Gram negative bacilli

1-Enterobacteriaceae Gram negative bacilli-rods

Enterobacteriaceae Are everywhere Part of normal flora of humans and most animals They are cause of -30-35% septisemia -more than 70% urinary tract infections -many intestinal infections

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

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

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

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.

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

Opportunistic bacteria Eschericia coli Klebsiella pneumoniae Proteus mirabilis

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

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

E.coli Grow rapidly on most culture media

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

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

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

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)

Pseudomonas aeruginosa

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

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.

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.

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!)

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

B. anthracis

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

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.

B. cereus

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

Corynebacterium diphtheriae

C. diphtheriae-ii exotoxins = diphtheria toxin

symptoms: pseudomembrane formation in the throat; can be fatal

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

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

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

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