CONSEQUENCES OF THE INOCULUM EFFECT AGAINST Β-LACTAMS IN METHICILLIN-SUSCEPTIBLE STAPHYLOCOCCUS AUREUS (MSSA) STRAINS

Öz

Objective: Some staphylococcal β-lactamases could destroy β lactams other than penicillin, including cefazolin (Cz) and ampi cillin-sulbactam (SAM), especially in the presence of higher inocu lum, which is called the inoculum effect (InE). We investigated the incidence and clinical implications of InE against different β-lac tams including in S.aureus (MSSA) strains isolated from bacteremic patients. Material and Methods: Patients with MSSA bacteraemia were included. MSSA strains were tested with the disk diffusion and broth microdilution method at standard and high inoculum. The presence and type of β-lactamases were confirmed by PCR plus DNA sequencing. InE was defined as a 4-fold or greater increase in minimal inhibitor concentration (MIC) values at high inoculum. Patient data were obtained retrospectively. Results: 85% of the 52 MSSA strains were Type A β-lactamase positive. 25%, 38.5%, and 3.8% of the strains showed InE against Cz, SAM, and ceftriaxone, respectively. The mortality rate in patients infected with MSSA strains showing SAMInE and treated with SAM was significantly higher than in those not treated with SAM (p=0.044, OR 7.8, 95). Conclusion: SAM was the most affected β-lactam by type A β lactamase of MSSA strains, followed by Cz, and this effect became more prominent with higher inoculum. SAM treatment of the patients infected with the MSSA strains showing SAMInE may increase mortality.

Anahtar Kelimeler

• Ampicillin-sulbactam
• bacteraemia
• cefazolin
• inoculum effect
• MSSA
• Staphylococcus aureus

METİSİLİNE DUYARLI STAPHYLOCOCCUS AUREUS (MSSA) SUŞLARININ β-LAKTAMLARA KARŞI İNOKULÜM ETKİSİ GÖSTERMESİNİN SONUÇLARI

Öz

Amaç: Bazı stafilokoksik β-laktamazlar, özellikle daha yüksek inokulum varlığında, sefazolin (Cz) ve ampisilin-sulbaktam (SAM) dahil olmak üzere penisilin dışındaki β-laktamları parçayalabilir ki buna inokulum etkisi (InE) denir. Bu çalışmada bakteriyemik hastalardan izole edilen S.aureus(MSSA) suşlarında farklı β-laktamlara karşı InE'nin insidansı ve klinik etkileri araştırılmıştır. Gereç ve Yöntemler: Çalışmaya MSSA bakteriyemisi olan hastalar dahil edildi. MSSA suşları, standart ve yüksek inokulumda disk difüzyon ve sıvı mikrodilüsyon yöntemi ile test edildi. β-laktama zların varlığı ve tipi PCR artı DNA dizilemesi ile doğrulandı. InE, yüksek inokulumda minimal inhibtör konsantrasyon (MİK) değerlerinde 4 kat veya daha fazla artış olarak tanımlandı. Hasta verileri retrospektif olarak elde edildi. Bulgular: 52 MSSA suşunun %85'i Tip A β-laktamaz pozitifti. Suşların %25'i, %38,5'i ve %3,8'i sırasıyla Cz, SAM ve seftriaksona karşı InE gösterdi. SAMInE gösteren MSSA suşlarıyla infekte olmuş ve SAM ile tedavi edilen hastalardaki ölüm oranı, SAM ile tedavi edilmeyenlere göre önemli ölçüde daha yüksekti (p=0,044, OR 7,8). Sonuç: MSSA suşlarının tip A β-laktamazı tarafından en çok etkile nen β-laktamın SAM olduğu, bunu Cz’nin takip ettiği ve bu etkinin daha yüksek inokulumla daha belirgin hale geldiği görülmüştür. SAMInE gösteren MSSA suşlarıyla infekte olmuş bakteriyemili hastaların SAM’la tedavisi ölüm oranını artırabilir.

Anahtar Kelimeler

• Ampisilin-sulbaktam
• bakteriyemi
• sefazolin
• inokulum etkisi
• MSSA
• Staphylococcus aureus

Kaynakça

1. Lam JC, Stokes W. The Golden Grapes of Wrath - Staphylococcus aureus Bacteremia: A Clinical Review. Am J Med 2023;136(1):19-26. google scholar
2. Lenhard JR, Bulman ZP. Inoculum effect of β-lactam antibiotics. J Antimicrob Chemother 2019;74(10):2825-43. google scholar
3. Weis S, Kesselmeier M, Davis JS, Morris AM, Lee S, Scherag A, et al. Cefazolin versus anti-staphylococcal penicillins for the treatment of patients with Staphylococcus aureus bacteraemia. Clin Microbiol Infect 2019;25(7):818-27. google scholar
4. European Committee on Antimicrobial Susceptibility Testing. Antimicrobial Susceptibility Testing, EUCAST Disk Diffusion Method 2024. April 14, 2025 2024, https://www.eucast.org/fileadmin/src/media/PDFs/EUCAST_files/Disk_ test_documents/2024_manuals/Manual_v_12.0_EUCAST_Disk_Test_2024.pdf . google scholar
5. Clinical and Laboratory Institute. Methods for dilution antimicrobial susceptibility tests f or bacteria that grow aerobically; Approved Standard— Ninth Edition. CLSI document M07-A9. 2012, Wayne, PA: Clinical and Laboratory Standards Institute, 1-63, ISBN 1-56238-783-9. google scholar
6. Nannini EC, Stryjewski ME, Singh KV, Bourgogne A, Rude TH, Corey GR, et al. Inoculum effect with cefazolin among clinical isolates of methicillin- google scholar
7. susceptible Staphylococcus aureus: frequency and possible cause of cefazolin treatment failure. Antimicrob Agents Chemother 2009;53(8):3437-41. google scholar
8. Song KH, Jung SI, Lee S, Park S, Kim ES, Park KH, et al. Inoculum effect of methicillin-susceptible Staphylococcus aureus against broad-spectrum betalactam antibiotics. Eur J Clin Microbiol Infect Dis 2019;38(1):67-74. google scholar

9. Saeki M, Shinagawa M, Yakuwa Y, Nirasawa S, Sato Y, Yanagihara N, Takahashi S. Inoculum effect of high concentrations of methicillin-susceptible Staphylococcus aureus on the efficacy of cefazolin and other beta-lactams. J Infect Chemother 2018;24(3):212-5. google scholar
10. Lo CK, Sritharan A, Zhang J, Li N, Zhang C, Wang F, et al. Clinical significance of cefazolin inoculum effect in serious MSSA infections: a systematic review. JAC Antimicrob Resist 2024;6(3):dlae069. google scholar
11. Bush K, Bradford PA. Epidemiology of β-Lactamase-Producing Pathogens. Clin Microbiol Rev 2020;33(2):e00047-19. google scholar
12. Livorsi DJ, Crispell E, Satola SW, Burd EM, Jerris R, Wang YF, Farley MM. Prevalence of blaZ gene types and the inoculum effect with cefazolin among bloodstream isolates of methicillin-susceptible Staphylococcus aureus. Antimicrob Agents Chemother 2012;56(8):4474-7. google scholar
13. Lee S, Kwon KT, Kim HI, Chang HH, Lee JM, Choe PG, et al. Clinical implications of cefazolin inoculum effect and β-lactamase type on methicillin-susceptible Staphylococcus aureus bacteremia. Microb Drug Resist 2014;20(6):568-74. google scholar
14. George CRR, Lahra MM, NguyenT, Gatus B. Disc Test for Detecting Staphylococcus aureus Strains producing type a and type C β-lactamases. Microbiol Spectr 2023;11(4):e0022023. google scholar
15. Mossman AK, Svishchuk J, Waddell BJM, Izydorczyk CS, Buckley PT, Hilliard JJ, et al. Staphylococcus aureus in non-cystic fibrosis bronchiectasis: prevalence and genomic basis of high inoculum β-lactam resistance. Ann Am Thorac Soc 2022;19(8):1285-93. google scholar
16. Mairi A, Pantel A, Sotto A, Touati A. OXA-48-like carbapenemases producing Enterobacteriaceae in different niches. Eur J Clin Microbiol Infect Dis 2018;37(4):587-604. google scholar
17. Jafari A, Falahatkar S, Delpasand K, Sabati H, Sedigh Ebrahim-Saraie H. Emergence of Escherichia coli ST131 Causing Urinary Tract Infection in Western Asia: A Systematic Review and Meta-Analysis. Microb Drug Resist 2020;26(11):1357-64. google scholar
18. Carvajal LP, Rincon S, Echeverri AM, Porras J, Rios R, Ordoñez KM, et al. Novel Insights into the Classification of Staphylococcal β-Lactamases in Relation to the Cefazolin Inoculum Effect. Antimicrob Agents Chemother 2020;64(5):e02511-9. google scholar
19. Lee SH, Park WB, Lee S, Park S, Kim SW, Lee JM, et al. Association between Type A blaZ Gene polymorphism and cefazolin inoculum effect in methicillin-susceptible Staphylococcus aureus. Antimicrob Agents Chemother 2016;60(11):6928-32. google scholar
20. Payne DJ, Cramp R, Winstanley DJ, Konowles DJ. Comparative activities of clavulanic acid, sulbactam, and tazobactam against clinically important betalactamases. Antimicrob Agents Chemother 1994;38(4):767-72. google scholar
21. Paul M, Zemer-Wassercug N, Talker O, Lishtzinsky Y, Lev B, Samra Z, et al. Are all beta-lactams similarly effective in the treatment of methicillin-sensitive Staphylococcus aureus bacteraemia? Clin Microbiol Infect 2011;17(10):1581-6. google scholar
22. Başaran S, Şimşek-Yavuz S, Çopur B, Yir A, Çağatay A, Öncül O, et al. Analysis of risk factors for mortality in methicillin-sensitive Staphylococcus aureus bacteremia: Cefazolin is associated with better ourcome. J Ist Faculty Med 2019;82(3):131-8. google scholar
23. Uda A, Onuma K, Shigemura K, Kitagawa K, Yan Y, Osawa K, et al. Impact of Cefazolin Shortage on Clinical Outcomes of Adult Patients with Bacteremia Caused by Methicillin-Susceptible Staphylococcus aureus in a Tertiary Care University Hospital. Antibiotics (Basel) 2021;10(10):1247. google scholar
24. Beganovic M, Cusumano JA, Lopes V, LaPlante KL, Caffrey AR. Comparative effectiveness of exclusive exposure to nafcillin or oxacillin, cefazolin, piperacillin/tazobactam, and fluoroquinolones among a national cohort of veterans with methicillin-susceptible Staphylococcus aureus bloodstream infection. Open Forum Infect Dis 2019;6(7):ofz270. google scholar
25. Hirai J, Asai N, Hagihara M, Kishino T, Kato H, Sakanashi D, et al. Comparative effectiveness of ampicillin/sulbactam versus cefazolin as targeted therapy google scholar
26. for bacteremia caused by beta-lactamase-producing methicillin-sensitive Staphylococcus aureus: a single-center retrospective study. Antibiotics 2022;11(11):1505. google scholar
27. Nannini EC, Stryjewski ME, Singh KV, Rude TH, Corey GR, Fowler VG Jr, et al. Determination of an inoculum effect with various cephalosporins among clinical isolates of methicillin-susceptible Staphylococcus aureus. Antimicrob Agents Chemother 2010;54(5):2206-8. google scholar
28. Skov R, Frimodt-Moller N, Espersen F. In vitro susceptibility of Staphylococcus aureus towards amoxycillin-clavulanic acid, penicillin-clavulanic acid, dicloxacillin and cefuroxime. APMIS 2002;110(7-8):559-64. google scholar
29. Buis DTP, van der Vaart TW, Prins JM, van der Meer JTM, Bonten MJM, Sieswerda E, et al. Comparative effectiveness of β-lactams for empirical treatment of methicillin-susceptible Staphylococcus aureus bacteraemia: a prospective cohort study. J Antimicrob Chemother 2023;78(7):1175-81. google scholar
30. Alexander JAN, Worrall LJ, Hu J, Vuckovic M, Satishkumar N, Poon R, et al. Structural basis of broad-spectrum β-lactam resistance in Staphylococcus aureus. Nature 2023;613(7943):375-82. google scholar