Plate culture of Enterobacter sakazakii performed during an antibiogram studyResistance to antibiotics was observed soon after these drugs were introduced into clinical medicine, but the phenomenon has increased in frequency and importance in recent years. Bacteria are highly adaptable and can develop resistance by mutation or by the acquisition of resistance genes from other organisms. The magnitude of the resistance problem varies by the specific antibiotic and pathogen (disease-causing organism). For example, despite years of exposure to penicillin, group A streptococci bacteria remain just as penicillin-susceptible as they ever were, but Staphylococcus aureus acquired a resistance to penicillin within a decade of its first use.

In general, pathogens acquired in the community are more susceptible to antibiotics than those acquired in the hospital. Furthermore, hospital-acquired bacteria are more likely to be resistant to multiple antibiotics. Unnecessary antibiotic use is a major factor in resistance development, so antibiotics are not prescribed when they can be of no benefit, as in viral infections. Lahey restricts the use of several of the most powerful antibiotics to infectious disease experts and other specialists, and we also monitor overall antibiotic use to ensure that it remains appropriate.

Particular pathogens that historically have shown antibiotic resistance:

  • Staphylococcus aureus and coagulase negative staphylococci are not only penicillin-resistant but also appear to be 50 percent or more resistant to semi-synthetic penicillins such as oxacillin. Vancomycin is widely used to treat such S. aureus infections.
  • Enterococcus faecium and Enterococcus faecalis have always been relatively resistant to antimicrobial agents. They have lately developed increasing resistance to vancomycin, otherwise a mainstay in their therapy. A new antibiotic, linezolid, is often used to treat vancomycin-resistant isolates, but resistance can develop to this agent as well.
  • Streptococcus pneumoniae is a community-acquired pathogen that has increased in resistance to penicillin and other antibiotics within the past decade. When the organism causes meningitis, alternative antibiotics must be used until penicillin susceptibility can be determined.
  • Klebsiella pneumoniae from some hospitals has acquired the ability to destroy the best available broad-spectrum cephalosporin antibiotics.
  • Pseudomonas aeruginosa can all too easily acquire resistance to multiple antibiotics, particularly in patients with chronic infection and those who have had many prior antibiotic exposures.Pharmaceutical companies continue to develop new antimicrobial agents for problem pathogens, but in the last few years primary research has been focused elsewhere. Unfortunately, the bacteria remain just as active in developing resistance. In addition to encouraging the wise use of available antibiotics, Lahey physicians are investigating the use of new agents and studying how bacteria develop resistance to individual drugs. Antibiotic resistance is a problem that will never disappear and therefore requires constant attention.