morphology & structure of spirochete, fungi & protozoa Microbiology (Doctor of Medicine course) for Virology discipline in Medicine by Sanskar Virmani, at School of Medicine, V. N. Karazin Kharkiv National University, Kharkiv, Ukraine. Presentation is free to use for non-monetary purposes if the author (i.e., me) is properly cited and given due credits. LinkedIn Profile: bit.ly/SanskarV_LinkedIn

2.  The phylum Spirochaetes (Greek spira, a
coil, and chaete, hair) contains gram-
negative, chemoheterotrophic bacteria
distinguished by their structure and
mechanism of motility.
 They are slender, long bacteria (0.1 to 3.0 μm
by 5 to 250 μm) with a flexible, helical shape.

3. The Spirochetes. Representative examples. (a) Cristispira sp. from a clam;
phase contrast ( 2,200). (c) Leptospira interrogans (2,200).

4. The Spirochetes. Representative examples.
(b) Treponema pallidum (1,000).

5.  Many species are so slim that they are only clearly
visible in a light microscope by means of phase-
contrast or dark-field optics.
 Spirochetes differ greatly from other bacteria with
respect to motility and can move through very
viscous solutions though they lack external rotating
flagella.
 When in contact with a solid surface, they exhibit
creeping or crawling movements. Their unique
pattern of motility is due to an unusual
morphological structure called the axial filament.

6. The axial fibrils or periplasmic flagella are visible around the protoplasmic
cylinder (6,000).

7.  The central protoplasmic cylinder contains
cytoplasm and the nucleoid, and is bounded
by a plasma membrane and a gram-negative
cell wall. Two to more than a hundred
flagella, called axial fibrils, periplasmic
flagella, or endoflagella, extend from both
ends of the cylinder and often overlap one
another in the center third of the cell.

8.  The most distinctive characteristic of this order,
however, is their method of motility, which
makes use of two or more axial filaments (or
endoflagella) enclosed in the space between an
outer sheath and the body of the cell. One end
of each axial filament is attached near a pole of
the cell. By rotating its axial filament, the cell
rotates in the opposite direction, like a
corkscrew, which is very efficient in moving the
organism through liquids.

10.  Bacterium can typically move about 100
times its body length in a second (or about
50 ), whereas a large fish, such as a tuna,
can move only about 10 times its body
length in this time.

11.  Many spirochetes are found in the human
oral cavity and are probably among the first
microorganisms described by van
Leeuwenhoek in the 1600s that he found in
saliva and tooth scrapings.

12.  The spirochetes include a number of
important pathogenic bacteria . The best
known is the genus Treponema (tre-po-
ne'mii), which includes Treponema pallidum
(pal'li-dum), the cause of syphilis.

14.  Borrelia Members of the genus Borrelia
(bor'rel-e-a) cause relapsing fever and Lyme
disease, serious diseases that are usually
transmitted by ticks or lice.

15.  Leptospirosis is a disease usually spread to
humans by water contaminated by
Leptospira (lep-to-spi' ra) species.
 The bacteria are excreted in the urine of
such animals as dogs, rats, and swine, so
domestic dogs and cats are routinely
immunized against leptospirosis.

16.  The common characteristic of being obligate
intracellular parasites-that is, they reproduce
only within a mammalian cell. The rickettsias
are gram-negative rod-shaped bacteria, or
coccobacilli.
 One distinguishing feature of most
rickettsias is that they are transmitted to
humans by bites of insects and ticks.

17. Rickettsias grow only within a host cell. such as the chicken embryo cell
shown here. Note the scattered rickettsias within the cell and the compact
masses 01 rickettsias in the cell nucleus.

18.  Rickettsia enter their host cell by inducing
phagocytosis. They quickly enter the cytoplasm of
the cell and begin reproducing by binary fission .
They can usually be cultivated artificially in cell
culture or chick embryos The rickettsias are
responsible for a number of diseases known as the
spotted fever group. These include epidemic
typhus, caused by Rickettsia prowazekii (ri -ket'se-a
prou-wa-ze' ke-e) and transmitted by lice; endemic
murine typhus, caused by R. typhi (ti 'Ie ) and
transmitted by rat fleas; and Rocky Mountain
spotted fever, caused by R. rickettsii (ri -ket 'se-e)
and transmitted by ticks.
 In humans, rickettsial infections damage the
permeability of blood capillaries, which results in a
characteristic spotted rash.

19.  The mycoplasmas are highly pleomorphic
because they lack a cell wall and can
produce filaments that resemble fungi, hence
their name mykes = fungus, and plasma
=formed ).

20.  Mycoplasma pneumoniae. Bacteria such as M.
pneumonrae have no cell walls, and their
morphology is irregular (pleomorphic]

21.  Cells of the genus Mycoplasma (mi-ko-plaz'ma)
are very small, ranging in size from 0.1 to 0,25
μm, with a cell volume that is only about 5% of
that of a typical bacillus. Because their size and
plasticity allowed them to pass through filters
that retained bacteria, they were originally
considered to be viruses.
 Mycoplasmas may represent the smallest self-
replicating organisms that are capable of a free-
living existence.

23.  The most significant human pathogen among the
mycoplasmas is M. pneumoniae (nu-mo'ne-I),
which is the cause of a common form of mild
pneumonia. Other genera in the order
Mycoplasmatales are Spiroplasma (spi-ro-plaz'ma),
cells with a tight corkscrew morphology that are
serious plant pathogens and common parasites of
plant-feeding insects, and Ureaplasma (u-re-a-
plaz'ma), so named because they can
enzymatically hydrolyze the urea in urine and are
occasionally associated with urinary tract infections.

24.  Members of the phylum Chlamydiae are
grouped with other genetically similar
bacteria that do not contain peptidoglycan in
their cell walls.

25.  Chlamydia and Chlamydophila which we will
call by the common name of the chlamydias,
have a unique developmental cycle that is
perhaps their most distinguishing
characteristic.

27.  They are gram-negative coccoid bacteria.
The elementary body shown is the infective
agent. Unlike the rickettsias, chlamydias do
not require insects or ticks for transmission .
They are transmitted to humans by
interpersonal contact or byairborne
respiratory routes.

28. Micrograph of Chlamydophilla in the cytoplasm of a host cell.
The elementary bodies are the infectious stage; they are dense, dark,
and relatively small. Reticulate bodies, the form in which chlamydias
reproduce within the host cell , are larger with a speckled appearance.
Intermediate bodies, a stage between the two, have a dark center.

29.  There are three species of the chlamydias that are
significant pathogens for humans. Chlamydia
trachomatis (kla-mi'de-a tra -ka'ma -tis) is the best
known pathogen of the group and responsible for
more than one major disease. These include
trachoma, one of the most common causes of
blindness in humans in the less developed
countries. It is also considered to be the primary
causative agent of both nongonococcal urethritis,
which may be the most common sexually
transmitted disease, and lymphogranuloma
venereum, another sexually transmitted disease.

31.  The genera Streptomyces, Frankia,
Actinomyces, and Nocardia are often
informally called actinomycetes (from the
Greek actina = ray) because they have a
radiate, or starlike, form of growth by reason
of their often-branching filaments.

32.  Superficially, their morphology resembles
that of filamentous fungi; however, the
actinomycetes are prokaryotic cells, and
their filaments have a diameter much smaller
than that of the eukaryotic molds.
 Some actinomycetes further resemble molds
by their possession of externally carried
asexual spores that are used for
reproduction.

33.  The actinomycetes are a fascinating group of
microorganisms.
 They are the source of most of the antibiotics
used in medicine today.
 They also produce metabolites that are used
as anticancer drugs, antihelminthics and
drugs that suppress the immune system in
patients who have received organ
transplants.

34.  The life cycle of many actinomycetes includes
the development of filamentous cells, called
hyphae, and spores. When growing on a
solid substratum such as soil or agar, the
actinomycetes develop a branching network of
hyphae.
 The hyphae grow both on the surface of the
substratum and into it to form a dense mat of
hyphae termed a substrate mycelium. Septae
usually divide the hyphae into long cells (20
μm and longer) containing several nucleoids.

36.  In many actinomycetes, substrate hyphae
differentiate into upwardly growing hyphae to
form an aerial mycelium that extends above
the substratum. The aerial hyphae form thin-
walled spores upon septation. These spores
are considered exospores because they do
not develop within a mother cell like the
endospores of Bacillus and Clostridium.
 If the spores are located in a sporangium,they
may be called sporangiospores.

37. Representatives of the Genus Actinomyces.
(a) A. naeslundii; Gram stain (1,000). (b) Actinomyces; scanning
electron micrograph (18,000). Note filamentous nature of the
colony.

38.  All fungi are chemoheterotrophs, requiring
organic compounds for energy and carbon.
 Fungi are aerobic or facultatively anaerobic;
only a few anaerobic fungi are known.

40.  Fungal colon ies are described as vegetative
structures because they are composed of
the cells involved in catabolism and growth.
The thallus (body) of a mold or fleshy fungus
consists of long filaments of cells joined
together; these filam ents are called hyphae
(singular: hypha) .

41.  In most molds, the hyphae contain cross-
walls called septa (singular: septum), which
divide them in to distinct, uninucleate (one-
nucleus) cell-like units.
 These hyphae are called septate hyphae. In
a few classes of fungi , the hyphae contain
no septa and appear as long, continuous
cells with many nuclei.These are called
coenocytic hyphae.

43.  The portion of a hypha that obtains nutrients is called the
vegetative hypha; the portion concerned with reproduction is the
reproductive or aerial hypha, so named because it projects
above the surface of the medium on which the fungus is
growing.
 Aerial hyphae often bear reproductive spores. When
environmental conditions are suitable, the hyphae grow to form
a filamentous mass called a mycelium, which is visible to the
unaided eye.

44.  Yeasts are nonfilamentous, unicellular fungi that are
typically spherical or oval. Budding yeasts, such as
Saccharomyces (sak-a- ro -mi'ses), divide
unevenly. In budding, the parent cell forms a
protuberance (bud) on its outer surface. As the bud
elongates, the parent cell's nucleus divides, and
one nucleus migrates into the bud. Cell wall
material is then laid down between the bud and
parent cell , and the bud eventually breaks away.

45.  One yeast cell can in time produce up to 24
daughter cells by budding. Some yeasts
produce buds that fail to detach themselves;
these buds form a short chain of cells called
a pseudohypha. Candida albicans (kan'did-
a al'bi-kanz) attaches to human epithelial
cells as a yeast but usually requires
pseudohyphae to invade deeper tissues.

46.  Fission yeasts, such as Sacchoromyces , divide
evenly to produce two new cells. During fission,
the parent cell elongates, its nucleus divides,
and two daughter cells are produced. Increases
in the number of yeast cells on a solid medium
produce a colony similar to a bacterial colony.
Saccharomyces species produce ethanol in
brewed beverages and carbon dioxide for
leavening bread dough.

47.  Some fungi, most notably the pathogenic species, exhibit
dimorphism-two forms of growth. Such fungi can grow
either as a mold or as a yeast. The moldlike forms produce
vegetative and aerial hyphae; the yeastlike forms
reproduce by budding.
 Dimorphism in pathogenic fungi is temperature dependent:
at 37C, the fungus is yeastlike, and at 25°C, it is moldlike.

48.  Filamentous fungi can reproduce asexually by fragmentation of
their hyphae. In addition, both sexual and asexual reproduction
in fungi occurs by the formation of spores. Fungal spores can
be either asexual or sexual.
 Asexual spores are formed by the hyphae of one organism.
When these spores germinate, they become organisms that are
genetically identical to the parent.
 Sexual spores result from the fusion of nuclei from two opposite
mating strains of the same species of fungus.
 Fungi produce sexual spores less frequently than asexual
spores. Organisms that grow from sexual spores will have
genetic characteristics of both parental strains.

49.  Asexual spores are produced by an individual
fungus through mitosis and subsequent cell
division; there is no fusion of the nuclei of cells.
Two types of asexual spores are produced by
fungi .
 One type is a conidiospore, or conidium
(plural : conidia), a unicellular or multicellular
spore that is not enclosed in a sac. Conidia are
produced in a chain at the end of a
conidiophore. Such spores are produced by
Aspergillus (a-sper-jil'lus).

50.  Conidia formed by the fragmentation of a
septate hypha into single, slightly thickened
cells are called arthroconidia. One species
that produces such spores is Coccidioides
immitis.

51.  Another type of conidium, blastoconidia,
consists of buds coming off the parent cell.
Such spores are found in some yeasts, such
as Candida albicans and Cryptococcus.

52.  A chlamydoconidium is a thick-walled spore
formed by rounding and enlargement within
a hyphal segment. A fungus that produces
chlamydoconidia is the yeast C. albicans.

53.  The other type of asexual spore is a
sporangiospore, formed within a sporangium,
or sac, at the end of an aerial hypha called a
sporangiophore. The sporangium can contain
hundreds of sporangiospores. Such spores are
produced by Rhizopus.

54.  A fungal sexual spore results from sexual reproduction,
which consists of three phases:
 I. Plasmogamy. A haploid nucleus of a donor cell (+)
penetrates the cytoplasm of a recipient cell (-).
 2. Karyogamy. The (+) and (-) nuclei fuse to form a diploid
zygote nucleus.
 3. Meiosis. The diploid nucleus gives rise to haploid nuclei
(sexual spores), some of which may be genetic
recombinants.
 The sexual spores produced by fungi characterize the
phyla.
 In laboratory settings, most fungi exhibit only asexual
spores. Consequently, clinical identification is based on
microscopic examination of asexual spores.

56.  Any fungal infection is called a mycosis.
Mycoses are generally chronic (long-lasting)
infections because fungi grow slowly. Mycoses
are classified into five groups according to the
degree of tissue involvement and mode of entry
into the host: systemic, subcutaneous,
cutaneous, superficial, or opportunistic. Fungi
are related to animals. Consequently, drugs that
affect fungal cells may also affect animal cells.
This fact makes fungal infections of humans
and other animals often difficult to treat.

58.  Protozoa are unicellular, eukaryotic
chemoheterotrophic organisms. Among the
protozoa are many variations on this cell
structure. The term protozos means "first
animal," which generally describes its
animal-like nutrition. In addition to getting
food, a protozoan must reproduce, and
parasitic species must be able to get from
one host to another.

59.  Protozoa reproduce asexually by fission, budding, or schizogony.
 Schizogony is multiple fission; the nucleus undergoes multiple
divisions before the cell divides. After many nuclei are formed, a small
portion of cytoplasm concentrates around each nucleus, and then the
single cell separates into daughter cells.
 Sexual reproduction has been observed in some protozoa.
 The ciliates, such as Paramecium, reproduce sexually by conjugation,
which is very different from the bacterial process of the same name.
 During protozoan conjugation, two cells fuse, and a haploid nucleus
(the micronucleus) from each cell migrates to the other cell. This
haploid micronucleus fuses with the haploid micronucleus within the
cell. The parent cells separate, each now a fertilized cell. When the
cells later divide, they produce daughter cells with recombined DNA.
 Some protozoa produce gametes (gametocytes), haploid sex cells.
During reproduction, two gametes fuse to form a diploid zygote.

61.  Protozoa are mostly aerobic heterotrophs, although many
intestinal protozoa are capable of anaerobic growth. Two
chlorophyllcontaining groups, dinoflagellates and euglenoids,
are often studied with algae.
 All protozoa live in areas with a large supply of water. Some
protozoa transport food across the plasma membrane. However,
some have a protective covering, or pellicle, and thus require
specialized structures to take in food.
 Ciliates take in food by waving their cilia toward a mouthlike
opening called a cytostome.
 Amoebas engulf food by surrounding it with pseudopods and
phagocytizing it.
 In all protozoa, digestion takes place in membrane-enclosed
vacuoles, and waste may be eliminated through the plasma
membrane or through a specialized anal pore.

62. Ciliates_(a) Paramecium is covered with rows of cilia. It has specialized structures
for ingestion (mouth). elimination of wastes (anal pore), and the regulation of
osmotic pressure (contractile vacuoles). The macronucleus is involved with protein
synthesis and other ongoing cellular activities. The micronucleus functions in
sexual reproduction.
(b) Voricella attaches to objects in water by the base of its stalk. The
springlike stalk can expand al lowing Vorticella to feed in different areas.
Cilia surround its cytostome.

63. Amoebozoa. (a) To move and to engulf food. Amoebas (such as this Amoeba
proteus) extend cytoplasmic structures called pseudopods. Food vacuoles are
created when pseudopods surround food and bring it into the cell.
(b) Entamoeba histolytica. The presence of ingested red blood cells is
diagnostic for Entamoeba

64. Archaezoa. (a) Chilomastix. This
flagellate. found in the human intestine.
may be mildly pathogenic. The cysts
survive for months
outside a human host. The fourth
flagellum is used to move food into the
oral groove. where food vacuoles are
formed.
(b) Trichomonas vaginalis.
This flagelate causes urinary and genital
tract infections. Notice the small
undulating membrane.