from patients who are immunocompromised or suffering from underlying disease. P. penneri was isolated significantly more often from stools of patients with diarrheal disease than from healthy patients, so P. penneri may play a role in some diarrheal disease. The invasive potential of this microorganism has also been demonstrated in a case of P. penneri bacteremia and concomitant subcutaneous thigh abscess in a neutropenic patient with acute lymphocytic leukemia and in nosocomial urosepsis in a diabetic patient from whom the organism was also subsequently isolated from bronchoalveolar lavage fluid and a pulmonary catheter tip. Furthermore, in an experiment conducted in India, P. penneri strains were isolated as the sole pathogen in all patients having underlying disease postoperatively. Most isolates of P. penneri from the experiment were found to be multiple drug-resistant including resistance to amoxy-clavulanic acid combination. In another study, P. penneri was found to be more resistant to the penicillins and cephalosporins than P. mirabilis and mostly in patients with urogenital infections. Moreover, the urease enzyme of P. penneri is thought to be a significant cause of kidney stone formation. Consistent with this belief, the organism has been isolated from the center of a stone removed from a patient with persistent P. penneri bacteriuria. These data substantiate the need for species-level identification of P. penneri in the clinical setting. Several virulence factors of P. penneri can make infections from this invasive pathogen more pronounced, persistent, and harder to eradicate. These include adherence due to the presence of fimbriae or afimbrial adhesins, invasiveness, swarming phenomenon, hemolytic activity, urea hydrolysis, proteolysis, and endotoxicity. Swarming motility is the coordinated translocation of a bacterial population driven by flagellar rotation in film or on fluid surfaces. An emerging concept in microbiology, the fundamental role of swarming motility remains unknown. However, it has been observed to be correlated with an elevated resistance to certain antibiotics. Production of IgA proteolytic enzymes has also been reported in P. penneri. Secretory immunoglobulins of the IgA class are produced by mucous tissue and are particularly resistant to enzymatic breakdown by proteases. The ability to degrade a host’s secretory IgA may provide P. penneri with an advantage by permitting it to evade the host immune response, therefore gaining valuable time for the bacterium to establish a foothold for infection. However, the major mechanism of antimicrobial resistance is caused by hyperproduction of the chromosomally encoded β-lactamase, sometimes by plasmids. These inducible