MICROBIOLOGY
LECTURE OUTLINE 9
GRAM POSITIVE PATHOGENS OF MAN
[note: Information in your textbook is organized by portal of entry/region
affected by the disease. Use textbook index for specific pages, and/or
consult with other valid references.]
THE COCCI
Two major groups of gram positive, pathogenic cocci are:
STAPHYLOCOCCI
A. two species associated with man:
** a. alpha toxin
- beta hemolytic, damages macrophages and platelets
- produces tissue damage after the establishment of a focus of infection
**b. beta toxin
- beta hemolytic, hot-cold hemolysin
**c. delta toxin
- beta hemolytic
**d. gamma toxin
- beta hemolytic
- toxic substances released which kill leukocytes, particularly neutrophils and macrophages
- cause scaled skin syndrome
- TSS characterized by hypotension, fever, scarlet feverlike rash, desquamation of the skin upon recovery, multisystem involvement without disseminated infection
- an exotoxin produced in food prior to consumption
- staphylococcal food poisoning: ingestion of pre-formed enterotoxin
- enterotoxin is heat stable: not destroyed by cooking
STREPTOCOCCI
examples:
Group A, Type 13, beta-hemolytic streptococci
Group D, Type 3, alpha-hemolytic streptococci
- streptolysin O oxygen labile
- streptolysin S oxygen stabile
- hyaluronidase: spreading factor
- streptokinase: digests fibrin
- proteinases
- nucleases: DNase, RNase
- rheumatic fever
- acute glomerulonephritis
THE BACILLI
2 representative genera are:
Clostridia:
C. botulinum
C. perfringens
C. tetani
Mycobacteria: M. tuberculosis and M. leprae
The Clostridia
- causes botulism, a type of food poisoning which is actually an intoxication with a powerful exotoxin secreted into the food by the organism.
- preformed toxin must be present in the food before ingestion. Toxin is destroyed by heat.
- organism is a strict anaerobe, can not tolerate high concentrations of either salt or sugar, and does not produce the toxin at a pH of 4.5 or below. Therefore, toxin is found only in non-acid, canned foods such as beans, peas and mushrooms.
- symptoms: double vision, difficulty in swallowing, muscle weakness, nausea, vomiting. Toxin is a neurotoxin - death may occur due to paralysis of respiratory
muscles. Mortality: 30 - 65% untreated cases.
- treatment: prompt administration of the antitoxin (an antiserum injection).
- depends upon the ingestion of large numbers of viable cells
- most frequent source: meat and meat products
- toxin is produced during sporulation of the organism in the small intestine. Incubation is about 8 to 24 hours.
- symptoms: acute abdominal pain, diarrhea, usually no vomiting
- duration: less than 24 hours after onset
- C. perfringens is the most common causative agent, but other clostridia may be involved (C. novyi, C. septicum, and C.histolyticum).
- usually a mixed infection involving clostridia, facultative anaerobes, various organisms
- deep wounds, necrotic due to lack of oxygen because of diminished blood supply or the growth of aerobes and facultative anaerobes are the initiation sites for this disease.
- in necrotic areas: clostridial spores can germinate, vegetative cells liberate toxins and exoenzymes which destroy more tissue. Carbohydrates are fermented and gas is produced. This gas increases the pressure in the tissue and decreases blood supply. This causes more necrosis and allows the spread of the organisms.
- a number of toxins are produced - called lethal toxins - as many as 12 different ones. One of the most common is the alpha toxin, a lecithinase. This enzyme degrades lecithin which is an integral component in host cell plasma membranes.
- incubation: 8 to 48 hours depending on extent of contamination and severity of the wound. Individuals with diabetes are particularly susceptible because of reduced circulation and increased carbohydrates present in blood and tissue.
- treatment: surgical cleaning of wounds; amputation above necrosed areas; antitoxin and antibiotic therapies; hyperoxygen chamber
- causative agent of tetanus or lockjaw
- direct cause of the disease is a potent exotoxin secreted by cells growing in tissue. This toxin is absorbed into the blood and is thereby delivered to areas some distance from the local infected site. Toxin effects the synthesis and liberation of acetylcholine and causes muscle spasm.
- must be anaerobic - deep wounds or necrotic areas (low O2)
- incubation: 5 - 10 days, but many be as long as several weeks
- treatment: preventative - tetanus toxoid injections, initially three doses; lasts 10 or more years. In the case of a traumatic injury, a booster is usually given. Note: no one who has ever been vaccinated with the toxoid has ever developed this disease.
- if the individual has never been vaccinated with the toxoid, then the antitoxin is administered. This is an injection of preformed antibodies and provides temporary passive immunity. Toxoid vaccination is usually also done, but is not an effective treatment.
1. Mycobacterium tuberculosis
- causative agent of tuberculosis, a respiratory infection (usually)
- primary infection: Mycobacteria are inhaled, cause lesions in the lower respiratory tract called tubercles. Bacteria are usually found intracellularly within phagocytes inside of the tubercle. M. tuberculosis can survive within phagocytes and WBCs.
- primary lesions may develop into exudative lesions, characterized by growth of organisms within WBCs and tissue macrophages. Organisms my be spread by lymphatics. After the development of host CMI, exudative lesions may become productive lesions.
- productive lesions may heal or continue to be active
- if the productive lesion heals, the tubercle becomes fibrous and calcified. Organisms are trapped within, and can remain alive for years. Humoral antibodies are not protective; CMI must develop as the protective immune response.
- treatment: INH (isoniazid) and an antibiotic (streptomycin or rifampin).
- diagnosis: chest X ray and skin sensitivity test (tine test). Tine test uses tuberculin or purified protein derivative to test for a delayed hypersensitivity reaction.
2. Mycobacterium leprae
- never grown in artificial culture; can be grown in rabbit foot pads and in armadillos. Currently armadillos are usually used.
- organisms prefer lowered temperatures, 30 C rather than 37 C. Therefore, they grow in the extremities: hands, toes, nose, ear. They destroy nervous tissue, causing loss of sensation. The affected body parts are prone to injury without the host's knowledge. Injury may lead to secondary bacterial infections.
- leprosy or Hansen's disease 2 major forms
- incubation: up to 20 years. Disease is particularly slow and chronic. Death occurs from complications in tuberculoid leprosy.
- treatment: sulfone drugs and antibiotics (dapsone and rifampin)
last modified: May, 2003 [page/figure/table reference 4th edition, Nester ]