Prevalence of carbapenemases among high-level aminoglycoside-resistant Acinetobacter baumannii isolates in a university hospital in China

Abstract

The prevalence of aminoglycoside resistant enzymes has previously been reported and extended-spectrum β-lactamase among <i>Acinetobacter baumannii</i>. To track the risk of multidrug-resistant <i>A. baumannii</i>, the present study aimed to determine the prevalence of carbapenemases in high-level aminoglycoside resistant <i>A. baumannii</i> over two years. A total of 118 strains of <i>A. baumannii</i> were consecutively collected in the First Affiliated Hospital of Chengdu Medical College, Chengdu, China. These isolates were investigated on the genetic basis of their resistance to aminoglycosides. The results showed that 75 (63.56%) isolates were high-level resistant to aminoglycosides, including gentamicin and amikacin (minimum inhibitory concentration, ≥256 µg/ml). Aminoglycoside-resistant genes <i>ant(2″)-Ia</i>, <i>aac(6')-Ib</i>, <i>aph(3')-Ia</i>, <i>aac(3)-Ia</i>, <i>aac(3)-IIa</i>, <i>armA</i>, <i>rmtA</i>, <i>rmtB</i>, <i>rmtC</i>, <i>rmtD</i>, <i>rmtE</i>, <i>rmtF</i>, <i>rmtG</i>, <i>rmtH</i> and <i>npmA</i>, and carbapenem-resistant genes <i>bla</i>_OXA-23, <i>bla</i>_OXA-24, <i>bla</i>_OXA-51, <i>bla</i>_OXA-58, <i>bla</i>_SIM, <i>bla</i>_IMP, <i>bla</i>_NDM-1 and <i>bla</i>_KPC, were analyzed using polymerase chain reaction. The positive rate of <i>ant(2″)-Ia</i>, <i>aac(6')-Ib</i>, <i>aph(3')-Ia</i>, <i>aac(3)-Ia</i> and <i>aac(3)-IIa</i> was 66.95, 69.49, 42.37, 39.83 and 14.41%, respectively. <i>armA</i> was present in 72.0% (54/75) of <i>A. baumannii</i> isolates with high-level resistance to aminoglycosides. The remaining nine 16S ribosomal RNA methlyase genes (<i>rmtA</i>, <i>rmtB</i>, <i>rmtC</i>, <i>rmtD</i>, <i>rmtE</i>, <i>rmtF</i>, <i>rmtG</i>, <i>rmtH</i> and <i>npmA</i>) and aminoglycoside-modifying enzyme gene <i>aac(6')-Ib-cr</i> were not detected. Among the 54 <i>armA</i>-positive isolates, the prevalence of the carbapenem resistant <i>bla</i>_OXA-23 and <i>bla</i>_OXA-51 genes was 79.63 and 100%, respectively. <i>armA</i>, <i>ant(2″)-Ia</i> and <i>aac(6')-Ib</i> were positive in 43 isolates. The results of multilocus sequence typing revealed 31 sequence types (STs) in all clinical strains. Among these STs, the high-level aminoglycoside-resistant <i>A. baumannii</i> ST92, which mostly harbored <i>bla</i>_OXA-23, was the predominant clone (29/75). In conclusion, <i>A. baumannii</i> harboring carbapenemases and aminoglycoside-resistant enzymes are extremely prevalent in western China, emphasizing the need to adopt surveillance programs to solve the therapeutic challenges that this presents.