Acta Veterinaria et Zootechnica Sinica ›› 2020, Vol. 51 ›› Issue (3): 602-611.doi: 10.11843/j.issn.0366-6964.2020.03.020

• BASIC VETERINARY MEDICINE • Previous Articles     Next Articles

The Relationship between Cell Wall Thickening of Staphylococcus aureus and Resistance to β-lactams

MA Qiang, WANG Yihui, CHANG Jiawei, WAN Jiahong, WEI Yanqin, WANG Guiqin*   

  1. College of Agriculture, Ningxia University, Yinchuan 750021, China
  • Received:2019-07-11 Online:2020-03-25 Published:2020-03-20

Abstract: This study was conducted to reveal the resistance mechanism of Staphylococcus aureus to β-lactams, which may associate with thickening of the cell wall. From 2016 to 2018, we collected milk samples from clinical and subclinical mastitis in some dairy farms in Ningxia region. Separation and identification of S. aureus were conducted by using chromogenic medium, microscopic examination and PCR. The resistance in S. aureus isolates to 14 antibacterials was detected by micro-dilution method, to understand the resistance rate and multi-drug resistance of S. aureus isolates in the region. Transcription levels of pbpB, murG, glmU and atlR genes that are related to cell wall thickening were detected by qRT-PCR. Furthermore, phenotypes were examined by the transmission electron microscopy. Our goal was to discover the mechanism of cell wall thickening. The results indicated that we isolated and identified 261 strains of S. aureus, including 9 strains of Methicillin-resistant Staphylococcus aureus (MRSA). Antimicrobial susceptibility determination showed that the isolates have high resistance rate to β-lactams, the resistance rate to ampicillin was 79.69% and that to penicillin was 78.54%. Multi-drug resistance was distributed by isolates with 3, 7 and 8 resistance, in particular, one of the isolates could tolerate 14 antibacterials. The results of qRT-PCR showed that 4 related genes were significantly up-regulated (P<0.01 or P<0.001). The cell wall of JY21 (Methicillin sensitive Staphylococcus aureus, MSSA) was significantly thicker than the control group at the concentration of 64 and 128 μg·mL-1 penicillin (P<0.001), and the cell wall was rough with nodular processes. Whereas, with the penicillin concentration increased from 64 μg·mL-1 to 128 μg·mL-1, and the cell wall was no longer significantly thickened (P>0.05). MRSA WLD10 showed no significant cell wall thickening (P>0.05). In conclusion, these data illustrated that cell wall thickening is a resistance mechanism for S.aureus to β-lactams in Ningxia. Simultaneously, the reason for cell wall thickening is mainly the excessive synthesis of peptidoglycan and the decrease of cell autolysis. Cell wall thickening is a critical resistance mechanism for the MSSA JY21. However, for MRSA WLD10, it's not the case.

Key words: Staphylococcus aureus, resistance, cell wall, β-lactams

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