Cath Lab Digest

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  From a microbiological perspective, successful wound healing is dependent on the hosts' ability to maintain control over the micro-organisms that inevitably colonize wound tissue. Since the mid-1960s, research has shown that microbial (or, more specifically, bacterial) numbers have a significant impact on wound healing; there is widespread perception that the presence of 100,000 or more bacterial cells per gram of wound tissue is a key determinant in delayed wound healing and infection. Today, this 10⁵ guideline has a significant influence on wound care practice, and quantitative tissue biopsy or superficial swab samples are routinely used to determine whether a wound is infected and/or unlikely to heal. But is it really that simple? Are micro-organisms so predictable, irrespective of type? Should the diagnosis of wound infection be based primarily on microbiological findings rather than clinical observations? If the 10⁵ guideline is reliable, can it be applied to both acute and chronic wounds?

Micro-organisms and Man

  In normal life, an essential and mutually beneficial relationship exists between micro-organisms and man. The vast numbers of micro-organisms that naturally colonize the human body (approximately 10¹⁵ cells) are critical to health because they protect the host from opportunistic pathogens through a process known as colonization resistance.¹ On the skin, relatively small populations of resident bacteria such as Staphylococcus epidermidis and skin diphtheroids help prevent colonization by more pathogenic bacteria such as Staphylococcus aureus. In the human colon (large intestine), extremely dense populations of predominantly anaerobic bacteria (involving more than 400 different species in total) form a stable, symbiotic relationship with the host, despite the fact that many of these micro-organisms are potentially pathogenic.

  If the resident flora of the human body is disturbed, the health status of the host will likely be affected. One example is antibiotic-associated diarrhea. Oral administration of antibiotics such as ampicillin and clindamycin suppresses the resident gut flora; subsequently, unrestricted toxins are produced by an anaerobic bacterium (Clostridium difficile), causing inflammation and necrosis of the gut wall. In this situation, a change in environmental conditions favors growth of, and virulence expression in, C. difficile - factors that, collectively, are critical to the onset of infection.

Micro-organisms and Wounds

  Wound tissue is susceptible to contamination by micro-organisms (predominantly bacteria) from the external environment. Obvious sources include periwound skin (normal resident skin flora) and micro-organisms introduced following traumatic injury (nonresident exogenous flora). However, the majority of wound contaminants are derived from the mucosal surfaces of the host (endogenous flora), particularly the oral cavity and gut. In these sites, microbial colonization is dense and diverse and involves both anaerobic and aerobic bacteria (anaerobes outnumber aerobes by a factor of up to 1,000 to one² ).