A dramatic example is that of immunocompromised
patients (AIDS (Box 11.6), cystic fibrosis, transplantation,
etc.) who are victims of nosocomial infections (from the
Greek “nosokomeone”, which means hospital and describes
what is contracted in hospital) by opportunistic microbial taxa
(bacteria, fungi, parasites). In these individuals whose immune
system is affected, opportunistic enterobacteria, usually nonpathogenic, such as Pseudomonas aeruginosa, Klebsiella
pneumoniae, or the Burkholderia cepacia complex
(Vandamme et al. 2007) colonize organs such as the lungs,
where they multiply to very high densities, produce biofilms
Box 11.5: Antibiotic Resistance and Infectious Diseases
Patrick Mavingui
An antibiotic is a chemical substance, natural or
synthetic, capable of compromising the growth of
bacteria (antibacterial antibiotic) or fungi (antifungal
antibiotic). Antibiotics act on specific targets by
inhibiting or disrupting biosynthetic pathways essential for the development of microbes. Different microbial taxa such as Actinobacteria and some eukaryotic
microorganisms are capable of producing antibiotics
(cf. Chap. 9). Following major use in human and
veterinary therapeutics to fight against microbial
infections, the emergence of antibiotic resistance of
pathogenic microorganisms, usually sensitive, has
become a major public health problem.
Several factors are at the origin of the current
resistance. First, they include genetic factors intrinsic
to the microbes. Random mutations at the DNA level
that alter the targets of antibiotics (mutational
resistance) are infrequent and represent only
10–20 % of the resistance encountered in hospitals.
The nonspecific mechanisms such as efflux pumps or
the production of matrix polysaccharides are also
involved in tolerance to antibiotics. Second, there is
resistance acquired by horizontal transfer of plasmids
carrying the genes for antibiotic resistance (hydrolytic
or inactivating enzymes). They are the most numerous
and correspond to 80–90 % of resistant isolates in the
clinic. This is the case of Staphylococcus aureus
MRSA (methicillin resistant) and XDR Mycobacterium tuberculosis (ultra-resistant TB). Extrinsic
predisposing factors are those that facilitate the passage and movement of resistant microbes found in the
environment (air, water, soil), plants, and animals. The
massive use of antibiotics in different sectors of
human activity (human and veterinary medicine,
feed, food, etc.) is to be related to the proliferation of
resistance, as evidenced by the high frequency of
resistant strains in hospitals where antibiotics are commonly used.
The resurgence of multiple resistances in microbes
requires the constant development of new antimicrobial molecules but also the application of more
appropriate preventive strategies. The use of
antibiotics should be carefully considered and rigorously applied.
Box 11.6: AIDS and Its Opportunistic Infectious
Process
Patrick Mavingui
The Syndrome of Acquired Immune Deficiency or
AIDS is caused by infection by the HIV (Human
Immunodeficiency Virus) retrovirus identified by the
team of Luc Montagnier (Barre ´-Sinoussi et al. 1983),
which earned him and Franc ¸oise Barre ´-Sinoussi the
Nobel Prize for Medicine in 2008. HIV is transmitted
through body fluids (blood, breast milk, vaginal
secretions, semen). Since its discovery in 1981,
AIDS has reached pandemic levels because it has
killed more than 25 million people, and 40 million
people live with HIV in almost all regions of the
world (UNAIDS, January 2006 http://www.unaids.
org). In the absence of a vaccine, the disease progression can be delayed for several years by the administration of an antiretroviral triple therapy and improved
hygiene of people with HIV. Uncontrolled, the disease
leads to a weakening of the immune system and opens
the door to opportunistic infections responsible for
diseases such as pneumonia and Kaposi’s sarcoma
that kill infected patients. Many fungi are among the
opportunistic pathogens and include the genera Candida which causes candidiasis; Cryptococcus responsible for cryptococcosis; Histoplasma, the causative
agent of histoplasmosis; or Aspergillus causing aspergillosis. New fungal pathogens are increasingly
identified. For some species, the pathogenesis
mechanisms are still unknown and cause problems.
There are also a large number of bacteria involved in
these opportunistic infections (cf. Chap. 15).
11 Microorganisms and Biotic Interactions
427
patients (AIDS (Box 11.6), cystic fibrosis, transplantation,
etc.) who are victims of nosocomial infections (from the
Greek “nosokomeone”, which means hospital and describes
what is contracted in hospital) by opportunistic microbial taxa
(bacteria, fungi, parasites). In these individuals whose immune
system is affected, opportunistic enterobacteria, usually nonpathogenic, such as Pseudomonas aeruginosa, Klebsiella
pneumoniae, or the Burkholderia cepacia complex
(Vandamme et al. 2007) colonize organs such as the lungs,
where they multiply to very high densities, produce biofilms
Box 11.5: Antibiotic Resistance and Infectious Diseases
Patrick Mavingui
An antibiotic is a chemical substance, natural or
synthetic, capable of compromising the growth of
bacteria (antibacterial antibiotic) or fungi (antifungal
antibiotic). Antibiotics act on specific targets by
inhibiting or disrupting biosynthetic pathways essential for the development of microbes. Different microbial taxa such as Actinobacteria and some eukaryotic
microorganisms are capable of producing antibiotics
(cf. Chap. 9). Following major use in human and
veterinary therapeutics to fight against microbial
infections, the emergence of antibiotic resistance of
pathogenic microorganisms, usually sensitive, has
become a major public health problem.
Several factors are at the origin of the current
resistance. First, they include genetic factors intrinsic
to the microbes. Random mutations at the DNA level
that alter the targets of antibiotics (mutational
resistance) are infrequent and represent only
10–20 % of the resistance encountered in hospitals.
The nonspecific mechanisms such as efflux pumps or
the production of matrix polysaccharides are also
involved in tolerance to antibiotics. Second, there is
resistance acquired by horizontal transfer of plasmids
carrying the genes for antibiotic resistance (hydrolytic
or inactivating enzymes). They are the most numerous
and correspond to 80–90 % of resistant isolates in the
clinic. This is the case of Staphylococcus aureus
MRSA (methicillin resistant) and XDR Mycobacterium tuberculosis (ultra-resistant TB). Extrinsic
predisposing factors are those that facilitate the passage and movement of resistant microbes found in the
environment (air, water, soil), plants, and animals. The
massive use of antibiotics in different sectors of
human activity (human and veterinary medicine,
feed, food, etc.) is to be related to the proliferation of
resistance, as evidenced by the high frequency of
resistant strains in hospitals where antibiotics are commonly used.
The resurgence of multiple resistances in microbes
requires the constant development of new antimicrobial molecules but also the application of more
appropriate preventive strategies. The use of
antibiotics should be carefully considered and rigorously applied.
Box 11.6: AIDS and Its Opportunistic Infectious
Process
Patrick Mavingui
The Syndrome of Acquired Immune Deficiency or
AIDS is caused by infection by the HIV (Human
Immunodeficiency Virus) retrovirus identified by the
team of Luc Montagnier (Barre ´-Sinoussi et al. 1983),
which earned him and Franc ¸oise Barre ´-Sinoussi the
Nobel Prize for Medicine in 2008. HIV is transmitted
through body fluids (blood, breast milk, vaginal
secretions, semen). Since its discovery in 1981,
AIDS has reached pandemic levels because it has
killed more than 25 million people, and 40 million
people live with HIV in almost all regions of the
world (UNAIDS, January 2006 http://www.unaids.
org). In the absence of a vaccine, the disease progression can be delayed for several years by the administration of an antiretroviral triple therapy and improved
hygiene of people with HIV. Uncontrolled, the disease
leads to a weakening of the immune system and opens
the door to opportunistic infections responsible for
diseases such as pneumonia and Kaposi’s sarcoma
that kill infected patients. Many fungi are among the
opportunistic pathogens and include the genera Candida which causes candidiasis; Cryptococcus responsible for cryptococcosis; Histoplasma, the causative
agent of histoplasmosis; or Aspergillus causing aspergillosis. New fungal pathogens are increasingly
identified. For some species, the pathogenesis
mechanisms are still unknown and cause problems.
There are also a large number of bacteria involved in
these opportunistic infections (cf. Chap. 15).
11 Microorganisms and Biotic Interactions
427