Neisseria are cocci that live on mucosal surfaces of the human body. They are fastidious, or difficult to culture, and they require high levels of moisture, nutrient supplements, and carbon dioxide. Also, Neisseria are microaerophilic, meaning that they require low levels of oxygen. For optimal growth and for the purposes of identification, Neisseria spp. are grown on chocolate agar (i.e., agar supplemented by partially hemolyzed red blood cells). Their characteristic pattern of growth in culture is diplococcal: pairs of cells resembling coffee beans ( [link] ).
The pathogen responsible for pertussis ( whooping cough ) is also a member of Betaproteobacteria. The bacterium Bordetella pertussis , from the order Burkholderiales , produces several toxins that paralyze the movement of cilia in the human respiratory tract and directly damage cells of the respiratory tract, causing a severe cough.
[link] summarizes the characteristics of important genera of Betaproteobacteria.
| Class Betaproteobacteria | ||
|---|---|---|
| Example Genus | Microscopic Morphology | Unique Characteristics |
| Bordetella | A small, gram-negative coccobacillus | Aerobic, very fastidious; B. pertussis causes pertussis (whooping cough) |
| Burkholderia | Gram-negative bacillus | Aerobic, aquatic, cause diseases in horses and humans (especially patients with cystic fibrosis); agents of nosocomial infections |
| Leptothrix | Gram-negative, sheathed, filamentous bacillus | Aquatic; oxidize iron and manganese; can live in wastewater treatment plants and clog pipes |
| Neisseria | Gram-negative, coffee bean-shaped coccus forming pairs | Require moisture and high concentration of carbon dioxide; oxidase positive, grow on chocolate agar; pathogenic species cause gonorrhea and meningitis |
| Thiobacillus | Gram-negative bacillus | Thermophilic, acidophilic, strictly aerobic bacteria; oxidize iron and sulfur |
- What characteristic do all Betaproteobacteria share?
Part 2
When Marsha finally went to the doctor’s office, the physician listened to her breathing through a stethoscope. He heard some crepitation (a crackling sound) in her lungs, so he ordered a chest radiograph and asked the nurse to collect a sputum sample for microbiological evaluation and cytology. The radiologic evaluation found cavities, opacities, and a particular pattern of distribution of abnormal material ( [link] ).
- What are some possible diseases that could be responsible for Marsha’s radiograph results?
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Gammaproteobacteria
The most diverse class of gram-negative bacteria is Gammaproteobacteria , and it includes a number of human pathogens. For example, a large and diverse family, Pseudomonaceae , includes the genus Pseudomonas . Within this genus is the species P. aeruginosa , a pathogen responsible for diverse infections in various regions of the body. P. aeruginosa is a strictly aerobic, nonfermenting, highly motile bacterium. It often infects wounds and burns, can be the cause of chronic urinary tract infections, and can be an important cause of respiratory infections in patients with cystic fibrosis or patients on mechanical ventilators. Infections by P. aeruginosa are often difficult to treat because the bacterium is resistant to many antibiotics and has a remarkable ability to form biofilms. Other representatives of Pseudomonas include the fluorescent (glowing) bacterium P. fluorescens and the soil bacteria P. putida , which is known for its ability to degrade xenobiotics (substances not naturally produced or found in living organisms).