Streptococcus pseudoporcinus bacteremia in a Type II-respiratory failure patient with coronary artery disease: A case report

Introduction

Streptococcus pseudoporcinus is a beta-hemolytic coccus arranged in short chains, usually found in the female genitourinary tract. The bacterium was first isolated from the female genito‑urinary tract in the year 2006. It is usually recovered from the female genital tract as a colonizer.1 Currently little is known about epidemiology of this organism or its role as a human pathogen; except for few case reports of causing obstetric disorders such as chorioamnionitis and preterm delivery, skin infections such as cellulitis. Recently invasive infection such as bacteremia was reported from a patient having syphilis and HIV co-infection. 2, 3 Here, we report a case of Streptococcus pseudoporcinus bacteremia in a patient having coronary artery disease with type-2 respiratory failure.

Case History

A 50‑year‑old female patient came to the emergency department with complaints of severe breathlessness since one day and pedal edema, generalised malaise, decreased urine output, abdominal distension with on and off a fever for 3 days. She was referred to our tertiary care centre in intubated state for cardiogenic shock. She was on central line (day 2), peripheral line on right hand with 20 gauge venflon (day 2), urinary catheter (day 2) and on oropharyngeal tube (day 2). She was a known case of type-2 diabetes mellitus and systemic hypertension for 12 years and is on medication for the same. She has a h/o left ventricular dysfunction with ejection fraction of 49% with normal coronaries on angiogram done four years back.

On physical examination, she was drowsy but arousable and morbidly obese. Her Glasgow Coma Scale (GCS) was E3 VT M6, temperature was 101°F, pulse 120 beats per minute, respiration rate was 20 per minute, blood pressure 150/80 mmHg (with noradrenaline 0.3 µg/min) and SPO₂ was 100% with mechanical ventilation. On auscultation, bilateral air entry was equal, bilateral extensive crepitations were present. Her blood sample was sent for routine hematological investigations. The diagnostic test results are displayed in Table 1.

Figure 1

Growth of streptococcus pseudoporcinus on blood agar.

Figure 2

Streptococcus pseudoporcinus showing CAMP positive on blood agar

Patient was started on Inj. Piptaz (4.5 gm Q6H IV), as a part of empirical therapy. Paired blood culture samples were sent. Her both the blood culture samples showed growth of small 0.5–1 mm in diameter, white circular colonies with a wide zone of β‑hemolysis on blood agar after 24 hour of incubation (Figure 1). The isolate was catalase positive, bacitracin resistant, CAMP (Christie–Atkins–Munch-Peterson) test positive (Figure 2) and bile esculin hydrolysis negative. The isolate was identified to be Streptococcus pseudoporcinus by the VITEK2 Compact system (bioMérieux). The isolate was sensitive to penicillin, cefotaxime, clindamycin, erythromycin, vancomycin, linezolid, cotrimoxazole and ciprofloxacin tested by Kirby Bauer’s disk diffusion testing on Mueller Hinton blood agar (MHBA). Based on the antimicrobial susceptibility report patient was started on Inj. clindamycin (6o mg IV, TDS for 3 days) immediately.

Discussion

We present a case of severe invasive infection due to Streptococcus pseudoporcinus. This patient presented with fever and underlying type-2 respiratory failure with coronary artery syndrome. His paired blood culture specimens yielded S. pseudoporcinus; definitive source of this isolate is unclear. S. pseudoporcinus usually colonizes gastrointestinal and genitourinary tracts. 1, 3 In this case it may be a colonizer from her gastrointestinal tract, which would have ultimately led to her clinical disease via aspiration.

Streptococcus pseudoporcinus is a beta-hemolytic gram-positive, catalase-negative, nonmotile coccus arranged in short chains and can sometimes be confused with Streptococcus agalactiae (group B Streptococcus) because of its recovery from vaginal-rectal specimens, similar colony morphology and biochemical reactions, and frequent cross reactivity with Lancefield group B reagents. 5, 6 In contrast to S. agalactiae, which displays a narrow zone of beta-hemolysis, S. pseudoporcinus exhibits a large zone. Additionally, S. agalactiae is esculin hydrolysis negative and hippurate hydrolysis positive and while the opposite is true for S. pseudoporcinus. 2, 7 In our case, definite bacterial isolate identification was made using the VITEK2 compact system, which is a reliable automated tool for species identification of this streptococci.

Identification by conventional biochemical tests may be at times difficult. Unavailability of automated identification system, can make differentiation between S. pseudoporcinus and S. agalactiae difficult and has probably led to an underestimation of the former’s role and frequency in human colonization and disease.

Stoner et al. reported that 5.4% of women had genital cultures that were positive for S.pseudoporcinus, which suggests that the colonization of S. pseudoporcinus in healthy individuals is not rare. 8 Though little is known about the pathogenicity of S. pseudoporcinus in human disease, the literature suggests the possibility of adverse obstetric outcomes. It has been associated with chorioamnionitis and preterm delivery.

Few case reports are available in the literature regarding its association with human infections including genitourinary infection, a wound infection of a finger as a result of trauma, another with left lower leg cellulitis, causing endocarditis and a case report with pneumonia and empyema. Although the clinical significance of S. pseudoporcinus has not been completely established, it is important to report the identification when we recover the organism from bacterial cultures. 1, 2, 3, 5, 4

Previous studies reported that S. pseudoporcinus is highly susceptible to β-lactam antibiotics. And some isolates are resistant to erythromycin, clindamycin and tetracycline. 3, 6 However, this isolate was uniformly susceptible to all tested antimicrobial agents.

Conclusion

In conclusion, the increase in the number of isolates identified as S. pseudoporcinus is most likely related to improvements in identification methods and greater awareness of this organism rather than its recent emergence in the human population. Controlled studies in which microbiologic testing is performed to distinguish between S. agalactiae and S. pseudoporcinus are needed in order to determine if the latter is consistently identified as the true causative agent in various clinical conditions including invasive infections such as bacteremia.

As it is usually susceptible to many anti-streptococcal antimicrobial agents, inaccurate identification does not lead to treatment failure; however, we should keep in mind that S. pseudoporcinus could emerge as a serious medical problem in the near future, as with other β-hemolytic streptococci.

Source of Funding

None.

Conflicts of interest

There are no conflicts of interest.