18 Questions
What is the appearance of Klebsiella colonies on MacConkey agar?
Lactose-fermenting red colonies
What is a unique characteristic of Klebsiella pneumoniae in terms of hydrogen sulphide production?
They do not produce hydrogen sulphide
What are the virulence factors of Enterobacter species on MacConkey agar?
Pink colored mucoid colonies
Which Enterobacter species is urease negative among the commonly encountered ones?
E.aerogenes
What is the red-colored pigment produced by Serratia marcescens?
Prodigiosin
Which genus of bacteria may occasionally cause meningitis and septicemia?
Enterobacter
Name three species of Serratia that are of clinical significance.
S.liquifaciens, S.rubidaea, S.marcescens
At what temperature is the pigment prodigiosin best formed in Serratia marcescens?
15-20°C
What are the typical biochemical test results for Serratia marcescens on Triple Sugar Iron (TSI) agar?
A/A or K/A; +/- gas (does not ferment lactose), Citrate +, Motility +, Urea +/-
Which bacterial group includes Proteus, Morganella, and Providencia species?
4-Proteus-morganella-providencia group
What is the characteristic method of movement for Proteus species on solid media?
Swarming
What is the virulence factor associated with Proteus species that results in rapid hydrolysis of urea?
Urease
What are the growth characteristics of Enterobacteriaceae?
Gram-negative rods, either motile with peritrichous flagella or nonmotile; grow well on MacConkey's agar; grow aerobically and anaerobically (facultative anaerobes); ferment glucose with gas production; catalase-positive, oxidase-negative, and reduce nitrate to nitrite.
How can lactose-fermenting colonies be distinguished from non-lactose-fermenting colonies of Enterobacteriaceae?
Culture on 'differential' media that contain special dyes and carbohydrates (eg, EMB, MacConkey agar) distinguishes lactose-fermenting (colored) from non-lactose-fermenting colonies (nonpigmented).
What are some common characteristics of Klebsiella, Enterobacter, and Serratia within the Enterobacteriaceae family?
Klebsiella, Enterobacter, and Serratia are clinically significant members of Enterobacteriaceae; they are gram-negative rods with specific growth and biochemical characteristics.
What are some virulence factors associated with Enteroaggregative Escherichia coli (EAEC)?
Enteroaggregative Escherichia coli (EAEC) can produce biofilms, adhere to epithelial cells, and secrete toxins that contribute to its pathogenicity.
How are nosocomial infections related to Enterobacteriaceae?
Enterobacteriaceae are common causes of nosocomial infections due to their ability to colonize healthcare environments and infect vulnerable patients.
Why is the antigenic structure of Enterobacteriaceae considered complex?
The complex antigenic structure of Enterobacteriaceae consists of various antigens that contribute to their diversity and ability to evade host immune responses.
Study Notes
Klebsiella
- Produce extracellular polysaccharides, giving a mucoid appearance to colonies
- Do not produce hydrogen sulfide
- Fimbriated, nonmotile, and nonsporing
- Lactose-fermenting, urease-positive, and indole-negative
- Over 80 serotypes based on capsular K antigens and somatic O antigens
Enterobacter
- Motile, capsulated, and form pink, mucoid colonies on MacConkey agar
- MR negative, VP positive, indole negative, citrate positive
- 12 species, with E. aerogenes and E. cloacae most commonly encountered in clinical specimens
- E. aerogenes is urease negative, while E. cloacae is urease positive
- Associated with opportunistic infections, including UTI, respiratory tract infection, and cutaneous wounds
Serratia
- Motile, gram-negative coccobacilli that may form capsules
- S. marcescens is the most frequently encountered species
- Form smooth, convex colonies with crenated edges and produce a red-colored pigment (prodigiosin)
- TSI A/A or K/A, +/- gas, citrate +, motility +, urea +/-
- Produce DNase, lipase, and gelatinase
Proteus-Morganella-Providencia group
- Proteus species move actively by means of peritrichous flagella, resulting in "swarming" on solid media
- Urease positive, resulting in rapid hydrolysis of urea with liberation of ammonia
- Produce infections in humans, including urinary tract infections and bacteremia, pneumonia, and focal lesions in debilitated patients
- Providencia species are usually urease negative and do not swarm on solid media
- Recognized by their 'fruity' smell
Test your knowledge on the characteristics of Klebsiella pneumoniae, including their appearance on agar plates, motility, sporing, and biochemical properties. Explore their association with human infections and exceptions within the species.
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