Proteus penneri lurking in the intensive care unit: An important often ignored nosocomial pathogen.

Patients in the intensive care unit (ICU) carry a poor prognosis not only owing to their critical illness but also due to predisposition to nosocomial infections. In addition to their association with increased morbidity and mortality, patients have to bear the onslaught of nosocomial infections with drug-resistant microorganisms, including methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant Enterococci (VRE) and extended spectrum β-lactamase (ESBL) producing Gram-negative bacteria, which can pose considerable therapeutic problems.[1] Nosocomial infections can affect any part of the body but respiratory tract infections are the most frequent in the ICU, followed by central line infections, urinary tract infections and wound infections.[2]

In the present report, we describe the isolation of Proteus penneri, a known nosocomial pathogen with underestimated pathogenic potential. Over a period of three months (January-March 2010), in a mini cluster outbreak, we isolated P. penneri from the different clinical samples of 11 ICU patients. The male:female ratio of these 11 patients was 7:4. Three patients were above 60 years of age while majority (seven patients) belonged to 20-60 years with one patient less than 20 years. The clinical diagnoses were as varied as perforation peritonitis, pulmonary oedema, chronic liver disease with post-operative pancreatic necrosectomy, diaphragmatic hernia with splenectomy, respiratory distress with C3-C6 cord oedema, bronchial asthma with cardiac arrest, fracture cervical spine with anterior decompression with stabilization, diabetes mellitus with hypertension and cerebrovascular accident, etc. All the patients were on mechanical ventilation and had urinary catheters inserted. Nine patients had central venous catheters as well. P. penneri was isolated from tracheobronchial secretions from 10 of these patients (repeated isolation in 6 patients) and from the abdominal drainage fluid from 1 patient. All isolations were in mixed cultures with either of Klebsiella spp., Pseudomonas aeruginosa or Acinetobacter spp. The same isolate was recovered in pure cultures from urine in two patients and one of them also had bacteremia due to P. penneri. Mortality was the outcome in four patients, probably due to multiple reasons.

All the strains isolated had similar resistogram; they were resistant to augmentin, gentamicin, amikacin, ceftazidime and cefipime whereas these were sensitive to ciprofloxacin, cefoperazone/sulbactam, piperacillin/tazobactam and imipenem. All these patients were administered combination drugs along with imipenem and they responded clinically well with the subsequent cultures of tracheobronchial secretions showing no growth of P. penneri.

This bacterium belongs to the tribe Proteeae of family Enterobacteriaceae. In 1982, the name P. penneri was proposed for a group of bacteria previously known as Proteus vulgaris indole negative or P. vulgaris biogroup 1.[3] Regardless of its wide distribution, it was considered as an uncommon cause of infections in human beings. This has been isolated from many different clinical sources, including surgical wound infections, urine and blood. Nosocomial transmission, although uncommon, but has been reported. In a review of 27 cases, Krajden et al. documented the isolation of P. penneri from urine, abdominal, neck, groin, hip wounds, conjunctiva, sacral decubitus and sputum.[4] All of these were hospital-associated infections. It has been implicated in a case of bacteremia and concomitant subcutaneous thigh abscess in a neutropenic patient with acute lymphocytic leukemia[5] and in nosocomial urosepsis in a diabetic patient from whom the organism was also subsequently isolated from bronchoalveolar lavage fluid and a pulmonary artery catheter tip.[6] The urease enzyme of P. penneri is also believed to be a leading cause of kidney stone formation; indeed, the organism has been isolated from the center of a stone removed from a patient with persistent P. penneri bacteriuria.[3]

Although the number of cases in this report is limited, it is obvious that P. penneri is yet another agent capable of causing significant nosocomial infection and thus warrants appropriate antibiotic therapy. Virtually all P. vulgaris, P. penneri strains are capable of producing inducible β-lactamases that will hydrolyze primary and extended-spectrum penicillins and cephalosporins as highlighted by Liassine et al. in their report.[37] Therefore, to conclude, infections due to nosocomial bacterium like P. penneri with proven pathogenicity in critically ill patients of ICU should not be dismissed lightly by the clinicians, instead these warrant appropriate therapeutic strategies combined with continued emphasis on effective infection control practices.