Some of the most common tests performed on patients are the procurement
of tissue or body fluids for direct detection of pathogenic organisms
to prove or disprove the presence of infection. The results of these
tests are critical in guiding the selection of antibiotics for targeted
therapy. The following clinical microbiology principles must be
Severity or Degree of Risk:
There is a difference between an otherwise healthy patient with
a complaint of dysuria consistent with a UTI versus a patient with
neutropenia and a high fever. The first needs a simple urinalysis with
a routine bacterial culture. The second needs a “pan” culture
(as in the prefix “pan-,” meaning “all” or “every”),
which includes a pair of blood cultures, urinalysis with culture
and sensitivity, sputum sample if a productive cough is present),
and a chest x-ray to rule out pneumonia. The second patient also
needs prompt treatment with empiric broad-spectrum antibiotics because
she is at high risk of septicemia and death.
Broad Coverage with Empiric Antibiotics:
Initiation of antibiotics that broadly cover a
newly recognized infection in a timely and appropriate manner often
is lifesaving. Selecting the wrong antibiotic, the wrong dose, an
improper route, or delaying treatment, however, can increase morbidity
Whenever feasible, specimens should be obtained and cultures
performed before antibiotics are started. However, antibiotics should
never be delayed in the face of a possible life-threatening infection,
such as meningitis. After the culture data become available, antibiotic
therapy can be narrowed or “de-escalated” to the
antibiogram of the recovered organism.
Collections of pus and infected fluids such as abscesses and
empyema must be drained if at all possible. Failure
to drain pockets of infection can compromise the outcome. The classic
example is necrotizing fasciitis, which is a surgical
emergency. Without surgery, mortality approaches 100%.
True Infection versus Contamination and Colonization:
True infection is almost always accompanied by inflammation,
usually marked by the presence of neutrophils in clinical specimens
(absent in neutropenia) and clinical signs and symptoms. The presence
of a large number of epithelial cells in a sample or the growth
of normal skin flora often signifies contamination and colonization
secondary to improper collection of specimens, although there are
Drug resistance is a serious problem in modern medicine. In
the past medicine stayed ahead of antimicrobial resistance with
the development of new antibiotics to overcome new resistance patterns.
Now, as vancomycin-resistant enterococci spread throughout the health
care system and new clones of methicillin-resistant Staphylococcus aureus become more prevalent,
antibiotic resistance is minimized only through proper antibiotic
stewardship. To this end the CDC has launched a 12-step program
for preventing antimicrobial resistance in hospitals.
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