Important bacterial genera in foods
Morphological characteristics :
Cell shape
Cell size
Cells arrangement
Gram stain +ve or –ve
Flagella ,Capsule or Spores formation.
Cultural characteristics
No. / Colonycharacteristics / Observations1 / Size / Verysmall,Small,Medium,large,verylarge
2 / Form / Punctiform,circular,filamentous,irregular,
rhizoid,spindle
3 / Elevation / Flat,raised,convex,pulvinate,umbonate
4 / Margin / Entire,undulate,lobate,erose,filamentous,curled
5 / Color / White,grey,yellow,black,orange,pink,red,etc
*6 / Haemolysis / haemolysisα,βorƔ
7 / Pigmentproduction / Colorofthe pigmentproduction
**8 / Odor / Fruity,freshlycut apple,fishy,fecalorputrid,bleach,pungent
9 / Opacity / Transparent,Opaque,Translucent
10 / Surface / Smooth,Glistening,Rough,dull
11 / Consistency / Buttery,viscid,Brittle,mucoid
Staining :
1. Prepareandheat-fixasmearof theorganismtobestudied.Covertheslidewithcrystalviolet.
Allow oneminutefor thisprimarystain andthenwash off (thoroughlyandquickly,butgently)
withaminimumamountof tapwater,as anexcessapplicationof watertendstodecolorize.
Drainoff mostof thewaterontoapapertowel.
2. Covertheslidewithiodinesolutionfor oneminute.Theiodineactsas amordant (fixer) andwillformacomplexwiththecrystalviolet,fixingitintothecell.Rinsebrieflywithtap water,andthendrainoff mostof thewater.
3. Tilttheslidelengthwiseoverthesinkandapplythealcohol-acetonesolutiondropwise – such thatthesolutionwashes evenlyovertheentireslidefromoneendtotheother.Continue inthismannerfor about10-15 seconds andthenrinseimmediatelywithtapwater.If applied properly,thealcohol-acetoneshoulddecolorizecellswithagram-negativetypeof cellwallbut notthosewithagram-positivetypeof cellwall.Drainoff mostof thewater.
4. Any decolorized,gram-negativecellsneedtobestainedinordertobevisibleand differentiatedfromgram-positivecells.Covertheslidewithsafraninfor oneminuteandthen rinsebriefly.Safraninserves as thecounterstain inthisprocedure;a“counterstain”stainsthe decolorizedcellsdifferentlythanthosewhichhadretainedtheprimarystainthroughoutthe procedure.Gently(withoutrubbing)blottheslidedry.
5. For eachsmear,focus withthe10X objective,andthenswitchimmediatelytothe100X (oil-immersion)objectivefor the“official”observations,makingsure you addedagenerous drop of immersionoiltothesmearbeforemovingthe100X lensintoposition.Goingfrom10X to
100X (skipping the intermediateobjectivelens) isour standard operatingprocedure. Observe thecellsfor morphologyandgramreaction.Regardingthelatter,recordeachculture as “gram-positive”(purplecells)or “gram-negative”(pinkcells).
Biochemical characteristics
characteristicsochemical c