Case History
A 57 year old male presented to the ED with the chief complaint of fever (103 degrees Fahrenheit), urinary retention, backache and headache. The patients past medical history is significant for penile cancer status post total penectomy with perineal urethrostomy and pelvic lymph node dissection approximately 12 months prior, recent urinary tract infection (2 weeks prior, treated with 7days of antibiotics), recent pace maker placement (2 months prior), Group B Streptococcus cellulitis of the left leg complicated by bacteremia (7 months prior). The patient requires use of in and out catheters for urination as a result of the penectomy and perineal urethrostomy; however he has had difficulty with catheterization recently secondary to urethral stenosis.
Physical examination revealed the right inner thigh to be erythematous, warm, and mildly tender, clinically consistent with cellulitis. The cellulitis appeared to be spreading along the medial aspect of the thigh and involving the lower leg. While in the ED, two sets of blood cultures were obtained and a urinalysis was significant for 1+ blood, 1+ nitrite, 1+ leukocyte esterase. He was subsequently treated with intravenous fluids and ceftriaxone and admitted to the hospital.
Laboratory Identification
Both sets of the blood cultures were positive (3/4 bottles), with the first bottle being positive after 11 hours of incubation. Gram smears of the bottles revealed the presence of gram positive cocci resembling Streptococcus. Per laboratory procedure, the positive bottles were analyzed utilizing the Luminex Verigene platform and resulted as Streptococcus species. The blood culture broth was subcultured to sheep blood agar and revealed a pure isolate of medium sized slightly opaque gray colonies with a large zone of beta hemolysis. The bacteria were found to be catalase negative and PYR negative. The organism was identified by a latex agglutination assay as Group C streptococci.
Discussion
Group C streptococci designates Streptococcus species which react with Lancefield group C typing serum. Group C streptococci are comprised of several different Streptococcus species including S. dysgalactiae subspecies equisimilis, S. dysgalactiae subspecies dysgalactiae, S. equi subspecies equi, and S. equi subspecies zooepidemicus. The most commonly isolated species in human clinical specimens is S. dysgalactiae subspecies equisimilis. Group C streptococci are considered normal flora of human skin, nasopharynx, gastrointestinal tract and genital tract. The mode of transmission for these organisms includes endogenous isolates gaining access to sterile sites and person to person transmission. No definitive unique virulence factors have been identified to date; however similar virulence factors to those of S. pyogenes and S. agalactiae are likely. The diseases caused are similar to those caused by S. pyogenes and S. agalactiae including bacteremia, endocarditis, arthritis and skin and soft tissue infections. Disease generally occurs in patients in immunocompromised states or with multiple comorbidities. There have been documented cases of zoonotic infections with S. equi subspecies zooepidemicus in patients with farm animal exposure, however not all infections are associated with animal exposure. S. equi subspecies zooepidemicus is a causative agent of bovine mastitis and has been documented as the etiologic agent in several outbreaks attributed to ingestion of inadequately pasteurized dairy products. Group C streptococci are susceptible beta-lactam antibiotics, and penicillin is considered the drug of choice for treatment.
References
- Forbes BA, Sahm DF, Weissfeld AS. Bailey & Scott’s Diagnostic Microbiology. Mosby; 2007.
- Koneman EW. Koneman’s Color Atlas and Textbook of Diagnostic Microbiology. Lippincott Williams & Wilkins; 2006.
- Pelkonen S, Lindahl SB, Suomala P, et al. Transmission of Streptococcus equi subspecies zooepidemicus infection from horses to humans. Emerging Infect Dis. 2013;19(7):1041-8.
-Justin Rueckert, DO is a 2nd year anatomic and clinical pathology resident at the University of Vermont Medical Center.
-Christi Wojewoda, MD, is the Director of Clinical Microbiology at the University of Vermont Medical Center and an Associate Professor at the University of Vermont.
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