well trained microbiologist knows that morphology trumps millimeters… — Medical Notes Dr. Ayman Radwan — TG.ME

well trained microbiologist knows that morphology trumps millimeters , it is never zone of inhibition alone ............. we discussed in details earlier thethe in vitro vs. in vivo discordance , when the culture result does not tell the whole story followed by the (heterogenous VISA) ,when the culture lies (say sensitive to vancomycin) but we hit a bedside failure . we highlighted (h VISA ,MSSA) and the consequence of selective pressure and recently we discussed the master of deceiving , pseudomonas -as multilayered approach with introductory overview on types of resistance , Ambler classification and some clinical pitfalls in HAP coverage and dual antipsedomonal in HAP complicated by septic shock (if you missed this ,catch up #foundational_microbiology ) .............. today , it is (Vancomycin-Variable Enterococci (VVE) enterococci can be genotypically positive for vanA or vanB resistance genes but appear deceptively susceptible on an initial disk test, eventually developing resistance upon further exposure that is why both the EUCAST and CLSI guidelines emphasize the importance of subjective zone edge assessment هنا من التكات اللى بتفرق دكتور/أخصائي الميكرو الشاطر عن غيره انه 1. The 24-Hour Incubation Rule (No Shortcuts) Enterococcus plates must be incubated for a full 24 hours (not 16–18 hours like ordinary Gram-positives) before reading Vancomycin. Slow-growing resistant subpopulations or delayed genetic reversions in VVE need that extra time to manifest physically on the agar. حتى لو البكتريا زرعت كويس فى الطبق ميطلعش التقرير إلا بعد 24 ساعة لأن البكتريا ممكن تطور المقاومة بعد التعرض للمضاد الحيوي بفترة (2) ميتغرش بقطر النتيجة ويرفع الطبق فى الشمس لو الحواف حادة sharp edge means true susceptibility لكن لو الحواف مهزوزة او لاحظت خطوط من البكتريا تجاوزت الخط الواضح fuzzy lines mean a higher suspicion of VVE , postpone the final report do confirmatory test (Brain Heart Infusion (BHI) agar containing 6mcg/mL of Vancomycin ) the gold standard will be genomic testing (e.g., standard multiplex PCR or the BioFire FilmArray Blood Culture Identification Panel) targeting the vanA and vanB genes. NB: other gene mutation as van M ,van c ..ect will be discussed on the advanced level .............. then how to treat VVE/VRE? VVE /VRE oral options for uncomplicated urinary tract infections (UTIs) include:- Ampicillin (only if the isolate is susceptible, meaning no PBP5 mutations/beta-lactamase), Nitrofurantoin, or Fosfomycin. NB: Nitrofurantoin and Fosfomycin remain highly effective for lower UTIs even if the strain is Ampicillin-resistant. For systemic infections (like bacteremia) or complicated UTIs where oral UTI-specific drugs cannot be used: Use Linezolid 600 mg/ 12 h. if not suitable , use daptomycin high-dose (8 -12mg/kg)* not the standard 6mg/kg ((as VRE can rapidly develop daptomycin resistance under standard dosing pressure)) +/-beta-lactam (like Ceftaroline or Ampicillin) for a synergistic "see-saw" effect on the cell wall. NB: Mutations in the mprF or prsA genes often lead to daptomycin resistance but a simultaneous decrease in beta-lactam resistance (the see-saw effect), making combination therapy highly effective. This genetic profile can be identified through whole-genome sequencing (WGS). always consult infectious disease specialist if available NB: Iam not one , Iam just an internist ,endocrinologist