Bacchi RR(1)et al. • The most common bacteria that cause hospital infections today
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ARTIGO DE REVISÃO / ARTÍCULO DE REVISIÓN / Review
The most common bacteria that cause hospital
infections today
As principais bactérias causadoras de infecção hospitalar na atualidade
Ricardo Rodrigues Bacchi1
Camila Pollyana de Souza Sampaio 2
Juana Darc Mendes Barbosa Maynart2
Isabella Mota Dias2
Leonardo Tadeu Souza Costa2
Marta Pollyanna 2
Rev Panam Infectol. 2014;16(4):226-230
http: www.revistaapi.com
Received 22 August 2013
ABSTRACT
This is a literature review that aims to analyze the main bacteria
that cause hospital infections as well as the most frequent types of
infections, mechanisms of resistance of bacteria and its prevention,
as hospital infection is seen as a worrying factor for having high
rates of mortality and is considered a public health problem. A good
knowledge of epidemiology is a facilitator to control such infections,
making it clear that knowledge is one of the greatest forms of
prevention. Therefore, knowledge of epidemiology and the exercise
of the hospital infection control are important issues that are in the
process of change.
Keywords: Cross infection; Resistance; Antigens, Bacterial
Accepted 6 December 2014
RESUMO
¹Graduação em Ciências Biológicas - Modalidade
Médica pelo Centro Universitária Barão de Mauá.
Mestrado em Avaliação das Atividades Físicas e
Desportivas pela Universidade de Trás-os-Montes e Alto
Douro - Portugal. Especialista em Bioquímica Médica
pelo Centro Universitário Barão de Mauá. Professor
efetivo da Universidade Estadual de Montes Claros
(UNIMONTES). Professor/tutor do curso de medicina
das Faculdades Unidas do Norte de Minas (FUNORTE),
Montes Claros, MG, Brasil.
²Graduados em Biomedicina – Bacharelado –
especialização em Análises Clínicas pelas Faculdades
Unidas do Norte de Minas – FUNORTE, Montes Claros,
MG, Brasil.
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Trata-se de uma revisão bibliográfica que visa analisar as principais bactérias que causam infecção hospitalar, bem como os tipos
de infecções mais freqüentes, os mecanismos de resistências das
bactérias e suas formas de prevenção, já que a infecção hospitalar
é vista como um fator preocupante, por ter índices elevados de mortalidade, e ser considerada problema de saúde pública. O conhecimento sobre epidemiologia é um meio facilitador para o controle de
tais infecções, sendo que o conhecimento é uma das maiores formas
de prevenção. Portanto, o conhecimento sobre epidemiologia e o
exercício do controle das infecções hospitalares são questões importantes que estão em processo de mudanças.
Palavras-Chave: Infecção hospitalar; Resistência; Bactérias
INTRODUCTION
Nosocomial infection is any infection contracted during the period of
hospitalization and usually develops after the imbalance of human
bacterial flora, after invasive procedures and after contact with the
hospital microbiota itself (1).
Rev Panam Infectol 2014;16(4):226-230
It is all infection that is related to hospitalization,
when the hospital, after clinical laboratory, has
not detected the pathogen which is causing this
infection, proving that the patient has not had it at the
beginning of hospitalization and until 72 hours after,
time required for presenting a symptomatic evidence.
Hospital infection is seen as a worrying factor and for
having high rates of mortality is considered a public
health problem (2-3).
The hospital environment offers various resistant
infectious agents. The inpatients have a higher risk
of acquiring infections due to the hospital nature,
as they will be exposed to microorganisms which, in
their daily routine, they would not come into contact.
These patients are more weakened and their defenses
against infections are debilitated, for this reason
it becomes necessary for realization of invasive
procedures, technical conducive to the development
of a nosocomial infection (2).
It is necessary to emphasize the responsibility
of the hospital to inform patients, staff and visitors,
showing ways to prevent and control these infections,
as they shall contribute to the infection reduction (4).
Bacterial resistance to antimicrobials is connected
to genetics, because these microorganisms have the
genes encoding various biochemical mechanisms
that prevent the action of these drugs. This resistance
may be caused by mutations, the transferring
of the resistance causing gene present in the
microorganism, but in some microorganisms the
resistance mechanism is natural (5).
This article aims to analyze the main bacteria which
cause infection in the hospital environment, as well as
the most frequent types of infections, the mechanisms
of resistance of bacteria and their prevention.
MOST FREQUENT BACTERIA
Klebsiella pneumoniae
Klebsiella pneumoniae is known by doctors as the
enterobacteria which causes community-acquired
pneumonia, as occurs mostly in immunocompromised
patients. Klebsiella spp generates relevant pediatric
infections in premature infants. The treatment
of infections caused from strains of Klebsiella
pneumoniae has been hampered by the fact that some
strains are carrying plasmids that encode enzymes
known as beta-lactamases, generating resistance
to betalactamic drugs. It has been observed that
the beta-lactamase producing strains also present a
resistance to other antimicrobial drugs. This situation
is resulting in a state of public health concern,
causing epidemic outbreaks(6).
Klebsiella pneumoniae carbapenemase (KPC) has
an important mechanism of resistance in hospital
settings worldwide. Its analysis is prominent in order
to reduce its spread, contributing to the reduction
of morbidity and mortality related to different
infectious diseases, in which it is indispensable
the action of Commission of Hospital Infection
Control, and microbiological monitoring. KPC is an
enzyme produced by Gram-negative enterobacteria,
carbapenems participate of a class used in the
treatment of multiresistant infections involving
Enterobacteriaceae (7).
Enterobacteria are resistant to some antibiotics
by acquiring mutations or by R-factors (TRABULSI et
al., 2005 8). The resistance of Klebsiella pneumonia
is due to the presence of beta-lactamase SHV-1 by a
plasmid capable of producing enzymes such as cAMP,
metallo-beta-lactamase (MBL) and carbapenases
(KPC), beyond that it may express resistance through
loss of porins(9).
Staphylococcus aureus
Staphylococcus aureus is from the coccus of Gram
positive and catalase-positive bacterium, it is a
spherical, motionless, non-sporulating and, usually,
non-encapsulated bacterium and it can cause
diseases that differ in simple infections such as
pimples, boils and cellulitis and severe infections
which are meningitis, pneumonia, endocarditis, toxic
shock syndrome, among others(10).
Staphylococcus aureus has as its primary reservoir
the man where this organism is the most common
agent of pyogenic infections localized in skin or in
deeper regions as boils, folliculitis, osteomyelitis,
endocarditis, pneumonia, septicemia and other fatal
events. This microorganism can be found colonized in
various parts of the body such as the nasal passages,
throat, intestines and skin, and nasal cavity has been
identified as the area with the most often positive and
the most important source. Hands have been one of
the main means of transmission of the bacterium to
the hospital, from a patient infected to a susceptible
one, from an infected patient to the care executor
and from care executor to a susceptible patient, thus
contributing significantly to the increase of resistant
bacteria (11).
In hospitals, reservoirs are represented by the
microorganism colonized patients, employees and
the environment itself, in which the bacterium
Staphylococcus aureus is responsible for over 30%
of cases of hospital infections. The features which
associates the Staphylococcus aureus with virulence
are coagulase production and beta hemolysis, where
microbiologists identify this microorganism for its
ability to ferment mannitol (12).
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Bacchi RR(1)et al. • The most common bacteria that cause hospital infections today
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The resistance of Staphylococcus aureus to
antimicrobial is denominated by the acquisition of
resistance genes in other bacteria of the same species
or possibly other species and / or by mutations in
their genes. The resistance by mutation occurs due
to a change at the site of action of the antibiotic,
while resistance by obtaining resistance genes often
involves destruction or inactivation of antibiotics.
The penicillin resistance is conferred by producing
enzymes, beta-lactamases capable of inactivating
these drugs. As for methicillin resistance is provided
by a gene, mecA, which encodes a protein that binds
to penicillin with low affinity for the antimicrobial (8).
Pseudomonas aeruginosa
Pseudomonas aeruginosa is a bacterium present
in the hospital environment, which generates
many disorders for being a pathogen that causes
infections in different parts of the body, especially
in immunocompromised patients. Moreover, it is one
of the main pathogens found in hospital effluents.
This microorganism has the ability to stay in various
environments for a long time, furthermore it develops
resistance to antimicrobials(13).
This microorganism is a gram-negative, facultative
aerobic, it tolerates wide variations in temperature,
has minimal nutritional requirements and it is present
in soil, plants, fruits and vegetables with a preference
for moist environments(14). Pseudomonas aeruginosa
has natural resistance to most antibiotics used to
treat infections caused by Gram-negative bacteria,
but it can also achieve antibiotic resistance after prior
exposure(8).
This microorganism has a peculiar characteristic
of presenting low sensitivity to antimicrobial agents,
in addition to having various resistance mechanisms
such as production of beta-lactamase, hyper
expression of efflux pumps and loss or reduced
expression of outer membrane proteins(13).
Staphylococcus epidermidis
Staphylococcus epidermidis is one of the bacteria
found on the skin of individuals and can be introduced
in the intensive care unit by health professionals or
patients, and thus cause opportunistic infections
during and after invasive procedures. Patients with
low resistance are susceptible to suffer septicemia
and endocarditis related to implants, prosthetics and
catheters by Staphylococcus epidermidis, although,
in most cases, it is difficult to affirm with accuracy
that this bacterium is related to infections rather than
being part of the normal flora of the skin(15).
Staphylococcus epidermidis has its resistance
profile very similar to S. aureus, its resistance is
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suggested due to a probable transfer of resistance
genes from one species to another, or biofilm
formation(8). Biofilm producing bacteria are highly
resistant to antibiotics due to the environment provided
by the biofilms, which represents a mechanical
barrier against antibiotics. The biofilm formation is
a major virulence factor resulting from biosynthesis
of polysaccharide of adhesion intercellular, promoting
cell aggregation, biofilm accumulation and offering
a protective shield against the immune system and
against antibiotic(16).
MEANS OF INFECTIONS
There are numerous infections that affect patients in
a hospital environment, however the most studied are
urinary infections, respiratory infections and catheter
structure(2).
The urinary tract infection (UTI) comprises one
of the fundamental types of nosocomial infections,
being the urinary catheter the relevant factor for
patients acquire the infection, having as co-factors,
among others, the duration and mechanism of the
procedure, hygiene and the catheterization type(3).
Characterized by bacterial invasion and
multiplication in any urinary tract segment, these
infections are able to compromise ureters and
kidneys, causing pyelonephritis and the ureterites, as
well as the bladder, urethra and prostate, leading to
cystitis, urethritis and prostatitis, respectively(17).
The main microorganisms capable of colonize
and cause infections in the urinary tract belong to
Enterobacteriaceae family, this being composed by
gram-negative rods, facultative anaerobes, oxidasenegative, glucose fermenters and capable of reducing
nitrate to nitrite. Within this family, it stands out
as uro-pathogenic microorganisms the species
Escherichia coli, Pseudomonas aeruginosa, Proteus
mirabilis and Klebsiella sp. (18-8).
Some species of gram-positive cocci such as
Staphylococcus
saprophyticus,
Staphylococcus
aureus and Enterococcus faecalis have great aptitude
for spreading through urinary tract thus causing
infection(18).
In respiratory infections, pneumonia is more
frequent in some countries, as in some of the Europe,
for instance. The high mortality rate due to pneumonia
is related to the fragility of the patient due to their
low immunity and the place of detention, being an
environment full of microorganisms. Besides the
infection acquired in the hospital, these patients have
other diseases, reason for which was received at the
hospital, so rapid treatment with corresponding drug
administration is important for obtaining a successful
Rev Panam Infectol 2014;16(4):226-230
treatment. To facilitate treatment, it would be ideal
as a primary factor, the immediate discovery of the
pathogen, facilitating the choice of medication(19).
There are many factors related to the central
venous catheter infections, among them, it stands
out the clinical conditions of the patients who need
central access, migration of microorganisms present
on the skin of the patient to the catheter, the use
of parenteral nutrition and handling catheter for
administration of drugs(20).
In cardiac surgery, wound infection by
Staphylococcus aureus, in addition to increase the
length of hospital within 30 days, it can increase
mortality significantly. Among nosocomial infections,
surgical site infection is the second most frequent
cause, supplanted only by urinary tract infection. The
organisms most frequently associated with surgical
site infection are Staphylococcus aureus, negative
coagulase staphylococci and Gram-negative bacilli(21).
Infections that occur after coronary artery bypass
grafting should be studied, revealing the causative
microorganism in order to analyze the local microbiota
relating it to sex and age(22).
Ants are a possible danger to public health when
present in hospitals because they act as mechanical
vectors of microorganisms, by having the ability to
transport them. These insects are adapted to live in
the wild, household and even hospital because they
are attracted to food or medications, especially those
sweetened. These arthropods, due to their great
mobility, can circulate for many environments from
hospitals and can convey pathogenic microorganisms.
The circulation of a large number of people favors the
presence of these insects in hospitals (23).
Even the hospital environment contributes to
the spreading of pathogens, due to being occupied
by patients colonized and / or infected by these
pathogens, and in addition to that the presence of
bacteria on inanimate surfaces and equipment is very
common (24).
Biosecurity should be applied in hospitals in order
to employ precautions in order to minimize the risks of
cross-contamination between patients, professionals
and environment. The biosecurity actions correspond
to adoption of standards and procedures that are
safe and appropriate for maintaining the health of
patients, visitors and healthcare professionals. The
actions that are related to the implementation of
biosafety policies, with regard to biological risks,
particularly regarding accidents involving biological
materials and biological containment measures
through isolations and precautions should be part of
the general program of infection control, prioritizing
and establishing policies that will minimize the risk of
transmission of infection among health care workers
and patients. Among these actions, it may be cited the
use of personal protective equipment (PPE) in patient
care, encouraging professionals immunization against
hepatitis, tetanus and other infections depending on
institutional risks and hand washing before and after
any procedure(25).
CONCLUSION
The knowledge of epidemiology and the exercise of
the hospital infection control are important issues
that are in the process of change. Understanding
the mechanisms of transmission, associated with
increased resource laboratory diagnostics showed
significant concepts for the control of these infections.
The hand asepsis, isolation of transmitted diseases
and specific treatment to each type of infection
are evaluated as the best practicable means which
results in the prevention and control of nosocomial
infections.
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Correspondência
Ricardo Rodrigues Bacchi
Av. Aderaldino Fernandes Silva, 210 - Bairro:
Barcelona Parque
CEP: 39401-820 - Montes Claros - MG
E-mail: [email protected]