Survival of Microorganisms on Inanimate Surfaces - Use of Biocidal Surfaces for Reduction of Healthcare Acquired Infections - page 17

tolerable against antimicrobial agents [ 23 ] as well as against physical cold plasma
[ 71 , 72 ]. The reason for the unspecific increased tolerance is the production of
extracellular substances like polysaccharides, proteins and DNA after attachment to
surfaces. A precondition for biofilm formation is the presence of certain amounts of
humidity. The biofilm matrix restrains water and nutrients and protects the micro-
organisms against environmental influences [ 28 , 39 ]. Because of that, once formed
biofilms are an important factor of persistence of microorganisms on surfaces in
nature as well as in industrial or medical areas [ 22 , 29 , 12 ]. The persistence on
inanimate surfaces is prolonged and depends of the environmental conditions,
especially the humidity. Also on hospital surfaces biofilms were demonstrated on
a number of objects and surfaces, such as sterile supply buckets, opaque plastic
doors, venetian blind cords, and sink rubbers, and it was possible to cultivate viable
bacteria. Currently, there is not enough research to elucidate whether presence or
absence of biofilm affect the risk of transmission or possibility for cross-
transmission. However, multi-drug resistant bacteria may not only be protected
within biofilms, which may be the mechanism why they persist within the hospital
environment [ 114 ], but may also exchange virulence factors among their own
species or to other species present in biofilms as well [ 29 , 43 , 109 ].
2.3.5.4 Other Factors
A number of other factors may influence the survival of microorganisms on
surfaces. Clearly, the material character of a surface itself may play in important
role. However, inconsistent results are reported for the influence of type of mate-
rials on microbial survival. Some authors described that the type of material did not
affect the persistence of Echovirus, Adenovirus, Para-Influenza virus, Rotavirus,
Respiratory syncytial virus, Poliovirus, or Norovirus. Other investigators found that
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 [ 64 , 65 ]. Other factors for a longer persistence of viruses include the
presence of faecal suspension and a higher bio-inoculum [ 66 , 64 , 65 ]. Interestingly
and by nature, Urease activity enhances the survival of Haemophilus influenzae at a
reduced pH [ 77 ].
2.3.6 Limitations on the Knowledge of Microbial Survival
on Inanimate Surfaces
Laboratory studies to determine the survival and persistence do not reflect the
clinical situation, in which surfaces can be simultaneously contaminated with
various nosocomial pathogens, different types of bodily and other fluids, secretions,