Molecular characterization of Klebsiella oxytoca isolated from breast cancer tissues with evaluation of some breast cancer risk factors in Salaheddin Province – Iraq

Introduction: Cancer comprises a heterogeneous group of diseases that can originate in almost any organ or tissue of the body. It is characterized by the uncontrolled proliferation of abnormal cells that extend beyond their usual boundaries, invading adjacent tissues and potentially spreading to distant organs. This dissemination, known as metastasis, represents the leading cause of cancer-related mortality. The terms neoplasm and malignant tumor are commonly used interchangeably with cancer. Objective: The present thesis aims to conduct a microbiological, molecular and serological investigation of breast cancer patients in Salah Al-Din Governorate-Iraq, with a focus on identifying bacterial isolates and assessing associated risk factors. Materials and Methods: This study was carried out between July 1, 2024, and August 31, 2025, in Salah Al-Din Governorate, Iraq. A total of 60 breast cancer tissue samples were collected, along with 40 blood samples for serological testing( progesterone and cholesterol ). The patients enrolled in this study were between 45 and 70 years of age. Results :Microbiological culture of breast cancer tissue swabs revealed that 60% of samples exhibited bacterial growth, whereas 40% showed no growth. Among the culture-positive cases, Gram-positive bacteria (55.6%) were more prevalent than Gram-negative bacteria (44.4%). Of the 36 positive cultures, 28 isolates were successfully identified at the species level, while 8 represented mixed cultures. The most frequently isolated bacterium was Klebsiella oxytoca (4/28; 14.3%), Klebsiella oxytoca was isolated from breast tissue of breast cancer patients for the first time in Iraq and for the second time worldwide, as it had previously been isolated in the United States. Other isolates included Cedecea lapagei (2/28; 7.1%), Serratia fonticola (2/28; 7.1%), and Sphingobacterium thalpophilum (1/28; 3.6%). Antibiotic susceptibility testing of K. oxytoca isolates demonstrated complete resistance to ampicillin, nalidixic acid, gentamicin, and levofloxacin, with variable resistance to other antibiotics. Moderate susceptibility (50%) was observed for imipenem and meropenem. Molecular analysis revealed the presence of the resistance gene blaNDM in approximately 50% of K. oxytoca isolates. In contrast, the virulence-associated genes entB, luxS, and mrkA were not detected in any of the tested isolates, indicating their absence. Progesterone levels among the participants were within the normal range in 90% of cases, while 10% showed levels above the normal range. Cholesterol levels were within the normal range in 90% of cases, with 10% above the normal range. Conclusion: Bacteriological culture of breast tissue samples showed 60% positivity (36/60), with 55.6% Gram-positive and 44.4% Gram-negative isolates. Klebsiella oxytoca was the predominant isolate (14.3%) and was recovered from breast cancer tissue for the first time in Iraq and the second time worldwide. The isolates exhibited multidrug resistance, moderate sensitivity to imipenem and meropenem, and carried the blaNDM gene (420 bp), while virulence genes entB, luxS, and mrkA were absent. Progesterone and cholesterol at normal range in about 90 % of cases