UNIVERSITY OF COLORADO SCHOOL OF MEDICINE DEPARTMENT OF PATHOLOGY RESIDENCY TRAINING PROGRAM

9
UNIVERSITY OF COLORADO SCHOOL OF MEDICINE DEPARTMENT OF PATHOLOGY RESIDENCY TRAINING PROGRAM MICROBIOLOGY Case Studies 01/16/2007 Note: Move to the next slide by either clicking on the background screen or on the right arrow button below. Go to previous page by clicking the back button. On each answer page, click the “back” button to return.

description

UNIVERSITY OF COLORADO SCHOOL OF MEDICINE DEPARTMENT OF PATHOLOGY RESIDENCY TRAINING PROGRAM MICROBIOLOGY Case Studies 01/16/2007. - PowerPoint PPT Presentation

Transcript of UNIVERSITY OF COLORADO SCHOOL OF MEDICINE DEPARTMENT OF PATHOLOGY RESIDENCY TRAINING PROGRAM

Page 1: UNIVERSITY OF COLORADO SCHOOL OF MEDICINE DEPARTMENT OF PATHOLOGY RESIDENCY TRAINING PROGRAM

UNIVERSITY OF COLORADOSCHOOL OF MEDICINE

DEPARTMENT OF PATHOLOGY

RESIDENCY TRAINING PROGRAM

MICROBIOLOGYCase Studies 01/16/2007

Note: Move to the next slide by either clicking on the background screen or on the right arrow button below. Go to previous page by clicking the back button. On each answer page, click the “back”

button to return.

Page 2: UNIVERSITY OF COLORADO SCHOOL OF MEDICINE DEPARTMENT OF PATHOLOGY RESIDENCY TRAINING PROGRAM

The colonies shown in the photograph of the surface of a 5% sheep blood agar plate were recovered from a post-operative wound culture.

Based on the colony morphology, what presumptive bacterial species identifications might be made?

Can Staphylococcus aureus be ruled out?

ANSWER

Case Study Ia: Wound Infection

Page 3: UNIVERSITY OF COLORADO SCHOOL OF MEDICINE DEPARTMENT OF PATHOLOGY RESIDENCY TRAINING PROGRAM

Illustrated in the photograph is the gram stain appearance of a smear prepared from one of the isolated colonies seen in the previous screen.

The observation of relatively large gram-positive cells arranged in distinct tetrads would support the colony appearance of coagulase-negative Staphylococcus species or Micrococcus species.

What additional tests might be performed to establish a more definitive identification?

ANSWER

Case Study Ia: Wound Infection

Page 4: UNIVERSITY OF COLORADO SCHOOL OF MEDICINE DEPARTMENT OF PATHOLOGY RESIDENCY TRAINING PROGRAM

In view of the colony morphology and the microscopic features as previously observed, the resistance to furazolidone and susceptibility to bacitracin, what

species identification is most likely?

IS THIS ISOLATE CLINICALLY SIGNIFICANT?

ANSWER

As illustrated in the

photograph, the unknown isolate is susceptible to 0.04 ug of bacitracin ("A") disk, but resistant to the 100 ug/ml furazolidone ("FX") disk.

Case Study Ia: Wound Infection

Page 5: UNIVERSITY OF COLORADO SCHOOL OF MEDICINE DEPARTMENT OF PATHOLOGY RESIDENCY TRAINING PROGRAM

DIAGNOSIS: Wound Infection

Etiologic Agent: Micrococcus luteus

Page 6: UNIVERSITY OF COLORADO SCHOOL OF MEDICINE DEPARTMENT OF PATHOLOGY RESIDENCY TRAINING PROGRAM

SUMMARY

Colonies entire, convex, smooth with, lemon-yellow or orange-yellow pigment

Gram-Positive cocci in tetrads

Bacitracin susceptible

Furazolidone resistant

MICROCOCCUS SP.

QUIT

Case Study Ia: Wound Infection

Steps to the Identification of Micrococcus species

Page 7: UNIVERSITY OF COLORADO SCHOOL OF MEDICINE DEPARTMENT OF PATHOLOGY RESIDENCY TRAINING PROGRAM

These colonies are circular, entire, convex, and smooth. A distinct lemon-yellow pigment is observed. Hemolysis is absent.

Although a presumptive identification of Staphylococcus aureus might be made, the observation of a lemon-yellow rather than a golden yellow pigment might suggest the possibility of a Micrococcus species.

A gram stain should be performed to further investigate this possibility.

BACK

Page 8: UNIVERSITY OF COLORADO SCHOOL OF MEDICINE DEPARTMENT OF PATHOLOGY RESIDENCY TRAINING PROGRAM

• The formation of tetrads suggests either a Staphylococcus species other than S. aureus, or Micrococcus species.

• Several tests are available to separate Staphylococcus from Micrococcus species.

• Most commonly, the differential resistance to furazolidone and bacitracin (“A” disk) is performed, as illustrated in the following screen.

• Micrococcus sp. also utilize carbohydrates oxidatively and produce acid only in the OF open tube; Staphylococcus species are fermentative.

• Micrococcus species also are resistant to the action of lysozyme and will grow in lysozyme broth.

BACK

Page 9: UNIVERSITY OF COLORADO SCHOOL OF MEDICINE DEPARTMENT OF PATHOLOGY RESIDENCY TRAINING PROGRAM

This isolate was further identified as Micrococcus luteus. The recovery of Micrococcus species from clinical specimens is usually considered to be of minimal significance. In the case presented, a repeat culture should be procured if the infection

persists, as the Micrococcus luteus most likely represents contamination by a skin commensal.

BACK