1. No category

Hospital ecology of bacteria
Åsa Melhus
Dept. of Medical Sciences/Section
of Clinical Bacteriology
Uppsala University
Preantibiotic era (billions of years)
•
•
•
•
Diversification in natural ecosystems
Duplications, mutations
Mutation frequency 10-5-10-9
In an infectious focus there are 105bacterial cells
• Strategy behind combined treatments
– Mutation frequency for drug 1 = 10-7
– Mutation frequency for drug 2 = 10-7
– Total mutation frequency = 10-14
Preantibiotic thinking
Selective pressure
Changes due to the antibiotie era (70 år)
• Horisontal transfer
What is the point in combining now?
Production of antibiotics an evolutionary
experiment and an dead-end?
• A major part of the current antibiotics
drugs (Abs) are derived from
Streptomyces spp.
• The production is initiated by signal
substances (lactones) that take part in
quorom sensing (QS) systems, appears
late (stationary phase)
• QS regulates: metabolism, virulence,
physiology, competence, motility,
symbiosis, etc.
Aminov RI. Environment Microbiol 2009;11:2970-88
Cont.
• Relatively few species produce antibiotic
substances, but several have receptors for
these signal substances, including
humans (tetracyclines, macrolides,
ketolides, quinolones)
• The function of Ab resistance can be to
attenuate the signal intensity – negative
feedback of QS
• Many Ab drugs aim for the protein
synthesis, the most expensive activity a
cell has. Save energy during tough times?
Inhibition of quorom sensing in a
P.aeruginosa isolate with a macrolide
Biofilm
Bacteria are relatively resistant to antibiotics,
disinfectants, chemicals and attacks from other
microorganisms in the biofilm form
When the bacteria produce biofilms, they
produce slime/extra-cellular matrix
Pseudomonas aeruginosa
During the first and the last phases we are
able to attack the bacteria with antibiotics
Pre-operative measures (washing the skin repeatedly and
antibiotic profylaxis) are there to prevent the initiation
Stink trap from a sink
Outbreaks involving sinks
• Karlskrona: Several patients over several
years at an intensive care unit (ICU). At
least 2 sinks contaminated, caused
infections with VIM-producing P.aeruginosa. Clear mortality.
• Uppsala: 4 patients at an ICU. 1 sink
contami-nated, caused infections with
ESBL-producing K.pneumoniae
• Kristiansand: 7 patients at an ICU. 2
sinks? Caused infec-tions with KPCproducing K.pneumoniae
Findings in ICU sinks at
Uppsala University Hospital
Unit
Species
Number of isolates
NEO
P.aeruginosa
8
Citrobacter sp.
7
K.pneumoniae
1
S.maltophilia
4
Other non-fermenters
8
P.aeruginosa
5
S.maltophilia
6
M.morganii
2
E.cloacae
2
Citrobacter sp.
1
P.aeruginosa
11
S.maltophilia
1
K.pneumoniae
1
M.morganii
2
Citrobacter sp.
1
Other non-fermenters
1
Non-fermenters
1
BRIVA
CIVA
CF-center
Resistant isolates in the sink
• P.aeruginosa: ciprofloxacin >
piperacillin/tazobactam > ceftazidime
• S.maltophilia: co-trimaxoazole R
• Enterobacteriaceae: ESBL-producers (1
also resistant to tobramycin, ciprofloxacin,
co-trimoxazole), derepressed AmpC
mutants
The hormesis concept
Subinhibitory concentrations of:
- tobramycin increases the biofilm production in P.aeruginosa, E.coli
- beta-lactams increases the production of adhesins + the transfer of
plasmids up to 1,000 times in S.aureus
Martinez JL et al. A global view of antibiotic resistance. FEMS Microbiol Rev 2009;33:44-65.
Resistance and virulence can be coselected
Example of bacteria with coselection
• E.coli ST131 with CTX-M-14/-15
• EHEC with ESBL-production
• MRSA with PVL
• Hospital-acquired coagulase-negative
staphylococci
• The predominating VRE clones
• C.difficile ribotypes 027, 078
Enterococci
• Low-virulent bacteria, favored by a high
consumption of cefalosporines, quinolones
• VRE have caused hospital outbreaks worldwide
• vanA has crossed genus boundaries to
methicillin-resistant S.aureus
• E. faecium (complex-17) that has spread
globally. Characterized by
–
–
–
–
ampicillin resistance,
a pathogenicity island
an association with hospital outbreaks
Complex-17 is an example of cumulative evolutionary
processes that improved the relative fitness of
bacteria in hospital environments.
The importance of the cell wall
structure
• Gram-positive
– Easy to kill with disinfectants
– Withstands desiccation quite well – can
survive for months in the hospital
environment. Enterococci can be found
almost anywhere
• Gram-negative
– More difficult to kill with disinfectants
– Needs humitidy for environmental survival,
exception Acinetobacter
Cell walls
Spores have the ultimate cell wall
Produced mainly by Bacillus, Clostridium spp.
Relative resistant to heat, radiation, chemicals,
enzymes, antibiotics
Consists of a chromosome, a minimum of essential proteins, ribosomes and a
high concentration of calcium.
Wall structure: inner membrane, 2 peptidoglycan layers, outer membrane,
keratin-like protein capsule.
C.difficile
• C. difficile now rivals MRSA as the most
common organism to cause HAIs in the
US
• Attributable mortality of CDI is 5%–10%,
leading to an estimated 14,000–20,000
deaths in the US each year alone.
Trelleborg
• There have been numerous reports of an
increase in infection severity
• Most reports have been associated with
the BI/NAP1/027 strain
Cont.
• BI/NAP1/027 strain produces
– more toxin A and B
– more spores
– a third toxin (binary toxin)
– highly resistant to fluoroquinolones.
• A strain commonly found in animals,
ribotype 078 is similar to 027, has a higher
14-day mortality in UK than 027
Extremely often the toilet lid is not closed
Problematic bacteria in the
hospital environment
• Enterobacteriaceae family
• Pseudomonas aeruginosa
• Acinetobacter
• MRSA
• VRE
• Clostridium difficile