Include intestinal pathogens
– Shigella dysenteriae (cause of bacillary dysentery) – Salmonella typhimurium (cause of gastroenteritis)
– Salmonella typhi (infects via intestinal route and causes typhoid fever)
Some don't have an intestinal habitat but resemble E. coli
– Protius is a common saprophyte of decaying organic matter – Yersimia pestis causes bubonic plague
– Erwinia is a plant pathogen
Bacteria
11. Enterics
Escherichia coli
• Live in lower intestines of mammals as part of intestinal flora -considered as necessary for proper digestion of food – human being discharges 0.1 to 10 trillion cells/day in fecal matter
• Coliform bacteria: All aerobic and facultative anaerobic non-spore forming, gram negative, rod shaped bacteria that can ferment lactose and produce gas within 48 hours at 35°C
– Includes fecal coliforms and bacteria similar to fecal coliforms but living in the ground
• Usually harmless but can cause illness specially when they get out of intestinal tract
– Cause honeymoon sickness when escape into the urinary tract (into the bladder)
– Cause fatal peritonitis when escape into the abdomen
(inflammation of peritonium – inner surface of the abdominal cavity and membrane covering of organs of the abdomen)
11. Enterics
Escherichia coli
• Some strains are toxicogenic and can cause food poisoning (from eating contaminated meat) – harbor both heat stable and and heat labile enterotoxins
• Some strains are enteropathogenic and can cause (acute but uncomplicated) intestinal tract infections, uncomplicated UT infections and neonatal meningitis
• Growing antibiotic resistance is a problem
• Considered as model organism of bacteria and is most studied in biology
– Among the first for entire chromosomal DNA base sequence determination
– used as indicator of fecal pollution of water – total and fecal coliform counts are used – can sometimes be misleading (also found in environments other than intestine, paper mills
– used in the experiments in cell biology, physiology, and
genetics and considered as the workhorse of molecular biology – Plays important role in modern biological engineering
– Often used as factories for producing substances like insulin
Bacteria
Bacteria
11. Enterics
Salmonella typhi
Causes typhoid - an extremely serious gastrointestinal tract infection with symptoms of
– High or intense spiking fever that raises slowly and chills
– Brady cardia (slow heart beat), unrelenting headache and myalgia (muscle pain)
– lack of appetite, constipation, and stomach pain – flat rose coloured spots on the trunk
– Becoming delirious and suffering intestinal hemorrhage – Delusions and confusion
Has long (about 2 weeks) incubation period
– Food or water borne (fecal contamination from infected person – The bacteria multiply in blood stream and get absorbed into
digestive tract and then eliminated from body as waste
– Recoverers are chronic carriers (harbor salmonella in gall bladder)
Diagnosis: by blood, bone marrow and stool culturing and Widal test (serological test)
Treatment: Antibiotics like amphicillin, chloramphenicol, trimetho-sulfa-methoxazole and ciproflaxacin – development of
resistance is a problem (multidrug resistant typhoid fever)
Bacteria
11. Enterics
Salmonella typhimurium
• Causative of gastroenteritis - also called stomach flu/gastric flu
• Non-inflammatory infection of upper bowel or inflammatory infection of colon – infection limited to stomach is gastritis and infection limited to small bowel is enteritis
• Acute but self-limiting infection (lasts <10 days)
• Symptoms: poor feeding (in infants), vomiting and fever, and rapidly followed by diarrhea
• Treatment: Oral/intravenous rehydration therapy Shigella dysenteriae
• Causative of bacillary dysentery (water borne disease
transmitted via fecal-oral route) – also known as shigellosis
• Symptoms: abdominal discomfort or fully blown dysentery
characterized by cramps, diarrhea and dehydration, fever, and vomiting, and blood, pus or mucus in stools (mucosal ulceration and rectal bleeding!)
• Common melody suffered by AIDS individuals
Bacteria
11. Enterics
Yerisimia pestis
• Causative plague – primarily a disease of redents and humans are infected when bitten by a rat flea, Xenopsylla cheopis
• Multiplication of the bacteria inside the flea blocks its stomach and cause insatiable hunger
• Hungry flea vorasiously bite the host and vomit bacteria contaminated blood into the wound
• In the absence of normal host the flea seeks alternative sources of blood (bites human being and spread the disease)
• Initial symptoms are chills, fever, diarrhea, headache and inflammation of lymph nodes
• Plague has a long history as a biological weapon
Bacteria
12. Vibrio
Comma shaped bacteria or bacteria with curved rod morphology Very common bacteria in aquatic environments
Have similarities with pseudomonads and enterics in structural and metabolic properties
– Like enterics these are facultative
– Like pseudomonads these have polar flagella, these are oxidase-positive, and do not ferment sugars
– Prefer salt water while Pseudomonads favor fresh water
Certain marine vibrios exhibit bioluminescence (blue-green light)
– saprophytes in dead fish or symbionts on living fish and
invertebrates – benefit fish through bioluminescence and get in return benefited by protected habitat and supplies of nutrients – Bioluminescence is catalyzed by luciferase - it diverts electrons
from respiratory electron transport chain and forms excited peroxide that leads to emission of light
Include Vibrio cholerae, causative of Asiatic cholera (an intestinal disease with pathology similar to diarrheal disease)
Bdellovibrio, a tiny curved rod, is a parasite of other Gram-negative bacteria (E. coli) - enters periplasmic space, obtains nutrients from cytoplasm and undergoes odd type of reproductive cycle
Bacteria
12. Vibrio
Vibrio cholerae
• Causative agent of water and food borne disease cholera
– For successful infection threshold dose of inoculum (about one million cells!) is needed
– Ingested bacteria, if survive stomach‟s acidic conditions reach small intestine and produce enterotoxins (cholera toxin)
– This toxin opens ion channels of cells of the intestinal lining and cause flow out of water into intestinal lumen from cells through osmosis – consequence is profuse and potentially lethal secretary diarrhea
– Blood group influences susceptibility : O group - most susceptible;
AB - most resistant, and A - more resistant than B
– People with weak immune system, decreased gastric acidity and malnourished are more susceptible
• Treatment: Aggressive rehydration and replacement of
electrolytes, and tetracycline for reducing duration and severity
• Can be prevented by better water supply & sanitation systems
– Proper disposal & treatment of waste produced by victims – Sewage treatment and water treatment
(boiling/filtration/chlorination)
– Warning systems about contaminated water resources
Bacteria
13. Nitrogen fixing bacteria
N2 fixation
• Reduction of N2 to NH3 - requires substantial reducing power (electrons) and energy (ATP)
• Produced NH3 is assimilated into amino acids and proteins
• Complicated process mediated by nitrogenase which is found only in prokaryotes and limited to a few select genera