Phenotypic and genotypic Detection of Some Antimicrobial Resistance Mechanisms among Multidrug-Resistant Acinetobacter baumannii Isolated from immunocompromised Patients in Egypt

Acinetobacter spp. are Gram-negative bacteria that have become one of the most difficult pathogens to treat. The species A. baumannii, largely unknown 30 years ago, has risen to prominence particularly because of its ability to cause infections in immunocompromised patients. It is now a predominant pathogen in many hospitals as it has acquired resistance genes to virtually all antibiotics capable of treating Gram-negative bacteria, including the fluoroquinolones and the cephalosporins. The aims of this study were to (i) evaluate the antimicrobial susceptibility of Acinetobacter baumannii isolated from immunocompromised host (ii) phenotypic assessmentof the prevalent mechanism of resistance among multi drug resistant Acinetobacter spp. (iii) evaluate the prevalence of metallo β-lactamases (MBLs)phenotypically and genotypically among multidrug resistant A. baumannii. Seventy-two nonreplicated A. baumannii isolates were recovered from 631 clinical specimens referred for bacteriological cultures from immunecompromised patients of all age groups and both sexes admitted in El-Demerdash Hospital and National Cancer Institute (NCI) Cairo-Egypt. Isolates were identified conventionally using standard biochemical tests and also using Microscan (Dade Behring, West Sacramento, USA). Both manual (following the CLSI protocol) and automated methods (using Microscan system) were used to detect antimicrobial susceptibility pattern of Acinetobacter isolates. Different potential resistance mechanisms were investigated in 45 carbapenem resistant A. baumannii phenotypically. Genotypic detection of MBLs was carried out using PCR. Acinetobacter baumannii represents the predominant Acinetobacter isolates (83.3%). The mean age group of patient with Acinetobacter infection was more than 55 years old (36.1%). A. baumannii exhibited high resistance rate to the majority of commercially available drugs including imipenem (66.6%), meropenem (73.3%) andcefazolin & cephalothin (100%). Isolates show moderate susceptibility to tetracycline (40% of the isolates were susceptible) and gentamicin (33.3%). MDR A. baumannii represent 75% of the Acinetobacter isolates (45/72). Using phenotypic tests; none of the carbapenem-resistant A. baumannii were carbapenemase producers and44.4%wereAmpC β-lactamase positive. MBLs were detected in 55.6% using phenotypic tests and in 44.4% of isolates using PCR. Moreover Efflux pump was detected in 77.8% of isolates. Conclusions: Multidrug resistant A. baumanniiis a problematic organism in immunosuppressed patients since it became resistant to the majority of commercially available antimicrobials with different resistance mechanisms. Metallo-β-lactamase production is an important mechanism of carbapenem resistance and AmpC - β-lactamase could be a contributory factor for meropenem resistance among MDRAB isolates. This underlies the importance of their accurate identification and reporting to prevent the emergence of absolute resistance to the useful drugs against Acinetobacter spp. in Egypt.