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November
13, 2003
Scientific
Reponse from Medipharm USA
Nomenclature
and Classification of Living Things:
Swedish
botanist Carl von Linné was the first scientist to introduce
the scientific community to a binomial (two part) system
of identification of living organisms. In that system,
an organism is first given a genus identification, based
on physical attributes of the organism. In addition, a
species identification is also used to further group organisms
with similar characteristics. All living organisms have
thereafter been identified using this system. The binomial
identification for man is Homo sapiens , and cattle
are either Bos taurus or Bos indicus .
Both genus and species names are generally italicized.
What
is an antibiotic?
By
definition, the word antibiotic refers to a compound that
is anti- or against “bios”, or life. Commonly, antibiotics
are end-products of microbial fermentations that inhibit
the growth of other organisms. Penicillin and tetracycline
are examples of commonly used antibiotics.
Over
the span of the last two decades, the human medical community
has called for the decrease in the use of antibiotics, both
in human and veterinary medicines. Antibiotics have been
used in animal production agriculture, because of the increased
production returned from usage of these compounds. Dollars
spent on these compounds often improve the profitability
of producing livestock.
As
pressure from the scientific community to discontinue feeding
antibiotics to livestock has increased, one of the alternatives
to using antibiotics in livestock production has been the
introduction of probiotics.
What
is a probiotic?
Bacterial
species that promote “a healthy intestinal tract microbial
population” have received the designation of probiotic bacteria.
Certain bacteria of a non-pathogenic nature have been
found to have the ability to colonize the G.I. tract and
actually support the wellness of the host. Lactobacillus
acidophilus is the most familiar example of a probiotic.
When antibiotic therapy or a case of enteritis reduces
the normal microfloral populations in the gut, a culture
of Lactobacillus acidophilus is often fed to help
replace the missing lactic acid producing-bacteria of the
digestive tract.
There
are more than forty microorganisms recognized by AAFCO (Association
of American Feed Control Officials) as beneficial bacteria.
As a crude analogy, AAFCO can be viewed as a type of “Supreme
Court of the Feed Industry”. Feed ingredients not recognized
by AAFCO are not allowed in animal feedstuffs. Through scientific
feeding trials, production benefits have been demonstrated
when these cultures have been used without the inclusion
of feed-grade antibiotics. In addition, documents substantiating
the safety of these cultures have been submitted to the
Center of Veterinary Medicine , a branch of the Food and
Drug Administration. These cultures have thus had federal
review, and have been found “to present no safety concerns
when used as direct-fed microbial products,” as described
in official publication of AAFCO.
What
exactly is Enterococcus faecium ?
For
reasons described above, bacteria are identified by genus
and species. For example, Escherichia coli is
a familiar example of the typical organism nomenclature
given to all living things. However, identification often
goes beyond the genus and species levels. When it comes
to bacteria, even within a genus and species, there can
be consistent genetic differences that make one E. coli
different from another. When there are sufficient
genetic differences that consistently characterize an organism
within the same genus and species, a strain designation
can be assigned. Many non-pathogenic (non-disease causing)
strains of E. coli are desirable inhabitants of
the gastrointestinal tract. Examples of non-pathogenic
strains of E. coli include strains JM101, JM109,
DH5, and HB101. However, there are pathogenic (disease-causing)
strains of E. coli that can cause infections in
humans and animals. The more common pathogens in livestock
include the familiar strain designations K88, K99, 987P,
and the notorious O157:H7 strain in humans and animals.
These are the ones you hear the most about and it’s important
to remember that strain designations are not unique
strictly to pathogenic bacteria. Non-pathogenic
bacteria also have strain designations.
Enterococcus
faecium is a species of bacteria that has been characterized
as part of the normal gastrointestinal microbial flora in
domestic livestock and humans. It is a naturally
occurring bacterium that grows in human and animal intestinal
contents, period. They have been colonizing G.I.
tracts of most living creatures for years and they’re here
to stay. And there’s no way to “make them go away”.
Depending on the composition of a human diet or an animal
ration, up to 100 million (1 x 10 8 ) colony forming units
(CFU), or live bacteria, have been isolated per
gram of fecal material Huycke et al, 1998).
Thus, it naturally constitutes a major population in the
gut. Bacteria are essential in the gastrointestinal tract.
Although enzymes are excreted by humans and animals to
digest foods and feedstuffs, a considerable portion of consumed
dietary ingredients are broken down by the action of intestinal
microflora (bacteria).
What
is Enterococcus faecium strain M74?
Enterococcus
faecium strain M74 is a proprietary strain of probiotic
bacteria initially patented and marketed by Medipharm, a
Swedish company. This particular strain of Enterococcus
faecium was isolated from the intestinal tract of
a healthy human infant. It had unique characteristics
that made it an ideal candidate for a probiotic culture.
As more research dollars were invested, Medipharm was
able to learn about the genetic stability and antibiotic
susceptibility of their strain of Enterococcus faecium
. M74 has been registered with NCIMB (National Collection
of Industrial, Food and Marine Bacteria) in Aberdeen , UK
since 1988, a bacterial collection bank with more than 8,500
bacterial strains in their possession. The NCIMB number
for Enterococcus faecium strain M74 is 11181.
Enterococcus
faecium strain M74 has been studied extensively.
The strain has excellent genetic stability, as demonstrated
by a report from the Department of Microbiology at Lund
University , Lund , Sweden . In 1996, Dr. Sten Stahl published
a report comparing a sample of Enterococcus faecium
strain M74 harvested in 1982 and a sample that had
been subcultivated 40 times and freeze-dried 20 times over
the course of nearly 10 years. Dr. Stahl reported to Medipharm
that the plasmid profiles of the two cultures were still
identical after all the subculturings of M74. Thus, no
plasmids capable of transferring antibiotic resistance have
crept into the genome of M74.
What
makes M74 such a unique strain of Enterococcus faecium
can be demonstrated by reviewing its antibiotic susceptibility
profile. Many strains of Enterococcus faecium
are resistant to the typical beta-lactam antibiotics; penicillin
and ampicillin ( Murray , 1998). However, Enterococcus
faecium strain M74 has been shown to be susceptible
to these clinically relevant antibiotics. One can appreciate
the benefits of documenting strain identification within
a genus and species of bacteria. There are genetic reasons
for the unique strain assignment and it’s the genetics that
dictate antibiotic susceptibility as well as resistance.
Work done by Dr. Gerhard Reuter, Freie University , Berlin
, Germany demonstrated that M74 was also shown to be susceptible
to other clinically relevant antibiotics. It was sensitive
to gentamicin, chloramphenicol, a combination of sulfonamides
and trimethoprim, ciprofloxacin, and tetracycline. It
has also shown susceptibility to all the major glycopeptide
antibiotics, including avoparcin, teicoplanin, and vancomycin.
Dr. Reuter clearly demonstrated that Enterococcus
faecium strain M74 did not produce the VanA 39kDal
marker protein, a marker for vancomycin resistance. For
feed-grade antibiotics, Enterococcus
faecium strain M74 was susceptible to tylosin, salinomycin,
flavomycin, and virginiamycin. Because the organism is
classified as a member of Enterococcus , it was
found to be resistant to oxacillin, chephalotin, clindamycin,
and rifampin, characteristics that are expected for bacteria
in that genus. It should be noted that rifampin is not
clinically relevant in human and veterinary medicine.
Lastly,
Dr. Reuter conducted a study using different strains of
Enterococcus faecium . In this study, he looked
at the ability of several strains to transfer vancomycin
resistance by assessing successful conjugation rates when
compared to control strains of Enterococcus faecium
. Conjugation can be viewed as “bacterial mating”,
or partial transfer of DNA from one cell to another. When
Enterococcus faecium strain M74 was tested in
a conjugation-rate study (determination of the number of
bacteria that successfully conjugated or transferred genetic
material with a known vancomycin-resistant donor strain),
M74 had the lowest conjugation rate of all strains of Enterococcus
faecium that were tested! For the vancomycin-susceptible,
rifampin-resistant international control strain, Enterococcus
faecium strain 64/3, the conjugation rate was greater
than 2 x 10 -4 . An easier way to think of it, out of
2 x 10 4 (20,000) colony forming units, one cell successfully
acquired the antibiotic resistance. When M74 was tested,
the successful conjugation rate was 5.5 x 10 -7 . In simpler
language, out of 55 million (5.5 x 10 7 ) CFU, only one
cell successfully conjugated with the antibiotic-resistant
strain, a more than 1,000-fold difference.
Is
the feeding of Enterococcus faecium safe for animals?
To
date, there have been no well-documented and characterized
cases of disease
attributed
to E. faecium infection in animals (Devries
and Pot, 1995). In fact, there are numerous studies published
in the scientific literature that demonstrate effectiveness
when Enterococcus faecium probiotic cultures are
fed to livestock. In one particular calf study, calves
were fed a negative control diet (no probiotics or growth-promoting
levels of antibiotics), a diet containing a culture of Enterococcus
faecium strain M74, or a diet containing the familiar
growth-promoting antibiotic zinc bacitracin (Burgstaller
et al, 1983). Results from the study clearly demonstrated
that both the probiotic culture of E. faecium strain
M74 and the zinc bacitracin diets performed equally well,
and both treatments significantly out-performed the performance
of the negative control diet. In light of these results,
might not the probiotic culture accomplish the same result
on the natural intestinal microflora as low-level feed antibiotics,
shifting microbial population that favor enhanced performance,
only without inducing antibiotic resistance? These cultures
are delivering what the medical community has requested
of the animal feeding industry; cost-effective performance
without the use of antibiotics.
In
another study with dogs, feeding a culture of E. faecium
statistically significantly increased the serum titres
(levels of circulating antibodies) to antigens contained
in common dog vaccines, when compared to controls that were
not feed the E. faecium probiotic culture (Benyacoub
et al, 2003). In dairy cattle, feeding live yeast and
two strains of Enterococcus faecium to fresh cows
increased dry matter intake, milk yield, and milk protein
content as compared to negative control cows (Nocek, et
al, 2003). There are countless other studies showing the
benefits of feeding probiotic cultures of E. faecium
to livestock, all without incident. These products
increase feed costs when fed to livestock. Thus, in order
to justify their use, economics dictate that the return
for their use must exceed their input cost. Probiotic
cultures of E. faecium are doing just that.
Furthermore, Enterococcus faecium strain M74 has
been reviewed by the European Union and has been granted
the status of an approved, safe probiotic. The EU requires
considerable documentation in order to approve new feed
additive probiotic cultures. Enterococcus faecium
strain M74 has achieved that status.
And
what about humans?
Enterococcus
faecium strain M74 and other strains have been used
as a human probiotic for more than 25 years. More recently,
Sarantinopoulus et al (2002) published a paper describing
the benefits of using Enterococcus faecium strains
as adjunct cultures in the making of Feta cheese for human
consumption. Leroy et al (2003) studied the effects of
adding a strain of Enterococcus faecium that was
a natural isolate from cheese as a co-culture for the production
of Cheddar cheese. This bacterium was used because of
its ability to inhibit the growth of Listeria monocytogenes
, an extremely important food-borne pathogen. Hugas
et al (2003) reported that species of enterococci were used
in processed meat fermentations for years. “Despite the
concern about pathogenicity of enterococci, recent studies
point out that food and meat enterococci, especially Enterococcus
faecium , have a much lower pathogenicity potential
than clinical strains.” The authors stressed the benefits
of the control of Listeria monocytogenes in sliced,
vacuum-packed cooked meat products when Enterococcus
faecium strains were used. There are countless other
papers in the literature supporting the use of Enterococcus
faecium probiotics in humans. Carefully selected
and researched strains of Enterococcus faecium
are safe and effective probiotics.
Devries
and Pot reported in 1995 that Enterococcus faecium
had received recent attention in the scientific literature.
Increasing reports had surfaced describing an increase
in the incidence of nosocomial infections in humans due
to some strains of Enterococcus faecium that have
become resistant to the antibiotic vancomycin. By definition,
nosocomial infections are those infections “obtained while
admitted to a hospital”. But again, these infections
have only been identified in long-term antibiotic therapeutic
situations and in patients hospitalized with debilitating
disease. Since that time, the medical community has designated
these types of infections as VRE or vancomycin-resistant
enterococcal infections.
What
causes VRE and how serious are they?
There
is still much to learn about vancomycin-resistant enterococcal
VRE infections. However, recent publications have “painted
an accurate picture” of the current thinking by medical
professionals world-wide. Huycke et al (1998) published
a paper in Emerging Infectious Diseases, a bimonthly, peer-reviewed
scientific journal published by the National Center for
Infectious Diseases (NCID), a division of the US
Center for Disease Control (CDC).
In that paper, the authors reported that two species of
Enterococcus are the primary causes of VRE in
humans. Enterococcus faecalis is implicated in
80 % of all VRE and Enterococcus faecium in the
remaining 20 %. In addition, although the exact transfer
mechanisms in hospital outbreaks are not known, there is
epidemiological evidence to suggest that spread of the organisms
between patients is probably via the hands of health-care
personnel or via medical devices.
The
authors continue by saying that prior to VRE diagnosis,
patients with VRE were initially treated with antibiotics
such as cephalosporins, clindamycin, ciprofloxacin, aminoglycosides,
and metronidazole. In fact, these antibiotics are thought
to be equally, if not more responsible, for VRE than use
of vancomycin. The major risk factors were also characterized
by Huycke et al. Patients undergoing prolonged hospitalization,
or having a high illness score, intraabdominal surgery,
renal insufficiency, feeding tubes, or exposure to certain
hospital locations, nurses, or contaminated objects and
surfaces, could increase the incidence of VRE. The authors
also stated that antibiotic induced alterations
in the normal intestinal microflora may set the stage for
intestinal colonization of the gut with VRE by simply removing
normal gut bacteria that would normally exclude potential
pathogens.
Rice
(2001) also published a paper in Emerging Infectious Diseases.
His data indicated that 95 % of all US VRE were attributed
to ampicillin- and vancomycin-resistant Enterococcus
faecium . Rice admitted that although Enterococcus
faecium VRE had a higher incidence in the US, these
infections were less pathogenic than VRE caused by Enterococcus
faecalis . “In fact, many VRE ( Enterococcus
faecium ) infections resolve without antimicrobial-drug
therapy.” He did comment that VRE were more serious
in patients with prolonged hospital stays, liver transplants,
exposure to intensive care units, exposure to antibiotics,
and hematologic malignancies. Several other articles in
the scientific literature corroborate these findings.
Lipsitch
and Samore (2002) stated that “antimicrobial use and patient-to-patient
transmission are not independent pathways for promoting
of antimicrobial resistance, rather they are inextricably
linked.” The problems associated with VRE are iatrogenic
(doctor induced). It becomes a serious “Catch 22”. The
medical community wants to take every precaution in successfully
treating patients in their care. However, the indiscriminant
use of antibiotics and inadequate control measures are creating
serious health problems in hospitals.
Weinstein
(2001) summed it up best. The medical community has an
understanding of the causes of VRE. The author states,
“ Antimicrobial-drug resistance in hospitals is
driven by the failures of hospital hygiene, selective pressures
created by overuse of antibiotics, and mobile genetic elements
that can encode bacterial resistance mechanisms .”
McDonald et al (1997) reported that glycopeptide antibiotic
(i.e. vancomycin or teicoplanin) usage for three weeks in
duration caused an increase in fecal shedding of VRE in
normal, healthy individuals. Again, this supports the
hypothesis that the exposure to these antibiotics is what
induces the formation of antibiotic-resistant species and
not genetic mutation. Peterson and Noskin (2001) compared
data on nosocomial infections 24 months prior and 60 months
after instituting an in-house molecular typing of bacterial
isolates protocol (bacteria identification) in conjunction
with an infection control program. The authors reported
a 23 % decrease in nosocomial infections after this plan
had been instituted. Northwestern Memorial Hospital in
Chicago , as of 2001, had a nosocomial infection rate that
was 43 % below the national average.
Spontaneous
mutations in bacterial genetic material can occur. However,
they are relatively rare, and mutants that do survive are
thought to be destroyed by natural host resistance mechanisms.
But, when a patient is treated extensively with antibiotics,
resistant mutants can actually colonize a patient, taking
advantage of their ability to compete over nonresistant
strains that were susceptible to the antibiotic. Carmelli
et al (2002) stated that given the complex genetic “gymnastics”
that are required to initiate vancomycin resistance, the
spontaneous appearance of resistance in an individual is
unlikely.
VRE
typically appear in hospitalized patients as a consequence
of long-term critical care and antibiotic therapy. Vancomycin-Resistant
Enterococci (VRE) have not been found as normal fecal microflora
of humans in the United States ( Murray , 1998). Therefore,
this is not a disease that spontaneously erupts like the
common cold, spreading and infecting the masses across the
US . It’s limited to hospital settings. The author goes
on to state that “ recent data suggest that these
antimicrobial resistances may not be inherent in the microorganisms,
but acquired after exposure to antibiotics. ”
Dr.
Barbara Murray at the Baylor College of Medicine has been
intensely studying VRE infections in humans. In fact,
she has isolated a strain of VRE and the organism she is
researching is Enterococcus faecium strain DO
and is also referred to in other publications as strain
TX0016 and TEX16. She posts information on a website;
http://hgsc.bcm.tmc.edu/microbial/efaecium/. The strain
she has isolated would be considered a pathogenic strain
of Enterococcus faecium . Because there could
be meaningful insights gained from determining the genetic
sequence of this pathogen, the US Department of Energy’s
Joint Genome Institute has advertised it completed the sequencing
in one day. Dr. Murray can now use the information to
research ways of controlling other vancomycin-resistant
enterococci.
Wegener
et al (1999) and others have reported the existence of a
reservoir population of VRE in the intestinal tracts of
healthy humans throughout Europe . In spite of this community-wide
distribution, the incidence of VRE infections in hospitals
in Europe have increased at a lower rate than cases in the
US . The authors related that despite the fact that the
healthy European community carries VRE in their intestinal
tracts, the VRE problem in Europe has not grown to the same
proportion as infections in the US. Wegener et al speculate
that this is probably because of the heavy use of antibiotics
in hospitals and the spread of VRE by carrier hospital personnel.
VRE infections may be extremely serious and even life-threatening.
However, an understanding of how they originate helps
hospital personnel find ways to manage and minimize the
occurrences these outbreaks.
Can
humans contract VRE from animals?
Wegener
et al (1999) addressed this very question. In the EU,
the glycopeptide/growth promotant avoparcin was approved
for administration to swine and poultry. Based at the
Danish Veterinary Laboratory in Copenhagen , Wegener et
al studied the incidence of VRE in these food-producing
animals. When swine herds or poultry flocks were fed avoparcin,
colonies of VRE were identified in fecal samples from those
livestock. When these species of animals were sampled
in countries not feeding the glycopeptide antibiotic, VRE
were not isolated from fecal samples. The researchers
go on to say that colonization of humans by VRE has generated
a community pool of VRE within the healthy human population
in some countries in Europe . VRE were hypothesized to
originate from food animals fed avoparcin, based on the
inability to find VRE in vegetarians.
Starting
in 1986, Sweden banned the use of all antimicrobial growth
promotants in livestock. However, it wasn’t until 1995 that
other EU countries took similar action. Denmark banned
avoparcin in 1995 and by 1997, all EU countries followed
suit. In Germany , after the ban of avoparcin, the incidence
of VRE in poultry and the human community was drastically
reduced. Poultry samples decreased in the incidence of
VRE from 100 % in 1994 to 25 % by 1997. The human VRE-positive
population dropped from 13 % in 1994 to 3 % in 1997. Thus,
a VRE reservoir can be practically managed by
refraining
from adding antibiotics to livestock feeds.
The
US never approved the use of avoparcin in livestock, due
to the carcinogenic effects of the additive. Thus, one
would not expect a resident VRE population in livestock
within the US . In 1997, the FDA instituted a ban on the
use of vancomycin in veterinary medicine, further preventing
glycopeptides from inducing VRE in food and companion animals.
Therefore, the likelihood of humans contracting spontaneous-erupting
VRE from animals is unlikely.
For
more information, the National Center
for Infectious Diseases (NCID), a division
of the US Center for
Disease Control (CDC) , sponsors a publication
entitled Emerging Infectious Diseases. This journal is
a bimonthly, peer-reviewed scientific journal. Articles
are available for public scrutiny at their website; www.cdc.gov/ncidod/diseases/eid/index.htm
. By using the search engine for past articles, most
of the references listed below are available for your review.
Summary
and Conclusions:
1.
Enterococcus faecium is a normal G.I. tract bacterium
that constitutes an integral part of the intestinal microflora
for most living creatures, including man. It cannot be
removed from the environment and will continue to be a portion
of the intestinal microflora for years to come.
2.
As the world community continues to demand that animal
food products are produced with no antibiotics whenever
possible, probiotics are going to play an increasingly greater
role in the future.
3.
Carefully selected and researched strains of Enterococcus
faecium are well-documented as safe and effective
probiotics. They have been proven safe and effective in
humans and livestock and have been recognized as such in
the European Union, the United States , by the FDA, and
in other countries as well.
4.
Although certain clinically challenging strains of Enterococcus
faecium have been identified, their existence has
been attributed to indiscriminate use of antibiotics in
humans and animals, and such strains often turn into outbreaks,
spreading rapidly when proper hospital sanitation procedures
are lacking.
5.
The medical community has supported the use of beneficial
probiotic cultures in humans. Despite the literature citations
listed here, no authors in the volumes of research papers
describing this problem have ever mentioned that these pathogenic
strains of Enterococcus faecium were associated
with the feeding of E. faecium as a probiotic,
nor have they called for the prohibition of probiotic
use.
References:
Benyacoub,
J., G.L. Czarnecki-Maulden, C. Cavadini, T. Sauthier, R.E.
Anderson, E.J.
Schiffrin, and T. von der Weid. 2003. Journal of Nutrition.
133:1158-1162.
Burgstaller,
G., R. Ferstl, and W. Peschke. 1983. The use of Lactiferm
in the fattening
performance
of calves. Medipharm Dossier to the EU for approval of
Enterococcus faecium strain M74 in fattening calves.
Approved December, 1999.
Carmelli,
Y., G.M. Eliopoulus, andM.H. Samore. 2002. Antecedent
treatment with
different antibiotic agents as a risk factor for vancomycin-resistant
Enterococcus .
Emerging Infectious Diseases. 8:(#8). August, 2002.
Devries,
L.A. , and B. Pot. 1995. The genus Enterococcus
. In The Genera of Lactic Acid
Bacteria, Vol. 2 (eds Wood, B.J.B., and W.H. Holzapfel).
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Professional, London , UK , pp. 327-367.
Hugas,
M., M. Garriga, and M.T. Aymerich. Functionality of enterococci
in meat
products. International Journal of Food Microbiology.
88:223-233.
Huycke,
M.M, D.F. Sahm, and M.S. Gilmore. 1998. Multiple-drug
resistant
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the future. Emerging
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Leroy,
F., M.R. Foulique Moreno, and L. De Vuyst. 2003. Enterococcus
faecium RZS
C5,
an interesting bacteriocin producer to be used as a co-culture
in food
fermentation.
International Journal of Food Microbiology. 88:235-40.
Lipsitch,
M., and M.H. Samore. 2002. Antimicrobial use and antimicrobial
resistance: a
population perspective. Emerging Infectious Diseases.
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McDonald,
L.C., M. J. Kuehnert, F.C. Tenover, and W.R. Jarvis. Vancomycin-resistant
enterococci outside the health-care setting: prevalence,
sources, and public health
implications. Emerging Infectious Diseases. 3:311-317.
Murray,
B.E. 1998. Diversity among multidrug-resistant enterococci.
Emerging
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Nocek,
J.E., W.P. Kautz, J.A. Leedle, and E. Block. 2003. Direct-fed
microbial
supplementation on the performance of dairy cattle during
the transition period.
Journal
of Dairy Science. 86:331-335.
Peterson,
L.R., and G.A. Noskin. 2001. New technology for detecting
multidrug
resistant pathogens in the clinical microbiology laboratory.
Emerging Infectious
Diseases. 7:306-311.
Rice,
L.B. 2001. Emergence of vancomycin-resistant enterococci.
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Conference on
Nosocomial
and Health-Care Associated Infections, March, 2000, Atlanta
, GA.
Sarantinopoulos,
P., G. Kalantzopoulos, and F. Tsakalidou. 2002. Effect
of
Enterococcus faecium on microbiological,
physiochemical and sensory
characteristics of Greek Feta cheese. International Journal
of Microbiology. 76:93-105.
Wegener,
H.C., F.M. Aarestrup, L.B. Jensen, A.M. Hammerum, and F.
Bager. 1999.
Use
of antimicrobial growth promoters in food animals and Enterococcus
faecium
resistance
to therapeutic antimicrobial drugs in Europe . Emerging
Infectious
Diseases.
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Weinstein,
R.A. 2001. Controlling antimicrobial resistance in hospitals:
infection
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