Abstract：
BACKGROUND: Patients infected with difficult-to-treat Pseudomonas aeruginosa are likely to receive meropenem (MEM) empirically before escalation to ceftolozane/tazobactam (C/T). We assessed whether pre-exposure to MEM affected C/T resistance development on C/T exposure.
METHODS: Nine clinical P. aeruginosa isolates were exposed to MEM 16 mg/L for 72 h. Then, isolates were serially passaged in the presence of C/T (concentration of 10 mg/L) for 72 h as two groups: an MEM-exposed group inoculated with MEM pre-exposed isolates and a non-MEM control group. At 24 h intervals, samples were plated on drug-free and drug-containing agar (C/T concentration 16/8 mg/L) and incubated to quantify bacterial densities (log10 cfu/mL). Growth on C/T agar indicated resistance development, and resistant population was calculated by dividing the cfu/mL on C/T plates by the cfu/mL on drug-free agar.
RESULTS: At 72 h, resistant populations were detected in 6/9 isolates. In five isolates, MEM exposure significantly increased the prevalence of ceftolozane/tazobactam-resistance development; the percentages of resistance population were 100%, 100%, 53.5%, 31% and 3% for the MEM-exposed versus 0%, 0%, 2%, 0.35% and ≤0.0003% in the unexposed groups. One isolate had a similar resistant population at 72 h between the two groups. The remaining isolates showed no development of resistance, regardless of previous MEM exposure.
CONCLUSIONS: MEM exposure may pre-dispose to C/T resistance development and thus limit the therapeutic utility of this β-lactam/β-lactamase inhibitor. Resistance may be a result of stress exposure or molecular-level mutations conferring cross-resistance. Further in vivo studies are needed to assess clinical implications of these findings.
METHODS: Nine clinical P. aeruginosa isolates were exposed to MEM 16 mg/L for 72 h. Then, isolates were serially passaged in the presence of C/T (concentration of 10 mg/L) for 72 h as two groups: an MEM-exposed group inoculated with MEM pre-exposed isolates and a non-MEM control group. At 24 h intervals, samples were plated on drug-free and drug-containing agar (C/T concentration 16/8 mg/L) and incubated to quantify bacterial densities (log10 cfu/mL). Growth on C/T agar indicated resistance development, and resistant population was calculated by dividing the cfu/mL on C/T plates by the cfu/mL on drug-free agar.
RESULTS: At 72 h, resistant populations were detected in 6/9 isolates. In five isolates, MEM exposure significantly increased the prevalence of ceftolozane/tazobactam-resistance development; the percentages of resistance population were 100%, 100%, 53.5%, 31% and 3% for the MEM-exposed versus 0%, 0%, 2%, 0.35% and ≤0.0003% in the unexposed groups. One isolate had a similar resistant population at 72 h between the two groups. The remaining isolates showed no development of resistance, regardless of previous MEM exposure.
CONCLUSIONS: MEM exposure may pre-dispose to C/T resistance development and thus limit the therapeutic utility of this β-lactam/β-lactamase inhibitor. Resistance may be a result of stress exposure or molecular-level mutations conferring cross-resistance. Further in vivo studies are needed to assess clinical implications of these findings.
摘要：
背景：感染难以治疗的铜绿假单胞菌的患者在升级为头孢洛扎/他唑巴坦（C/T）之前可能会根据经验接受美罗培南（MEM）。我们评估了暴露于MEM之前是否会影响C/T暴露时的C/T抗性发展。
方法：将9株临床铜绿假单胞菌暴露于16mg/L的MEM中72h。然后，分离株在C/T（浓度为10mg/L）存在下连续传代72h，分为两组：MEM暴露组接种了MEM预暴露分离株，非MEM对照组。每隔24小时，将样品铺在无药物和含药物的琼脂(C/T浓度16/8mg/L)上并孵育以定量细菌密度(log10cfu/mL)。在C/T琼脂上的生长表明抗性发展，通过将C/T平板上的cfu/mL除以无药物琼脂上的cfu/mL来计算抗性群体。
结果：在72小时，在6/9分离株中检测到抗性群体。在五个分离物中，MEM暴露显着增加头孢洛扎/他唑巴坦抗性发展的患病率；抗性人群的百分比为100％，100%,53.5%,暴露于MEM的31%和3%，与0%相比，0%,2%,未暴露组0.35%和≤0.0003%。两组之间在72小时时，一个分离株具有相似的抗性种群。其余的分离株没有出现耐药性，无论以前的MEM暴露。
结论：MEM暴露可能会导致C/T耐药性的发展，从而限制了这种β-内酰胺/β-内酰胺酶抑制剂的治疗效用。抗性可能是应激暴露或赋予交叉抗性的分子水平突变的结果。需要进一步的体内研究来评估这些发现的临床意义。
方法：将9株临床铜绿假单胞菌暴露于16mg/L的MEM中72h。然后，分离株在C/T（浓度为10mg/L）存在下连续传代72h，分为两组：MEM暴露组接种了MEM预暴露分离株，非MEM对照组。每隔24小时，将样品铺在无药物和含药物的琼脂(C/T浓度16/8mg/L)上并孵育以定量细菌密度(log10cfu/mL)。在C/T琼脂上的生长表明抗性发展，通过将C/T平板上的cfu/mL除以无药物琼脂上的cfu/mL来计算抗性群体。
结果：在72小时，在6/9分离株中检测到抗性群体。在五个分离物中，MEM暴露显着增加头孢洛扎/他唑巴坦抗性发展的患病率；抗性人群的百分比为100％，100%,53.5%,暴露于MEM的31%和3%，与0%相比，0%,2%,未暴露组0.35%和≤0.0003%。两组之间在72小时时，一个分离株具有相似的抗性种群。其余的分离株没有出现耐药性，无论以前的MEM暴露。
结论：MEM暴露可能会导致C/T耐药性的发展，从而限制了这种β-内酰胺/β-内酰胺酶抑制剂的治疗效用。抗性可能是应激暴露或赋予交叉抗性的分子水平突变的结果。需要进一步的体内研究来评估这些发现的临床意义。
