Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (1445 page)

   Significant pathogens may not be recognized in mixed cultures.

   Submission of multiple cultures or cultures of several affected sites may be required for detection, especially in chronic infections. The structure and milieu of abscesses may prevent effective antibiotic treatment. They are avascular spaces, and their outer capsule may prevent entry of antimicrobial agents. In addition, antibiotics may be inactivated by the acidic environment and degradative enzymes present. Adjunctive surgical therapy may be required, especially for large collections of pus.

   
Common pitfall:
Collection of specimens from sites other than the active site of infection, such as sinus tracts, often yields growth of endogenous flora unrelated to the infection.

   Other Considerations

   Pyogenic infections are usually associated with heavy growth (10
⁵
CFU/mL) of the responsible pathogen.

   Polymicrobial infections are often treated successfully with surgical and/or empirical antimicrobial therapy. Extensive culture analysis with identification and susceptibility of multiple isolates is usually not clinically indicated.

   Certain pathogens are associated with specific types of wound infections, such as
P
.
aeruginosa
with penetrating foot wounds through sneakers and
P
.
multocida
with cat bites. These infections may require special laboratory techniques for optimal detection; alert the laboratory when suspected.

YERSINIA ENTEROCOLITICA
CULTURE (RULE OUT)

   Definition

   
Yersinia enterocolitica
is an infrequent cause of bacterial diarrheal infection, usually in children. Infection has been associated with ingestion of undercooked pork, dairy products, and tainted water. Infection can also be transmitted by the fecal–oral route. Symptoms are fairly nonspecific: fever, abdominal pain, and diarrhea, which may be bloody. Abdominal pain in adults may mimic appendicitis. This test is a specialized stool culture for the detection of GI infection caused by
Y
.
enterocolitica
.

   Use

   Cold enrichment, holding stool suspended in buffered saline at 4°C prior to subculture onto enteric media, may improve recovery in heavily contaminated specimens.
Y
.
enterocolitica
may be isolated using a selective medium, like MacConkey agar. Many laboratories use a more selective medium, like CIN agar (cefsulodin–ingrasan–novobiosin), to improve recovery.
Y
.
enterocolitica
isolation may be improved by culture incubation at 25°C.

   
Turnaround time:
Cultures are examined for 48 hours. Several days are required for isolation and identification of suspected isolates.