to be predominantly gram-positive aerobic alpha-hemolytic Streptococcus , space infections of greater than 48 hours tend to become more anaerobic and gram-negative. Therefore,
empiric selection should, at least in part, be based on when the symptoms started and when the patient has first presented for care.
Table 1: Predominant Cultivable Flora from Various Sites of the Oral Cavity
Prevalence
Gingival Crevice
Dental Plaque
Tongue
Saliva
Group
Predominant Organism
Anaerobes Gram + cocci
Rare
++ ++
+
++
Peptostreptococcus
++
++
+
Gram – cocci
Veillonella
+ +
Rare Rare
+++
++ ++
Gram + rods
Actinomyces, Eubacterium, Lactobacillus, Leptotrichia
++
Gram – rods Aerobes Gram + cocci
Fusobacterium, Bacteroides, Prevotella, Porphyromonas
++++
++++
+++ Rare
+++ Rare +++ Rare
Streptococcus, Staphylococcus
Rare
Rare
Gram – cocci* Moraxella
++
++
++
Gram + rods
Lactobacillus, Corynebacterium
Rare
Rare
Rare
Gram – rods*
Enterobacteriaceae
* Note that gram-negative aerobes are the least commonly encountered organisms in the normal oral flora. Note . Adapted from “Bacterial Diversity in Human Subgingival Plaque,” by B. J. Paster, S. K. Boches, J. L. Galvin, R. E. Ericson, C. N. Lau, V. A. Levanos, … F. E. Dewhirst, 2001, Journal of Bacteriology, 183(12), 3770-3783. SPECTRUM OF ACTIVITY
Antibiotics are often classified according to their spectrum of activity . Narrow-spectrum antibiotics typically cover either gram- positive or gram- negative bacteria, but are usually not effective against both, while extended-spectrum antibiotics are effective against a variety of both gram- positive and gram-negative
bacteria. Broad-spectrum antibiotics are effective against both gram-positive and gram-negative bacteria and often other bacteria, such as anaerobes, as well (Teoh et al., 2021). Table 2 categorizes the spectrum of activity for the most common antibiotics used to treat orofacial infections.
Table 2: The Spectrum of Activity for the Most Commonly Used Antibiotics in Treating Orofacial Infections Narrow Extended Broad • Clindamycin
• Cephalosporins (cephradrine, cephalexin, cefadroxil, cefaclor, cefuroxime) • Extended-Spectrum Penicillins (ampicillin, amoxicillin) • Fluoroquinolones (ciprofloxacin, levofloxacin, moxifloxac
• Augmentin (amoxicillin plus clavulanate) • Macrolides (erythromycin, clarithromycin, azithromycin) • Sulfonamides and Trimethoprim (Bactrim, Septra, Co-Trimoxazole) • Tetracyclines (tetracycline, doxycycline)
• Metronidazole • Penicillin G, V • β -Lactamase-Resistant Penicillins (cloxacillin, dicloxacillin)
Bactericidal and bacteriostatic antibiotics Another classification system for antibiotics depends on whether they are bacteriostatic or bactericidal . Bacteriostatic antibiotics prevent the growth of bacteria, keeping them in a stationary phase of growth. Bactericidal antibiotics kill bacteria regardless of where they may be in their growth cycle. In reality, there are not two distinct categories of antimicrobial agents (one that exclusively kills bacteria and another that only inhibits bacterial growth), as some bactericidal antibiotics may fail to kill every organism within twenty-four hours (e.g., if the inoculum is large), and some bacteriostatic antibiotics will kill some bacteria within twenty-four hours (often more than 90% to 99% of the inoculum), but not enough (more than 99.9%) to be called bactericidal . These in vitro microbiological determinations are based on laboratory findings in which bactericidal or bacteriostatic antibiotics can be influenced by test duration, growth conditions, extent of reduction in bacterial numbers, and bacterial density (Pankey & Sabath, 2004). The more pertinent in vivo , or clinical,
definitions are more arbitrary and most antibiotics may be better described as being potentially both bactericidal and bacteriostatic, since bacteriostatic agents are often bactericidal against susceptible organisms at high concentrations. There are certainly clinical situations in which bactericidal action is considered necessary over bacteriostatic treatments. These include endocarditis, meningitis, osteomyelitis, and neutropenia. In general, OHCPs should remember that bacteriostatic and bactericidal antibiotics are equivalent for the treatment of most infectious diseases in immunocompetent patients, while bactericidal agents are preferred when patient immune defenses are impaired or if the infection is particularly deep-seeded. Table 3 summarizes which antibiotics most commonly prescribed for the treatment of orofacial infections fall into which category.
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