Med Micro Chapter 3 and 22

Escherichia coli

A rapid indole test is performed on the lactose fermenter, with a positive result. This organism can be presumptively identified as

Inoculate culture, perform a Gram stain, and incubate remaining spinal fluid at 35 to 37C

A spinal fluid specimen is submitted for Gram staina nd culture during an afternoon shift. The physician also requests that an aliquot be saved for possible serological studies, which are only performed on day shift

An obligate anaerobe

An abdominal abscess specimen received in the laboratory produced abundant growth when grown anaerobically but produced no growth when the culture plates were incubated aerobically. This culture contains:

Colistin-nalidixic acid agar

Antibiotic, selects for gram-positive bacteria

Modified Thayer-Martin agar

Antibiotic, selects for pathogenic Neisseria

Bacteroides fragilis

Appropriate anaeroboic media were inoculated and incubated. Lombard Dowell media were inoculated from colonies growing on the anaerobic sheep blood agar. At 48 hours, the following results were observed on the LD plates: The anaerobic growth is most likely

Capnophilic

Bacteria that prefer growth under increased CO2

Sheep blood agar, MacConkey agar, chocolate agar, and Middlebrook

Based on the patient's history and the findings in the smears, which of the following are most appropriate media for primary plating

Beta hemolysis

Complete hemolysis of blood

1.4x10^5/ml

Determine the colony count per ml of urine

Eosin-methylene blue agar

Differential recovery of gram-negative bacilli

MacConkey agar

Differential recovery of gram-negative bacilli

Blood agar

Enriched, nonselective

Chocolate agar

Enriched, nonselective

The colonies on MacConkey should be considered to be pathogenic, and those on CNA, normal flora

Examination of the plates at 24 hours' incubation reveals heavy growth of a mucoid lactose fermenter on the MacConkey plate. A few alpha hemolytic colonies are observed on the CNA plate. Which statement most likely describes these observations?

Two to three sets per 24 hours are usually sufficient to diagnose bacteremia

General guidelines for collection of blood cultures state:

Gram-negative bacilli

Growth was evident on the anaerobic blood agar and PEA plates; no growth was observed on the KV. Growth was observed in the lower third of the thioglycollate tube, and a foul odor was very evident in this tube. Which group of anaerobes can be eliminated as the possible infecting organism?

Patient developed an infection while in the hospital

How do you account for the discrepancy between the first and second specimens?

Group D Streptococcus

If the organism is bile esculin positive, it can be classified as

35 to 37 C

Most pathogenic bacteria prefer an incubation temperature of:

Normal flora may be no longer be isolated

Not a consequence of delay in specimen delivery

During the acute stage of the illness

Optimal collection time to diagnose gastrointestinal infection caused by bacterial or viral pathogens

Hektoen enteric agar

Selective for fecal pathogens

It is suitable for culture and does not seem to be contaminated

The Gram stain from the sputum specimen revealed numerous segmented neutrophils, many gram-negative bacilli, and few gram-positive cocci. An occasional squamous epithelial cell was seen. What can be said about the quality of this specimen?

Performing Gram stain and catalase

The aerobic plates revealed a moderately heavy growth of a medium-sized, creamy white colony with narrow zone beta hemolysis on the blood agar plate. No growth was seen on the MacConkey agar. Which of the following is the most appropriate action to identify this organism?

Gram-negative bacilli

The blood cultures were positive. What do you think a Gram stain performed on a subculture of the blood culture would reveal?

Enterobacter cloacae

The following biochemical profile was obtained for the lactose fermenter. It can most likely be identified as:

COcci in chains

The gram stain morphology of this isolate will most probably show gram-positive

E. coli

The lactose fermenter was determined to be indole negative by the spot indole test. Which of the following organisms are not possible choices for identification of this isolate?

M. kansasii

The mycobacterium produced the followng results. It can be most likely identified as

Psuedomonas aeruginosa

The nonlactose fermenter produced a bluish-green pigment on MacConkey agar and may be presumptively identified as:

Endogenous infection from patient's normal flora

The source of this pathogen is most likely:

Oxidase, X and V factors, porphyrin

The specimen was plated on 5% sheep blood agar, chocolate agar, CNA, MacConkey agar, and anaerobic blood, and into thioglycollate. After 48 hours' incubation, growth was observed only on the chocolate agar. Which of the following tests are most appropriate in the identification?

Clostridium perfringens

This anaerobe is most likely

Photochromogen

This mycobacterium is classified as a

Coagulase

To differentiate normal skin flora from the pathogenic Staphylococcus, which of the following tests is most appropriate?

Anaeroboic blood, thioglycollate, PEA, and KV

Tubudity and hemolysis were noted in the anaerobic blood culture vial at 18 hours' incubation. A Gram stain revealed many gram-negative bacilli. You would expect this anaerobe to grow on/in which of the following anaerobic media?

A clean-catch midstream specimen should be collected to determine the presence of a urinary tract infection

What can be said about the quality of the specimen for culture?

Double zone of hemolysis

What observation of the anaerobic blood agar would have been an important clue to this bacterium's identification?

More than one is correct

Which of the following are possible species for this Mycobacterium?

Oxidase + Growth at 42C + Glucose/Oxidized + LDC - ADH + ODC -

Which of the following biochemical profiles most likely correlates with the correct identification of the nonlactose fermenter?

5% sheep blood agar, MacConckey agar, chocolate agar, CNA

Which of the following indicate the most appropriate plating media for the sputum specimen?

Haemophilus influenzae or Neisseria meningitidis

Which of the following should be considered as the possible pathogen?

All of the above

Which of the following should be monitored as part of the quality control program in the microbiology laboratory?

Indole, motility, decarboxylase patterns

Which of the following tests are most appropriate in the identification of the pathogen(s)?

VP, citrate, motility

Which of the following tests are most helpful in the final identification of this organism?

CAMP. bile esculin, and PYRase

Which of the following tests are most needed to identify this isolate?

Report findings that suggest normal mixed bacterial flora

he routine culture showed a mixed flora of a moderate amount of viridans Streptococcus, a few Haemophilus, and a few corynebacteria. What is the next step toward working up this culture?

Oral cavity

not considered a sterile site

A syringe filled with pus obtained before administration of antibiotics

optimal wound specimen for culture of anaerobic organisms

Clean-catch midstream

specimen of choice for bacterial culture of urine

Shortly before the fever spikes

the optimal time to collect blood cultures is

Reflects the normal oropharyngeal flora

the sputum specimen

Rejected

throat swab is submitted for anaerobic culture should be