Molecular Characterization of β-Lactamase-Resistant <i>Klebsiella aerogenes</i> Isolated from Raw Milk in Bangladesh

The number of dairy farms in Bangladesh is steadily increasing, yet the characterization of common pathogenic organisms such as <i>Klebsiella aerogenes</i> remains underexplored. Due to the overwhelming challenges of antimicrobial resistance, the transmission of antibiotic resistance genes, and mobile colistin resistance (<i>mcr</i>) genes through zoonotic organisms, this study aimed to characterize <i>K. aerogenes</i> in raw milk in Sylhet. In this study, a total of 234 raw milk samples were collected from different dairy farms and milk-selling points in Sylhet. Then, isolates were detected by <i>16S rRNA</i> gene through PCR after standard cultural and biochemical tests. Furthermore, antibiotic sensitivity test was performed using the disc diffusion method, followed by screening of antibiotic-resistant genes (TEM, CTX-M, CTX-M-1, CTX-M-2a, SHV, OXA-1, CMY, and NDM-1) and <i>mcr</i> genes (<i>mcr</i>-1 to <i>mcr-9</i>). Finally, partial sequencing of <i>16S rRNA</i> was performed to study the genetic diversity. Among 234 samples, 86 (36.44%) were positive for <i>Klebsiella</i> and exhibited variation in resistance levels to amoxicillin (100%), ampicillin (100%), ceftazidime (100%), tetracycline (100%) followed by azithromycin (89.54%), cefoxitin (86.04%), gentamicin (83.74%), and cefuroxime (77.90%). All the samples harbored the <i>bla</i>_TEM gene (100%) and showed negative results when screening for <i>mcr</i> genes. The phylogenetic outcome reported that those isolates were closely related to <i>K. aerogenes</i>. According to our findings, the majority of the isolates were resistant to several antibiotics and contained the <i>bla</i>_TEM gene, which may represent a significant risk to the overall well-being of the population. These findings underscore that raw milk could be a potential harbor for multidrug resistance <i>K. aerogenes</i>, raising concerns about antimicrobial resistance transmission through traditionally processed dairy products, as such products are often prepared without proper heat treatment. The study emphasizes the need for strict hygiene practices and mandatory pasteurization measures during processing to reduce potential public health risks.