Characterization of Acinetobacter baumannii Isolated from Raw Milk

SIMPLE SUMMARY: Although milk is a significant nutrient source for humans, it can be associated with various bacterial infections. Acinetobacter species can be found in milk due to residual water in milking machines, milk pipelines or coolers, the inadequate cleaning of dairy equipment, tainted udders and teats, the improper transport and storage of milk and the inadequate cleaning of dairy equipment, causing diseases. Most members of the genus Acinetobacter are opportunistic commensals with limited virulence and are clinically insignificant. However, Acinetobacter infections have recently increased in severity due to the frequent use of mechanical breathing devices, venous catheters and antibiotics, and they pose significant public health concerns. Acinetobacter baumannii (A. baumannii) is an opportunistic pathogen that causes various nosocomial infections. Studies using animal models and clinical data demonstrated that A. baumannii is a highly virulent species. It is a significant pathogen, especially due to the emergence of multidrug-resistant (MDR) strains and their association with many nosocomial infections and community-acquired infections. ABSTRACT: Acinetobacter baumannii (A. baumannii) 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 A. baumannii and investigate their antimicrobial resistance and biofilm formation. Our findings revealed that, among the 100 samples, Acinetobacter spp. were found in 13 samples based on CHROM agar results. We further characterized them using rpoB and 16S-23SrRNA sequencing and gyrB multiplex PCR analysis and confirmed that 9 out of the 13 Acinetobacter spp. isolates were A. baumannii and 4 were other species. The A. baumannii 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, bla(OXA-51) and bla(OXA-23) genes were amplified in 100% and 55.5% of the A. baumannii isolates, respectively, while the bla(OXA-58) gene was not amplified. Furthermore, the metallo-β-lactamases (MBL) genes bla(IMP) and bla(NDM) were found in 11.1% and 22.2% of isolates, respectively, while bla(VIM) was not amplified. Additionally, eight A. baumannii 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 A. baumannii, which could be a public health concern.