CORYNEBACTERIUM

Scientific classification

Kingdom:BacteriaPhylum:ActinobacteriaClass:ActinobacteriaOrder:ActinomycetalesFamily:CorynebacteriaceaeGenus:CorynebacteriumSpecies:C. diphtheriae

Corynebacterium

Introduction

Corynebacterium diphtheriae is a pathogenic bacterium that causes diphtheria.

It is also known as the Klebs-Löffler bacillus, because it was discovered in 1884 by German bacteriologists Edwin Klebs (1834 – 1912) and Friedrich Löffler (1852 – 1915).

Basic characteristic

Corynebacteria belong in the family Mycobacteriaceae and are part of the CMN group (Corynebacteria, Mycobacteria and Nocardia).

The family Mycobacteriaceae are Gram-positive, nonmotile, catalase-positive and have a rod-like to filamentous morphology (Corynebacteria are often pleomorphic).

As a group, they produce characteristic long chain fatty acids termed mycolic acids.

Pathogenic species

C. diphtheriae is the etiologic agent of diphtheria.

These organisms colonize the mucus membranes of the respiratory tract and produce the enzyme neuraminidase which splits N-acetylneuraminic acid (NAN) from cell surfaces to produce pyruvate which acts as a growth stimulant.

Lab diagnosis

Gram stain is performed to show gram-positive, highly pleomorphic organisms with no particular arrangement (classically resembling Chinese characters).

Special stains like Alberts's stain and Ponder's stain are used to demonstrate the metachromatic granules formed in the polar regions.

Metachromacity is the phenomenon by which different parts of an organism can get stained in two or more different colours just by applying a single dye.

Cont.

The granules are called as polar granules, Babes Ernst Granules, Volutin, etc.).

An enrichment medium, such as Löffler's serum, is used to preferentially grow C. diptheriae.

After that, use a selective plate known as tellurite agar, which allows all Corynebacteria (including C. diphtheriae) to reduce tellurite to metallic tellurium.

The tellurite reduction is colormetrically indicated by brown colonies for most Cornyebacteria species or by a black halo around the C. diphtheriae colonies.

Special test

A low concentration of iron is required in the medium for toxin production. At high iron concentrations, iron molecules bind to an aporepressor on the betabactiophage, which carries the Tox gene. When bound to iron, the aporepressor shuts down toxin production.

Elek’s test for toxogenecity is used to determine whether the organism is able to produce the diphtheria toxin or not.

Antimicrobial sensitivity

The bacterium is sensitive to the majority of antibiotics, such as the penicillins, ampicillin, cephalosporins, quinolones, chloramphenicol, tetracyclines, cefuroxime and trimethoprim.

BACILLUS AND CLOSTRIDIUM

Bacillus

Bacillus sp.

Scientific classification

Domain:BacteriaDivision:FirmicutesClass:BacilliOrder:BacillalesFamily:BacillaceaeGenus:Bacillus

Basic Characteristics

Bacillus is a genus of Gram-positive rod-shaped bacteria and a member

of the division Firmicutes. Bacillus species can be obligate aerobes  or facultative anaerobes, and test positive for the enzyme catalase.[

Cont.

Ubiquitous in nature, Bacillus includes both free-living and pathogenic species.

Under stressful environmental conditions, the cells produce oval endospores that can stay dormant for extended periods. 

Nature application

the source of a natural antibiotic protein barnase (a ribonuclease), 

Alpha amylase used in starch hydrolysis,

the proteasesubtilisin used with detergents,

the BaMH1 restriction enzyme used in DNA research.

Medically important

B. anthracis, which causes anthrax, B. cereus, which causes a 

foodborne illness similar to that of Staphylococcus.

Other species

A third species, B. thuringiensis, is an important insect pathogen, and is sometimes used to control insect pests.

B. subtilis, an important model organism. It is also a notable food spoiler, causing ropiness in bread and related food. 

B. coagulans is also important in food spoilage.

Laboratory diagnosis

Using mannitol salt agar Incubated for a day Rod shape Oval endospore at one end Cell wall composed of techoic acid

Clostridium

Scientific classification

Domain:BacteriaPhylum:FirmicutesClass:ClostridiaOrder:ClostridialesFamily:ClostridiaceaeGenus:Clostridium

Basic characteristics

Gram positive Obligate anaerobe Producing endospore Rod-shaped Consists of around 100 sp. Free-living bacteria

Endospore in clostridium

Pathogenic species C. botulinum – causing botulism by producing

toxin in food/wound. Able to paralyse infant’s breathing muscles. Sometimes contain in honey but for adult, it is safe because it poorly compete with bacteria present in GI

C. difficile – overgrowth other bacteria in the gut during antibiotic therapy n cause pseudomembranous colitis

C. perfringens (C.welchii) – causing food poising until gas gangrene. Contain in salt raising bread

C. tetani – causing tetanus in muscle C. sordellii – causing death to women after

childbirth

Clostridium botulinum

Clostridium difficile

Toxin production

Neurotoxin production is the unifying feature of the species C. botulinum.

Seven types of toxins have been identified and allocated a letter (A-G).

Most strains produce one type of neurotoxin but strains producing multiple toxins have been described. 

Example: C. botulinum producing B and F toxin types have been isolated from human botulism cases in New Mexico and California.

Interesting info..

C. botulinum produces a potentially lethal neurotoxin that is used in a diluted form in the drug Botox, which is carefully injected to nerves in the face, which prevents the movement of the expressive muscles of the forehead, to delay the wrinkling effect of aging.

It is also used to treat spasmodic torticollis and provides relief for approximately 12 to 16 weeks

MYCOBACTERIUM TUBERCULOSIS

Scientific classification

Kingdom:BacteriaPhylum:ActinobacteriaOrder:ActinomycetalesSuborder:CorynebacterineaeFamily:MycobacteriaceaeGenus:MycobacteriumSpecies:M. tuberculosis

In cell

Introduction

1st discovered by Robert Koch Causative agent for tuberculosis Acid-fast bacili Aerobic (strictly aerobe) Pathogen of the mammalian

respiratory system Have a waxy coating (mycolic acid)

Lab diagnosis

Lowenstein-Jensen medium Flourescent microscopy Caseous granuloma Acid-fast staining

In culture

Cont.

Best shown in Zielh-Neelsen staining (acid fast stain)

It doesn’t retain crystal violet stain because lack of outer cell membrane

M. tuberculosis divides every 15–20 hours, which is extremely slow compared to other bacteria, which tend to have division times measured in minutes 

Cont.

It is a small bacillus that can withstand weak disinfectants and can survive in a dry state for weeks. Its unusual cell wall, rich in lipids (e.g.,mycolic acid), is likely responsible for this resistance and is a key virulence factor.

Macrophages unable to digest the bacteria because of its unique cell wall

Strain variation

Most of the different pathogenic strain associate with the different geographic regions

Some of it are newly discover but some are antibiotic-resistant

However, the hyper virulent strains are under M. tuberculosis

The end