Bacterial and Mycotic Infections in Immunocompromised Hosts: Clinical and Microbiological Aspects

Abstract

The incidence of opportunistic fungal infection has been increased in the last few decades. The ability of the yeast fungi to cause disease human is primarily depending on the immunological status of the host and the environmental exposure. Several reasons have been proposed for the high incidence of invasive fungal infections, that includes the use of broad-spectrum antibiotics, antineoplastic and immunosuppressive agents, organ transplants, cancer therapies and HIV infection.Among the opportunistic fungal pathogens, Candida and Cryptococcusis species are the major yeasts, which causesmucosal infections or to deep-seated mycoses of inner organs especially in immunocompromised patients. Candida albicans is the most common cause of invasive fungal infection in immunocompromised hosts and causes candidiasis. Cryptococcusis is the second most common fungal opportunist, which causes symptomatic Cryptococcosis.These pathogenic yeast fungi have developed many virulence mechanisms to colonize and cause disease in human host. Host immune status is the crucial determining fatctor for the type of invasive fungal infection to the patients at risk. Diagnosis is often difficult because of nonspecific clinical symptoms. Currently, diagnosis of yeast infections is largely based on microbial culture, morphological, biochemical and histopathology.Development of molecular diagnosis and management of opportunist fungal yeast infection in immucompromised patients remains challenging. Introduction The prevalence of opportunistic mycoses has been rising over the last few decades. Opportunistic yeast fungi usually do not cause disease in healthy host, but theycan cause disease in people when the immune system is weakened. Development of medicine, surgery and transplantology during the last thirty years has caused a dramatic increase in the number of immunologically debilitated individuals. Although several fungi cause infection in normal humans, most of them are opportunistic and influence immunocompromised hosts. Patients with immunological impairment, HIV infection, leukopenia, post-surgery, organ transplantation or cancer therapy are at the risk of developing opportunisticmycoses [1]. The most frequently diagnosed fungal infections in immunocompromised patients are usually caused by Candida, Cryptococcusis, Aspergillus or Zygomycetes [2,3]. Among these fungal pathogens, Candida and Cryptococcusis species are the yeast pathogens, most frequently isolated fromimmunocompromised hosts in clinical practice. The Candida remains the most commom cause of invasiveyeast infections and Cryptococcusisis the second most common lethal fungal opportunist which causes symptomatic Cryptococcosis. Candida albicans is a normal flora of the human mucus, which causes vaginal candidiasis in more than 70% of healthy women atleast once in their life time. However, the yeast infection and clinical problemsassociated with immunocompromised patients are often causes severe illness or death. The pathogenic C. neoformans infects humans upon inhalation and causes the most common fungal meningoencephalitis in immunocompromised individualsworldwide.Acute neutrophilic meningitis is most frequently observed in Candida meningitis, whereas Cryptococcusis neoformans typically causes the chronic lymphocytic meningitis. Normally, when the fungus enters the body through the skin, mucosal membrane or by inhalation, defense cells such as the white blood cells, neutrophils and mononuclear phagocytes kill the fungi by phagocytosis. In immunocompromised patients, however, the risk of fungal infection is increased due to reduced number of phagocytes. Serious fungal infections affecting the immunocompromised people can be associated with impairment of T-lymphocytes and mononuclear phagocytes, which causes defective cell-mediated immunity. Candidiasis is most notable in patients with hematologic malignancies, hematopoietic stem cell transplant and organ transplant recipients. The patients hospitalized in critical care units supported with the use of invasive devices and broad-spectrum antibiotics have increased predispositions of Candida infection. Although, the incidence of Cryptococcosis is much lower in developed countries, it remains a leading opportunistc infection of patients with solid organ transplants, hematologic malignancies and AIDS. Human diseases resulting from the environmental exposure to the yeast blastospores of Candida or basidiospores of Cryptococcusis species are increased significantly ever since the increased onset of the HIV epidemic and other immunocompromised individuals. Candida Introduction The yeast Candida albicans is the most prevalent opportunistic fungal pathogens of human. Candida can live as a harmless commensal of humans, and is carried in almost half of the population [4]. Colonization of Candida in distinct sites including skin, oral gastrointestinal tract and vaginal mucosal surfaces are extremely common in healthy individuals. However, in response to change in the host defense environment, itcan convert from a benign commensal to a disease-causing pathogen. In immunocompromised patients, it can cause infection of the mucosal epithelia followed by dissemination and colonization of internal organs and cause broad spectrum infections in the oral, gastrointestinal, genital tracts and systemic infections in other organs [5].The Candida infection is more Madhu Dyavaiah1*, Subasri2 and Geetha N Prashanth2 1School of Life Sciences, Department of Biochemistry and Molecular Biology, Pondicherry University, India 2Department of Biotechnology, University of Mysore, India *Corresponding author: Madhu Dyavaiah, PhD., Assistant Professor, School of Life Sciences, Department of Biochemistry and Molecular Biology, Pondicherry University, Pondicherry 605 014, India, Tel: 917708027294; E-mail: madhud14@yahoo.co.in