21 terms

MICRO 1.3b - Bacteria in Normal Flora

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Bacteroides sp.
G(-) bacilli/coccobacilli

• Most common/prevalent bacteria in the lower intestinal tract (colon)
• Implicated in initiation of colitis and colon cancer
Anaerobe
Bifidobacterium
G(+) bacilli

• Lactic acid former, "friendly bacteria" of the intestines
• Non-spore former
Bifidobacterium bifidum
• Most common normal flora in the intestine of breastfed infants, preventing colonization by pathogens
Used in yogurts, incorporated into probiotics
Clostridium sp.
G(+) bacilli





Clostridium difficile
Can cause antibiotic-associated diarrhea or pseudomembranous colitis
Clostridium perfringens
• Commonly isolated from feces
• Causes gangrene
Clostridium tetani
• Transiently associated with normal flora
• Can be isolated from the feces of about 25% of population
Corynebacteria
G(+) bacilli • Consistent part of skin flora
• Also implicated in acne formation
Corynebacterium diphtheria
• Causes diphtheria
• Was considered a member of the normal flora
Enterococcus faecalis
G(+) cocci, in short chains
• Formerly Strep. faecalis
• Regular component of intestinal flora
• Emerged to be antibiotic-resistant nosocomial pathogen
Escherichia coli
G(-) bacilli, single/pairs
• Consistent resident of the colon (small intestine)
• Some strain can cause intestinal infections and neonatal meningitis
• UTI (non-complicated) - common among females because of the proximity of vaginal canal to anal opening
• Rare among males, usually secondary to STD
• Other commensal enteric bacteria:
o Klebsiella
o Enterobacter
o Citrobacter
Haemophilus influenzae
G(-) coccobacilli, single/pairs .
• Normal inhabitant of the nose, pharynx, and mouth
• Causes superinfection
• Frequent secondary invader to viral influenza
• Still a leading cause of bacterial meningitis in infants and young children in the Philippines
Lactobacillus
G(+) bacilli • Seen in oral cavity, contribute to acid formation that can lead to dental caries
Lactobacillus acidophilus
• Common normal flora among bottle-fed infants
• Colonizes vaginal epithelium during reproductive years
• Protective to the vagina
• Maintains low vaginal pH to inhibit growth of pathogens
Neisseria sp.
G(-) cocci in pairs
• Frequent inhabitant of the upper respiratory tract, mainly the pharynx
Neisseria meningitidis
• Colonizes nasopharynx
• Can cause bacterial meningitis or meningococcemia
Pseudomonas aeruginosa
G(-) bacilli, motile
• Water-loving opportunistic pathogen
• Can invade any human tissue
• One of the leading causes of nosocomial (hospital-acquired) infections (usually in patients that are intubated)
• Usually from an exogenous source
• Water-loving
Staphylococci sp.
G(+) cocci, in clusters Staph. epidermidis
• Highly adapted to many environments
• Present in almost all surfaces
Staph. aureus
• Normal flora of the nasal membranes
• Potentially pathogenic
• Transmitted from nasal membranes of asymptomatic carrier to a susceptible host
• Can cause recurrent boil, stye, carbuncles•
Streptococcus sp.
G(+) cocci, in chains Streptococcus mutans

• normal flora of the tooth surfaces
• primary bacterium involved in plaque formation
• cause dental caries by destroying enamel and producing cavitations
• opportunistic bacterium
Streptococcus pneumoniae
• Present in upper respiratory tract of about 50% of the population
• Can invade lower respiratory tract and cause pneumonia
• Most common cause of bronchopneumonia and meningococcemia in children, along with Haemophilus influenzae and Neisseria meningitidis
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