Bacteria Commonly Found on Surfaces of the Body

++ = Almost Always+ = common

* = Normal flora, but potential opportunistic pathogen in humans (they are both aerobic and anaerobic)

(1) Staphylococcus epidermidis - highly adapted to diverse environments of its human host.

(2) Staphylococcus aureus - potential pathogen;eading cause of human bacterial disease; can be transmitted from the nasal membranes of an asymptomatic carrier to a susceptible host.

(3) Streptococcus mutans - primary opportunistic bacterium involved in plaque formation and initiation of dental caries. (4) Enterococcus faecalis - regular component of intestinal flora; European countries use it as the standard indicator of fecal pollution, instead of E. coli as used in the U.S.currently a significant, antibiotic-resistant, nosocomial pathogen. (5) Streptococcus pneumoniae - in the upper respiratory tract of ~0% of population.If it invades the lower respiratory tract it can cause pneumonia.Streptococcus pneumoniae causes 95% of all bacterial pneumonia. (6) Streptococcus pyogenes refers to the Group A, Beta-hemolytic streptococci.

(7) Neisseria sp.Gram-negative cocci; frequent inhabitants of the upper respiratory tract, mainly the pharynx.

(7a) Neisseria meningitides - responsible for bacterial meningitis and can colonize until host develops immunity against it.

(8) E. coli - consistent resident of the small intestine, many other enteric bacteria may reside here as well, including Klebsiella, Enterobacter and Citrobacter. Some strains ofE. coli are pathogens causing intestinal infections, urinary tract infections(UTIs) and neonatal meningitis. (9) Pseudomonas aeruginosa - opportunistic pathogen in humans can invade almost any tissue; leading cause of hospital-acquired (nosocomial) Gram-negative infection; source is often from outside the host (exogenous).

(10) Haemophilus influenzae - frequent secondary invader to viral influenza;leading cause of meningitis in infants and children until Hflu type B vaccine availability.

(11) Bacteroides sp.- most prevalent bacteria in the lower intestines and colon; Gram-negative, anaerobic, non-sporeforming bacteria; implicated in the initiation colitis and colon cancer.

(12) Bifidobacteria- Gram-positive, non-sporeforming, lactic acid bacteria; so-called "friendly" bacteria in human intestine; BifidobacteriUM bifidum is the predominant bacterial species in the intestine of breast-fed infants, where it presumably prevents colonization of potential pathogens; often used in yogurt and probiotics.

(13) Lactobacilli - in the oral cavity probably contribute to acid formation that leads to dental caries. Lactobacillus acidophilus colonizes the vaginal epithelium during child-bearing years establishing low pH that inhibits the growth of pathogens.

 (14) Clostridium sp. - numerous species colonize the bowel.Clostridium perfringens is commonly isolated from feces. Clostridium difficilemay colonize the bowel and cause "antibiotic-induced diarrhea" or pseudomembranous colitis.

(15) Clostridium tetani - is an example of a bacterium that is "transiently associated" with humans as a component of the normal flora; can be isolated from feces in up to 25% of the population; its endospores are probably ingested with food and water;does not colonize the intestine.

(16) The corynebacteria, and certain related propionic acid bacteria, are consistent skin flora.Some have been implicated as a cause of acne.Corynebacterium diphtheriae, the agent of diphtheria, was considered a member of the normal flora before the widespread use of the diphtheria toxoid, which is used to immunize against the disease.