Biology: Gram Positive Bacteria

Gram Positive Bacteria

• Gram positive bacteria include:
  • Firmicutes (Low GC Gram positive bacteria)
  • Actinobacteria (High GC Gram positive bacteria)
• Examples of non-spore forming bacteria:
  • Lactic acid bacteria (Streptococcus, Lactococcus, Lactobacillus)
  • Streptomyces, Corynebacteria, Mycobacteria, Staphylococcus, Listeria
  • Mycoplasma

Spore Forming Bacteria

• Examples of spore forming bacteria:
  • Clostridium
  • Bacillus
• Main characteristics of spore forming bacteria:
  • Form a distinctive type of dormant cell - the endospore
  • Highly resistant to heat, UV, toxic chemicals, and ionizing radiation
  • Typical G+ cell wall, but stain variably
  • Typical habitat is soil

Endospore Forming Bacteria

• Spore structure:
  • Exosporium: thin delicate layer of mostly protein
  • Spore coat(s): multiple layers of spore specific proteins
  • Cortex: loosely packed peptidoglycan
  • Spore protoplast or core: normal cell wall, plasma membrane, cytoplasm, and nucleoid
• Properties of the core:
  • Dipicolinate protects DNA
  • Dehydrated, only 10-30% of the water content of the vegetative cell
  • pH is more acidic than vegetative cell
  • Abundant small acid-soluble spore proteins (SASPs) give resistance to dry heat, desiccation, and UV
  • Carbon source during outgrowth
• Properties of the core:
  • Low metabolic activity (low O2 uptake)
  • No macromolecular synthesis
  • Low enzymatic activity
  • Low or absent mRNA synthesis

Germination

• Spores will remain dormant for decades, even in optimal conditions
• Examples of Bacillus species: Bacillus cereus, Bacillus anthracis

Bacillus Anthracis

• Causes anthrax, a serious infectious disease that occurs naturally in soil and affects domestic and wild animals
• Forms:
  • Cutaneous anthrax: most common form, affects animal workers, spores germinate in skin abrasions, symptoms include skin ulcer, black eschar, and can become systemic
  • Gastrointestinal anthrax: ingestion of undercooked contaminated meat, symptoms include nausea, severe abdominal pain, vomiting, and bloody diarrhea
  • Pulmonary anthrax: inhalation of spores, symptoms include flu-like symptoms, fever, myalgia, cough, headache, vomiting, and chest pain
• Virulence:
  • Capsule made of poly-D-glutamate polypeptide
  • Smooth mucoid colonies
  • pX02 plasmid
  • Toxin encoded on pX01 plasmid, consisting of 3 parts: PA (binding domain), EF (Edema factor), and LF (Lethal factor)
• Diagnosis:
  • G+ rod
  • Central (non-staining spore) occurs in soil and in culture, but not in clinical samples
  • Identified in blood, skin lesions, or respiratory secretions, or by measuring specific antibodies in the blood
• Treatment:
  • Penicillin, doxycycline, and fluoroquinolones (such as ciprofloxacin)
  • To be effective, treatment should be initiated early
• Prevention:
  • Pasteur demonstrated efficacy of vaccine
  • Attenuated vaccine possesses some toxicity
  • Used for occupational exposure
  • Control also relies on sterilization of wool, etc. from areas where anthrax is endemic
  • Three vaccines: Georgian/Russian, UK, and US vaccines

Bacillus Cereus

• One of the most abundant aerobic sporeformers found in soil
• Distinctive loosely spreading (Medusa) colonies, superficially resembling fungi
• Toxins are amongst the most powerful poisons known to man, 1 million times more toxic than rattlesnake poison

Clostridium Botulinum

• Found in soil, water, and decaying vegetation
• Fatal food poisoning that follows ingestion of preformed toxin from growth of organism in food
• Intoxification
• Anaerobic conditions (incompletely sterilized canning) may germinate spores, grow into vegetative cells, and produce deadly toxin
• Botulinum toxin:
  • May occasionally infect wounds
  • Infant botulism can result from ingestion of spores in soil and dust, germinating in intestine (anaerobic)
  • Honey added to formula feed found to contain spores
• Diagnosis:
  • Clinical
  • ELISA for toxin in food or suspect food is injected into mice
  • Culture is attempted
• Prevention:
  • Antitoxin is given to suspected cases
  • In contrast to spores, toxin is heat labile, therefore cooking inactivates
  • BOTOX (Botulinum toxin type A) is used to treat patients with overactive muscles, lasting for several months

Clostridium Tetani

• Causative agent of tetanus
• First described by Hippocrates
• Etiology discovered in 1884 by Carle and Rattone
• Commonly found in soil and intestines of animals (humans transiently)
• Terminal spore produces a drumstick shape
• Tetanus:
  • Spores are introduced into the body through a wound
  • After germination, organisms secrete exotoxins, causing more tissue damage, resulting in rapid spread of the organisms
  • Carbohydrate may be fermented, resulting in the production of large quantities of gas in tissue, constricting blood vessels
• Diagnosis and Identification:
  • Clinical picture
  • X-ray for gas
  • Definitive diagnosis requires isolation and identification
• Prevention and Treatment:
  • Cleansing of wounds
  • Antibiotics have little effect in necrotic areas
  • Surgery may be necessary to remove affected parts

Clostridium Perfringens

• Diagnosis and Identification:
  • Clinical picture
  • X-ray for gas
  • Usually on clinical picture (smell from protein digestion is characteristic)
  • Organism may be cultivated on Robertsons meat media and on blood agar incubated anaerobically
  • G+ large rods
  • Rancid smell on meat media
  • Hemolytic
• Prevention and Treatment:
  • Cleansing of wounds
  • Antibiotics have little effect in necrotic areas
  • Surgery may be necessary to remove affected parts
  • Additionally, C. perfringens is an important cause of food poisoning in man and animals by production of enterotoxins

Clostridium Difficile

• Causes pseudomembranous colitis, a severe colitis following antibiotic therapy
• Overgrowth of Clostridium difficile, a normal flora of many people
• Produces toxins
• Diarrhea is a common complication of antibiotic therapy, 20% of cases are caused by Clostridium difficile
• C. difficile is recognized as the most common nosocomial gastrointestinal infection
• Lesions: 2-10 mm

Spores and Activation

• Spores can be activated by various treatments, including heat shock, storage at low temperature (4°C), and germination in favorable conditions.
• The process of activation involves three stages: activation, germination, and outgrowth.

Longevity of Spores

• Spores are extremely stable and can survive for long periods, with some recorded instances of 70 years and even 25-40 million years.
• The oldest living cells in nature are spores, which can remain dormant for millions of years.

Bacillus

• Bacillus is a type of aerobic or facultative anaerobe that can form spores.
• They are mainly found in soil, but some species can be parasites or pathogens.
• Bacillus anthracis is a specific species that causes anthrax, a disease that affects animals and humans.

Anthrax

• Anthrax is a serious infectious disease that occurs naturally in soil and commonly affects domestic and wild animals.
• There are three main forms of anthrax: cutaneous, gastrointestinal, and pulmonary.
• Cutaneous anthrax is the most common form, accounting for around 2000 cases per year, and typically affects animal workers.
• Gastrointestinal anthrax is rare and occurs when contaminated meat is ingested, leading to symptoms such as nausea, vomiting, and diarrhea.
• Pulmonary anthrax is the most severe form, with a high mortality rate, and occurs when spores are inhaled.

Bacillus cereus

• Bacillus cereus is a type of aerobic sporeformer that is commonly found in soil.
• It can cause food poisoning, with two types of poisoning: short-incubation (emetic) and long-incubation (diarrheal).
• The short-incubation type occurs within 1-6 hours of eating and is caused by a heat-stable emetic toxin, while the long-incubation type occurs 6-18 hours after eating and is caused by an enterotoxin.

Clostridium

• Clostridium is a type of anaerobic sporeformer that is found in soil, water, and the intestinal tract of animals.
• They are fermentative and lack a cytochrome system and electron transport phosphorylation.
• They can produce highly toxic proteins (exotoxins) that can cause disease.
• Clostridium botulinum is a specific species that causes botulism, a fatal food poisoning.

Botulism

• Botulism is a fatal food poisoning that occurs when preformed toxin from Clostridium botulinum is ingested.
• The toxin is produced when the organism grows in food, and can be inactivated by heat.
• The disease can also occur when spores are ingested and germinate in the intestine, causing infant botulism.

Clostridium tetani

• Clostridium tetani is a specific species that causes tetanus, a disease that occurs when spores are introduced into the body through a wound.
• The organism is commonly found in soil and intestines of animals.
• The disease can be treated with antitoxin, and prevention involves proper wound care and vaccination.

This quiz covers the characteristics and examples of gram positive bacteria, including spore forming and non-spore forming bacteria. Learn about Firmicutes, Actinobacteria, and more.