General introduction:

Membrane  filtration  systems  are  especially  used  when the  sample  like  drinking  water  or  fruit j uices   which can  easily  pass through the filter  and  contain  really small  amount  of  microorganisms  less than   1 CFU/ ml.

About coliform bacteria and why do we do this test:  

Coliform   bacteria  are   present   in  the  environment and  feces  of  all  warm-blooded  animals  and   humans. Coliform  bacteria  are  unlikely  to  cause  illness. However,  their  presence  in  drinking  water   indicates that  disease-causing  organisms  (pathogens)  could  be in the  water  system.  Most  pathogens   that  can contaminate  water  supplies  come  from  the  feces  of humans  or  animals.  Testing  drinking   water   for   all  possible   pathogens   is   complex,   time-consuming,   and  expensive.   It   is   easy   and   inexpensive to test for coliform  bacteria.  If testing detects coliform  bacteria  in a water sample, water   services  search  for  the  source of  contamination  and  restore  safe  drinking  water.  There are  three   groups  of  coliform  bacteria.  Each  is  an indicator  of  drinking  water  quality  and  each  has  a different   level  of  risk. Total  coliform  is  a  large collection  of  different  kinds  of  bacteria.  Fecal coliform  are types   of  total  coliform  that  exist  in  feces.  E.  coli  is  a  subgroup  of  fecal  coliform.  Labs  test  drinking  water   samples for total  coliform.  If total  coliform  is  present, the  lab  also tests the sample for fecal  coliform   or E. coli, depending on the lab testing method.    Total  coliform  bacteria  are  common  in  the  environment  (soil  or  vegetation)  and  are  generally   harmless.  If  a  lab  detects  only  total  coliform  bacteria  in  drinking  water,  the  source  is  probably   environmental  and  fecal  contamination  is  unlikely.  However,  if  environmental  contamination  can   enter  the  system,  pathogens  could  get  in,  too.  It  is  important  to  find  and  resolve  the  source  of  the   contamination.     Fecal  coliform  bacteria  are  a  subgroup  of  total  coliform  bacteria.  They  exist  in  the  intestines  and   feces  of  people  and  animals.  The  presence  of  fecal  coliform  in  a  drinking  water  sample  often   indicates  recent fecal  contamination. That  means there  is  a  greater  risk that  pathogens  are  present.   E.  coli  is  a  subgroup  of  the  fecal  coliform  group.  Most  E.  coli  bacteria  are  harmless  and  exist  in  the   intestines  of   people  and  warm-blooded  animals.  However,  some  strains  can  cause illness. The presence of  E.  coli  in  a  drinking  water sample usually  indicates  recent  fecal  contamination. That   means there is a greater risk that pathogens are present. Note:  E.  coli  outbreaks  receive  a  lot  of  media coverage. A specific strain of E.coli  bacteria known as E. coli O157:H7 causes most of those   outbreaks.  When  a  drinking  water  sample  is   reported as  “E. coli  present,”  it does not mean  that   O157:H7   is   present. However, it does indicate recent fecal contamination. Boiling or disinfecting contaminated drinking water destroys all forms of  E. coli, including   O157:H7.

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