Saturday, October 12, 2013

Automation in Micrbiology (Part II)

Automated non radiometeric methods
• MGIT( mycobactrium growth indicator tube)

-- modified middle brook 7H9 with florescent quenching based oxygen.

-- with the utilization of oxygen during growth florescence is released and detected.

-- either fully automated or manual reading.

b) Bactialert 3D system

Figure our Bactialert in Mansoura University Hospital
c) VersaTrek culture system

2- automated system for biochemical reactions
1st API:
 A plastic strip holding mini-test tubes is inoculated with a saline suspension of a pure culture reacts with dessicated medium in each tube, sometimes oil is added to the surface for anerobes.

 incubation in a humidity chamber for 18-24 hours at 37°C, the color reactions are read.

 The reading are converted to a seven-digit code which is called the Analytical profile index(API)
A.Uninoculated control

B.Red slant and red butt, no black color= no fermentation of glucose, sucrose or lactose. No Hydrogen sulfide produced

C.Red slant and black butt= no lactose or sucrose fermentation, H2S has been produced

D.Red slant with yellow butt= no lactose or sucrose fermentation, lactose is fermented, no H2S has been produced

E.Yellow slant, yellow butt and black coloration= Lactose, sucrose and glucose fermented, and H2S has been produced

F.Yellow slant, yellow butt and lifting and/or cracking of media, no black coloration= Lactose, sucrose and glucose fermented, H2S has not been produced but gas has been produced

G.Yellow slant, yellow butt and no lifting and/or cracking of media, no black coloration= Lactose,sucrose glucose,

2nd microscan
3rd Vitek 2
4th Rapid-ANA II

 Depend on the presence of pre-existing bacterial enzymes and so the rapid detection.

 The results are avaliable within 4-6 hrs.


Figure Microscan in Mansoura University hospital
Figure Microscan® Gram Positive Breakpoint Combo panels Type 20

Vitek 2
3-Automated susceptibility testing methods
 A series of commercially available automated and semi-automated methods

 Most of the methods combine bacterial identification and susceptibility testing reagents in a single panel or card.

 The goal of the automated methods is to reduce the time necessary to produce accurate identification and susceptibility test result.

 Indeed, results may be available for some bacterial species in as little as 6 hrs.

 Overall, automated systems work well, although they have traditionally shown problems with certain resistance phenotypes, including oxacillin-resistant S. aureus isolates and Pseudomonas aergnosa.

 Finally, the detection of resistance due to induction of B-lactamases
( Enterobacteriaceae), and third-generation cephalosporins), has been addressed in many of the automated systems by use of low concentrations of B-lactams as screening tests.
Inhibition Zone Test
AST using turbidimetery

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