Eguale Tadesse, Birungi Josephine, Asrat Daniel, Njahira Moses N, Njuguna Joyce, Gebreyes Wondwossen A, Gunn John S, Djikeng Appolinaire, Engidawork Ephrem
Aklilu Lemma Institute of Pathobiology, Addis Ababa University, P.O. Box 1176, Addis Ababa, Ethiopia.
Biosciences Eastern and Central Africa-International Livestock Research Institute (BecA-ILRI) Hub, P O Box 30709, Nairobi, Kenya.
Antimicrob Resist Infect Control. 2017 Jan 17;6:13. doi: 10.1186/s13756-017-0171-6. eCollection 2017.
Beta-lactam and quinolone antimicrobials are commonly used for treatment of infections caused by non-typhoidal (NTS) and other pathogens. Resistance to these classes of antimicrobials has increased significantly in the recent years. However, little is known on the genetic basis of resistance to these drugs in isolates from Ethiopia.
isolates with reduced susceptibility to beta-lactams ( = 43) were tested for genes encoding for beta-lactamase enzymes, and those resistant to quinolones ( = 29) for mutations in the quinolone resistance determining region (QRDR) as well as plasmid mediated quinolone resistance (PMQR) genes using PCR and sequencing.
Beta-lactamase genes () were detected in 34 (79.1%) of the isolates. The dominant gene was TEM, recovered from 33 (76.7%) of the isolates, majority being TEM-1 (24, 72.7%) followed by TEM-57, (10, 30.3%). The OXA-10 and CTX-M-15 were detected only in a single Concord human isolate. Double substitutions in A (Ser83-Phe + Asp87-Gly) as well as C (Thr57-Ser + Ser80-Ile) subunits of the quinolone resistance determining region (QRDR) were detected in all Kentucky isolates with high level resistance to both nalidixic acid and ciprofloxacin. Single amino acid substitutions, Ser83-Phe ( = 4) and Ser83-Tyr ( = 1) were also detected in the A gene. An isolate of . Miami susceptible to nalidixic acid but intermediately resistant to ciprofloxacin had Thr57-Ser and an additional novel mutation (Tyr83-Phe) in the C gene. Plasmid mediated quinolone resistance (PMQR) genes investigated were not detected in any of the isolates. In some isolates with decreased susceptibility to ciprofloxacin and/or nalidixic acid, no mutations in QRDR or PMQR genes were detected. Over half of the quinolone resistant isolates in the current study 17 (58.6%) were also resistant to at least one of the beta-lactam antimicrobials.
Acquisition of TEM was the principal beta-lactamase resistance mechanism and mutations within QRDR of A and C were the primary mechanism for resistance to quinolones. Further study on extended spectrum beta-lactamase and quinolone resistance mechanisms in other gram negative pathogens is recommended.
β-内酰胺类和喹诺酮类抗菌药物常用于治疗非伤寒沙门氏菌（NTS）及其他病原体引起的感染。近年来，对这两类抗菌药物的耐药性显著增加。然而，关于埃塞俄比亚分离株对这些药物耐药的遗传基础知之甚少。
对43株对β-内酰胺类药物敏感性降低的分离株检测编码β-内酰胺酶的基因，对29株对喹诺酮类药物耐药的分离株，使用聚合酶链反应（PCR）和测序检测喹诺酮耐药决定区（QRDR）的突变以及质粒介导的喹诺酮耐药（PMQR）基因。
在34株（79.1%）分离株中检测到β-内酰胺酶基因。主要的β-内酰胺酶基因是TEM，从33株（76.7%）分离株中检出，多数为TEM-1（24株，72.7%），其次是TEM-57（10株，30.3%）。仅在1株协和人分离株中检测到OXA-10和CTX-M-15。在所有对萘啶酸和环丙沙星均具有高水平耐药性的肯塔基分离株中，检测到喹诺酮耐药决定区（QRDR）的A亚基（Ser83-Phe + Asp87-Gly）和C亚基（Thr57-Ser + Ser80-Ile）发生双取代。在A基因中还检测到单氨基酸取代Ser83-Phe（4株）和Ser83-Tyr（1株）。1株对萘啶酸敏感但对环丙沙星中度耐药的迈阿密沙门氏菌分离株，其C基因中有Thr57-Ser和另一个新突变（Tyr83-Phe）。在所检测的分离株中均未检测到质粒介导的喹诺酮耐药（PMQR）基因。在一些对环丙沙星和/或萘啶酸敏感性降低的分离株中，未检测到QRDR或PMQR基因的突变。在本研究中，超过半数（17株，58.6%）的喹诺酮耐药分离株也对至少一种β-内酰胺类抗菌药物耐药。
获得TEM是主要的β-内酰胺酶耐药机制，A和C亚基的QRDR内的突变是对喹诺酮类药物耐药的主要机制。建议进一步研究其他革兰氏阴性病原体中的超广谱β-内酰胺酶和喹诺酮耐药机制。
