Name of anaerobic bacteria and susceptible antibiotic against them
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Anaerobic Bacteria & Susceptible Antibiotics
Classification of Clinically Important Anaerobes
Gram-Negative Rods (most clinically significant)
| Organism | Key Infections |
|---|---|
| Bacteroides fragilis group | Intra-abdominal abscesses, bacteremia, soft tissue infections |
| Bacteroides thetaiotaomicron | Intra-abdominal infections |
| Prevotella spp. | Oral, pulmonary, gynecologic infections |
| Fusobacterium nucleatum | Oral, pulmonary, head/neck infections |
| Fusobacterium necrophorum | Lemierre syndrome, tonsillar abscess |
| Porphyromonas spp. | Periodontal disease, oral infections |
Gram-Positive Cocci
| Organism | Key Infections |
|---|---|
| Peptostreptococcus spp. | Abscesses (brain, lung, abdomen), skin/soft tissue |
| Veillonella spp. | Opportunistic, oral cavity |
Gram-Positive Rods (non-spore-forming)
| Organism | Key Infections |
|---|---|
| Actinomyces spp. | Cervicofacial actinomycosis, pelvic, thoracic actinomycosis |
| Cutibacterium (Propionibacterium) acnes | Acne, shunt/prosthetic device infections |
| Mobiluncus spp. | Bacterial vaginosis |
| Lactobacillus spp. | Endocarditis (rare) |
Gram-Positive Rods (spore-forming — Clostridium)
| Organism | Key Infections |
|---|---|
| Clostridium perfringens | Gas gangrene, food poisoning |
| C. difficile | Pseudomembranous colitis |
| C. tetani | Tetanus |
| C. botulinum | Botulism |
Antibiotic Susceptibility Table
(+ = usually susceptible, − = resistant, V = variable)
| Anaerobe | Penicillin | β-Lactam + β-Lactamase Inhibitor | Cefoxitin | Carbapenems / Tigecycline | Clindamycin | Metronidazole | Moxifloxacin |
|---|---|---|---|---|---|---|---|
| B. fragilis | − | + | + | + | V (resistance increasing) | + | + |
| B. thetaiotaomicron | − | + | V | + | V | + | V |
| Other B. fragilis group | − | + | V | + | V | + | + |
| Prevotella spp. | V | + | + | + | + | + | + |
| Fusobacterium nucleatum | V | + | + | + | + | + | V |
| Fusobacterium necrophorum | + | + | + | + | + | + | V |
| Porphyromonas spp. | + | + | + | + | + | + | + |
| Peptostreptococcus spp. | + | + | + | + | + | V | + |
| Cutibacterium acnes | + | + | + | + | + | − | + |
| Veillonella | + | + | + | + | + | + | + |
| Actinomyces | + | + | + | + | + | V | + |
Source: Goldman-Cecil Medicine, Table 273-5; Jawetz Medical Microbiology 28e
Drug of Choice Summary
| Drug | Best Use Against Anaerobes |
|---|---|
| Metronidazole | Drug of choice for B. fragilis and most gram-negative anaerobes; below-diaphragm infections; NOT effective alone for mixed infections (lacks aerobic coverage) |
| Clindamycin | Preferred for infections above the diaphragm (oral, pulmonary, head/neck); NOT for B. fragilis due to increasing resistance |
| Carbapenems (imipenem, meropenem, ertapenem, doripenem) | Broadest coverage; excellent against most anaerobes including B. fragilis; resistance uncommon |
| β-Lactam + β-Lactamase inhibitor (ampicillin-sulbactam, piperacillin-tazobactam, amoxicillin-clavulanate) | Broad spectrum; overcomes β-lactamase of B. fragilis and Prevotella |
| Penicillin G | Drug of choice when infection does NOT involve β-lactamase-producing Bacteroides/Prevotella; good for Actinomyces, Peptostreptococcus, Porphyromonas, F. necrophorum |
| Cefoxitin / Cefotetan | Alternative; some B. fragilis coverage; resistance emerging |
| Tigecycline | Good in vitro activity including B. fragilis group |
| Chloramphenicol | Broad anaerobic coverage; reserved for severe infections |
Key Clinical Points
- All anaerobes are resistant to aminoglycosides — never use aminoglycosides as monotherapy for anaerobic infections.
- B. fragilis universally produces β-lactamase → penicillin alone always fails; use a β-lactamase inhibitor combination or metronidazole.
- Clindamycin resistance in B. fragilis group has increased significantly over the past decade — metronidazole or carbapenems preferred for abdominal infections.
- Treatment always combines surgical drainage/debridement with antimicrobial therapy.
- Cutibacterium acnes is intrinsically resistant to metronidazole; use penicillin or clindamycin.
- For pelvic infections, add doxycycline to cover co-pathogens (Chlamydia, Mycoplasma).
Sources: Jawetz Melnick & Adelberg's Medical Microbiology 28e | Goldman-Cecil Medicine | Harrison's Principles of Internal Medicine 22e | Medical Microbiology 9e (Murray)
LEMON criteria
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LEMON Criteria — Assessment of the Difficult Airway
The LEMON mnemonic is a rapid, systematic bedside tool used to predict difficult direct laryngoscopy (DL) and endotracheal intubation. It has reasonable sensitivity and high negative predictive value for identifying a difficult airway.
The LEMON Law (Scoring System — Max 10 Points)
| Letter | Component | Specific Findings | Points |
|---|---|---|---|
| L | Look Externally | Facial trauma | 1 |
| Large incisors | 1 | ||
| Beard or mustache | 1 | ||
| Large tongue | 1 | ||
| E | Evaluate the 3-3-2 Rule | Incisor distance < 3 fingerbreadths (mouth opening) | 1 |
| Hyoid-mental distance < 3 fingerbreadths (submandibular space) | 1 | ||
| Thyroid-to-mouth (chin) distance < 2 fingerbreadths (laryngeal position) | 1 | ||
| M | Mallampati Score | Mallampati score > 3 (Class III or IV) | 1 |
| O | Obstruction | Epiglottitis, peritonsillar abscess, Ludwig angina, neck hematoma, glottic edema, trauma | 1 |
| N | Neck Mobility | Limited neck mobility (ankylosing spondylitis, rheumatoid arthritis, cervical collar) | 1 |
| Total | 10 |
Higher scores = greater difficulty. Patients in the difficult intubation group have higher LEMON scores.
Each Component Explained
L — Look Externally
Clinical gestalt on first inspection. Highly specific but insensitive when used alone. Signs include: facial trauma/distortion, large protruding teeth, beard/mustache (interferes with mask seal), macroglossia, obesity, short neck, or receding chin.
E — Evaluate the 3-3-2 Rule
Assesses airway geometry for direct laryngoscopy. Three separate measurements:
- 3 fingers between open incisors → assesses mouth opening (inter-incisor gap)
- 3 fingers along the floor of the mandible from the mentum → assesses submandibular space to accommodate the tongue
- 2 fingers from the laryngeal prominence (thyroid cartilage) to the underside of the chin → assesses laryngeal position; a high-riding larynx creates an acute angle making glottis visualization impossible
A patient with a receding mandible + high-riding larynx is exceptionally difficult to intubate by DL.
M — Mallampati Score
Classifies visibility of oral pharynx with mouth fully open and tongue protruded:
- Class I — Soft palate, fauces, uvula, tonsillar pillars visible → Easy
- Class II — Soft palate, fauces, uvula visible
- Class III — Soft palate, base of uvula visible → Moderate difficulty
- Class IV — Only hard palate visible → High difficulty
Note: ~50% of ED patients requiring intubation cannot cooperate. A laryngoscope blade can substitute as a tongue depressor in obtunded patients.
O — Obstruction / Obesity
Any supraglottic obstruction that can make visualization or tube passage mechanically impossible:
- Epiglottitis
- Peritonsillar abscess
- Ludwig angina
- Neck hematoma
- Head and neck cancer
- Glottic polyps or edema
Obesity itself accelerates oxyhemoglobin desaturation and complicates BMV, even if DL is not independently impaired.
N — Neck Mobility
Neck extension is essential for optimal DL (sniffing position). Severely restricted by:
- Ankylosing spondylitis
- Rheumatoid arthritis
- Cervical immobilization (trauma collar)
- Cervical fusion
Modest limitations are tolerable; severe restriction can make DL impossible.
Modified Variants
| Variant | Additional Element |
|---|---|
| LEMONS | "S" = Oxygen Saturation — low SpO₂ shortens safe apnea time, reducing time available for intubation |
| HEAVEN | Alternative mnemonic: Hypoxemia, Extremes of size, Anatomic challenges, Vomit/blood, Exertional, No access (useful for both DL and VL) |
Clinical Application
- LEMON is most validated for direct laryngoscopy; predictors of difficult video laryngoscopy (VL) are less well characterized.
- When a difficult airway is anticipated: prepare rescue devices (video laryngoscope, LMA, gum elastic bougie, surgical airway kit).
- Consider pre-marking the cricothyroid membrane with ultrasound when a failed airway is anticipated.
- A failed airway is defined as: inability to maintain SpO₂ >90%, inadequate ventilation with BMV, or >3 failed intubation attempts.
Sources: Rosen's Emergency Medicine, 9e (Box 1.1) | Roberts & Hedges' Clinical Procedures in Emergency Medicine (Fig. 6.4) | Walls Manual of Emergency Airway Management, 5e
Antibiotic coverage for empyema
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