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Liang B, Xiong Z, Liang Z, Zhang C, Cai H, Long Y, Gao F, Wang J, Deng Q, Zhong H, Xie Y, Huang L, Gong S, Zhou Z. Genomic Basis of Occurrence of Cryptic Resistance among Oxacillin- and Cefoxitin-Susceptible mecA-Positive Staphylococcus aureus. Microbiol Spectr 2022; 10:e0029122. [PMID: 35608351 PMCID: PMC9241717 DOI: 10.1128/spectrum.00291-22] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2022] [Accepted: 04/27/2022] [Indexed: 11/20/2022] Open
Abstract
The oxacillin- and cefoxitin-susceptible mecA-positive Staphylococcus aureus is a novel "stealth" methicillin-resistant S. aureus (MRSA) type. Here, we sequenced the whole genome of two oxacillin- and cefoxitin-susceptible mecA-positive MRSA isolates from breast abscesses in a lactating woman and a nasal swab of a healthy student in Guangzhou for investigating the mechanism underlying its occurrence. The reversion of these isolates was selected by exposure to sub-MICs of cefoxitin with or without mupirocin. The mecA expression of both parental strains and their revertants was determined, and the whole genome of the revertants was sequenced. Comparative whole-genome analyses performed for both strains revealed that mecA of the clinical strain was mutated by a single-bp insertion at the 262nd position in the tandem repeat region of the gene, and this mutation that led to the formation of a premature stop codon. The colonizing strain was mutated by a novel G-to-A base substitution in the second promoter region (-35 bp) of mecA. The mecA expression level of strain 697 revertant was 37 times higher than that of the parental strain. Although the mecA expression level was even higher for parental strain 199 compared with that for its revertant, its cDNA sequence contained a single-bp insertion. Collectively, both the missense and single substitution mutations of the second promoter of mecA could render MRSA isolates as "stealth" MRSA, thereby emphasizing the importance of combining phenotype tests with mecA or penicillin-binding protein 2a detection for the identification of MRSA. IMPORTANCE The oxacillin- and cefoxitin-susceptible mecA-positive Staphylococcus aureus is a novel type of "stealth" methicillin-resistant S. aureus (MRSA), which is difficult to be detected using conventional methods. To investigate the genomic basis of their occurrence, we sequenced the whole genome of two previously recovered oxacillin- and cefoxitin-susceptible mecA-positive MRSA isolates from breast abscesses in a lactating woman and a nasal swab of a healthy student in Guangzhou. Complete SCCmec structure was absent except for mecA in clinical isolate 199. Additionally, a novel single-base pair insertion was observed in the clinical strain, which resulted in premature termination and a frameshift mutation. The colonizing isolate 697 had a Scc-mec-type IVa, and the second promoter region (-35 bp) of mecA was mutated by a novel G-to-A base substitution. The reversion of oxacillin- and cefoxitin-susceptible mecA-positive S. aureus to resistant MRSA isolates was selected by exposure to subminimum inhibitory cefoxitin with or without mupirocin.
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Affiliation(s)
- Bingshao Liang
- Clinical Laboratory, Guangzhou Women and Children’s Medical Center, Guangzhou Medical University, Guangzhou, People’s Republic of China
| | - Zhile Xiong
- Clinical Laboratory, Guangzhou Women and Children’s Medical Center, Guangzhou Medical University, Guangzhou, People’s Republic of China
| | - Zhuwei Liang
- Clinical Laboratory, Guangzhou Women and Children’s Medical Center, Guangzhou Medical University, Guangzhou, People’s Republic of China
| | - Chao Zhang
- Clinical Laboratory, Guangzhou Women and Children’s Medical Center, Guangzhou Medical University, Guangzhou, People’s Republic of China
| | - Hao Cai
- Clinical Laboratory, Guangzhou Women and Children’s Medical Center, Guangzhou Medical University, Guangzhou, People’s Republic of China
| | - Yan Long
- Clinical Laboratory, Guangzhou Women and Children’s Medical Center, Guangzhou Medical University, Guangzhou, People’s Republic of China
| | - Fei Gao
- Clinical Laboratory, Guangzhou Women and Children’s Medical Center, Guangzhou Medical University, Guangzhou, People’s Republic of China
| | - Jielin Wang
- Clinical Laboratory, Guangzhou Women and Children’s Medical Center, Guangzhou Medical University, Guangzhou, People’s Republic of China
| | - Qiulian Deng
- Clinical Laboratory, Guangzhou Women and Children’s Medical Center, Guangzhou Medical University, Guangzhou, People’s Republic of China
| | - Huamin Zhong
- Clinical Laboratory, Guangzhou Women and Children’s Medical Center, Guangzhou Medical University, Guangzhou, People’s Republic of China
| | - Yongqiang Xie
- Clinical Laboratory, Guangzhou Women and Children’s Medical Center, Guangzhou Medical University, Guangzhou, People’s Republic of China
| | - Lianfen Huang
- Clinical Laboratory, Guangzhou Women and Children’s Medical Center, Guangzhou Medical University, Guangzhou, People’s Republic of China
| | - Sitang Gong
- Department of Gastroenterology, Guangzhou Women and Children’s Medical Center, Guangzhou Medical University, Guangzhou, People’s Republic of China
| | - Zhenwen Zhou
- Clinical Laboratory, Longgang District Maternity and Child Healthcare Hospital, Shenzhen, People’s Republic of China
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