Detection of bla OXA-145, bla OXA-224, bla OXA-539, and bla OXA-675 Genes and Carbapenem-Hydrolyzing Class D β-Lactamases (CHDLs) in Clinical Isolates of Pseudomonas aeruginosa Collected from West of Iran, Hamadan

Abstract

Carbapenem-hydrolyzing class D β-lactamases (CHDLs) are on the rise and are a major public health problem worldwide. Pseudomonas aeruginosa is resistant to carbapenem; currently, the most effective treatment option is being increasingly reported. This study aimed to identify blaOXA-145, blaOXA-224, blaOXA-539, and blaOXA-675 genes in CHDL strains. Samples were collected from clinical specimens admitted to the hospital. Antibiotic susceptibility was determined using the disk diffusion methods. CHDL strains were detected using a phenotypic method (disk diffusion). The PCR method was used to identify blaOXA-145, blaOXA-224, blaOXA-539, and blaOXA-675 genes. Piperacillin-resistant strains (n = 9, 17.4%) had the lowest frequency, and cefoxitin-resistant strains (n = 100, 91.7%) had the highest distribution in P. aeruginosa isolates. Also, 29.35%, 12.8%, and 8.2% were multidrug-resistant, extensively drug-resistant, and pan drug-resistant, respectively. MBL-producing P. aeruginosa and KPC-producing P. aeruginosa were detected, respectively, in 47.7% and 37.6% of isolates. Biofilm formation was observed in 63.3% of P. aeruginosa isolates. The frequency of OXA genes was as follows: blaOXA-145 gene in 30 isolates (27.5%), blaOXA-224 in 24 isolates (22.0%), blaOXA-539 in 22 isolates (20.1%), and blaOXA-675 in 13 isolates (11.9%). However, 19 (17.4%) isolates carry all blaOXA-145, blaOXA-224, blaOXA-539, and blaOXA-675 genes. The antimicrobial resistance and OXA genes among biofilm former strains were significantly higher than those of nonbiofilm former strains (p < 0.05). The emergence of carbapenem-resistant isolates of P. aeruginosa has posed serious threats to the community because they exhibit multiple drug resistance, thus limiting the therapeutic options for clinicians.

Figure 1

Antibiotic resistance pattern in clinical isolates of P. aeruginosa. PIP: piperacillin; GEN: gentamycin; AMK: amikacin; CIP: ciprofloxacin; CAZ: ceftazidime; CTX: ceftriaxone; IMI: imipenem; MER: meropenem; ERT: ertapenem; FOX: cefoxitin; CFX: cefazolin; CPE: cefepime; MDR: multiple drug resistance; XDR: extensively drug-resistant; PDR: pan drug-resistant.

Figure 2

The result of phenotypic detection of MBL-producing Pseudomonas aeruginosa by the EDTA-imipenem microbiological (EIM) test in Pseudomonas aeruginosa. (a) EDTA + imipenem; (b) imipenem. Top: MBL positive strain; bottom: MBL negative strain; MBL considered positive when the zone diameter difference between imipenem + EDTA and imipenem discs was larger than 7 mm (right). The result of phenotypic detection of carbapenemase-producing P. aeruginosa by the modified Hodge test (left).

Figure 3

The amplification and gel electrophoresis agarose of 1.5% of blaOXA genes in P. aeruginosa. Top: blaOXA-539 with 185 bp and blaOXA-224 with 168 bp; wells 1 and 17: positive control, well 18: negative control, wells 3–9: positive strains with blaOXA-539; wells 11–18: positive strains with blaOXA-224. Down: blaOXA-145 with 204 bp and blaOXA-675 with 138 bp; wells 1 and 14: positive control, well 15: negative control wells 2–7: positive strains with blaOXA-145, wells 8–14: positive strains with blaOXA-145. M: ladder 100 bp.