Amikacin-resistant Acinetobacter species mediated by the aphA6 gene associated with clinical outcome at an academic complex hospital in KwaZulu-Natal Province, South Africa

Abstract

Background. Drug-resistant Acinetobacter species present serious therapeutic and infection control policy challenges globally. Although aminoglycosides have played a crucial role in the treatment of infections with multidrug-resistant (MDR) Acinetobacter spp., recent reports indicate that these bacteria are developing resistance to aminoglycosides around the globe.

Objectives. To determine the association between amikacin resistance and clinical outcomes of patients. The minimum inhibitory concentrations (MICs) of amikacin against Acinetobacter spp. and genes associated with resistance were also investigated.

Methods. Clinical information from 107 patients with Acinetobacter spp. cultured from clinical specimens was recorded during ward rounds at an academic complex hospital in KwaZulu-Natal Province, South Africa, including clinical outcomes, history of antibiotics prescribed and microbiological investigations. The 107 Acinetobacter isolates were investigated for susceptibility to antimicrobial agents in use at local hospitals. Genes related to amikacin resistance (aphA6 and aacA4) were investigated by polymerase chain reaction (PCR) and sequencing. Analysis was performed on the relationship between clinical outcomes and antimicrobial resistance patterns, as well as on the amikacin MICs in resistant isolates (n=6) v. their PCR results.

Results. The majority (5/6, 83.3%) of patients with amikacin-resistant Acinetobacter infection were discharged, and 1/6 (16.7%) died. No underlying clinical factors were significantly associated with clinical outcome. Amikacin resistance was observed in 6/107 isolates (5.6%), with MICs of 32 µg/mL (n=3) and ≥64 µg/mL (n=3) for the amikacin-resistant isolates. All 6 of these isolates were also extensively drug-resistant (XDR). The aphA6 gene (797 base pair) was detected in all amikacin-resistant isolates.

Conclusions. Most tested Acinetobacter isolates were susceptible to amikacin, underscoring the crucial role of this antibiotic in the treatment of MDR Acinetobacter spp. in our hospital. The emergence of XDR isolates is of serious concern and necessitates close monitoring and surveillance.