An Overview of Selected Bacterial Infections in Cancer, Their Virulence Factors, and Some Aspects of Infection Management

SIMPLE SUMMARY: Bacterial involvement in cancer can be grouped into three categories: (i) direct association of bacteria in the processes of cancer development, (ii) secondary infection as a consequence of a patient’s weakened immune system, and (iii) utilization of bacteria in cancer therapeutics. Regarding a bacterial etiological or cancer-causing role, effective prevention strategies could be formulated after obtaining a precise understanding of the pathological mechanisms. Therefore, looking into the virulence factors of relevant bacterial species is critical in support of altering treatment plans with a proactive approach. This review has attempted to analyze both clinical/epidemiological and laboratory studies to understand bacterial mechanisms in cancer formation, particularly the virulence factors of Helicobacter pylori and Chlamydia. From secondary infections in cancer patients, microorganisms such as Pseudomonas aeruginosa, Escherichia coli, and Klebsiella species are commonly isolated. In general, these are highly diverse bacterial species and they have an exceptional ability to adapt and develop resistance against antimicrobial agents. Using an improved understanding of the pathogenic mechanisms of bacteria, it is necessary to review the topic of antimicrobial stewardship to optimize patient outcomes. Analysis of prophylactic antibiotic usage must also be addressed. Recent findings certainly support further examination of bacterial products that can be evaluated for their utilization as anti-cancer therapeutic agents. ABSTRACT: In cancer development and its clinical course, bacteria can be involved in etiology and secondary infection. Regarding etiology, various epidemiological studies have revealed that Helicobacter pylori can directly impact gastric carcinogenesis. The Helicobacter pylori-associated virulence factor cytotoxin-associated gene A perhaps plays an important role through different mechanisms such as aberrant DNA methylation, activation of nuclear factor kappa B, and modulation of the Wnt/β-catenin signaling pathway. Many other bacteria, including Salmonella and Pseudomonas, can also affect Wnt/β-catenin signaling. Although Helicobacter pylori is involved in both gastric adenocarcinoma and mucosa-associated lymphoid tissue lymphoma, its role in the latter disease is more complicated. Among other bacterial species, Chlamydia is linked with a diverse range of diseases including cancers of different sites. The cellular organizations of Chlamydia are highly complex. Interestingly, Escherichia coli is believed to be associated with colon cancer development. Microorganisms such as Escherichia coli and Pseudomonas aeruginosa are frequently isolated from secondary infections in cancer patients. In these patients, the common sites of infection are the respiratory, gastrointestinal, and urinary tracts. There is an alarming rise in infections with multidrug-resistant bacteria and the scarcity of suitable antimicrobial agents adversely influences prognosis. Therefore, effective implementation of antimicrobial stewardship strategies is important in cancer patients.