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.