Top 10 Deadly Fastidious Bacteria Lab Scientists Must know

Fastidious bacteria are the “high-maintenance” organisms of the microbial world. They demand specific nutrients and environmental conditions to grow. These organisms may need enriched media, particular gases (e.g., CO₂), specific pH, or temperature for optimal growth. This makes their isolation and identification more challenging than those of obligate organisms.

Unfortunately, they are not just difficult to culture, they’re also linked to some of the deadliest infections.

This list highlights the top 10 fastidious bacteria every lab scientist must be aware of, their clinical significance, and how to identify them in the lab. This is arranged in no particular order.

1. Table of Contents

   • 1 Haemophilus influenzae
   • 2 Neisseria gonorrhoeae
   • 3 Campylobacter jejuni
   • 4 Streptococcus pneumoniae
   • 5 Mycobacterium tuberculosis
   • 6 Bordetella pertussis
   • 7 Treponema pallidum
   • 8 Corynebacterium diphtheriae
   • 9 Helicobacter pylori
   • 10  Legionella pneumophila

   Haemophilus influenzae

A small, pleomorphic Gram-negative coccobacillus, a fastidious bacteria often met in the laboratory.

• Significance: Causes meningitis, Respiratory Tract Infections, and otitis media.
• Requirement: Requires X factor (hemin) and V factor (NAD) for growth, under 5-10% CO₂ conditions.
• Media: Grows on chocolate agar but not on plain blood agar unless supplemented with the needed factors.

2. Neisseria gonorrhoeae

An intracellular Gram-negative diplococcus, usually found in the midst of pus cells, under the microscope.

• Significance: Gonorrhea and neonatal conjunctivitis, disseminated gonococcal infections (skin leisions, arthritis)
• Requirements: Needs enriched media under 5-10% CO₂.
• Media: Chocolate media and selective media like Thayer-Martin agar to suppress contaminants.

3. Campylobacter jejuni

A curved, comma-shaped Gram-negative bacillus with a characteristic “seagull wing” morphology.

• Significance: A major cause of foodborne gastroenteritis and Guillain-Barré syndrome.
• Requirement: Requires selective media under microaerophilic conditions ie reduced oxygen amount at 42°C for optimal growth.
• Media: campylobacter- selective agar, Charcoal Cefoperazone Deoxycholate Agar ( CCDA)

4. Streptococcus pneumoniae

A Gram-positive lancet-shaped diplococcus,

• Significance: Causes pneumonia, meningitis, and otitis media, bacteraemia, sinusitis.
• Requirement: Requires enriched media under 5% CO₂.
• Media: Blood agar with colonies displaying alpha-haemolysis (greenish discoloration around colonies).

5. Mycobacterium tuberculosis

An acid fast bacilli, with waxy cell walls that resist Gram staining.

• Significance: Causes tuberculosis, a leading infectious killer.
• Requirements:    Requires lipid-rich media and slow-growing (takes 4-8 weeks).
• Media: Löwenstein-Jensen medium or Middlebrook media

6. Bordetella pertussis

A small Gram-negative coccobacillus,

• Significance: The bacteria behind whooping cough, a life-threatening illness in unvaccinated children.
• Requirement: Demands Nicotinamide-enriched media and long incubation period.
• Media: Bordet-Gengou, Charcoal agar or Regan-Lowe agar media with nicotinamide

7. Treponema pallidum

A spirochete that does not Gram stain and is observed using dark-field microscopy.

• Significance: The cause of syphilis, a sexually transmitted infection with severe complications if untreated. Also, congenital syphilis (passed from mother to baby).
• Requirement: Requires living cells or animal models for growth
• Media: Cannot be cultured on artificial media. Therefore, in the lab, VDRL serological is done to detect its presence.

8. Corynebacterium diphtheriae

A Gram-positive, club-shaped bacillus arranged in “Chinese letter” formations.

• Significance: Produces diphtheria toxin, causing respiratory and systemic complications.
• Requirement: Requires reduced oxygen (microaerophilic conditions) at 42°C.
• Media: Grows best on Loeffler’s medium or Tellurite agar, forming black colonies.

 

9. Helicobacter pylori

A Gram-negative flagellated helical bacterium

• Significance: Causes Stomach ulcer, and other gastrointestinal diseases including stomach cancer.
• Requirements: Needs enriched media under microaerophilic conditions (oxygen 5-10%) and increased carbon dioxide (10%) for a long incubation period (3-7 days)
• Media: Campylobacter selective agar CCDA with antibiotics to remove contaminants. Columbia Agar or Brucella Agar supplemented with 5-10% sheep or horse blood.

10.  Legionella pneumophila

A slender, faintly staining Gram-negative rod, though not a popular fastidious bacteria, it shouldn’t go unnoticed.

• Significance: Responsible for Legionnaires’ disease (severe pneumonia) and Pontiac fever (a milder, flu-like illness).

• Requirement: Needs cysteine-supplemented media, iron salts, and charcoal to neutralize toxic compounds.
• Media: Buffered Charcoal Yeast Extract (BCYE) agar

 

Fastidious bacteria may be tough to grow in the lab, but they’re even tougher on patients when left undiagnosed. Understanding their specific requirements is important to accurately identify them whenever a sample comes into the laboratory.

Of course some of these fastidious bacteria have serological method of identification, but we need to be equipped to meet all the terms and conditions of these organisms when the need arises.