Jaimee G, Halami P M
Department of Microbiology and Fermentation Technology, CSIR- Central Food Technological Research Institute, Mysore 570020, India.
Department of Microbiology and Fermentation Technology, CSIR- Central Food Technological Research Institute, Mysore 570020, India.
Microb Pathog. 2017 Sep;110:546-553. doi: 10.1016/j.micpath.2017.07.049. Epub 2017 Jul 31.
High level aminoglycoside resistance (HLAR) in the lactic acid bacteria (LAB) derived from food animals is detrimental. The aim of this study was to investigate the localization and conjugal transfer of aminoglycoside resistance genes, aac(6')Ie-aph(2″)Ia and aph(3')IIIa in different Enterococcus species. The cross resistance patterns in Enterococcus faecalis MCC3063 to clinically important aminoglycosides by real time PCR were also studied. Southern hybridization experiments revealed the presence of aac(6')Ie-aph(2)Ia and aph(3')IIIa genes conferring HLAR in high molecular weight plasmids except in Lactobacillus plantarum. The plasmid encoded bifunctional aac(6')Ie-aph(2″)Ia gene was transferable from Enterococcus avium (n = 2), E. cecorum (n = 1), E. faecalis (n = 1) and Pediococcus lolii (n = 1) species into the recipient strain; E. faecalis JH2-2 by filter mating experiments thus indicating the possible risks of gene transfer into pathogenic strains. Molecular analysis of cross resistance patterns in native isolate of E. faecalis MCC3063 carrying aac(6')Ie-aph(2″)Ia and aph(3')IIIa gene was displayed by quantification of the mRNA levels in this study. For this, the culture was induced with increasing concentrations of gentamicin, kanamycin and streptomycin (2048, 4096, 8192, 16384 μg/mL) individually. The increasing concentrations of gentamicin and kanamycin induced the expression of the aac(6')Ie-aph(2″)Ia and aph(3')IIIa resistance genes, respectively. Interestingly, it was observed that induction with streptomycin triggered a significant fold increase in the expression of the aph(3')IIIa gene which otherwise was not known to modify the aminoglycoside. This is noteworthy as streptomycin was found to confer cross resistance to structurally unrelated kanamycin. Also, expression of the aph(3')IIIa gene when induced with streptomycin, revealed that bacteria harbouring this gene will be able to overcome streptomycin bactericidal action at specific concentrations. HLAR in E. faecalis MCC3063 may be due to the combined expression of both the aac(6')Ie-aph(2″)Ia and aph(3')IIIa genes which could be therapeutically challenging. A combined expression of both the genes in E. faecalis MCC3063 may yield HLAR which could be therapeutically challenging. The study highlights the significant alterations in the mRNA expression levels of aac(6')Ie-aph(2″)Ia and aph(3')IIIa in resistant pathogens, upon exposure to clinically vital aminoglycosides.
源自食用动物的乳酸菌（LAB）中的高水平氨基糖苷类耐药性（HLAR）是有害的。本研究的目的是调查不同肠球菌物种中氨基糖苷类耐药基因aac(6')Ie-aph(2″)Ia和aph(3')IIIa的定位及接合转移。还通过实时PCR研究了粪肠球菌MCC3063对临床上重要氨基糖苷类药物的交叉耐药模式。Southern杂交实验表明，除植物乳杆菌外，在高分子量质粒中存在赋予HLAR的aac(6')Ie-aph(2)Ia和aph(3')IIIa基因。通过滤膜交配实验，质粒编码的双功能aac(6')Ie-aph(2″)Ia基因可从鸟肠球菌（n = 2）、盲肠肠球菌（n = 1）、粪肠球菌（n = 1）和罗伊氏片球菌（n = 1）转移至受体菌株粪肠球菌JH2-2，这表明基因转移至致病菌株存在潜在风险。本研究通过定量mRNA水平展示了携带aac(6')Ie-aph(2″)Ia和aph(3')IIIa基因的粪肠球菌MCC3063天然分离株的交叉耐药模式分子分析。为此，分别用浓度递增的庆大霉素、卡那霉素和链霉素（2048、4096、8192、16384μg/mL）诱导培养物。浓度递增的庆大霉素和卡那霉素分别诱导了aac(6')Ie-aph(2″)Ia和aph(3')IIIa耐药基因的表达。有趣的是，观察到用链霉素诱导会使aph(3')IIIa基因的表达显著增加，而该基因原本并不被认为会修饰氨基糖苷类药物。这一点值得注意，因为链霉素被发现可赋予对结构不相关的卡那霉素的交叉耐药性。此外，用链霉素诱导时aph(3')IIIa基因的表达表明，携带该基因的细菌在特定浓度下能够克服链霉素的杀菌作用。粪肠球菌MCC3063中的HLAR可能是由于aac(6')Ie-aph(2″)Ia和aph(3')IIIa这两个基因的联合表达，这在治疗上可能具有挑战性。粪肠球菌MCC3063中这两个基因的联合表达可能产生HLAR，这在治疗上可能具有挑战性。该研究突出了耐药病原体中aac(6')Ie-aph(2″)Ia和aph(3')IIIa的mRNA表达水平在接触临床上重要的氨基糖苷类药物后的显著变化。
