Gram-Negative Rods. General Classification. Based on source or site of infection 1. Enteric tract 2. Respiratory tract 3. Animal sources. Source or site of infection. Enteric tract Both within and outside: Escherichia, Salmonella Primarily within: Shigella , vibrio , Campylobacter
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1. Enteric tract
2. Respiratory tract
3. Animal sources
Both within and outside:
Shigella, vibrio, Campylobacter
Outside only: Klebsiella-Enterobacter-Serratia group, Proteus-Providencia-Morganella group,
Haemophilus, Legionella, Bordetella
Brucella, Francisella, Pasteurella, Yersinia
Gram negative rods:
O antigen: outer polysaccharide portion of the lipopolysaccharide (repeating 3-4 oligosaccharide sugars 15-20 times). A basis for the serologic typing (about 2000 types of Salmonella and 150 types of E. coli).
H antigen:on the flagellar protein (in E.coliand Salmonella and not in Klebsiella and shigella). Unusual H antigens in Salmonella called phase 1 and phase 2. The organism can reversibly change in antigenicity to evade the immune response.
K polysaccharide antigen: In encapsulated organisms such as Klebsiella. Identified by quellung(capsular swelling) reaction in the presence of specific antiseraused for epidemiologic purposes. In S. typhi, it is called Vi (or virulence) antigen.
Suspected specimens are inoculated onto 2 media: 1. Blood Agar 2. A selective differential medium (MacConkey’s agar or eosin-methylene blue, EMB agar. The differential ability is based on lactose fermentation as the most important criterion in identification of these organism. Non lactose fermenters form colorless colonies. Selective effect is exerted by bile salts or bacteriostatic dyes
Triple sugar Iron Agar (TSI)
Almost enough to identify the genus but array of 20 or more biochemical tests to identify the species.
Triple Sugar Iron Agar
- Iron or Ferrous sulfate
- 3 sugars: glucose, lactose, and sucrose
If the bacterium Produces urease:
Urea is hydrolyzed to NH3and CO2 ---> light orange changes to reddish purple (in Proteus and K pneumoniae
Indicator: Bromothymol blue
If the bacterium can utilizes ammonium dihydrogen phosphate (a salt of ammonium) and sodium citrate as sole source of nitrogen and carbon, the indicator turns to blue at alkalin pH due to releasing ammonia.
Usually in Salmonella, Shigella and E.colifinal detection (serotyping) by agglutination Ag+Ab test.
So, E.coli is the indicator for fecal contamination of water supply:
Lactose fermentation, Acid and gas production, growth at 44.5 C and typical colony on EMB.
4 colony count per dL in drinking water is indicative of unacceptable fecal contamination.
2. The most common cause of sepsis among negative rods
3. One of the 2 important causes of neonatal meningititis (the other is the group B streptococci) due to colonization of vagina by these organisms in about 25% of pregnant women.
Enterohemorrhagic E. coli
Very similar to Shigella species (in biochemical and morphological traits)
Meat products or sewage-contaminated vegetables
Attributed to 3 features which facilitate ascending infection into bladder:
- Enterocolitis (S. typhimurium)
- Enteric fever (typhoid fever) (S. typhi and S. paratyphi)
- Septicemia with metastatic abscesses (S. choleraesuis)
An invasion of the epithelial and subepithelial tissue of the small and large intestines.
Penetration both through and between the mucosal cells: Inflammation and diarrhea.
PMN response limits the infection to the gut and the adjacent mesenteric lymph nodes.
The dose of Salmonella required: at least 100,000 while for Shigella: 100 organisms.
Infection begins in the small intestine but few gastrointestinal symptoms occur.
Accounts for only about 5-10% of Salmonella infections and occurs in:
More common in patients with chronic disease or children with enterocolitis.
It leads to seeding of many organs, with osteomyelitis, pneumonia, and meningitis as most common sequelac.
Nausea, Vomiting, Abdominal pain and diarrhea with or without blood
The disease is self-limited. Treatment only in the very young and very old.
S. typhimurium: the most common cause of enterocolitis.
- The illness is slow, with fever and constipation rather than vomiting and diarrhea.
- After the first week, bacteremia becomes sustained. High fever, tender abdomen, and enlarged spleen occur.
- Little or no enterocolitis
- Focal symptoms: bone, lung, or meninges.
Plague or black death
Transmission of the bacteria among urban rats with the rat flea as vector.
This cycle predominates during times of poor sanitation, eg. Wartime, when rats proliferate and come in contact with the fleas in the sylvatic cycle.
During its next blood meal the flea regurgitates the organisms into the next animal. Because the proventriculus is blocked, the flea gets no nutrition. becomes hungrier loses its natural host selectivity for rodents more readily bites a human. The bacteria inoculated by bite spread to the regional lymph nodes become swollen and tender called buboes and this plague is called bubonic plague.
The organisms can reach high concentrations in the blood and disseminate to form abscesses in many organs. The endotoxin-related symptoms, including disseminated intravascular coagulation and cutaneous hemorrhages, probably were the genesis of the term ‘black death’.
Pneumonic plague can arise either from inhalation of an aerosol or from septic emboli that reach the lung.
have two biotypes (El Tor and cholerae) and 3 serotypes (Ogawa, Inaba and Hikojima)
Poor sanitation, malnutrition, overcrowding and inadequate medical services.
Quarantine measures failed to prevent the spread of the disease due to many asymptomatic carriers.
Adherence to the cells of brush border of the gut is related to secretion of mucinase: dissolves the glycoprotein coating over the intestinal cells.
(yellow colonies with average size and thin edge)
Pyocyanin (colors the pus in a wound blue-green)
Pyoverdin /Fluorescein (a yellow-green pigment that fluoresces under ultraviolet light
In the lab, these pigments diffuse into the agar, imparting a blue-green color that is useful in identification of the species.
An opportunistic pathogen. e.g. in those with extensive burns (skin host defenses are destroyed), those with chronic respiratory disease (such as cystic fibrosis), immunosuppressed, those with catheters.
From these sites, the organism can enter the blood, causing sepsis with mortality rate of over 50%.
Detecting cytochrome C oxidase enzyme
Indicator: 1% tetra methyl-para-phenylenediaminedihydrochloride
- Seen only by darkfield microscopy, silver impregnation, or immunofluorescence.
- No growth in bacteriologic media.
- Larger than two others
The ulcer heals spontaneously, but spirochetes spread widely in tissues.
Secondary lesions are rich in spirochetes and highly infectious but heal spontaneously.
In the remainder, the disease progresses to the late, tertiary stage.
Early congenital syphilis occurs in children between 0 and 2 years old.After, they can develop late congenital syphilis.
malformations of teeth or bones and by active mucocutaneous syphilis at birth or shortly thereafter, and by ocular or neurologic changes.
Babies with congenital syphilis can have symptoms at birth, but symptoms can develop two weeks to three months later, including:
When infected infants become older children and teenagers, late-stage syphilis symptoms may occur, including damage to:
Demonstrating spirochetes by darkfield or immunofluorescence microscopy.
Antibodies are detectable in the majority of patients at the time the primary lesion appears.