General Characteristics
-Teichoic acids are linked to either the cytoplasmic membrane (the lipoteichoic acids) or to the cell wall peptidoglycan. Teichoic acids are unique to Gram-positive bacteria and play roles in adherence and triggering Gram-positive shock as the cell wall is broken down.
-A variety of cell surface proteins are present, which are organism specific.
-Gram-positive bacteria have no outer membrane and therefore no hydrophobic barrier to limit access of larger antibiotics to the peptidoglycan.
- Genus: Staphylococcus. Common name: Staphylococci
- Features
- Gram-positive cocci generally in tight grapelike clusters or, in specimens, as singlets, pairs, or short chains as well as clusters.
- Catalase-positive, breaking down hydrogen peroxide into water and oxygen.
- Facultative anaerobes producing energy more efficiently aerobically.
- Haloduric (salt-tolerant).
- Speciated medically on the basis of coagulase and hemolysis.
- Genus: Streptococcus. Common name: Streptococci
- Features
- Gram-positive cocci in chains or pairs. They tend to be oval.
- Distinguished from staphylococci on the basis of the catalase test. Streptococci are catalase-negative, aerotolerant anaerobes that grow in full oxygen but ferment both in the presence and absence of oxygen.
- Subdivided or speciated by three different systems: serology, hemolysin production, and biochemical properties.
- Serology using Lancefield’s antibodies to cell wall carbohydrates
- Streptococci that are positive for these carbohydrates are classified into Lancefield’s serogroups (e.g., Group A strep). There are now more than 20 groups.
- Bacteria that have these cell wall carbohydrates produce a pyogenic reaction.
- Some alpha-hemolytic streptococci including Strep. pneumoniae and the viridans streptococci lack these cell wall carbohydrates. They are not grouped using Lancefield’s antibodies and are not pyogenic.
- Hemolysin testing
- Biochemical tests
- Streptococci are mainly opportunists but can cause disease in debilitated patients or if they gain entry into the body.
- Genus: Enterococcus
- Features
- Catalase-negative, facultative anaerobes fermenting even in full oxygen; Streptococcal family.
- Alpha-hemolytic or nonhemolytic, Gram-positive cocci in chains that have the Group D streptococcal cell wall carbohydrate.
- Part of the normal human gastrointestinal (GI) flora.
- Tolerant of high concentrations of bile salts and NaCl.
- Have a high level of drug resistance that continues to increase due to efficient acquisition of plasmid transposon genes for drug resistance.
- Genus: Peptostreptococcus
- Features
- Peptostreptococci are obligate anaerobic streptococci
- They are part of the normal flora of the oral, intestinal, and genitourinary tracts
- Genus: Bacillus
- Features
- Gram-positive, spore-forming rods that may form chains. Although spores survive for decades in dry environments, they quickly germinate in rich moist conditions (e.g., a macrophage) and transform into metabolically active vegetative cells.
- They are aerobes (or facultative anaerobes) and grow well in ambient air.
- They cause anthrax (Bacillus anthracis) and food poisoning (Bacillus cereus).
- Genus: Clostridium. Common name: Clostridia
- Features
- Anaerobic, Gram-positive, spore-forming rods that can form chains.
- Cause botulism (Cl. botulinum) characterized by a flaccid paralysis; gas gangrene and food poisoning (Cl. perfringens); and tetanus (Cl. tetani), characterized by rigid spasms.
- Genus: Listeria. Listeria monocytogenes is the only human pathogen
- Features
- Short Gram-positive, non-spore-forming rod showing weak beta-hemolysis on blood agar.
- Motile in broth by tumbling. (They lack forward movement.)
- Facultative intracellular pathogens; they move from cell to cell by actin polymerization, which may propel the bacterium directly into an adjoining cell without exposure to extracellular milieu.
- Grows in the cold and, unlike most non-spore-forming pathogens, survives in the environment.
- Listeria monocytogenes is found in animal feces, rotting vegetation, and occasionally in soft cheeses, deli meats, and cabbage.
- Causes mild gastroenteritis, as well as septicemia in pregnant women, leading to potential fetal septicemia or meningitis, and may cause meningitis in immunocompromised patients.
- Genus: Erysipelothrix
- Features
- Aerobic Gram-positive, non-spore-forming rods.
- Found in animals and rotting organic material; entry is through traumatic implantation.
- Cause cutaneous erysipeloid primarily in fishmongers, butchers, and veterinarians.
- Genus: Corynebacterium
- Features
- Club-shaped, Gram-positive non-spore-forming bacteria.
- Found in Chinese character-like arrangement of cells.
- Aerobic and nonmotile.
- Part of normal flora; the non-toxin-producing corynebacteria found in the normal microbiota are called diphtheroids.
- Tox+ C. diphtheriae causes diphtheria, and Corynebacterium jeikeium causes infections via catheters and foreign bodies in immunocompromised hosts.
- Genus: Actinomyces
- Features
- Anaerobic, Gram-positive rods with some branching; nonmotile.
- Found in crevices between teeth and gums and female genital tract.
- Not acid-fast.
- These bacteria are related to mycobacteria.
- They have a similar cell wall but lack the extremely long chain fatty acids found in the mycobacterial cell wall. They have shorter fatty acid chains.
- Cause cervicofacial or pelvic infections following trauma that has resulted in necrotic tissue; colonies formed in tissue are sometimes described as “sulfur” granules.
- Genus: Nocardia.
- Features
- Gram-positive filamentous bacteria breaking up into rods.
- Aerobic soil organism.
- Often described as weakly or partially acid-fast as the slide will show some areas where the cells retain some of the carbol-fuchsin (hot pink red color).
- Related to mycobacteria—have a cell wall with shorter chain mycolic acids; are somewhat resistant to drying, so they are transmitted in dust.
- Cause tuberculosis-like (but not contagious) bronchopulmonary disease in immunocompromised patients.
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