The management of infectious diseases has proven to be a daunting task for clinicians worldwide, and the rapid development of antibiotic resistance among Gram-negative bacteria is making it even more challenging. The first-line therapy is empirical, and it most often comprises β-lactam antibiotics. Among Gram-negative bacteria, Proteus mirabilis, an important community and hospital pathogen associated primarily with urinary tract and wound infection, holds a special place. This review’s aim was to collate and examine recent studies investigating β-lactam resistance phenotypes and mechanisms of Proteus species and the global significance of its β-lactam resistance evolution. Moreover, the genetic background of resistance traits and the role of mobile genetic elements in the dissemination of resistance genes were evaluated. P. mirabilis as the dominant pathogen develops resistance to expanded-spectrum cephalosporins (ESC) by producing extended-spectrum β-lactamases (ESBL) and plasmid-mediated AmpC β-lactamases (p-AmpC). β-lactamase-mediated resistance to carbapenems in Enterobacterales, including Proteus spp., is mostly due to expression of carbapenemases of class A (KPC); class B (metallo-β-lactamases or MBLs of IMP, VIM, or NDM series); or class D or carbapenem-hydrolyzing oxacillinases (CHDL). Previously, a dominant ESBL type in P. mirabilis was TEM-52; yet, lately, it has been replaced by CTX-M variants, particularly CTX-M-14. ESC resistance can also be mediated by p-AmpC, with CMY-16 as the dominant variant. Carbapenem resistance in Proteus spp. is a challenge due to its intrinsic resistance to colistin and tigecyclin. The first carbapenemases reported belonged to class B, most frequently VIM-1 and NDM-5. In Europe, predominantly France and Belgium, a clonal lineage positive for OXA-23 CHDL spreads rapidly undetected, due to its low-level resistance to carbapenems. The amazing capacity of Proteus spp. to accumulate a plethora of various resistance traits is leading to multidrug or extensively drug-resistant phenotypes.

The management of infectious diseases has proven to be a daunting task for clinicians worldwide and the rapid development of antibiotic resistance among Gram-negative bacteria is making it even more challenging. The first-line therapy is empirical and it most often comprises β-lactam antibiotics. Among Gram-negative bacteria Proteus mirabilis, important community and hospital pathogen associated primarily with urinary tract and wound infection, holds a special place. This review’s aim was to collate and examine recent studies investigating resistance phenotypes and mechanisms of Proteus species and the global significance of its resistance evolution. P. mirabilis as the dominant pathogen develops resistance to expanded-spectrum cephalosporins (ESC) by producing extended-spectrum β-lactamases (ESBL) and plasmid-mediated AmpC β-lactamases (p-AmpC). β-lactamase-mediated resistance to carbapenems in Enterobacterales including Proteus spp. is mostly due to expression of carbapenemases of class A (KPC), class B (metallo-β-lactamases or MBLs of IMP, VIM or NDM series) or class D or carbapenem-hydrolyzing oxacillinases (CHDL). Previously, a dominant ESBL type in P. mirabilis was TEM-52, yet lately it has been replaced by CTX-M variants, particularly CTX-M-3 and CTX-M-65. ESC resistance can also be mediated by p-AmpC with CMY-16 as the dominant variant. Carbapenem resistance in Proteus spp. is a challenge due to its intrinsic resistance to colistin and tigecyclin. The first carbapenemases reported, belonged to class B, most frequently VIM-1 and NDM-5. In Europe, predominantly France and Belgium, a clonal lineage positive for OXA-23 CHD spread rapidly undetected, due to its low-level resistance to carbapenems. Amazing capacity of Proteus spp. to accumulate a plethora of various resistance traits leading to multidrug or extensively- drug- resistant phenotype.

Portopulmonary hypertension (PoPH) and hepatopulmonary syndrome (HPS) present two vascular complications of portal hypertension, which make opposite extremes occur against the same pathophysiological background. In PoPH, vasoconstriction predominates, along with gradual remodeling of pulmonary arteries, while HPS develops due to pathological vasodilation and creation of intrapulmonary shunts. Even though they come about by different mechanisms, both disorders significantly affect quality of life, survival, and the possibility of liver transplant. In the early phases, in clinical practice, symptoms are mainly mild and nonspecific, and overlapping with symptoms of advanced liver disease often delays forming a diagnosis. In PoPH, elevated pressures in pulmonary arteries and increased vascular resistance are observed, while HPS exhibits arterial hypoxemia with normal or lowered pulmonary pressure. Standard diagnostic workup includes echocardiography, right-heart catheterization, and analysis of the arterial gases. In patients with severe PoPH, pronounced pulmonary hypertension can represent absolute contraindication for liver transplantation due to risk of acute right heart failure during operation. Conversely, HPS usually resolves itself after a successful transplant, which confirms that the transplant is an indication of being potentially curative. Therapeutic possibilities for both states are still limited. In PoPH, specific vasodilators and supportive measures are applied, while HPS treatment is mostly supportive, directed at maintaining oxygenation until the transplant. Future research should be focused on the development of targeted therapies that address vascular remodeling, angiogenesis, and oxidative stress, as well as on the standardization of diagnostic criteria and multicentric cooperation. This approach would facilitate earlier recognition, a precise assessment of transplantability, and a better long-term outcome for patients with portal hypertension and lung vascular complications. Key Points: Portopulmonary hypertension (PoPH) and hepatopulmonary syndrome (HPS) represent two opposite vascular complications of portal hypertension, posing distinct challenges for liver transplantation. This review summarizes their pathophysiology, diagnostic pathways, and therapeutic strategies, emphasizing the importance of hemodynamic profiling and multidisciplinary management to optimize transplant outcomes.