Bacteria normal flora

Propionibacterium acnes (P. acnes), an anaerobic organism, is also found in the normal flora of the skin. This bacteria proliferates in the mixture of sebum and keratinocytes and can result in an inflammatory response producing a closed comedo or whitehead. More severe acne lesions such as pustules, papules, and nodules can also form with inflammatory acne and result in significant scarring if treated inadequately (Fig. 62-2). 

Many areas of the human body are colonized with bacteria— this is known as normal flora. Infections often arise from one s own normal flora (also called an endogenous infection). Endogenous infection may occur when there are alterations in the normal flora (e.g., recent antimicrobial use may allow for overgrowth of other normal flora) or disruption of host defenses (e.g., a break or entry in the skin). Knowing what organisms reside where can help to guide empirical antimicrobial therapy (Fig. 66-1). In addition, it is beneficial to know what anatomic sites are normally sterile. These include the cerebrospinal fluid, blood, and urine. 

FIGURE 66-1. Normal flora and concentrations of bacteria (organisms per milliliter). 

I Bite-wound infections generally are polymicrobial. On average, five different bacterial species can be isolated from an infected animal bite wound.3 Both the normal flora of the biter s mouth and that of the bite recipient s skin can be implicated. The bacteriology of the cat and dog mouth is quite similar. Pasteurella multocida, a gram-negative aerobe, is one of the predominant pathogens, isolated in up to 50% of dog and 75% of cat bites. S. viridans are the most frequently cultured bacteria from human bite wounds.3,43 Table 70-10 provides a comprehensive list of cat, dog, and human bite-wound pathogens. 

Normal flora Normal colonizing bacteria of a human host. 

Antibiotics alter the normal colonic flora, leading to loss of colonization resistance, which is the ability of the normal flora to protect against overgrowth of pathogens, especially when the anaerobic flora are depleted [15], In CDAD, the altered colonization resistance can allow for the overgrowth of C. difficile in the colon. The bacteria produces two toxins which cause disease (toxin A, an enterotoxin, and toxin B, a cytotoxin). The toxins of C. difficile inactivate Rho proteins, which results in the loss of cytoskeletal integrity in enterocytes. Cellular damage results in fluid loss, exudation and diarrhea. The most severe form of C. difficile diarrhea is pseudomembranous colitis, which can cause severe colitis, toxic colon and rarely colon perforation and death. 

To understand the role of antibiotics, it is important to understand their effects on the fecal flora. The normal flora consists of a complex bacterial population with 400-500 distinct species of bacteria (table 2a). More than 99% of the total organisms are accounted for by non-sporeforming anaerobic rods [28] the four major species are Bacteroides, bifidobacteria, eubacteria and peptostrepto-cocci [29], Other common species are Escherichia coli, Streptococcus viridans, Streptococcus salivarius and lacto-bacilli. Mette et al. [30] clarified the prevalence of species in fecal flora by listing the four most common anaerobes Bacteroides spp., Eubacterium spp., Bifidobacterium spp. and anaerobic cocci) and three common aerobes E. coli spp., Enterococcus spp. and Lactobacillus spp.) (table 2b). 

Bacteria involved in SSI are either acquired from the patient s normal flora (endogenous) or from contamination during the surgical procedure (exogenous). 

The vagina contains a normal flora of bacteria, mostly harmless, that feed on the cervical mucous nutrients. The bacterial flora (e.g.,... 

Bacteria present in the normal flora may exert beneficial effect and are able to degrade certain food components, produce certain B vitamins, stimulate the immune system, and produce digestive and protective enzymes. The normal flora also takes... 

Gastrointestinal colonization in adults or children by clostridial bacteria does not typically take place except under circumstances where the normal flora has been altered by antibiotic treatment (Cheiington, 1998). Botulism results from in vivo production of toxin, analogous to the pathogenesis of infant botulism (McCroskey and Hatheway, 1988 Chia et al, 1986). Support for this form of botulism is provided by demonstration of prolonged excretion of toxin and C. botulinum in stool and/or by the demonstration of C. botulinum spores but not preformed toxin in suspected foods. 

Etiology. Meibomian gland secretions are responsible for the lipid component of the precorneal tear film. The chemical composition of meibum and/or the lipase action of the normal lid bacteria is thought to contribute to or cause blepharitis and in many cases the dry eye that accompanies it. The composition of meibum has been found to be different in normal and blepharitis patients, and there is a distinct difference between the types of MGD as well. Most studies of lid flora in bacterial blepharitis cases did not find any appreciable isolates from meibum that were not found as normal flora on the lids, therefore disproving the theory that the meibomian glands act as a bacterial reservoir. 

The mix of trapped keratinocytes and sebum provide an environment for the normally-occurring bacteria Propionibacterium acnes to flourish. Although P. acnes, a partial anaerobe, resides in the follicle as normal flora, it triggers immune responses such that titers of antibodies to P. acnes are higher in patients with severe acne than in non-acne control subjects. 

As in infectious diseases, host factors are extremely important. Just as billions of normal flora make up 2-3% of the bacteria in an adult human body, so also are there billions of molecular processes in the normal brain. In deficient or excessive amounts, these molecules can cause disease, just as a few miscreant bacteria can produce an infectious disease. 

Antimierobial bodywashes are used to control the numbers of bacteria, where appropriate [15]. Because the organisms of potential concern are primarily Grampositive, the activity of antimicrobial agents used in antimicrobial bodywashes should be suitable for that use and so may be of limited spectrum. Most importantly, this will enable a proportion of the normal flora to remain. 

The subungual experiments conducted by McGinley and Leyden demonstrates the impact of subungual areas on normal flora population estimates of the hands. We conducted a study to determine if the subungual areas serve as a reservoir for marker bacteria when using the glove juice extraction method to evaluate liquid soap products [15]. 

Challenge Microorganisms. The antimicrobial spectrum of activity of the test products must be broad, versus 25 ATCC strains of 20 species of bacteria and 2 species of yeasts listed in 333.470(a)(l)(ii) of the TFM, plus 25 fresh clinical isolates of these same species of bacteria and yeasts. The challenge microorganisms include members of normal flora in humans, common environmental contaminants, or systemic pathogens. 

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