Gram Negative Bacteria Flashcards
E. Coli
Escherichia coli is part of the normal flora of the colon in humans and other animals but can be pathogenic both within and outside of the GI tract.
Among E. coli species, there are many serologically distinct combinations of the three strctural antigens: O, H, and K, and specific serotypes are associated with particular diseases.
Transmission of intestinal disease is commonly by the fecal–oral route, with contaminated food and water serving as vehicles for transmission
At least five types of intestinal infections that differ in pathogenic mechanisms have been identified: enterotoxigenic (ETEC), enteropathogenic (EPEC), enterohemorrhagic (EHEC), enteroinvasive (EIEC), and enteroaggregative (EAEC). E. coli all are basically the same organism, differing only by the acquisition of specific pathogenic traits.
The differences in virulence of various E. coli strains is correlated with the acquisition of plasmids, integrated prophages, and pathogenicity islands
Maintenance of fluid and electrolyte balance is of primary importance in treatment. Antibiotics may shorten duration of symptoms, but resistance is nevertheless widespread. Extraintestinal diseases require antibiotic treatment
Neisseria Meningitidis
Like N. gonorrhoeae, N. meningitidis is a nonmotile, gram-negative diplococcus, shaped like a kidney bean
one of the most frequent causes of meningitis, can also take the form of a fulminant meningococcemia, with intravascular coagulation, circulatory collapse, and potentially fatal shock, but without meningitis
The meningococcal polysaccharide capsule is antiphagocytic and, therefore, the most important virulence factor.
The epithelial lining of the nasopharynx acts as a barrier meaning colonization by N. meningitidisis generally asymptomatic
As a rare event, meningococci penetrate this barrier and enter the bloodstream where they rapidly multiply (meningococcemia).
If the disease is not severe, the patient may have only a fever and other nonspecific symptoms
But can also cross the blood-brain barrier and infect the meninges, causing acute inflammatory response: meningitis
Joint symptoms and a petechial and/or purpuric rash are commonly observed Within several hours the initial fever and malaise can evolve into severe headache, a rigid neck, vomiting, and photophobia
90 percent of cases of meningococcal disease are caused by serogroups A, B, and C, with B currently being the most common, after successful C vaccination programme
Salmonella enterica
rod-shaped, flagellated, facultative anaerobic, Gram-negative bacterium
S. typhimurium, S. enteritidis - food poisioning salmonellas
serovar Typhi/ Paratyphi A, B or C cause Enteric Fever
– Invasin - allows intracellular growth
– Fimbriae adhere to epithelium over ileal lymphoid tissue
(Peyer’s patches) → RE system
UK: travel-related – faecal-oral from contaminated food/water
Enteric fever - symptoms & signs
• Systemic disease (bacteraemia)
• Incubation period: 7-14 days
• Fever, headache, abdominal discomfort, constipation, dry cough
• Paratyphoid: generally milder
Legionella pneumophila
Thin, aerobic, pleomorphic, flagellated, nonspore-forming, Gram negative bacterium
the causative agent of Legionnaires’ disease
Aerosol spread - inhalation Human to human transmission does not occur
The bacteria are phagocytised by macrophages but prevent the phagosome fusing with a lysosome so evades destruction by the macrophage and instead uses the macrophage as a site to replicate and spread
Pseudomonas Aeruginosa
Gram -ve bacilli
Found in soil, water, plants, and animals.
Significant opportunistic pathogen and a major cause of nosocomial infections - pneumonia, nosocomial urinary tract infections, surgical site infections, infections of severe burns, and infections of patients undergoing either chemotherapy or antibiotic therapy.
P. aeruginosa is motile (it has polar flagella) and aerobic or facultative.
Can grow on a wide variety of organic substrates -water baths, hot tubs, intravenous (IV) tubing, and other water-containing vessels. This explains why the organism is responsible for so many nosocomial infections.
Pili on the bacteria mediate adherence, and mucoid strains predominate in patients with cystic fibrosis (CF).
P. aeruginosa causes both localized and systemic illness. Virtually any tissue or organ system may be affected. Individuals most at risk include those with impaired immune defenses.
It is difficult to find antibiotics effective because of its rapid development of resistance mutations and its own innate mechanisms of antibiotic resistance.
Pseudomonas infections typically occur in patients with impaired defenses. Therefore, aggressive antimicrobial therapy (often a combination of two bactericidal antibiotics, such as an aminoglycoside, an antipseudomonal β lactam, or a quinolone) is generally required
