Survival of Microorganisms on Inanimate Surfaces - Use of Biocidal Surfaces for Reduction of Healthcare Acquired Infections - page 16

Cytomegalie virus makes an exception, as it was more likely isolated from moist
surfaces [ 102 ].
Conversely to enveloped viruses, non-lipid enveloped viruses such as Adenovi-
rus, Enterovirus, and Rhinoviruses tend to survive longer at higher relative humid-
ity (70-90 % RH) [ 103 ]. For Rotavirus and Poliovirus conflicting results were
reported [ 64 , 65 ].
S. aureus can persist longer at low humidity [ 74 ]. However, for Enterococcus
faecalis the survival kinetic is decreased at 25 % RH compared to 0 % RH [ 97 ].
The survival of aerosolized Gram-negative bacteria including Pseudomonas
spp . , Enterobacter spp . and Klebsiella spp . improved at higher relative humidity
and low temperature [ 103 ]. Studies on airborne Gram-negative bacteria such as
S. marcescens , E. coli , Salmonella pullorum , Salmonella derby , and Proteus
vulgaris showed decreased survival at intermediate (approx. 50-70 % RH) to
high (approx. 70-90 % RH) relative humidity. For some airborne Gram-positive
bacteria, such as Staphylococcus epidermidis , Streptococcus haemolyticus , Bacillus
subtilis , and Streptococcus pneumoniae , their survival rate also decreased at inter-
mediate relative humidity ranging at 50-70 % RH [ 103 ]. Gram-positive cocci were
most prevalent in indoor air, followed by Gram-positive rods (e.g. Bacillus spp . and
Actinomycetes spp . ), Gram-negative rods and Gram-negative cocci [ 103 ]. The
reason for this bacterial behaviour is the design of bacterial cell wall, which allows
Gram-positive organisms to tolerate dry conditions better than Gram-negative
organisms. Because of a lipid double-layer structure with a thin peptidoglycan
(Murein) layer consisting of alternating residues of

-(1,4) N-acetylglucosamine
and N-acetylmuramic acid, the later are not so well protected against physical stress
and need higher RH in order to survive.

β

2.3.5.2 Temperature

The viral genome (viral DNA or RNA) is sensitive to the surrounding temperature.
Indeed, temperature is an important factor influencing the survival of a number of
viruses. 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
[ 64 , 65 ]. Constant temperatures

24 C appear universally to decrease airborne

>

bacterial survival [ 103 ].

2.3.5.3 Biofilm

Biofilm is the predominate form of life for microorganisms in a nutrient-sufficient
ecosystem. Adhesion triggers the expression of a sigma factor that depresses a large
number of genes so that bacteria within the biofilm are at least 500 times more