Question

Microbiology Case #1 (M-6)

A homeless, 59- year-old man, Ganiyu Hassan, presented to the emergency room complaining of fever and chills of 4 days’ duration, with dizziness over the last 24 hours. He also complained of intermittent diarrhea and constipation over the past 6 months with occasional bloody stool. He told the physician that he ate what he could due to his circumstances. The patient’s breathing was rapid, but his lung sounds were clear. His temperature was 103^oF. Hugh was hypotensive, tachycardic, and had an appreciable heart murmur. Blood was drawn for a complete blood count (CBC) and culture. A stool specimen was collected to test for occult blood, and a chest x-ray was performed. Results of the laboratory tests are shown in Table 1A and in the list following the chart.

Table 1A: Hematology Results

	Complete Blood Count
	Ganiyu Hassan	Reference Range
WBC	9.1	5-10 x 109/L
RBC	4	5-6 x 1012/L
Hb	122	135-175 g/L
Hct	0.4	.41-.53 L/L
MCV	100	80-100 fL
MCH	32	26-34 pg
MCHC	30	31-37 g/dL
RDW	15.6	11.0-14.5
Platelets	458	150-400 x 109/L
MPV	7.2 fL	6.5-12.0 fL
RBC morphology	2+ microcytosis
	1+ macrocytosis
	1+ ovalocytosis
	1+ basophilic stippling
	2+ hypochromia
	1+ polychromatophilia
	2+ toxic granulation
	Rare Döhle bodies
	Rare hypersegmentation
	2 nucleated RBCs
Differential
Polymorphonuclear neutrophils	52	25-60%
Bands	10	0-10%
Lymphocytes	35	20-50%
Monocytes	1	2-11%
Metamyelocytes	2	0%

The stool was positive for occult blood.

All blood cultures were positive within 24 hours.

Gram’s stains from the bottles revealed gram-positive cocci in chains.

Subcultures grew readily on BAP and produced small gray gamma-hemolytic colonies.

Additional biochemical testing yielded the following:

• catalase: negative
• bile esculine agar: growth with black precipitate
• growth in 6.5% NaCl: negative
• L-Pyrrolidonyl ß-naphthylamide PYR test: negative.

Questions

1. what would be the appropriate timing and number for the collection of routine blood cultures for this patient?

2. Contamination in blood cultures can be a problem. What step(s) should be followed to keep contamination rate low?

3. What criteria might be used to determine if a positive blood culture is due to contamination or bacteremia?

4. Does Ganiyu have bacteremia? Does Ganiyu have septicemia? What is the difference between the bacteremia and septicemia?

5. Given the Gram’s stain reaction and morphology of the bacteria, what might be some possibilities for the identity of the organism?

6. Given Ganiyu history, physical findings, other clinical data, and the further biochemical testing that was performed on this isolate, what is the likely identification of this organism?

7. If latex agglutination testing was performed, to which group would this organism belong?

8. What other testing methods might be employed to get a definitive identification of this organism by genus and species?

9. Hugh has a complex medical history and presentation.
   1. Describe his blood picture results in correct hematological terms?
   2. Give an explanation for toxic granulation.
   3. Give 2 reasons for macrocytes and ovalocytes
   4. Give reason for microcytes
   5. What other tests might be indicated for his occult blood results?

Answer 1

1.The appropriate time for routine blood cultures for Hassan should be starting from the day following 24hrs time frame.The count depends on the results of first four cultures.If the first four cultures were negative then the test can be once every day.If those are positive the cultures can be repeated once after the treatment course.

2. Steps to be taken to avoid blood culture contamination

Wipe the skin of the patient with antiseptic solution.

Avoid prolonged storage of blood in the labs that gives false results.

Education of phlebotomist about the best practices to avoid contamination.

Practicing of collecting blood cultures by Nurses is necessary as they are well trained.

Do not mix up the containers with stool and other cultures which may probably leads to contamination