Characterization of Acinetobacter baumannii Isolated from Raw Milk

Abstract

<i>Acinetobacter baumannii (A. baumannii)</i> is an opportunistic pathogen associated with nosocomial infections. In this study, 100 raw milk samples were collected from Qena, Egypt, and subjected to conventional and molecular assays to determine the presence of <i>A. baumannii</i> and investigate their antimicrobial resistance and biofilm formation. Our findings revealed that, among the 100 samples, <i>Acinetobacter</i> spp. were found in 13 samples based on CHROM agar results. We further characterized them using <i>rpo</i>B and <i>16S-23SrRNA</i> sequencing and <i>gyr</i>B multiplex PCR analysis and confirmed that 9 out of the 13 <i>Acinetobacter</i> spp. isolates were <i>A. baumannii</i> and 4 were other species. The <i>A. baumannii</i> isolates were resistant to β-lactam drugs, including cefotaxime (44%), ampicillin-sulbactam and levofloxacin (33.3% for each), imipenem, meropenem and aztreonam (22.2% for each). We observed different antimicrobial resistance patterns, with a multi-antibiotic resistant (MAR) index ranging from 0.2 to 0.3. According to the PCR results, <i>bla_OXA-51</i> and <i>bla_OXA-23</i> genes were amplified in 100% and 55.5% of the <i>A. baumannii</i> isolates, respectively, while the <i>bla_OXA-58</i> gene was not amplified. Furthermore, the metallo-β-lactamases (MBL) genes <i>bla_IMP</i> and <i>bla_NDM</i> were found in 11.1% and 22.2% of isolates, respectively, while <i>bla_VIM</i> was not amplified. Additionally, eight <i>A. baumannii</i> isolates (88.8%) produced black-colored colonies on Congo red agar, demonstrating their biofilm production capacity. These results showed that, besides other foodborne pathogens, raw milk should also be examined for <i>A. baumannii</i>, which could be a public health concern.