Microbiology, Parasitology & Entomology – By the end of this session, students are expected to be able to:
Read the complete lesson in an organized slide-by-slide format. This topic contains 30 learning sections from the source presentation.
LESSON CONTENTS — 30 SECTIONS
Session 4: Gram Negative Bacteria of Medical Importance
Learning Objectives
By the end of this session, students are expected to be able to:
- Define Gram negative bacteria
- Describe characteristics of Gram negative cocci bacteria
- Classify Gram negative bacilli of medical importance
- List laboratory diagnosis, diseases caused and drug of choice for Gram negative cocci bacteria
- Describe individual characteristics of Gram negative bacilli of medical importance
- Describe individual characteristics of Yersinia and Brucella
Definition of Gram Negative Bacteria
Gram negative bacteria: Bacteria which appears red, after losing the colour of primary
stain and adapting the colour of a counter stain (dilute carbofuchsin or safranin, or neutral red) when stained by Gram stain.
Examples of Gram negative bacteria of medical importance are neisseria species, salmonella species, haemophilus species, and vibrio cholerae.
Characteristics of Gram Negative Cocci
Bean shaped cocci
The pathogenics are intracellular (they live inside the host cell normally
polymorphonuclear cells like macrophages)
Oxidase positive
Have pilli
Non motile
Non sporing
Slide 5
NEISSERIA GONORRHOEAE
Neisseria gonorrhoeae, also known as gonococci, or gonococcus, is a species of Gram-negative coffee bean-shaped diplococci bacteria responsible for the sexually transmitted infection gonorrhea
Neisseria gonorrhea
Classification of Gram Negative Bacilli (rods) of MedicalImportance
Those related to gastrointestinal tract
Examples, Eschelichia colli, Salmonella species, Shigella species, Vibrio species (Enterobacteriaceae)
Those related to respiratory tract
Example, Haemophilus species
Related to Reticulo endothelial organs like liver and spleen
Example, Brucella species
According to Animal Source
Those which are transmitted from animals to humans (zoonotic organisms)
Examples Brucella species and Yersinia species
Characteristics of Vibrio Cholera and Escherichia Coli
Cholerae
Curved, comma shaped Gram negative rod
Oxidase positive
Motile
Tolerant to alkaline environment
Grows rapidly in the pH range of 7.4 to 9.6
Facultative anaerobe
Slide 11
E.Coli
Motile with or without capsule
Facultative anaerobe
Capable of growing at 44 Degree Centigrade
Lactose fermentors
Slide 13
Slide 14
Characteristics of Shigella and Salmonella
Gram negative rods
Non spore forming
Capable of aerobic and anaerobic respiration
Slide 16
Cont..
Characteristics of Yersinia and Brucella
Genus Yersinia
The genus Yersinia includes species which are short, pleomorphic Gram-negative rods that can exhibit bipolar staining.
Catalase-positive, oxidase-negative, and microaerophilic or facultatively anaerobic.
Most have animals as their natural hosts, but they can produce serious disease in humans.
Yersinia species of medical importance includes
Yersinia pestis, cause of plague in human
Yersinia pseudotuberculosis cause of disease which resembles tuberculosis
Yersinia enterocolitica, important causes of human diarrhea diseases
Characteristics of Yersinia Pestis
pestis is a Gram-negative rod that exhibits striking bipolar staining with special stains giving its characteristic safety pin appearance.
oNot motile
Grows as a facultative anaerobe on many bacteriologic media
Growth is more rapid in media containing blood or tissue fluids and fastest at 30 °C
Aerobic
Oxidase positive
Slide 20
Slide 21
Characteristics of Breucella Group
Gram negative rods
Intracellular
Aerobic
Oxidase positive
Non capsulated
Slide 23
Haemophilus Species [Haemophilus Influenza and HaemophilusDucreyi] (
General Characteristics
Small non motile Gram negative coccobacillae (rods with round ends)
Aerobic
Capsulated
Slide 25
Key Points
Gram negative bacteria lose the colour of primary stain and adapt the colour of secondary (Counter stain) stain.
There is a large group of Gram negative bacteria but only some causes diseases to man, including Neisseria spp, Haemophilus spp, Vibrio. Gonorhoea, N.meningitids, Vibrio cholera.
Most of these organisms are diagnosed by doing Gram staining, culture, serological tests.
Evaluation
What is the Gram negative bacteria related to gastrointestinal tract?
Which specimen is collected in order to diagnose cholera?
What are the diseases caused by Neisseria gonorrhoea
References
- Becker, F.J. & Silverton, R.E. (1985). Introduction to Medical Laboratory Technology
- 6th ed.) London: Butterworth.
- Brooks, G.F., Butel, J.S., Morse, S.A. et al, (2007). Medical Microbiology (24th ed.). New York: McGraw- Hill.
- Cook, G. (2000). Manson’s Tropical Diseases (22nd ed.). London: WB Saunders Company Ltd.,
- Greenwood, D., Richard, C.B.S, & John, F.P. (1992). Medical Microbiology (4th ed). Hong Kong: UK: ELBS with Churchill Livingstone, Medical Division of Longman Group, UK Ltd.
- Jawetz, Melnick, & Adelberg’s. (2007). Medical Microbiology (4th ed.). United States of
- America: The McGraw-Hill Companies, Inc.
Slide 29
Cont..
Levinson, W. (2004). Medical Micribiology and Immunology. (8th ed.). Examination & Board Review. (8th ed.). New York: International Edition Lange Medical Books /McGraw Hill Medical Publishing & Davson.
Monica, C. (1987). Medical Laboratory Manual for Tropical Countries. (2nd ed.). Volume 1. (2nd ed.). Oxford: ELBS Butterworth, Heinemann Ltd.
Monica, C. (1998). District Laboratory Practice in Tropical Countries. Part 1. Tropical Health Technology. Noida, India: Gapson Papers Ltd.
Monica, C. (2000). District Laboratory Practice in Tropical Countries. Part 2. Tropical Health Technology, UK: Cambridge University Press.
Satish, G. (1982). The Short Handbook of Medical Microbiology. New Delhi, India: Jaypee Brothers Medical Publishers PVT Ltd.
Wadsworth Centre. (2010). Bacteria: Escherichia coli. New York: State Department of Health. Retrieved May 5th, 2010 from www.wadsworth.org/databank/ecoli.htm.
Additional Study Notes
This section is separated from the source slides to make the lesson easier to revise.
Supplementary learning: For every microorganism or parasite, revise classification, morphology or structure, reservoir or habitat, transmission, life cycle or replication where applicable, diseases caused, appropriate specimens, laboratory diagnosis, prevention and general treatment principles taught in the course.
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