MCQ

• Neisseria & Moraxella


  Important genera of the family Neisseriaceae

  
• The main important species of Neisseria are N.meningitidis and N.gonorrhoeae
• Neisseria species can also form part of normal microbial flora of the respiratory tract and some may cause disease in animals
• N.Meningitidis serogroups


  Based on capsular polysaccharide antigens, more than 13 meningococcal serogroups have been identified
• Infections are caused mainly by groups A, B, C, Y, X and W135 with groups A and C and less commonly group B, being responsible for epidemics
• Neisseria


  • Gram negative cocci found in pairs (diplococci)
  • Intracellular bacteria
  • Have adjacent or joining sides that are flat (coffee beans) like structure
  • Non-motile and non-spore former bacteria
  • Rapidly killed by drying, sunlight, heat, and disinfectants
  • Ferment carbohydrate producing acid but not gas
• N.meningitidis


  • Causative agent of meningitis (meningococcal)
  • Capsulated, non-motile, non-spore forming and have a pili for attachment
  • Their capsule made of polysaccharide and accordingly they divided in to 13 group by slide agglutination or ELISA
  • Disease characterized by septicemia, pyogenic usually following Bacteraemia
• N.gonorrhoeae


  • Causative agent of gonorrhoea (gonococci)
  • Transmitted by sexual contact, can affect the fetus causing blindness or acute conjunctivitis
  • Also transmitted from contaminated bed material and towels
  • Infection in man may lead to sterility
  • Not-capsulated, but have polysaccharide phospho-lipid protein membrane outside of the cell wall with a role in pathogenicity and antibiotic resistance
• Moraxella catarrhalis


  • Previously placed in a separate genus named Branhamella, now included in the genus Moraxella based on DNA hybridization and 16S rRNA sequence comparisons
  • A fastidious, non-motile, Gram-negative, aerobic, oxidase positive, diplococcus that can cause infections of the respiratory system, middle ear, eye, central nervous system, and joints of humans
• Moraxella catarrhalis is commonly resistant to Penicillin, Ampicillin, and Amoxicillin
• Current research priorities involve trying to find a suitable vaccine for this genotypically diverse organism, as well as determining factors involved with virulence
• Salmonella


  Typical member of the Enterobacteriaceae, Gram negative bacilli able to grow on a wide range of relatively simple media, facultative anaerobic bacteria, distinguished from other member of the family Enterobacteriaceae by their biochemical characteristics and antigenic structure, motile, non-spore forming, attack sugar fermentatively, Oxidase negative and Urease negative
• Salmonella


  • Most are found in the intestinal tract of animal and poultry
  • Salmonella typhi and Salmonella para-typhi are found only in human and are excreted in faeces and urine of infected patients and are present in the gall bladder of long-term carriers
  • Infection is by ingestion of contaminated food or drinking contaminated water
  • Salmonella typhi is spreading mainly by water and Salmonella paratyphi (A&B) by food
  • Sensitive to heat (killed by proper cooking)
  • Not killed by drying and therefore survive in product such as dried eggs
  • In Schistosomasis endemic areas there is a high incidence of chronic Salmonella typhi and Salmonella para-typhi infections and carriers (Salmonella adhere to adult Schistosoma flukes)
• Medical important Salmonella species

  • Salmonella typhi
  • Salmonella para-typhi (A,B and C)
  • Salmonella typhimurium
  • Salmonella enterica

  
• Salmonella antigenic structure


  • Heat-stable polysaccharide which form part of the cell wall lipo-polysaccharide known as O antigen (somatic)
  • Flagellar antigen (formed from structural proteins (heat labile), has a biphasic form (I &II)
  • Some strain also produce surface polysaccharide heat-stable antigen known as Vi antigen which found in Salmonella typhi and Salmonella paratyphi (C) it is associated with the virulence of organism
• Salmonella grouping


  Grouped according to their O antigen in to many groups (A - Z) (51 - 61) and (64 - 66)
• Salmonellosis


  Disease caused by Salmonella, also known as Enteric fever or Typhoid fever
• Salmonellosis


  • Transmitted by ingestion of improperly cooked poultry meat and egg also by contaminated milk and milk product
  • Infected dose is 105 cells, but recently it is 100 cells
  • Characterized by fever with low pulse rates, headache, generalized pain, enlargement of spleen (splenomegaly), skin covered by rash (Rose spot), followed by anemia, TWBS are low, incubation period (7 - 14 days)
  • In those with urinary Schistosomasis, the condition is an immune complex disorder of the kidneys and is characterized by fever, edema, marked albuminouria and haematuria (Nephro-typhoid)
  • Salmonella para-typhi (A& B) associated with a disease of paratyphoid, usually mild and characterized by diarrhea and vomiting (less invasive)
  • Salmonella para-typhi (C) may cause septicemia, arthritis, and inflammation of gall bladder
  • Salmonella typhimurium cause food poisoning (acute gastroenteritis) characterized by nausea, vomiting, and law grate of fever
• Complications of Salmonellosis


  • Osteomylitis (inflammation of bone)
  • Abscesses of spleen
  • Typhoid arthritis
  • Very rare cause pneumonia and endocarditic
• Diagnosis of Salmonella


  1. Specimens (depending on the site of infection) include: (first week) blood, (second week) stool and (third week) urine

  2. Microscopy: Salmonella are a Gram negative usually motile rod, some strain are capsulated

  3. Culture: Salmonella are aerobic and facultative anaerobic, optimum temperature for growth is 35-37°C and pH range from (7 - 7,2), on MacConkey agar they are non-ferments lactose and producing smooth pale yellow colonies, on XLD they form red black colonies (alkaline), on DCA they form smaller in size, smooth, pale yellow (NLF), with the black center (except Salmonella paratyphi (A))

  4. Biochemical Test: Catalase (+ve), Oxidase (-ve), Motility (+ve), Production of acid and gas (+ve), O-F test Fermentative, Indole (-ve), Citrate utilization (-ve), MR (+ve), VP (-ve), H2S (-ve), Urease (-ve)

  
• Widal test


  Test done to detect the presence of Salmonella antibodies when culture facilities are not available, Salmonella antigen suspension were commercially available
• Causes of raised (O) and (H) titer other than active typhoid

  • Previous salmonella infection
  • Chronic salmonellosis associated with Schistosoma infection
  • Vaccination
  • Current infection with other salmonella species
  • Chronic liver disease
  • Rheumatic arthritis
  • Nephritic syndrome
  • Rheumatic fever
  • Malaria
• Treatment for Salmonellosis


  • Replacement of fluids and electrolytes
  • Antibiotics of choice: Ceftriaxone, Ciprofloxacin, Ampicillin, Co-trimoxzole
• Prevention of Salmonellosis


  • Public health and personal hygiene
  • Proper sewage treatment
  • Chlorinated water supply
  • Cultures of stool from food handlers to detect carriers
  • Hand washing prior to food handling
  • Pasteurization of milk and proper cooking of poultry, eggs and meat
• Shigella


  Member of Enterobacteriaceae, Gram negative bacilli, non-motile and non-spore forming bacteria, aerobic and facultative anaerobic, attack sugar fermentatively producing acid but never gas
• Medical important Shigella species

  • S. dysenteriae group A (serovars 1 to 10)
  • S. flexneri group B (serovars 1 to 6 and X and Y)
  • S. boydii group C (serovars 1 to 15)
  • S. sonnei group D (only one serovars)
• Shigella


  • Found only in the intestinal tract of human
  • Carriers of pathogenic strain can excrete the organism up to two weeks after infection and occasionally for long period of time
  • Very sensitive to environmental condition, killed by drying, sun light or by biochemical agents such as chlorine
  • In faeces collected for diagnosis of shigellosis the organisms are killed in half hour
• Shigella antigenic structure


  Somatic antigen it is made of lipo-polysaccharide used in serological and in epidemiological study
• Shigella toxins


  • Shiga toxin: (exotoxin) it is made of protein (heat labile) it's characteristic of S. dysenteriae and it has three activists (Cyto-toxic, Neuro-toxin and Entero-toxic)
  • Endotoxin: made of lipo-polysaccharide it is not release during Pathogenicity unless the organism lyses by autolysis or by action of antibiotic
• Shigellosis transmission


  • Transmitted by faecal-oral route
  • High incidence occurs in areas of poor sanitation and where water supplies are polluted
  • Lacks of personal and domestic hygiene are important in contribution of infection
  • Young children usually over 6 months of age are more frequently infected than adults
• Shigellosis


  Disease caused by Shigella, also known as bacillary dysentery, may be very severe or mild infection, sometimes has a high death rate especially among young children
• Shigellosis symptoms


  • Toxaemia, sometimes Bacteraemia, severe diarrhea lead to dehydration and protein loss
  • Inflammation and ulceration of the large intestine
  • Hemorrhage, abdominal pain and high fever
  • Diarrhea with mucus and blood
  • The total WBCS count is raised with neutrophilia
  • Incubation period of disease (24 - 48) hours
  • Self-limiting occur (2 - 5 days)
• Diagnosis of Shigella


  1. Specimens (depending on the site of infection) include: fresh stool or rectal swab in case of delayed the specimen must be transported using transported media such as (Cary-Blair or glycerol buffer saline)

  2. Macroscopic examination: (containing blood, mucus and alkaline pH has been detected)

  3. Microscopy: Shigella is a Gram negative usually non-motile rod, also it is non-capsulated organism

  4. Culture: Shigella are aerobic and facultative anaerobic, optimum temperature for growth is 35-37°C and pH range from (7 - 7,2), on MacConkey agar they are not ferments lactose and producing smooth pale yellow colonies, on XLD they form red colonies, on DCA they form smaller in size, smooth, pale yellow (NLF), without black center, SS agar is not suitable for isolating Shigellae as it inhibitory to most strain

  5. Biochemical Test: Catalase (+ve), Oxidase (-ve), Motility (-ve), Production of acid but no gas, O-F test Fermentative, Indole (-ve), Citrate utilization (-ve), MR (+ve), VP (-ve), H2S (-ve), Urease (-ve)
• Treatment for Shigellosis


  • Fluids and electrolytes replacement
  • Antibiotics of choice: Ciprofloxacin, Ampicillin, Co-trimoxzole
• Prevention of Shigellosis


  • Public health and personal hygiene
  • Proper sewage treatment
  • Chlorinated water supply
  • Cultures of stool from food handlers to detect carriers
  • Hand washing prior to food handling
  • There is No vaccine