Pseudomonas Trap (false positive test) as Pseudomonas harbors a… — Medical Notes Dr. Ayman Radwan — TG.ME

Pseudomonas Trap (false positive test) as Pseudomonas harbors a baseline, inducible chromosomal ampC gene, boronic acid testing will frequently yield positive results. However, high-level carbapenem resistance in this organism is rarely driven by AmpC alone; it typically requires concurrent OprD porin loss or MexAB-OprM efflux pump upregulation. If non-enzymatic permeability barriers are the true drivers of resistance, a positive boronic acid test can be highly misleading, as simply inhibiting the AmpC enzyme will not restore carbapenem efficacy. To overcome this dual barrier of hyper-expressed AmpC and active efflux, therapy must bypass the altered porin channels entirely. Ceftolozane/Tazobactam or Imipenem/Relebactam represent the premier targeted choices that is why we should not use Cefepime alone in this situation you can use Ceftazidime/Avibactam (2.5 g IV every 8 hours) or Imipenem/Relebactam to structurally inhibit the KPC enzyme before therapeutic initiation. for simplicity if positive use : Ceftolozane/Tazobactam (C) The Double-Negative Profile: When both EDTA and boronic acid assays fail to alter the carbapenem zone of inhibition, the resistance profile is non-enzymatic (absolute deletion of the outer membrane OprD porin channels coupled with the hyper-activation of intrinsic efflux MexAB-OprM ) it is completely independent of beta -lactamase production however we use Zerbaxa (Ceftolozane/Tazobactam) High-dose (3 g IV every 8 hours) as Ceftolozane is not available alone for simplicity you can override the boronic acid test , just consider MBL Vs non enzymatic +/-Amp C ......... if the EDTA test is negative but resistance remains absolute, you are dealing with a non-enzymatic profile or hyper-expressed AmpC. While Ceftolozane/Tazobactam is indeed the premier choice because Ceftolozane is optimized to evade MexAB-OprM efflux and resist AmpC degradation, Ceftazidime/Avibactam remains a highly valid option to neutralize hyper-produced AmpC if porin deletion is incomplete. .......................................... Advanced Level: The Phenotypic-MIC Mismatch -The Silent or Low-level Carbapenemase Trap In these bacteria, the resistance gene (such as blaNDM, blaOXA, or cfiA) is either suppressed by promoter mutations or lacks the genetic elements required for high-level expression then you can discard the Mic , It is false negative consider resistance and the best approach then is to order the golden genetic testing ........... and this is meropenem resistance as it should be explained my personal approach finally revealed ,stay tuned for the next episode By: Dr.Ayman A.Radwan #foundational_microbiology fast bullets 1-when to add anti MRSA ? according to IDSA/ATS 2016 HAP/VAP guidelines, MRSA coverage should be used in patients with risk factors for multidrug resistance or in units where >20% of S. aureus isolates are MRSA. or Prior Intravenous Antibiotic Use: The patient received any IV antimicrobial therapy within the preceding 90 days يبقى أي مريض فى المستشفى محجوز فى الرعاية هياخد فانكوميسين وأي مريض HAP with prior IV antibiotic use لازم تديله فانكوميسين (لو مبتعملش كده محتاج تسأل نفسك ليه المشلتت الطبي ده) a good doctor will use empirical vancomycin when needed and de escalate after 48 h according to nasal swab ..................... 2-When to Cover Pseudomonas aeruginosa? IDSA guidelines state that all empiric regimens for HAP must have activity against Pseudomonas aeruginosa and other Gram-negative bacilli. However, the decision to use one antipseudomonal drug versus two concurrent drugs from different classes depends on distinct risk parameters ........... Use ONE Antipseudomonal Agent in absence of the following ( septic shock "high mortality"-structural lung disease(bronchiectasis or cystic fibrosis) - admitted at unit where more than 10% of Gram-negative isolates are resistant to the drug) ⬇️⬇️KEEP READING⬇️⬇️