Gram Positive Bacteria Flashcards
Clostridium. Difficile
C. difficile is a minor component of the normal flora of the large intestine.
When antimicrobial treatment suppresses more predominant species in this community, C. difficile proliferates.
Pathogenic strains produce two toxic polypeptides, designated toxins A and B. Toxin A is an enterotoxin that causes excessive fluid secretion,stimulates an inflammatory response, and has a cytopathic effect
Toxin B is a cytotoxin that disrupts protein synthesis and causes disorganization of the cytoskeleton.
After its introduction to a site, the environment becomes persistently contaminated with spores, and new residents are easily colonized.
Virtually all antimicrobial drugspredispose to diaorrhea and colitis.
The three drugs most commonly implicated are clindamycin, ampicillin, and the cephalosporins.
The severity of disease varies widely from mild diarrhea through varying degrees of inflammation of the large intestine to a life-threatening pseudomembranous colitis
C. difficile can be cultured from stools, but more rapid and useful tests are demonstrate toxin production
Discontinuance of the predisposing drug and fluid replacement usually lead to resolution of the symptoms. Relapses, however, are common.
Clostridium perfringens
Gram-positive, rod-shaped, anaerobic,spore-forming pathogenic bacterium
Third most common cause of food poisioning
The toxin involved in gas gangrene is known as α-toxin, which inserts into the plasma membrane of cells, producing gaps in the membrane that disrupt normal cellular function
Clostrudium botulinum
Gram-positive, rod-shaped,anaerobic, spore-forming, motile bacterium with the ability to produce the neurotoxin botulinum
Botulism poisoning can occur due to preserved or home-canned food that has gone off.
The botulinum toxin can cause a severe flaccid paralytic disease and is the most potent toxin known to mankind, natural or synthetic, with a lethal dose of 1.3–2.1 ng/kg in humans.
The control of food-borne botulism caused by C. botulinum is based on thermal destruction
Clostridium tetani
rod-shaped, anaerobic, Gram positive
C. tetani is found as spores in soil or in the gastrointestinal tract of animals. Enters a host through a wound to the skin, then it replicates. High risk individuals are people exposed to soil or animal feces.
Pproduces a potent biological toxin, tetanospasmin, and is the causative agent of tetanus, a disease characterized by painful muscular spasms that can lead to respiratory failure and, in up to 10% of cases, death.
The tetanus toxin blocks inhibitory impulses, by interfering with the release of neurotransmitters. With diminished inhibition, the resting firing rate of the alpha motor neuron increases, producing rigidity, unopposed muscle contraction and spasm. Characteristic features are risus sardonicus (a rigid smile), trismus (commonly known as “lock-jaw”), andopisthotonus (rigid, arched back).
Tetanus can be prevented through the highly effective tetanus vaccine, which is a tetanus toxin inactivated with formaldehyde to be immunogenic but not pathogenic
Streptococcus Pneumoniae
Gram-positive, nonmotile, encapsulated cocci
S. pneumoniae is the most common cause of community-acquired pneumonia and adult bacterial meningitis and is an important cause of otitis media, sinusitis and mastoiditis.
It releases an α hemolysin that damages red cell membranes, causing colonies to be α hemolytic.
The polysaccharide capsule is both antiphagocytic and antigenic. Threrefore growth is facillitated prior to the appearance of anti-capsular antibodies and it is particularly dangerous to those with no functioning spleen.
Obligate parasite of humans and can be found in the nasopharynx of many healthy individuals
There are two types of pneumococcal vaccine:
_pneumococcal polysaccharide vaccine(_PPV) protects against the pneumococcal strains responsible for 85 to 90 percent of infections, including prominent penicillin-resistant strains and is indicated for the protection of high-risk individuals older than age 2 years
pneumococcal conjugate vaccine(PCV13) which is effective in infants and toddlers from 6 weeks
Viridans Streptococci
The viridans group of streptococci includes many gram-positive, catalase-negative, hemolytic species that constitute the main facultative oral flora.
The viridans streptococci are relatively avirulent, but S. mutans and S. sobrinus are components of dental plaque that produce lactic acid during metabolism of sugars, causing dental caries
In patients with abnormalheart valves, they can also infect these valves during a bacteremia, causing endocarditis.
Therefore, at-risk patients with rheumatic, congenital, or sclerotic valvular disease should receive prophylactic penicillin before undergoing dental procedures.
