Klebsiella pneumoniae

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Introduction

  • Klebsiella pneumoniae is a Gram-negative, non-motile, encapsulated bacillus

  • It belongs to the family Enterobacteriaceae

  • It is a facultative anaerobe

  • Normally present as a commensal in the human gastrointestinal tract

  • Acts as an opportunistic pathogen, especially in hospitalized and immunocompromised patients

  • Characterized by a thick polysaccharide capsule, which is a major virulence factor

  • Commonly causes pneumonia, urinary tract infections, septicemia, and wound infections

  • Produces mucoid colonies on culture media due to capsule production

  • Increasingly important due to multidrug resistance, including ESBL and carbapenemase production

  • A significant cause of nosocomial infections worldwide

General Character

Genus: Klebsiella
Species: Klebsiella pneumoniae
Family: Enterobacteriaceae

Gram Staining

Klebsiella pneumoniae is a Gram-negative bacterium.
On Gram staining, it appears pink due to the presence of a thin peptidoglycan layer and an outer lipopolysaccharide membrane.

Shape and Arrangement

  • Shape: Rod-shaped (bacilli)
  • Arrangement: Commonly seen as single cells; may occasionally form short chains

Oxygen Requirement

Klebsiella species are facultative anaerobes, meaning they can grow in both aerobic and anaerobic environments.

 

Morphology

  • Shape: Short, plump rod-shaped bacilli

  • Size: Approximately 1–2 µm in length and 0.5–0.8 µm in width

  • Gram Reaction: Gram-negative

  • Capsule:

    • Possesses a prominent polysaccharide capsule

    • Capsule gives a mucoid appearance to colonies

    • Best demonstrated by negative staining (India ink)

    • Important virulence factor – protects against phagocytosis

  • Motility: Non-motile (absence of flagella)

  • Spores: Non-spore forming

  • Arrangement: Occur singly, in pairs, or occasionally in short chains

  • Special Staining Features:

    • Capsule seen as a clear halo around the bacillus in capsule staining

 

Cultural Characteristics

1. Growth on Nutrient Agar

  • Produces large, smooth, convex, glistening colonies

  • Colonies are mucoid and sticky

  • Color: Greyish-white

  • Mucoid nature is due to abundant capsular polysaccharide

2. Growth on Blood Agar

  • Forms large, dome-shaped, mucoid colonies

  • Non-hemolytic (γ-hemolysis)

  • Colonies may show a stringy appearance when touched with a loop

3. Growth on MacConkey Agar

  • Produces large, pink, mucoid colonies

  • Lactose fermenter

  • Pink color due to acid production from lactose fermentation

  • Colonies are often very sticky and glistening

4. Growth in Liquid Media (Nutrient Broth)

  • Causes uniform turbidity

  • May produce a surface pellicle

  • Sometimes forms stringy sediment due to capsule

5. Special Features

  • Colonies show a positive string test (string >5 mm when stretched with loop)

  • Mucoid growth is an important diagnostic clue

6. Temperature and pH

  • Optimum temperature: 37°C

  • Can grow at room temperature

  • Optimum pH: 7.2–7.4

 

Biochemical Reactions

Catalase Test

  • Positive

  • Produces effervescence (bubbles) when hydrogen peroxide is added

Oxidase Test

  • Negative

  • Helps distinguish Klebsiella from oxidase-positive Gram-negative bacteria (e.g., Pseudomonas)

Lactose Fermentation

  • Positive

  • Ferments lactose with production of acid and gas

  • Produces pink, mucoid colonies on MacConkey agar

Indole Production

  • Negative in Klebsiella pneumoniae

  • Helps differentiate from indole-positive species such as Klebsiella oxytoca

Methyl Red (MR) Test

  • Negative

  • Indicates absence of mixed acid fermentation

Voges–Proskauer (VP) Test

  • Positive

  • Indicates production of acetoin via the butylene glycol pathway

 

Pathogenicity

Virulence Factors

  1. Capsule (K antigen)

    • Thick polysaccharide capsule

    • Inhibits phagocytosis and complement-mediated killing

    • Responsible for mucoid colonies

    • Major determinant of virulence

  2. Lipopolysaccharide (LPS / Endotoxin)

    • Causes fever, inflammation, shock

    • Contributes to sepsis

  3. Fimbriae (Pili)

    • Aid in adhesion to respiratory and urinary tract epithelium

    • Important in urinary tract infections

  4. Siderophores (e.g., Enterobactin)

    • Help in iron acquisition

    • Enhance bacterial survival in host tissues

  5. Biofilm Formation

    • Promotes persistence on medical devices (catheters, ventilators)

    • Contributes to antibiotic resistance

Diseases Caused

  1. Pneumonia

    • Classically causes lobar pneumonia

    • Produces thick, blood-tinged “currant jelly” sputum

    • Common in alcoholics, diabetics, elderly

  2. Urinary Tract Infections (UTI)

    • Common nosocomial pathogen

    • Associated with catheterization

  3. Septicemia (Bacteremia)

    • Can lead to septic shock

    • High mortality in immunocompromised patients

  4. Wound and Surgical Site Infections

    • Especially in hospitalized patients

  5. Liver Abscess

    • Seen particularly with hypervirulent strains

    • More common in diabetics

  6. Meningitis

    • Rare, but occurs in neonates and immunocompromised adults

Mode of Transmission

  • Endogenous flora of gastrointestinal tract

  • Spread via hands of healthcare workers

  • Contaminated hospital equipment

Predisposing Factors

  • Diabetes mellitus

  • Alcoholism

  • Chronic lung disease

  • Prolonged hospital stay

  • Mechanical ventilation

  • Immunosuppression

 

Laboratory Diagnosis

1. Specimen Collection

Depending on the clinical condition:

  • Sputum – pneumonia

  • Urine – urinary tract infection

  • Blood – septicemia

  • Pus / Wound swab – wound infections

  • CSF – meningitis

2. Direct Microscopy

  • Gram staining of specimen shows:

    • Gram-negative bacilli

    • Often seen singly or in pairs

    • Surrounded by a clear halo due to capsule

  • Capsule demonstration:

    • India ink / negative staining

    • Capsule appears as a clear zone around the bacillus

3. Culture

  • Nutrient agar: Large, smooth, mucoid colonies

  • Blood agar: Large, mucoid, non-hemolytic colonies

  • MacConkey agar:

    • Large pink mucoid colonies

    • Indicates lactose fermentation

  • String test: Positive (string >5 mm)

4. Biochemical Identification

Characteristic reactions include:

  • Lactose fermentation: Positive

  • Indole: Negative

  • Methyl Red: Negative

  • Voges–Proskauer: Positive

  • Citrate utilization: Positive

  • Urease: Positive (weak)

  • Motility: Negative
     IMViC pattern: – – + +

5. Automated and Molecular Methods

  • Automated systems: VITEK, MALDI-TOF MS

  • PCR: Detection of virulence genes and resistance genes (e.g., ESBL, carbapenemase genes)

6. Antimicrobial Susceptibility Testing

  • Performed by Kirby–Bauer disk diffusion or MIC determination

  • Important to detect:

    • ESBL-producing strains

    • Carbapenem-resistant Klebsiella pneumoniae (CRKP)

7. Serotyping (Specialized Labs)

  • Based on capsular (K) antigens

  • Used mainly for epidemiological studies

 

Antibiotic Resistance

1. β-Lactamase Production

a. ESBL (Extended-Spectrum β-Lactamases)

  • Hydrolyze:

    • Third-generation cephalosporins (ceftriaxone, ceftazidime)

    • Aztreonam

  • ESBL genes: CTX-M, TEM, SHV

  • ESBL producers appear sensitive in vitro but fail clinically

  • Clavulanic acid inhibits ESBL

b. AmpC β-Lactamases

  • Confer resistance to:

    • Cephalosporins

    • Cephamycins

  • Not inhibited by clavulanic acid

c. Carbapenemases (CRKP)

  • Hydrolyze carbapenems (imipenem, meropenem)

  • Important enzymes:

    • KPC (Klebsiella pneumoniae carbapenemase)

    • NDM-1 (New Delhi metallo-β-lactamase)

    • OXA-48

  • Lead to extensively drug-resistant (XDR) infections

2. Altered Outer Membrane Permeability

  • Loss or mutation of porin proteins

  • Decreases antibiotic entry

  • Commonly associated with carbapenem resistance

3. Efflux Pumps

  • Actively expel antibiotics out of the cell

  • Contribute to resistance against:

    • Fluoroquinolones

    • Tetracyclines

4. Target Site Modification

  • Fluoroquinolone resistance due to mutations in:

    • DNA gyrase (gyrA)

    • Topoisomerase IV (parC)

5. Plasmid-Mediated Resistance

  • Resistance genes carried on plasmids

  • Enables horizontal gene transfer

  • Leads to rapid spread in hospitals

6. Biofilm-Associated Resistance

  • Biofilm formation on:

    • Catheters

    • Ventilators

  • Reduces antibiotic penetration

  • Causes persistent infections

 

Prevention

1. Hospital Infection Control Measures

  • Strict hand hygiene (alcohol-based hand rubs / soap and water)

  • Use of personal protective equipment (PPE) when indicated

  • Contact precautions for infected or colonized patients

  • Isolation or cohorting of patients with MDR Klebsiella

2. Environmental and Equipment Control

  • Proper sterilization and disinfection of:

    • Ventilators

    • Catheters

    • Endoscopes

  • Regular cleaning of hospital surfaces

  • Use of single-use or properly disinfected devices

3. Device-Associated Infection Prevention

  • Aseptic insertion of urinary and intravascular catheters

  • Early removal of catheters and invasive devices

  • Proper care of:

    • Endotracheal tubes

    • Central venous lines

4. Antimicrobial Stewardship

  • Rational use of antibiotics

  • Avoid unnecessary:

    • Broad-spectrum antibiotics

    • Prolonged antibiotic therapy

  • Regular antibiotic sensitivity testing

  • Hospital antibiotic policy adherence

5. Surveillance and Screening

  • Routine surveillance cultures in high-risk units (ICU, NICU)

  • Early detection of:

    • ESBL-producing strains

    • Carbapenem-resistant Klebsiella pneumoniae

  • Prompt outbreak investigation

6. Patient-Related Preventive Measures

  • Good glycemic control in diabetics

  • Nutritional support in debilitated patients

  • Proper management of:

    • Chronic lung disease

    • Alcohol dependence

7. Community-Level Prevention

  • Avoid misuse of antibiotics

  • Public awareness about:

    • Antibiotic resistance

    • Hygiene practices

8. Vaccination

  • No licensed vaccine currently available against Klebsiella pneumoniae

  • Research ongoing targeting capsular polysaccharides

 

MCQs

1. Klebsiella pneumoniae belongs to which family?

A. Pseudomonadaceae
B. Enterobacteriaceae
C. Vibrionaceae
D. Neisseriaceae
Answer: B

2. Klebsiella pneumoniae is:

A. Gram-positive cocci
B. Gram-negative bacilli
C. Gram-positive bacilli
D. Gram-negative cocci
Answer: B

3. The arrangement of Klebsiella pneumoniae is usually:

A. Chains
B. Clusters
C. Singles or short chains
D. Diplococci
Answer: C

4. Which structure is the most important virulence factor of Klebsiella?

A. Flagella
B. Capsule
C. Pili
D. Spores
Answer: B

5. Klebsiella pneumoniae is:

A. Motile
B. Spore forming
C. Non-motile
D. Acid-fast
Answer: C

6. On Gram staining, Klebsiella appears:

A. Purple cocci
B. Pink rods
C. Blue spirals
D. Red cocci
Answer: B

7. Klebsiella pneumoniae is best described as:

A. Obligate aerobe
B. Obligate anaerobe
C. Facultative anaerobe
D. Microaerophile
Answer: C

8. Which staining method demonstrates capsule clearly?

A. Ziehl–Neelsen stain
B. Albert stain
C. India ink preparation
D. Giemsa stain
Answer: C

9. Colony appearance of Klebsiella on nutrient agar is:

A. Dry and rough
B. Pigmented
C. Mucoid and glistening
D. Swarming
Answer: C

10. On MacConkey agar, Klebsiella pneumoniae forms:

A. Colorless colonies
B. Pale colonies
C. Pink mucoid colonies
D. Green colonies
Answer: C

11. Lactose fermentation by Klebsiella produces:

A. Acid only
B. Gas only
C. Acid and gas
D. No fermentation
Answer: C

12. Hemolysis on blood agar by Klebsiella is:

A. Alpha hemolysis
B. Beta hemolysis
C. Gamma hemolysis
D. Double zone hemolysis
Answer: C

13. Catalase reaction of Klebsiella pneumoniae is:

A. Negative
B. Weak positive
C. Positive
D. Variable
Answer: C

14. Oxidase test for Klebsiella is:

A. Positive
B. Negative
C. Weakly positive
D. Variable
Answer: B

15. Indole reaction of Klebsiella pneumoniae is:

A. Positive
B. Negative
C. Variable
D. Delayed positive
Answer: B

16. IMViC pattern of Klebsiella pneumoniae is:

A. ++––
B. ––++
C. +–+–
D. –+++
Answer: B

17. Methyl Red test in Klebsiella is:

A. Positive
B. Negative
C. Weak positive
D. Variable
Answer: B

18. Voges–Proskauer test in Klebsiella is:

A. Negative
B. Weak negative
C. Positive
D. Variable
Answer: C

19. Citrate utilization test in Klebsiella is:

A. Negative
B. Positive
C. Variable
D. Weak
Answer: B

20. Urease test in Klebsiella is:

A. Strong positive
B. Negative
C. Weak to moderate positive
D. Variable
Answer: C

21. TSI reaction of Klebsiella pneumoniae is:

A. K/A
B. A/A without gas
C. A/A with gas
D. K/K
Answer: C

22. Hydrogen sulfide production by Klebsiella:

A. Positive
B. Negative
C. Weak positive
D. Variable
Answer: B

23. The string test in Klebsiella is:

A. Negative
B. Weak
C. Positive
D. Variable
Answer: C

24. Klebsiella pneumoniae commonly causes:

A. Pharyngitis
B. Lobar pneumonia
C. Otitis media
D. Diphtheria
Answer: B

25. Sputum in Klebsiella pneumonia is classically:

A. Frothy
B. Purulent
C. Rusty
D. Currant jelly
Answer: D

26. Klebsiella pneumonia is common in:

A. Children
B. Alcoholics
C. Athletes
D. Pregnant women
Answer: B

27. Which infection is commonly associated with catheterization?

A. Pneumonia
B. UTI by Klebsiella
C. Meningitis
D. Osteomyelitis
Answer: B

28. Klebsiella pneumoniae is a major cause of:

A. Community skin infections
B. Nosocomial infections
C. Viral pneumonia
D. Fungal sepsis
Answer: B

29. Endotoxin of Klebsiella is:

A. Exotoxin
B. Capsule
C. Lipopolysaccharide
D. Enzyme
Answer: C

30. Siderophores help Klebsiella by:

A. Capsule formation
B. Iron acquisition
C. Motility
D. Sporulation
Answer: B

31. ESBL production confers resistance to:

A. Aminoglycosides
B. Tetracyclines
C. Third-generation cephalosporins
D. Vancomycin
Answer: C

32. Carbapenem resistance in Klebsiella is due to:

A. ESBL only
B. Carbapenemases
C. Capsule
D. Biofilm alone
Answer: B

33. NDM-1 is a type of:

A. ESBL
B. Carbapenemase
C. Efflux pump
D. Porin
Answer: B

34. Biofilm formation is important in:

A. Community infections
B. Device-associated infections
C. Viral infections
D. Skin flora
Answer: B

35. Klebsiella pneumoniae is WHO listed as:

A. Low priority pathogen
B. Medium priority pathogen
C. Priority MDR pathogen
D. Vaccine preventable pathogen
Answer: C

36. Specimen of choice for Klebsiella pneumonia diagnosis:

A. Blood
B. Urine
C. Sputum
D. CSF
Answer: C

37. Best media for differentiation of lactose fermentation:

A. Blood agar
B. Chocolate agar
C. MacConkey agar
D. TCBS agar
Answer: C

38. Automated identification of Klebsiella can be done by:

A. ELISA
B. VITEK / MALDI-TOF
C. Western blot
D. Immunofluorescence
Answer: B

39. Antimicrobial susceptibility testing is essential because of:

A. Slow growth
B. Capsule
C. Multidrug resistance
D. Poor staining
Answer: C

40. Normal habitat of Klebsiella is:

A. Skin
B. Oral cavity
C. Gastrointestinal tract
D. Blood
Answer: C

41. Mode of transmission in hospitals is mainly:

A. Airborne
B. Vector-borne
C. Hands of healthcare workers
D. Food
Answer: C

42. Most effective preventive measure is:

A. Vaccination
B. Hand hygiene
C. Probiotics
D. Antivirals
Answer: B

43. Vaccine against Klebsiella pneumoniae:

A. Available
B. Under trial only
C. Not available
D. Mandatory
Answer: C

44. Capsule antigen of Klebsiella is known as:

A. O antigen
B. H antigen
C. K antigen
D. Vi antigen
Answer: C

45. Klebsiella meningitis is more common in:

A. Healthy adults
B. Neonates and immunocompromised
C. Athletes
D. Smokers only
Answer: B

46. Which test differentiates Klebsiella from E. coli?

A. Catalase
B. Oxidase
C. Motility
D. Gram stain
Answer: C

47. Which Klebsiella species is indole-positive?

A. K. pneumoniae
B. K. oxytoca
C. K. aerogenes
D. K. rhinoscleromatis
Answer: B

48. ESBL genes are usually carried on:

A. Chromosome only
B. Ribosome
C. Plasmids
D. Capsule
Answer: C

49. Klebsiella shows resistance spread mainly by:

A. Mutation only
B. Vertical transmission
C. Horizontal gene transfer
D. Spore formation
Answer: C

50. Most important preventive strategy in ICU is:

A. High-dose antibiotics
B. Prolonged catheter use
C. Infection control & stewardship
D. Empirical therapy
Answer: C

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