Gram positive bacilli

Gram positive bacilli :

Gram-positive bacilli are rod-shaped bacteria that retain the crystal violet stain used in the Gram staining procedure. They can be classified into several genera, including:

Bacillus: Includes species like Bacillus anthracis (causes anthrax) and Bacillus cereus (associated with food poisoning).

Clostridium: Anaerobic bacteria that include species like Clostridium tetani (causes tetanus), Clostridium botulinum (causes botulism), and Clostridium difficile (associated with antibiotic-associated diarrhea).

Listeria: Listeria monocytogenes is known for causing listeriosis, particularly in pregnant women and immunocompromised individuals.

Corynebacterium: Includes Corynebacterium diphtheriae, which causes diphtheria.

Propionibacterium: Often found on skin and can be associated with acne.

These bacteria can be important in both clinical microbiology and public health due to their pathogenic potential.

Medically Important Gram-Positive Bacilli Three general groups .Endospore-formers Bacillus, Clostridium.Non-endospore-formers Listeria.Irregular shaped and staining properties Corynebacterium, Mycobacterium.

        Bacillus species ( Spore-formers )

There are 48 species included in the genus bacillus with the following general characteristics: Gram-positive bacilli,       Spore former, Aerobic and facultative anaerobi.

  THE MOST IMPORTANT PATHOGENS:      1. Bacillus anthracis Agent of anthrax, a disease in livestock Bacillus sp. Humans acquire infection by contamination of wound or ingestion or inhalation of spores 2. Bacillus cereus Causes food poisoning                                                       

                   Bacillus anthracis

Morphology: Large gram positive bacilli   Non-motile Found in pairs or in long chains. Capsule could be demonstrated during growth in infected animals.    Spores are formed in culture, dead animal's tissue but not in the blood of infected animals.Spores are oval and centrally located Survival in Soil                   • Spores remain viable in soil for decades. • Changing environmental conditions (temp. rain etc.) help in survival and multiplication. 

Samples are collected depending on the site affected:Swab samples from cutaneous lesions and blood cultures.      Sputum and blood for pulmonary anthra. Gastric aspirate, feces and blood for enteric anthrax.                                                • Gram stained smears: Made from clinical samples, show large gram positive bacilli in long chains "Bamboo-like appearance".  • Giemsa stained smears: Purple bacilli with red capsule.                                            • Animal inoculation test: Experimental animals are injected intraperitoneally by a suspension of the test organism "Suspected B. anthracis culture". -The animal dies in 48-96 hours due to respiratory failure. -Large number of typical bacilli can be found in the blood and tissue of spleen of the infected animal.

Biochemical Identificatio:Sensitivity to penicillin : (Sensitive ) String-of-pearls test:(positive) ; As Bacillus anthracis is susceptible to penicillin, so when B. anthracis is grown on surface of a solid medium containing 0.05-0.50 units of penicillin/ml in 3-6 hrs the cells swell up. The cells become large, spherical and occur in chains on the surface of agar, resembling a string of pearls.                        Lysis by gamma phages: (Positive) This test accurately differentiate B.anthracis from other bacilllus species. Gamma Phage has the ability to lyse B. anthracis grown aerobically on blood or other nutrient agar and rarely lyses any other Bacillus species. 

PATHOLOGY There are different clinical forms of anthrax: CUTANEOUS ANTHRAX: 95-98% of anthrax cases are of this type. Infection occur through wounds, burns, which may progress to toxaemia and septicemia. The site of entry often produces a painless blister referred to as Malignant pustule. ENTERIC "INTESTINAL" ANTHRAX: Caused by the ingestion of infected meat. This form of the disease is severe and fata.PULMONARY ANTHRAX: Caused by the inhalation of large number of B. anthracis spores. It is usually fetal. This clinical form is commonly known as "wool sorter disease"

                       Bacillus cereus

• Gram-positive spore forming bacilli          • Bacillus cereus is a normal inhabitant of the soil, but it can be regularly isolated from foods such as grains and spices          • Produce β-hemolysis on blood agar Pathogenesis & clinical features  Spores are found on most raw foods like rice.      Spores are heat-resistant & survive rapid frying.Produce enterotoxin – ingested → food poisoning.Short IP – 4-6 hours – similar to Staphylococcal food poisoning (vomiting & diarrhoea) 

Pathogenesis To produce disease, the spore of the anthrax bacteria enters an opening in the body, either through a break in the skin, through ingestion into the GI tract, or through inhalation into the lungs. The spores are ingested at the site of entry by macrophages, in which they germinate into replicating bacteria and begin to produce toxins. When spores are inhaled, they are transported to the regional tracheobronchial lymph nodes, where germination occurs. The toxins cause edema, hemorrhage and tissue necrosis at the site. The bacteria enter the bloodstream and seed other organs. In inhalational cases, death occurs from a combination of respiratory failure with hemorrhagic mediastinitis, pleural effusions, overwhelming bacteremia, toxemia and often, meningitis.    

            Corynebacterium diphtheriae

Corynebacterium diphtheriae[a] is a Gram-positive 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). The bacteria are usually harmless unless they are infected by a bacteriophage that carries a gene that gives rise to a toxin.This toxin causes the disease.Diphtheria is caused by the adhesion and infiltration of the bacteria into the mucosal layers of the body, primarily affecting the respiratory tract and the subsequent release of an exotoxin. The toxin has a localized effect on skin lesions, as well as a metastatic, proteolytic effects on other organ systems in severe infections.Originally a major cause of childhood mortality, diphtheria has been almost entirely eradicated due to the vigorous administration of the diphtheria vaccination in the 1910s.

Diphtheria is no longer transmitted as frequently due to the development of the vaccine, DTaP. Although diphtheria outbreaks continue to occur, this often in developing countries where the majority of the population is not vaccinated.