Abstract
Macrolide-resistant methicillin-resistant Staphylococcus aureus (MAC-MRSA) is one of the most clinically relevant pathogens due to its significant ability of resistance acquisition to different antimicrobial agents. This study aimed to evaluate antimicrobial susceptibility and the use of different combinations of azithromycin with other antibiotics for combating MAC resistance. Seventy-two Staphylococci (38.5%) (n = 187), showed resistance to MACs; of these, 53 isolates (73.6%, n = 72) were S. aureus and 19 (26.4%, n = 72) were coagulase-negative staphylococci (CoNS). Out of the 53 S. aureus and 19 CoNS isolates, 38 (71.7%, n = 53) and 9 (47.4%, n = 19) were MRSA and methicillin-resistant CoNS, respectively. The constitutive MACs, lincosamides and streptogramin-B (cMLS) comprised the predominant phenotype among S. aureus isolates (54.7%) and CoNS isolates (78.9%). The PCR analysis showed that the ermC gene was the most prevalent (79.2%), followed by msrA (48.6%), and ermA (31.9%). Azithromycin combinations with either linezolid, ceftriaxone, gentamicin, or cefotaxime provided synergy in 42.1%, 44.7%, 31.6% and 7.9% of the 38 MAC-MRSA isolates, respectively. Statistical analysis showed significant association between certain MAC resistance genotypes and the synergistic effect of certain azithromycin combinations (p value < 0.05). In conclusion, azithromycin combinations with either linezolid, or ceftriaxone showed synergism in most of the MAC-resistant MRSA clinical isolates.
Highlights
Antimicrobial resistance is deemed to be a serious concern to modern medicine, as it certainly reduces the possibility of successful treatment of infectious diseases [1]
The PCR results showed that ermC was the most frequently occurring gene (79.2%), followed by the MAC-streptogramin resistance gene (msrA) gene (48.6%), the ermA gene (31.9%)
The distribution of the MAC-resistance phenotypes in our study agreed with the study carried out in China by Yao and coworkers, where the cMLS phenotype was the most predominant (95, n = 96) over the iMLS phenotype (1, n = 96) among S. aureus isolates from different clinical specimens [26]
Summary
Antimicrobial resistance is deemed to be a serious concern to modern medicine, as it certainly reduces the possibility of successful treatment of infectious diseases [1]. There is a wide range of MRSA infections, ranging from mild skin and soft tissue infections to life-threatening diseases, such as endocarditis, osteomyelitis, and pneumonia [3,4]. Owing to their prominent ability of resistance acquisition to different antimicrobial agents, in addition to the difficulty of treatment of this pathogen, MRSA strains create a major threat to public health [5,6]. This can be contradicted by the development of resistance mechanisms by MRSA isolates to overcome the high concentrations of these antimicrobials [5,7]
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