Inducible Resistance to β-Lactams in Oxacillin-Susceptible mecA1-Positive Staphylococcus sciuri Isolated From Retail Pork

Abstract

Most isolated strains of Staphylococcus sciuri contain mecA1, the evolutionary origin of mecA, but are sensitive to β-lactams (OS-MRSS, oxacillin-susceptible mecA1-positive S. sciuri). In order to improve the efficacy of antibiotic treatment, it is important to clarify whether the resistance of OS-MRSS to β-lactams is an inducible phenotype. In this study, three OS-MRSS strains with oxacillin MIC = 1 μg/ml were isolated from 29 retail pork samples. The resistance of OS-MRSS to β-lactams (MIC > 256 μg/ml) was found to be induced by oxacillin, and the induced resistance was observed to remain stable within a certain period of time. Interestingly, the induced β-lactam resistance was not caused by mecA1, heterogeneous resistance, or any genetic mutation, but mainly due to increased wall teichoic acid (WTA) synthesis that thickened the cell wall. The induced strains also showed slower growth rate, as well as decreased adhesion ability and biofilm thickness. These phenotypes were found to be achieved through altered gene expression in associated pathways, such as the citrate cycle and pentose phosphate pathway. The results challenge the traditional antibiotic sensitivity test. In the presence of β-lactam antibiotics, OS-MRSS that was initially sensitive to β-lactams was observed to gradually develop β-lactam resistance in several days. This often-neglected phenomenon in antibiotic sensitivity tests requires further research attention.

Elucidation of the Bovine Intramammary Bacteriome and Resistome from healthy cows of Swiss dairy farms in the Canton Tessin

“…A high association was observed between clindamycin resistance (lincosamides) and the presence of salA, as all resistant isolates (93%) also carried the gene. In contrast, as previously found by Cai et al (2021) , although 100% of the isolates carried the mecA1 gene, only 55% of the isolates showed resistance to oxacillin. For M. sciuri it is known that high-level mecA1 expression is required to observe oxacillin resistance in these bacteria.…”

Molecular Mechanisms of Drug Resistance in Staphylococcus aureus

“…It is considered a precursor of the mecA gene in S. aureus , and the mecA2 gene. M. sciuri oxacillin-susceptible (OS-MRSS, MIC oxacillin = 1 mg/L; according to current criteria, these are methicillin-resistant strains) and MRSS strains were described (they had two genes: mecA1 and mecA ) [ 22 ]. The mecA2 gene was described in M. vitulinus and S. capitis , the mecB gene in Macrococcus caseolyticus and S. aureus , the mecC gene in S. aureus and M. sciuri , the mecC1 gene in S. xylosus , the mecC2 gene in S. saprophyticus , and the mecD gene in M. caseolyticus [ 23 , 24 ].…”

The MIC distribution of dalbavancin differs between different coagulase-negative staphylococci

“…According to a previous study, an increased cell wall thickness in S. sciuri is a possible cause of β-lactam resistance. 16 This could perhaps explain the high percentage of decreased susceptibility to dalbavancin among S. sciuri strains.…”