Lecture 12. Spore Forming Gram Positive Rod PDF

Introduction to Microbiology Lecture 19 Endopores When faced with harsh environmental conditions, like depletion of any of several nutrients (carbon, nitrogen, or phosphorous). Some gram positive bacteria undergo a cycle of differentiation called sporulation. Sporulati...

Introduction to Microbiology Lecture 19 Endopores When faced with harsh environmental conditions, like depletion of any of several nutrients (carbon, nitrogen, or phosphorous). Some gram positive bacteria undergo a cycle of differentiation called sporulation. Sporulation involves the production of many new structures, enzymes, and metabolites along with the disappearance of many vegetative cell components. The spore contains a complete copy of the chromosome, the bare minimum concentrations of essential proteins and ribosomes, and a high concentration of calcium bound to dipicolinic acid The spore is a resting cell, highly resistant to desiccation, heat, and chemical agents. can exist for centuries as viable spores. When returned to favorable nutritional conditions, the spore germinates to produce a single vegetative cell. The location of the spore within a cell can assist in identification of the bacterium. The ultra structure and formation process of spores can vary from one species to another. (exact detailed structure is not exam material). Sporulation begins when a sporangium divides asymmetrically to produce two compartments: the mother cell and the forespore, which are separated by a septum. Next, the mother cell engulfs the forespore, and following membrane fission at the opposite pole of the sporangium, a double-membrane bound forespore is formed. Coat assembly begins just after the initiation of engulfment and continues throughout sporulation. The peptidoglycan cortex between the inner and outer forespore membranes is assembled during late sporulation. In the final step, the mother cell lyses to release a mature spore into the environment. Spores are capable of quickly germinating and resuming vegetative growth in response to nutrients. Overview Pathogens that will be discussed this lecture are Spore-Forming Gram-Positive rods Bacillus sepcies: The genus Bacillus includes large aerobic, gram-positive rods occurring in chains. Major pathogens include Bacillus anthracis and Bacillus cereus. Clostridium Species: a genus of Gram-positive rods, are obligate anaerobes. Major pathogens include Clostridium difficile. Clostridium perfringens, Clostridium tetani, Clostridium botulinum Overview Bacillus anthracis B. anthracis is a large (1 × 3 to 8 μm) organism arranged as single or paired Gram positive rods or as long, serpentine chains. Spores are are not seen in clinical specimens. Anthrax is primarily a disease of herbivores; humans are infected through exposure to contaminated animals or animal products. Exposure can also be part of biological warfare. Human B. anthracis disease is acquired by one of three routes: inoculation (Skin infections represent more than95% of cases), ingestion, and inhalation. Bacillus anthracis Bacillus anthracis Bacillus anthracis The major factors responsible for the virulence of B. anthracis are the capsule, edema toxin, and lethal toxin. The capsule made of poly-d-glutamic acid inhibits phagocytosis of replicating cells. Edema toxin is responsible for the fluid accumulation observed in anthrax. Lethal toxin is cytotoxic and stimulates macrophages to release proinflammatory cytokines. The spores germinate in the tissue at the site of entry, and growth of the vegetative organisms results in formation of a gelatinous edema and congestion. Almost all cases progress to shock and death within 3 days of initial symptoms unless anthrax is suspected and treatment is initiated immediately Bacillus anthracis Inhalation anthrax can be associated with a prolonged latent period (2 months or more), during which the infected Typically, cutaneous anthrax starts with the patient remains asymptomatic. Spores phagocytosed in the development of a painless papule at the site lungs; and transported by the lymphatic drainage to the of inoculation that rapidly progresses to an mediastinal lymph nodes, where germination occurs. ulcer surrounded by vesicles and then to a Hemorrhagic necrosis and edema of the mediastinum are necrotic eschar. early manifistations, Sepsis occurs and spread to other organs (GI ulcerations, meningitis) can take place. Bacillus cereus B. cereus and other Bacillus species are ubiquitous organisms, present in virtually all environments. B. cereus is responsible for two forms of food poisoning: vomiting disease (emetic form) and diarrheal disease (diarrheal form). The emetic form of disease results from consumption of contaminated rice. An intoxication caused by ingestion of the enterotoxin, not the bacteria. Thus the incubation period after eating the contaminated rice is short (1 to 6 hours), and the duration of illness is also short (