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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_5219_Библиотеки_им_академика_М_И_Перельмана.pdf
MDR inCandida: TheReal Storm
PrashanshaSrivastava, ShashikantTiwari, ManojKumar,
ManojV.Murhekar, andGauravRajDwivedi
Abstract
Systemic Candida infection is reported as a major cause of infection and death in
nosocomial and critically ill patients. The antifungal arsenal belongs to the lim-
ited class and is available to treat resistance in Candida that enhances the severity
of infection and cost of treatment. Even multidrug resistance (MDR) is rarely
reported but the frequency of MDR is increasing day by day. This book chapter
tries to focus on its pathogenesis, morphogenesis, available antifungals, and drug
resistance.
Keywords
Candida albicans · Nosocomial infections · Drug resistance · MDR · Antifungals
4
4.1 Introduction
Infection diseases were responsible for several pandemic emerging and reemerging
diseases. The last 3years witnessed the devastating effect of Covid-19. The postcovid impact was in the form of several complications and mucormycosis. Even fungi
are reported as one of the major monsters for human health but till date, mycosis is
underrated. Fungi are responsible for billions of infections and 1.5million deaths
annually. The last decade witnessed a sudden increase in immunocompromised
patients, and this situation made heaven for fungal infection.
Mycosis is classied into four types, namely, supercial, cutaneous, subcutaneous, and systemic infection. The major causative agents of systemic mycosis are
Candida, Aspergillus, and Cryptococcus. The species of Candida are reported as a
P. Srivastava · S. Tiwari · M. Kumar · M. V. Murhekar · G. R. Dwivedi (*)
ICMR-Regional Medical Research Centre, Gorakhpur, India
© The Author(s), under exclusive license to Springer Nature Singapore Pte
Ltd. 2024
S. Hameed, P. Vijayaraghavan (eds.), Recent Advances in Human Fungal
Diseases, https://doi.org/10.1007/978-981-97-4909-6_4
87
88
Fig. 4.1 Classication of
living organism
P. Srivastava et al.
major causative agent for invasive mycosis. Candida albicans is regarded as a leading cause of nosocomial blood stream infection. In view of the above problems, the
present book chapter is conceptualized to deal with infection caused by C. albicans
pathogenesis, morphogenesis, available antifungals, and drug resistance.
4.2 Classification ofLiving Organism
Current classication, i.e., three-domain system, for living beings is given and
explained by Carl Woese. This classication is based on ribosomal RNA (rRNA)
differences. rRNA is a functional unit, and the building block for ribosomes is present in a cell. Under this three-domain system, cellular life forms are sorted into three
category (domains) (Fig.4.1). The domains are as follows:
• Archaea
• Bacteria
• Eukarya
4.3 Eukarya Domain
The organisms falling in the Eukarya domain possess a well-developed membranebound organelle and nucleus. The Eukarya domain is further classied into kingdoms,
namely, Protista, Fungi, Plantae, and Animalia. Examples of every kingdom in this
domain include fungi, (molds and yeast), algae, amoeba, ferns, mosses, plants, sponges,
insects, and mammals. Earth is loaded with a remarkable diversity of eukaryotic species, ranging from microscopic to complex multicellular organisms. The estimation of
eukaryotic species present on earth is 8.7million, in which approx. 7% (611,000 species) of total eukaryotic population is contributed by fungal species, as given in data
(Mayer etal. 2013). The fungal species are in the race of survival since 1.5billion years
and are widely spread across the globe. The abundance of fungal species ranges from
three to 13million on earth, many of which are tiny that they can be visualized only
through microscope. There are more than 3million species yet to be identied.
4 MDR inCandida: TheReal Storm
When we think about “fungi,” we often picture mushrooms, fruiting bodies in
our imagination. However, it is worth nothing that most fungi don’t produce mushrooms. Fungus species showcase the vast complexity and adaptability of life on our
planet. Their habitats are very diverse ranging from soils to tissue of leaves, rainforests, and in depth of ocean. It is crucial to understand the capability of fungi to live
in such a diverse ecosystem and how it affects agriculture and human health. Fungi
are cryptic and are involved in many different things. They are associated with
decomposition, nutrient cycling, pathogenesis, and are mutualistically associated
with plants and other organisms. Of all fungal species, around 600 species are
involved in human pathogen (Mayer etal. 2013).
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4.4 Genus ofFungi Responsible forInfections inHumans
4.4.1 Cryptococcus
They are an encapsulated yeast species and cause disease named as Cryptococcosis.
They have a broad spectrum of hosts ranging from humans, dogs, to marine mammals. Infections in humans are primarily caused by two species, Cryptococcus neo-
formans and Cryptococcus gattii (Khawcharoenporn etal. 2007).
The globally distributed C. neoformans is commonly found as a coinfection with
human immunodeciency virus (HIV) infected patients. Initially, C. gattii was
found to be infecting the population of tropical and subtropical areas but in recent
studies, it was identied in the Mediterranean regions of Europe and the USA (Ellis
and Pfeiffer 1990; Kidd etal. 2007; Acheson etal. 2019) and are apparently able to
infect immunocompetent individuals.
4.4.2 Aspergillus
Species of aspergillus are reason behind Aspergillosis. Symptoms of this disease are
manifested in allergic, chronic, and invasive forms (Bongomin etal. 2017). About
11million of human population are affected by allergic forms, 3million of human
population with chronic form, and approximately 300,000 cases are reported with
invasive forms. These data explain itself about the global burden of the disease
(Bongomin et al. 2017). In the range of disease causing species of Aspergillus,
A. fumigatus is the most common culprit of disease due to adaptable nature to unfavourable conditions like high temperature and pH (Chang etal. 2004; Kwon-Chung
and Sugui 2013; Kim etal. 2014).
4.4.3 Mucorales
Species like Mucor, Rhizopus, and Lichtheimia of Mucorales are the reason behind
the disease called mucormycosis (Skiada etal. 2011, 2018). The incident rate of this
disease is about 0.1–0.3 per 100,000 people, excluding India and Pakistan, and
90
approximately 10,000 patients are identied infected per year (Bongomin et al.
2017; Prakash and Chakrabarti 2019).
P. Srivastava et al.
4.4.4 Candida
Candida species are commensal microorganism for skin, GIT, and genital tract of
healthy individual and shares its environment with normal human microora.
Candida species contributes to around 8% of all hospital acquired blood stream
infection, making them the fourth leading cause of deaths in intensive care units
(ICU). Approximately 11,000 deaths are related with candidemia per year (Pfaller
and Diekema 2007). Patients suffer from nosocomial infections due to increasing
cases of organ transplants per year, during which their immunity is suppressed for
longer duration and this is the reason that more patients are admitted in the ICU
(Zilberberg etal. 2008; Van Rhijn and Bromley 2021).
Among all genera of fungi, the genus Candida is the widespread human fungal
pathogen and is responsible for two types of infection:
(A) Supercial (mucosal and cutaneous)
(B) Systemic (Turner and Butler 2014)
In the Candida genus, majorly ve species are specically associated with 92%
cases of candidiasis (Turner and Butler 2014), which are Candida albicans (65.3%),
Candida glabrata (11.3%), Candida tropicalis (7.2%), C. parapsilosis (6.0%), and
Candida krusei (2.4%) (Turner and Butler 2014).
4.5 Worldwide Distribution ofSpecies
According to the geographical region and population of patients, the proportion of
species dominance varies (Fig.4.2).
Candida albicans is reported as one of the most prevalent species for invasive
candidiasis; however, non-albicans Candida spp. dominance varied intensely, as
represented in Fig.4.2.
4.5.1 Candida albicans
Candida albicans is an opportunistic pathogen that exists in a commensalistic relationship at gastrointestinal and genitourinary tracts in maximum population of
humans. In 75% of the human population, C. albicans is present as normal microora in the oral cavity. However, it becomes opportunistic pathogen for immunocompromised patients, (Kabir etal. 2012) but in healthy individuals, this colonization
generally remains benign (Mayer etal. 2013).
4 MDR inCandida: TheReal Storm
91
Fig. 4.2 Prevalence % of population based on non C. albicans species distribution (Pfaller and
Diekema, 2007)
4.5.2 Morphogenesis
Candida albicans possesses a unique characteristic that is morphological plasticity.
Morphological plasticity is dened as the ability to switch between two distinct
modes of proliferation. The distinctive attributes have captured attention due to its
apparent connection to the organism’s pathogenicity (Mukaremera etal. 2017).
Candida albicans is termed a dimorphic fungus because it exists in either a yeast
form or a hyphal form. Depending on the environmental conditions, they can
92
P. Srivastava et al.
proliferate into two modes: the hyphal mode and the yeast mode (Fig.4.3). In the
hyphal mode, the cells elongate continuously from one end to form an elongated
tube that are generally delineated by the formation of septum, and the yeast growth
mode, in which discrete cells divide by budding-off daughter cells that typically
disassociate from the mother cell.
Apart from the yeast-hyphal mode of proliferation, there are number of other
morphological forms which can be naturally found. These forms are associated with
specic cellular metabolic functions.
These naturally occurring morphologies include the following:
1. The opaque form which can be observed in mating-competent cells (Mukaremera
etal. 2017).
2. The chlamydospore form, a thickened cell wall formed typically under subopti-
mal growth conditions, and it is a mystery yet (Sudbery etal. 2004).
3. The pseudohyphal form, coexisting with yeast and hyphae during infection and
vegetative cultures (Sudbery etal. 2004). Pseudohyphae bear a resemblance to
both yeasts and hyphae, which are of elongated yeast cells (in branched chains)
with constraints at the septum.
The ability of C. albicans to switch between two morphologies that is from unicellular yeast cells to hyphae and pseudohyphae (multicellular and lamentous) and
vice versa critically promotes invasion of the pathogen and thus invasive disease
(Tsui etal. 2016). A unique difference of chitin content between yeast and hyphae
Yeast
Hyphae
Fig. 4.3 Distinct morphological features a fungal species
Pseudo
hyphae
A
4 MDR inCandida: TheReal Storm
93
has been observed where the hyphae wall has slightly higher chitin content in comparison to yeast cell wall (Garcia-Rubio etal. 2020).
4.5.3 Pathogenesis
Two major categories of infections are caused by C. albicans in humans. First, the
supercial infections, developed on skin, oral cavity or vaginal area. Second, the
deadly systemic infections, developed in GIT, GUT, etc.
The ability of C. albicans to infect such diverse host niches like skin, vagina, oral
cavity, GIT, and GUT is due to the production and secretion of various virulence factors and tness promoting factors. These factors make up the fungus to survive in a
condition of stress, and it helps to escape from the host immune system (Fig.4.4).
These factors are discussed later in this chapter. Yeast and hyphal forms play vital and
complimentary roles that are crucial for infection (Van Der Meer etal. 2010).
On the mucosal surface of 50–60% of healthy human beings, Candida spp. can be
observed. During immunosuppressive conditions like suffering from any disease or
any surgical organ transplant, this commensal bacterium breaches every barrier and
invades the intestine to reach blood stream (candidemia). With the help of virulence
factors, these species proliferate and cause disease in the body (invasive candidiasis).
For the successful establishment of infection and disease, fungi follow several
steps like adhesion, yeast-hyphal transition, invasion by using virulence factors,
escaping from host immune response, and adapting to host environment. These
steps are discussed further in detail.
4.5.4 Adherence
For the development of invasive disease, the rst step is the adherence of fungal cell
to abiotic surface (catheter) or biotic surface (host cells) (Fig.4.5). The oval-shaped
yeast form derived from nuclear division and budding is obliged for the adherence
B
Blood vessel
Fig. 4.4 Depicting the mechanism of pathogenesis by fungus. (a) Adhesion and colonization of
yeast cell. (b) Yeast to hyphal transition upon adherence. (c) Penetration by hyphae. (d) Spreading
in vascular system of host. (e) Fungus breaching the intestinal barrier from surgical wound
C
Intesne
E
D
94
Thigmotropism and
Adhesion
Dimorphism
invasion by damage
Fig. 4.5 Mechanism of adherence and invasion
P. Srivastava et al.
to host endothelial cells and invasion to blood stream (Noble etal. 2017) because
these forms of C. albicans carry a unique of set of proteins (adhesins), which leads
to the attachment with the host cells and also with other microorganisms or abiotic
surfaces (Garcia etal. 2011; Verstrepen and Klis 2006). The agglutinin-like sequence
(ALS) proteins and Hwp1, the hypha-associated adhesion are the best studied
C. albicans adhesins. These genes code for glycosylphosphatidylinositol (GPI)linked cell surface glycoproteins.
4.5.5 Morphological Switching
In response to favourable conditions, the fungus gets converted from commensal to
pathogenic. Whenever this opportunistic dimorphic fungus gets the opportunity to
invade any surface, immediately it switches from unicellular budding yeast to multicellular hyphae or pseudohyphae (Gow 1997; Brown and Gow 1999; Sudbery
etal. 2004; Braunsdorf et al. 2016; Trevijano-Contador et al. 2016; Mukaremera
etal. 2017). After the adherence of the yeast form to the host cell, the morphological
transition of yeast cell to hyphal cell occurs.
The hyphae form is made up of tubular cells that stay attached after cell division.
The hyphal form is prerequisite for tissue access during adhesion and invasion
(Lorenz etal. 2004; Fradin etal. 2005; Grubb etal. 2009; Naglik etal. 2011; Yang
etal. 2014; Erwig and Gow 2016). The importance of the hyphal form is that it
yields resistant from phagocytosis and the virulence factors (hyphae specic),
namely, host tissue degrading proteases (Sap4, Sap5, and Sap6), adhesins (Hwp1,
Als3, Als10, Fav2, and Pga55), and cytolytic peptide toxin (Ece1), aggrandize the
host cell damage during infection (Noble etal. 2017; Rogiers etal. 2019).
The patients who are suffering from systemic invasive candidiasis can either be
human or animal, and all the three forms, i.e., yeast, hyphal, and pseudohyphal, of
C. albicans can be found in their tissues (Di Carlo etal. 2013; Chin etal. 2014).
4 MDR inCandida: TheReal Storm
95
4.5.6 Invasion
The invasion of host cell by C. albicans follows two different mechanisms: induced
endocytosis and active penetration (Zakikhany etal. 2007; Dalle etal. 2010; Zhu
and Filler 2010; Naglik etal. 2011).
4.6 Induced Endocytosis
The fungus that started to express specied invasin proteins on the cell surface
enables the joining of host ligands: E-cadherin on epithelial cells (Phan etal. 2007)
and N-cadherin on endothelial cells (Phan etal. 2005), and this triggers the endocytosis of the fungal cell. Here, endocytosis is passive in nature because even killed
hyphae are likewise endocytosed (Park etal. 2005a; Dalle etal. 2010). So far, two
invasion proteins have been identied, namely, Als3, which are also involved in the
adhesion of yeast form and Ssa1 (Phan etal. 2007; Sun et al. 2010). Ssa1 is the
member of the heat shock protein 70 (Hsp70) family. To check the involvement of
these protein in adhesion and invasion, als3 and Ssa1 mutants are developed. Results
show both mutants (als3Δ/Δ and ssa1Δ/Δ) demonstrated reduced epithelial adherence and invasion, and less virulence was reported in an oropharyngeal candidiasis
murine model (Park etal. 2005a; Sun etal. 2010). By binding with E-cadherin, Als3
and Ssa1 started to induce clathrin-dependent endocytosis.
4.7 Active Penetration
Viable C. albicans hyphae is prerequisite for active penetration (Dalle etal. 2010).
Till date, the exact molecular mechanism and factors which intervene active penetration are not completely known. According to few reports, fungal adhesion and
physical forces are crucial (Wächtler etal. 2011). Secreted aspartic proteases (Saps)
are also involved in active penetration. Phospholipases and lipases do not have any
evidence in involvement to this process (Zhu and Filler 2010; Sun etal. 2010).
C. albicans release hydrolytic enzymes that start to damage epithelial cell–cell links
and enable degradation of the cell membrane (Cheng etal. 2005).
4.8 Virulence Factors ofCandida albicans
During infection, C. albicans inhabits various host niches, with changes (pH, nutrient availability, hypoxia, and CO2 levels) (Brown etal. 2014a; Hall 2015). One of
the striking features is adaptability that establish C. albicans as an effective pathogen to ourish in different conditions.
There are various virulence factors possessed by the fungus which helps in its
successful pathogenicity, and these are as follows:
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P. Srivastava et al.
1. Metabolic exibility: Inuences to the changes in the cellular metabolism, i.e.,
efcient use of alternate carbon source (Ene etal. 2012a).
2. Hydrolytic enzymes: Helps in degradation of host connective tissues, cleavage
of host immune factors (Hall 2015).
3. Candida lysin: Secretory cytolytic peptide damaging host immune cells.
4. Phenotype switching: From white to opaque cells, as opaque cells are resistant
to neutrophil engulfment (da Silva etal. 2016).
5. Yeast to hyphal transition: Occurs in response to temperature, serum, alkaline
pH, nutrient starvation, and CO2.
6. Countering nutritional host immunity: By expressing micronutrient transporters
(e.g., Rbt5/Als3 for Fe; Zrt1/Zrt2/soluble Pra1 for Zn) (Crawford and Wilson
2015), or redundant enzymes that use alternative micronutrients as cofactors (Li
etal. 2015).
7. Escape from phagocytosis: Vomocytosis, hyphal lysis of host cell, phagolyso-
somal neutralization pyroptosis.
8. Biolm formation: Resistant to antifungals and host immunity.
9. Evasion from host immune system: Changes in cell wall architecture and com-
position, masking of PAMPs (Lewis etal. 2012; Ene etal. 2012b; Hall and Gow
2013; Brown etal. 2014b; Hall 2015; Childers etal. 2016).
4.8.1 Innate Immune Responses toC. albicans Infection
When C. albicans becomes successful in the invading the host, the host immune
system starts to attack this foreign antigen. During host and pathogen interaction, it
is found that almost every component of the cell wall of Candida is involved.
Recognition of Candida is performed by host pattern recognizing receptors (PRR)
which binds with the ligand present on the pathogen that is pathogen-associated
molecular patterns (PAMPs) (da Silva etal. 2016; Gulati and Nobile 2016). This
recognition by host’s immune cells results in the initiation of various signalling
pathways that ultimately leads to phagocytosis and killing of the pathogen. Epithelial
cells, neutrophils, macrophages, and dendritic cells are the host immune cells
involved in the elimination process. Innate immune interactions involve 10 surface
receptors, including two Toll-like receptors (TLR2 and TLR4), six C-type lectin
receptors (Dectin-1, Dectin-2, MR, DC-SIGN, Mincle, and MBL), and two internal
receptors (TLR9 and NLRP3) that are responsible for the recognition of C. albicans
(Gulati and Nobile 2016). Majorly, the ligand of these receptors are carbohydrates,
present on the surface of hyphae, such as mannose derivatives and β-1,3-glucans.
These host receptor and pathogen ligand binding lead to the production of various
chemokines and cytokines. These chemical agents activate the phagocytic cells
which phagocytose the pathogen. Internalization of pathogen leads to the activation
of internal receptors, resulting in TLR9 or NLRP3 inammasome activation (Erwig
and Gow 2016; Gulati and Nobile 2016).
Apart from innate immune response, in combatting infection caused by C. albi-
cans in the blood stream, antibodies against the extracellular proteins, like mannans,