-By Y tambe – Y tambe’s file

Gram positive vs Gram negative cell well-MicrobeWiki

Biofilm Image-Anthony D’Onofrio