Gram negative bacilli

Transcription

1 Gram negative bacilli

2 1-Enterobacteriaceae Gram negative bacilli-rods

3 Enterobacteriaceae Are everywhere Part of normal flora of humans and most animals They are cause of % septisemia -more than 70% urinary tract infections -many intestinal infections

4 Pathogens Salmonella typhii Shigella species Yersinia pestis are always associated with disease

5 Salmonella most clinically significant isolates belong to the species Salmonella enterica: many serotypes: Salmonella typhi, Salmonella choleraesuis, Salmonella typhimurium, Salmonella enteritidis. The most common sources of human infections are poultry, eggs, dairy products

6 Salmonella The infectious dose for Salmonella Typhi infections is low, so person-to-person spread is common. gastroenteritis, septicemia, enteric fever, and asymptomatic colonization.

7 Shigella Bloody diarrhae transmitted person to person Because as few as 100 to 200 bacteria can establish disease, shigellosis spreads rapidly in communities where sanitary standards and the level of personal hygiene are low.

8 Yersinia A zoonozis Y. Pestis: Plague :many epidemics: rats-fleas Yersinia enterocolitica gastroenteritis

9 Opportunistic bacteria Eschericia coli Klebsiella pneumoniae Proteus mirabilis

10 Infections with enterobacteriacae Animal reservoir:most Salmonella species,yersinia species Human carrier(shigella species,s.typhi) Endogenous spread (E.coli)

11 Enterobacteriacea Grow rapidly Have simple nutritional requirements Ferment glucose Oxidase negative Distinguish them from nonfermentative gramnegative rods

12 E.coli Grow rapidly on most culture media

13 Escherichia coli Epidemiology Most common aerobic, gram-negative rods in the gastrointestinal tract Most infections are endogenous (patient's microbial flora), although strains causing gastroenteritis are generally acquired exogenously Diagnosis Organisms grow rapidly on most culture media Enteric pathogens, with the exception of EHEC, are detected only in reference or research laboratories

14 Laboratory diagnosis Culture: Selective differential media: MacConkey agar Eosin-methylene blue agar Y.enterocolitica: cold enrichment

15 Nonfermenters Pseudomonas aeruginosa Burkholderia cepacia Stenotrophomonas maltophila Acinetobacter baumannii Acinotobacter lwoffii Morexalla catarrhalis

16 Pseudomonas aeruginosa Epidemiology Ubiquitous in nature and moist environmental hospital sites (e.g., flowers, sinks, toilets, mechanical ventilation and dialysis equipment) Diagnosis Grows rapidly on common laboratory media Identified by colonial characteristics (e.g., beta hemolysis, green pigment, grapelike odor) and simple biochemical tests (e.g., positive oxidase reaction; oxidative utilization of carbohydrates)

17 Pseudomonas aeruginosa

18 Gram positive bacilli Bacillus spp. Corynebacterium diphteria Erysiphelothrix Listeria spp.

19 Bacillus spp After coagulase-negative staphylococci and diphtheroids, members of the genus Bacillus are the third most common skin contaminant found in clinical specimens. On Gram stain they are large, wide, Gram-positive rods, often occurring singly or in pairs, which can produce endospores. They may be confused with clostridia on direct stains from specimens.

20 Bacillus spp-iii a genus of Gram-positive bacilli which are commonly found in nature soil, water, airborne dust. members of natural flora in the human intestines. Most species of Bacillus are harmless saprophytes, two species are considered medically significant: B.anthracis B. cereus.

21 B. anthracis causes anthrax in cows, sheep, and sometimes humans. Anthrax is transmitted to humans via direct contact with animal products inhalation of endospores. ingestion Sources of infection are usually industrial or agricultural and the infection is classified as one of three types: CUTANEOUS INFECTION (95% of human cases) INHALATION ANTHRAX (rare) : Bioterrorism agent GASTROINTESTINAL ANTHRAX (very rare!)

22 Diagnosis Microscopy: Gram positive centrally located spore forming bacilli Culture: Blood agar Bacillus produces large, spreading, gray-white colonies with irregular margins: Medusa head

23 B. anthracis

24 B. anthracis

25 Diagnosis-II Typical skin lesion: Dark centered necrotic lesion Culture Blood agar: Medusa head-like colonies

26 B. cereus toxin-mediated food poisoning. It is known to inhabit many kinds of food Rice stew, cereal, milk. The two toxins released by the vegetative form of the bacilli vomiting diarrhea, (symptoms similar to those of Staphylococcus food poisoning). Because toxin production usually takes place after the infected foods are cooked, proper cold storage of food is recommended immediately after preparation.

27 B. cereus

28 Corynebacterium diphtheriae aerobic extracellular rods; club-shaped, has granules V, L, or Chinese Letter colonies = Dark gray or black on potassium tellurite medium

29 Corynebacterium diphtheriae

30 Corynebacterium diphtheriae

31 C. diphtheriae-ii exotoxins = diphtheria toxin

32 symptoms: pseudomembrane formation in the throat; can be fatal

33 Humans are the only reservoir for C. diphteria. Upper respiratory tract infections and skin lesions Horizontal transmission occurs via respiratory droplets

34 virulance factors Diphtheria exotoxin Storage granules (metachoromatic bodies) Contain phosphate polymers for high-energy reserve Stain with metachromatic dye : methylene blue

35 Growth on Loeffler medium Metachromatic staining of storage granules Growth on tellurite medium - black colonies

36 VACCINE & TOXOID Toxoid - inactive toxin is given as part of the DPT vaccine

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