Bacteria of medical importance- III: Gram (+) rods

Bacillus spp.

• gram (+), endospore-forming, some motile

• mostly saprobic (feed on dead tissue)

• aerobic and catalase positive

• source of antibiotics

• primary habitat = soil

cutaneous anthrax

spores enter through skin, black sore, least dangerous

Pulmonary anthrax

inhalation of spores

gastrointestinal anthrax

ingested spores

Clostridium spp.

• gram (+), spore forming rods

• anaerobic and catalase negative

  • give it O2 to kill it

• spores produced only under anaerobic conditions

• cause wound infections, tissue infections, and food intoxications

Clostridium perfrigens

• not highly invasive, requires damaged and dead tissue and anaerobic conditions

• conditions stimulate spore germination, release of exotoxins, and other virulence factors

• fermentation of muscle carbohydrates results in the formation of gas and further tissue destruction

treatment for gas gangrene

hyperbaric oxygen therapy (higher oxygen concentration)

Clostridium tetani

• common resident of soil and GI tracts of animals
  causes tetanus or lock jaw, a neuromuscular disease
  easily transmitted via fomites

• results in state of permanent muscle excitation

Clostridium difficle-associated disease (CDAD)

• part of normal flora of colon

• causes antibiotic-associated colitis

• produces enterotoxins that damage intestines

• major cause of diarrhea in hospitals

• increasingly common in community acquired diarrhea

Clostridium botulinum

• responsible for food poisoning

• contamination occurring inadequate food preservation (canning process)

  • sproes survive

Listeria monocytogenes

• causative agent of the food-borne illness listeriosis

• non-spore forming gram-positive

• ranging from coccobacilli to long filaments

• virulence attributed to ability to replicate in the cytoplasm of cells after inducing phagocytosis, avoids humoral immune system

Mycobacterium tuberculosis

• contains mycolic acid

• unique cell wall structure

• after 3-4 weeks, immune system attacks, forming tubercles, granulosomas consisting of a central core containing bacilli surrounded by leukocytes and lymphocytes

Mycoplasma

no cell wall

mantoux test

local intradermal injection of tuberculin purified protein derivative (PPD); look for red wheal to form in 48-72 hours

Acid Fast Staining

• acid fast organisms resist decolorization with acid alcohol and will remain pink/red

• all other cells will decolorize and will stain blue