LECTURE 7 (Gram -ve bacteria) Flashcards
What is Vibrio Cholera?
A member of the Vibrionaceae family, is a facultative anaerobic, Gram-negative, non-spore forming curved rod
MORPHOLOGY:
- Oxidase-positive, reduces nitrate and is motile (single polar flagellum)
- Distinguished from other vibrios by its biochemical reactions, O antigenic structure and production of Cholera toxin
What is Cholera?
An acute, diarrhoeal illness caused by infection of the intestine with the bacterium Vibrio Cholerae
INCUBATION PERIOD:
2 hours to 5 days
TRANSMISSION:
- fecal contamination of water and food
- shellfish
PATHOGENESIS:
- dependent on colonisation of V. cholerae and secretion of enterotoxin-cholera toxin
- v. cholerae attach to intestinal wall + cholera toxin is secreted and endocytosed by intestinal epithelial cells -> electrolyte channels are altered -> results in endoluminal fluid loss rich in chloride, bicarbonate, sodium and potassium [loss of fluid + electrolytes leads to cardiac + renal failure and acidosis and hypokalaemia]
SYMPTOMS:
- Rice-water stool
- Leg cramps
- Mild fever
- Vomiting
- Decrease urinary output
DIAGNOSIS:
- Isolation of V. cholerae from stool
- Shows colourless colonies on MacConkey’s agar since lactose is fermented slowly
- Organism is oxidase-positive, distinguishes from other members of enterobacteriaceae
TREATMENT:
- Salt solution
- IV fluids
- Antibiotics
PREVENTION:
- Cholera vaccines (Dukoral, Shanchol, Euvichol) require 2 doses for full protection
- Clean water + food supply
What are Campylobacters?
Campylobacters cause both diarrhoeal and systemic diseases and are among the most widespread causes of infection in the world
EXAMPLE: C. Jejuni
What is C. Jejuni?
Gram-negative rods with “gull wing” shaped that are non-spore-forming, motile bacteria with a single polar flagellum
LAB FINDINGS:
- Isolation by incubating at 42 degrees + using Skirrow’s medium prevents growth of other bacteria
- Blood free, CSM agar for isolation
TRANSMISSION:
- Domestic animals (cows, chicken, dogs) serve as a source
- Fecal-oral transmission
PATHOGENESIS:
Campylobacter have lipopolysaccharides with endotoxic activity (cytophatic extracellular toxins + enterotoxins) -> specific adhesions to proteins of host epithelium, invasion of intestinal cells and translocation of bacterium -> It multiplies in intestinal mucosa + secretes toxins which necrotise intestinal villi -> damage leads to loss of function [opening of shielding barrier + tight junctions, induction of inflammation, release of electrolytes -> bloody diarrhoea]
INCUBATION PERIOD:
2-5 days
SYMPTOMS:
- Gastroenteritis
- Bloody diarrhoea, dysentry, abdominal pain
- Nausea + vomiting
- Abdominal cramps
- Headache, fever, fatigue
COMPLICATIONS:
can progress to the autoimmune disease Guillain-Barré syndrome
DIAGNOSIS:
- Specimens = diarrhoeal stool/blood cultures from immunocompromised/elderly patients
- Smears
- Culture
TREATMENT:
Erythromycin or Ciprofloxacin
What is Guillain-Barré syndrome?
An autoimmune disorder in which the immune system mistakenly attacks healthy nerve cells, thus leading to weakness in the muscles, numbness and tingling
CAUSE:
It is attributed to the formation of antibodies against C. Jejuni that cross react with antigens on neurons
What are Helicobacters?
Curved gram negative rods that are strong urease-positive
[different from campylobacters since campylobacters are urease-negative]
What is H. Pylori?
A spiral-shaped, gram-negative, motile, urease positive rod that is oxidase and catalase positive
ISOLATION:
- grows in 3-6 days when incubated in a microaerophilic environment
- Skirrow’s medium
TRANSMISSION:
- person-to-person transmission
- interfamilial spread
PATHOGENESIS:
- found deep in mucous layer near epithelial surface -> toxins + lipopolysaccharide damage mucosal cells + ammonia produced by urease activity may also damage cells
- protease produced modifies the gastric mucous + reduces ability of acid to diffuse through the mucous
- can cause stomach cancer (MALT and gastric adenocarcinoma)
SYMPTOMS:
- Abdominal pain
- Gastric reflux + Belching
- Bloating + Distension
- IBS
- Constant bad breath
- Nausea
[associated with upper GI conditions e.g Chronic Gastritis, Peptic ulcer disease, Gastric malignancy]
DIAGNOSIS:
- Gastric biopsy specimens
- Smears + cultures
- Antibody detection
- Rapid tests
TREATMENT:
[antibiotics + drugs that reduce gastric acidity]
- Metronidazole + Bismuth subsalicylate/Bismuth subcitrate + Amoxicillin/Tetracycline for 14 days
What is Yersinia Enterocolitica?
A motile, gram-negative, rod-shaped bacteria that causes gastroenteritis.
TRANSMISSION:
- It is caused by the ingestion of contaminated foods with animals being the major source
- Fecal-oral route
PATHOGENESIS:
- INVASION = virulence factors allow binding to intestinal wall + systemic invasion into regional lymph nodes + bloodstream
- ENTEROTOXIN = caused diarrhoea
SYMPTOMS:
- Nausea + vomiting
- Diarrhoea
- Abdominal pain
- Fever
POST-INFECTION COMPLICATIONS:
- Erythema nodosum
- Reactive arthritis
DIAGNOSIS:
made by isolation of organism from faeces + blood
TREATMENT:
patients with sepsis should be given antibiotics
What is Bacteroides fragilis?
Gram-negative, rod-shaped bacteria that does not contain lipid A in its outer cell membrane (NO ENDOTOXIN!), has a capsule and has low virulence. It inhabits the human colon.
CLINICAL CORRELATION:
- When abdominal surgery is performed with bowel penetration, or when the intestine ruptures secondary to infection or ischemia THEN the bacteria forms ABSCESSES
- Following surgery, antibiotics (e.g Clindamycin, Metronidazole) are given as prophylaxis against it -> If an abscess forms, it must be surgically removed
What are Bacteroides Melaninogenicus?
It lives in the mouth, vagina and intestine and is involved in necrotising anaerobic pneumonias caused by aspiration of sputum from mouth + causes periodontal disease
What is Pseudomonas Aeruginosa?
An aerobic, motile, gram-negative, oxidase-positive bacteria that produces a green fluorescent pigment (PYOVERDIN) and a blue pigment (PYOCYANIN) which give infected wound dressings a greenish-blue colouration
EPIDEMIOLOGY:
usually found in water, soil and vegetation but colonises immunocompromised people with wounds, burns, urinary + respiratory tract
PATHOGENESIS:
1) P aeruginosa binds and secretes A-B exotoxin A (Exo A) which acts on protein synthesis
2) A type III injection secretion system delivers exoenzyme S to the cell cytoplasm
3) Elastase is secreted extracellularly + all toxins act to destroy the cell + bacteria may enter the blood
DIAGNOSIS:
Oxidase-positive colonies, pyocyanin production and ability to grow at 42 degrees distinguishes from other Pseudomonas species
TREATMENT:
Resistance to penicillins and ahminoglycosides is common
What are Burkholderia?
Oxidase-positive, aerobic gram-negative bacillus that grow in water soil, plants and animals
What are Acinetobacter?
Obligate aerobe, oxidate negative, non-lactose fermenter that are found in soil and water and cause a wide range of infections in the hospital
PATHOLOGY:
Resemble Enterobacteriaceae in growth pattern but cannot ferment carbohydrates or reduce nitrates
CLINICAL CORRELATION:
- Hospital acquired pneumonia
- Burn infections
- Foley catheter-associated urinary tract infections
TREATMENT:
resistant to penicillins, cephalosporins and aminoglycosides
What is Stenotrophomonas Maltophilia?
An increasingly common pathogen in hospitalised patients
INFECTIONS:
- pneumonia
- line-related bacteremia
It has a chance to thrive in people placed on broad antibiotic coverage for other pathogens
