The document provides an introduction to microbiology and classification of microorganisms that can infect the human body and cause disease. It discusses the five major groups of infectious agents: bacteria, viruses, fungi, protozoa, and helminthes. For each group, it describes examples of pathogens, how they are classified, and diseases they can cause in the eye, including conjunctivitis, keratitis, uveitis, optic neuritis, and others. It covers morphological classification of bacteria, gram staining, oxygen requirements, as well as viral, fungal, protozoan and parasitic diseases of the eye.

2. MICROBIOLOGY
BY: SUMAYYA NASEEM
Optometrist
School Eye Health Programme, Pakistan
CHEF International

3. Introduction to Microbiology
The agents of human infectious diseases belong to
5 major groups of organisms:
•Bacteria
•Viruses
•Fungi
•Protozoa
•Helminthes

4. • Out of these bacteria , fungi & protozoa are
unicellular.
• Some of the fungi are also relatively simple
multi cellular.
• The helminthes are complex multi cellular
and together with the protozoa are
commonly called parasites.
• Viruses are different from the rest as they
are not cells but can replicate only with in
cells.

5. • Collectively all of them are called micro
organisms.
• The organisms which are capable of
causing disease are called pathogenic
organisms.
• Some of the micro organisms are non.
Pathogenic and live on the body of human
beings and are called commensals.

6. A. BACTERIA:
Bacteria can be classified depending
upon:-
• Morphology
• Gram Staining
• Oxygen Requirement

7. MORPHOLOGICAL CLASSIFICATION
Bacteria are classified by shape into three
basic groups:-
• Cocci :- Round or Oval
• Bacilli :- Rod Shape
• Spirochetes :- Spiral like
• Intermediate shapes like cocco-bacilli may
exist

8. In addition to their characteristic shapes,
the arrangement of bacteria is important
e.g
• Cocci occurring in pairs called diplococci
• Cocci occurring in chains e.g. Streptococci
• Cocci occurring in grape like clusters e.g.
Staphylococci

10. CLASSIFICATION BASED ON
GRAM STAINING
• Because bacteria are colorless and usually invisible to light
microscopy.Colorful stains have been developed to visualize
them.
• The most commonly used is the Gram stain which separates
the organisms into:-
• GRAM +ve :- When bacteria stain blue in Gram stained
smear,e.g clostridia,C.B.D, streptococcus, staphlococcus
• GRAM –ve :- When bacteria stain red in Gram stained
smear ,e.g. N.gonarrhea, E.coli, Pseudomonas
• The difference is in the cell walls of GM +ve & GM –ve
bacteria.

11. CLASSIFICATION ACCORDING TO O2
REQUIRMENT
STRICT AEROBES
• They do not grow in the absence of oxygen but they
grow in the presence of oxygen e.g. E.coli
ANAEROBES
• They grow best in absence of oxygen e.g. clostridia
MICRO-AEROPPHILIC
• They require small amount of oxygen Intermediate
characters like facultative anaerobes are also found

12. NORMAL FLORA
The normal flora comprises a permanent population of
organisms that are normally present in the following
sites :-
• Skin e.g. staphylococci
• Respiratory tract e.g. Streptococci
• Intestinal tract e.g. E.Coli, Bacteroides
• Genitourinary tract e.g. Lactobacilli
The bacteria which are capable of causing disease are
called pathogenic, many but not all, infections are
communicable i.e. are spread from person to person

13. BACTERIAL INFECTIONS OF
THE EYE
In the eye bacteria can cause the following
diseases:-
1. Bacterial Conjunctivitis
2. Bacterial Keratitis
3. Bacterial Uveitis
4. Optic Neuritis
5. Stye

14. 1. BACTERIAL CONJUNCTIVITIS
Many different bacteria can cause conjunctivitis
e.g.
– STAPHYLOCOCCI can cause acute conjunctivitis.
– HAEMOPHILUS INFLUENZA causes seasonal
epidemics in hot dusty climate.
– Pneumococcus , Meningococcus and
Streptococcus cause acute conjunctivitis

15. – Trachoma caused by Chlamydia trachomatis is the most
common preventable cause of blindness through out the
world. It causes two patterns of diseases in the eye, The
severe form is trachoma & The milder form is inclusion
conjunctivitis.
― Granulomatous conjunctivitis : this is a rare form
caused by the organisms causing:-
• TB
• Syphilis

16. Bacterial Conjunctivitis

17. Trachoma

18. PREDISPOSING FACTORS FOR BACTERIAL
CONJUNCTIVITIS
• All the types of bacterial conjunctivitis are more common
and more serious in hot climates for the following reasons:-
• Warm & humid climates
• Dust and solar radiations which irritate the conjunctiva
• Flies which carries infections from eye to eye
• Over crowding
• Poor ventilation
• Poor hygiene

19. 2. BACTERIAL KERATITIS
Predisposing factors are:-
• Following injury
• In an unhealthy cornea
• Hot dry air or sand particles in
atmosphere
• Vit-A deficiency can also lead to primary &
secondary Keratitis

20. • Bacteria causing Keratitis are almost the
same as those causing conjunctivitis.
• This is because the epithelium of the cornea is
directly continuous with the epithelium of the
conjunctiva.
• A corneal ulcer develops if there has been a
loss of some of the epithelium due to the
infection.

21. Bacterial Ulcer

22. 3. BACTERIAL UVEITIS
Bacteria causing uveitis are:-
– Mycobacterion TB
– Mycobacterium Laprae
– Syphilis

23. Cell & Flare

24. 4. OPTIC NEURITIS
Bacterial infection can damage the optic
nerve in:-
• Typhoid
• Syphilis

25. Optic Neuritis

26. 5. STYE
• STYE is an infection of eyelash follicle by
staphylococci

27. Stye

28. B. VIRUSES
Viruses are acellular microorganisms with the
following properties:-
• The viruses have an internal core composed
either of DNA or RNA.
• Viruses must produce with in the cells.
• They do not undergo binary fission.
• Some viruses have an outer protein coat called
envelope.
• The size of largest virus i.e Pox virus is equal to
the smallest bacteria i.e Chalamydia.

29. Virus

30. CLASSIFICATION
Classification according to the nuclear
material
• RNA VIRUSES e.g. HIV, Polio virus
• DNA VIRUSES e.g. Herpes, CMV,
Adenovirus etc

31. VIRAL INFECTIONS OF THE
EYE
1. Viral Conjunctivitis
2. Viral Keratitis
3. Uveitis
4. Optic Neuritis
5. Herpes Zoster Opthalmicus

32. 1. VIRAL CONJUNCTIVITIS
Unlike bacteria, the viruses live inside the cells and are
therefore immune to antibiotics.
There are following types of viral conjunctivitis:
– ANDENOVIRUS Conjunctivitis
– MEASLES Conjunctivitis
– MOLLUSCUM CONTAGIOSUM
– HERPES SIMPLEX Conjunctivitis

33. There are typical sign and symptoms of viral
conjunctivitis i.e.
• The secretions are watery
• There is a gritty sensation in eye
• The blood vessels of conjunctiva are dilated
• Conjunctival scrapping shows lymphocytes and
a few monocytes

34. Viral Conjunctivits

35. 2. KERATITIS/CORNEAL ULCER
There are many different types of corneal ulcers. But they
have typical signs and symptoms i.e. :-
• Pain
• Blurred vision
• Photophobia
• Watering
Different type of viruses can lead to ulcer formation in a
diseased cornea but the common type of virus causing
corneal ulcer in an otherwise healthy eye is Herpes
Simplex. It spreads from person to person.

36. Dendritic Ulcer

37. 3. UVEITIS
Viral causes of uveitis include:-
•Herpes Simplex
•Herpes Zoster
•Cytomegalo virus

38. Uveitis

39. 4. OPTIC NEURITIS
Viruses can damage the optic nerve
especially in a debilitated / Malnourished
patient. The important one is :
• Measles

40. 5. OPHTHALMIC HERPES
ZOSTER
• This is also called shingles and is caused
by Herpes Zoster / varicella virus which
also causes chicken pox
• The virus infection only involves one
sensory nerve on one side of the body
• Herpes Zoster usually occurs in the elderly
or immuno suppressed patients

41. HZO

42. C. FUNGUS
• The study of fungi is called Mycology, and
the diseases they cause are called Mycoses.
• There are two types of fungi :-
(i) YEASTS
– Yeasts are unicellular
– They rarely form filaments
– They grow by asexual budding

43. (ii) MOLDS
• Molds are multicultural
• They grow as long filaments
• These filaments are called HYPHAE
• The network formed by filament is
MYCELIUM

45. FUNGAL INFECTIONS OF EYE
1. Conjunctivitis
2. Keratitis
3. Uveitis

46. 1.CONJUNCTIVITIS
• Fungi do not cause acute conjunctivitis, it
rather causes a granulomatous
inflammation with regional
lympodenopthy e.g. as in sporotrichosis

47. 2. KERATITIS/ CORNEAL
ULCERS
• Fungal infections of the cornea are
common in the hot humid climate of
tropics
• Fungi usually live on plant matter;
abrasions to the cornea from twigs, thorns
or seeds have a greater risk of fungal
contamination
• Aspergillus and
• Candida

48. Aspergillus niger & Candida
albicans

49. Aspergillus
Keratitis

50. 3. UVEITIS
Fungi Causing Uveitis Are:
• Candida
• Histopasma

51. Iritis

52. D. PROTOZOA
• Protozoa are unicellular parasites in turn
is a living organism which has adopted
itself to existence in or on another animal
called host.
• The protozoa can eat, respire and
reproduce without help.

53. PROTOZOA AFFECTING THE
EYE
1. ACANTHAMOEBA
• Acanthamoeba is a wide spread protozoan
organism found in most tap water.
• It can invade the cornea to produce a typical
chronic central ulcer.
• Usually affect soft contact lens wearers.

54. Keratitis due to Acanthamoeba

55. 2. TOXOPLASMA
• Toxoplasmosis is a common & important cause of
chorioretinitis.
• The protozoan is wide spread throughout the
world.
• The main host in the life cycle of toxoplosma is
cat.
• Cysts are found in cat’s faeces.

56. • The secondary host is usually man or some other animal
& if the cysts are eaten they are changed into active
infective form.
• They invade the tissues & blood producing a generalized
illness with lymphadenopathy, then again forming tiny
cysts.
• To complete the life cycle the cat becomes infected by
eating meat containing these cysts.
• If a pregnant woman become infected, then the organism
cross the placenta & infect the fetus
• In the fetus they infect the CNS & Retina leading to
inflammation in the retina & choroids i.e. chorioretinitis

58. PARASITES AFFECTING THE
EYE
• Infections by parasites are one of the features of tropical
diseases & there is a vast range of parasites which can infect
the body. Important features of parasitic diseases of the eye
are:-
• Most are spread by insect vector
• The warm climate encourages the growth & survival of the
parasites, their larvae & their eggs out side the human body
• Poor sanitations & poor water supply
• People living in close contact with domestic animals
• Poverty & poor cooking facilities
• Some of these parasites have complex life cycles, living in two
or even three different hosts to complete their life cycle

59. Important Parasitic Diseases
Some of the important parasitic diseases are:-
• Onchocerciasis
• Loiasis
• Toxocara
• Cysticercosis
• Hydatid disease

60. 1. ONCHOCERCIASIS
• This is a parasitic disease caused by Onchocerca volvulus which is a
filarial worm.
• Large number of larval microfilaria are found in the skin and eyes.
• Onchocerciasis is spread by the bite of black fly.
• This fly breeds in the fast flowing rivers. The disease is commonly
called river blindness.
• About a quarter million people are blind and half a million partially
sighted from this disease.

62. Sclerosing keratitis in Onchocerciasis

64. 2. LOIASIS
• It is also caused by filarial worm, carried by fly.
• The life cycle is similar to O. volvulus except that it
is the adult worm which causes the symptoms &
there is no threat to the sight
• The site of bite is called CALABAR swelling

65. Loa Loa Worm under the
Conjunctiva

66. Calabar Swelling

67. 3. TOXOCARA
• Toxocara is a nematode living in the intestine of
dog.
• The larva is called visceral larva migrans leads
to a generalized Ant / post uveitis.

68. 4. CYSTICERCOSIS
• It is caused by pork tape worm i.e. tenia
solium.
• They from orbital & into ocular cysts.

69. 5. HYDATID DISEASE
• Hydatid disease is caused by dog
tapeworm echinococcus granulosus most
common site of infection is liver but may
enter the orbit.
• Rupture of cyst can lead to Anaphylaxis.