Gram negative bacteria session 4

OPTOMETRY · SEMESTER 2

Microbiology and Parasitology

CONCEPTS ON GRAM NEGATIVE BACTERIA

Gram Negative Bacteria of Medical Importance

Objectives

Define gram negative bacteria
List Gram Negative bacteria of medical importance
Identify characteristic of gram negative bacteria of ocular importance

Mention eyes diseases caused by gram negative bacteria of ocular importance List laboratory diagnosis, diseases caused and drug of choice for gram negative cocci bacteria 2

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 cholera.

LIST GRAM NEGATIVE BACTERIA OF MEDICAL IMPORTANCE

Neisseria Gonorrhoea

Pseudomonas aeruginosa
Escherichia coli
Chlamydia trachomatis
Klebsiella pneumoniae
Haemophilus influenzae
Moraxella species

Identify characteristic of gram negative bacteria of ocular importance

Cell wall structure .they have a thin peptidoglycan layer much thinner gram positive bacteria, possess an outer membrane outside the peptidoglycan.

Outer membrane present. cointains lipopolysaccharide (LPS), which is a major virulence factor.

Periplasmic space: Lies between inner and outer membranes, containing enzymes that can contribute to antibiotic resistance.

Staining property: Do not retain crystal violet stain during Gram staining, take up the counterstain (safarin) in appear pink/red under the microscope 5

Identify characteristic of gram negative bacteria of ocular importance continue

Virulence factors (important in eye infections) Endotoxin (LPS):Can trigger severe inflammation in contributes to corneal damage and intraocular inflammation.

Exotoxins and enzymes: some produce proteases and toxins that destroy corneal tissue.
Biofilm formation: particularly relevant in contact lens- related infections.
Antibiotic resistance
Outer membrane acts as a barrier to many antibiotics
Often possess β-lactamases and other resistance mechanisms
Makes infections harder to treat compared to Gram positive organisms

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

EYES DISEASES CAUSED BY GRAM NEGATIVE BACTERIA OF OCULAR IMPORTANCE

Species

Diseases They

Cause
Symptoms
Drug of Choice
Neisseria
Gonorrhoea
(gonococci)
Human cell is
the only host
Beta lactamase
group

Bacteria conjunctivitis (Pink Eye)

Note: Neisseria Gonorrhoeae can caused hyperacute, severe from that may damage the cornea quickly Redness, discharge (often purulent),irritation Doxycycline

Azithromycin
Pseudomonas aeruginosa
Keratitis (Corneal infection)
Ciprofloxacin

Neisseria spp under gram stain

Classification of gram-negative bacilli (rods) of medical importance

According to the site of infection

Those related to gastrointestinal tract examples, Eschelichia colli, Salmonella species, shigella species, Vibrio species (Enterobacteriaceae) Those related to respiratory tract

example, haemophilus species, pseudomonas aeruginosa,
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 11

Characteristics of vibrio cholera and Escherichia coli

V.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

Vibrio Cholera

Vibrio cholerae on gram stain

Characteristics of E.coli

Motile with or without capsule
Facultative anaerobe
Capable of growing at 44 degree centigrade
Lactose fermentors

Escherichia coli on gram stain

E.coli

EYES DISEASES CAUSED BY GRAM NEGATIVE BACTERIA OF OCULAR IMPORTANCE

Species
Diseases they Cause

Lab Diagnosis

Drug of Choice
Chlamydia trachomatis
Trachoma
Chronic infection leading to scarring of the eyelid and cornea
A leading caused of preventable blindness in some regions
Tetracycline
Erythromycin
Doxycycline

E. Coli

Klebsiella pneumoniae
Endophthalmitis
several infection inside the eye (often after surgery or trauma)
Pain ,vision loss, redness
This is a medical emergency
Ceftazidime

EYES DISEASES CAUSED BY GRAM NEGATIVE BACTERIA OF OCULAR IMPORTANCE

Species

Diseases They

Cause
Symptom
Drug of Choice
Haemophilus influenzae
Moraxella species

Orbital Cellulitis

Moraxella keratitis
Infection of tissues around the eye
Symptoms: swelling ,pain , fever, reduce eye
movement
Peripheral cornea ulcer
Chloromphenical
Co-trimoxazole
Ciprofloxacin

Haemophilus Species [Haemophilus Influenza and Haemophilus Ducreyi]

General Characteristics

Small non motile
Gram negative coccobacillae (rods with round ends)
Aerobic
Capsulated

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.). NewYork: 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 longmanGroup, UK ltd.

Jawetz, melnick, & adelberg's. (2007). Medical microbiology (4th ed.). United states of America: the mcgraw-hill companies,