Mehndiratta P L, Bhalla P, Ahmed A, Sharma Y D
Department of Microbiology, National Staphylococcal Phage Typing Center, Maulana Azad Medical College, New Delhi, India.
Indian J Med Microbiol. 2009 Apr-Jun;27(2):116-22. doi: 10.4103/0255-0857.45363.
To characterize methicillin-resistant Staphylococcus aureus (MRSA) strains by molecular typing based on polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) of spa gene and to assess the utility of spa genotyping over bacteriophage typing in the discrimination of the strains.
Studies were undertaken on 125 MRSA strains representing the most predominant phage types and the non phage typeable strains. Strains were typed by bacteriophage typing and PCR-RFLP of spa gene. DNA sequence analysis of the amplified spa gene fragment of the representative RFLP patterns was performed using standard protocols.
All the strains resistant to oxacillin were found to contain mec A gene. Fifty-two per cent of these strains were typeable by the international basic set of 23 phages. Five different PCR-RFLP patterns were observed among 125 MRSA strains. Non phage typeable strains were differentiated into four PCR-RFLP patterns. Sequencing of the spa gene from the representative strains of each RFLP pattern confirmed the length of these restriction fragments due to variation in the 24 bp and the 174 bp tandem repeats. It also revealed the presence of three new spa repeat patterns.
The study demonstrates the importance of spa genotyping in the discrimination of MRSA strains, which were otherwise indistinguishable by bacteriophage typing. spa genotyping allowed differentiation of strains within a particular phage type. Nucleotide sequencing of isolates of different PCR-RFLP patterns indicated a correlation between the RFLP patterns of a variable number of tandem repeats and the phage type. The study provides valuable information on the epidemiological characterization of MRSA strains.
通过基于spa基因的聚合酶链反应-限制性片段长度多态性（PCR-RFLP）的分子分型来鉴定耐甲氧西林金黄色葡萄球菌（MRSA）菌株，并评估spa基因分型在区分菌株方面相对于噬菌体分型的实用性。
对125株MRSA菌株进行研究，这些菌株代表了最主要的噬菌体类型和不可用噬菌体分型的菌株。通过噬菌体分型和spa基因的PCR-RFLP对菌株进行分型。使用标准方案对代表性RFLP模式的扩增spa基因片段进行DNA序列分析。
所有对苯唑西林耐药的菌株均发现含有mec A基因。这些菌株中有52%可用国际基本的23种噬菌体进行分型。在125株MRSA菌株中观察到5种不同的PCR-RFLP模式。不可用噬菌体分型的菌株被分为4种PCR-RFLP模式。对每种RFLP模式的代表性菌株的spa基因进行测序，证实了由于24 bp和174 bp串联重复序列的变异导致的这些限制性片段的长度。还揭示了三种新的spa重复模式。
该研究证明了spa基因分型在区分MRSA菌株方面的重要性，否则这些菌株通过噬菌体分型无法区分。spa基因分型能够区分特定噬菌体类型内的菌株。对不同PCR-RFLP模式分离株的核苷酸测序表明，可变数量串联重复序列的RFLP模式与噬菌体类型之间存在相关性。该研究为MRSA菌株的流行病学特征提供了有价值的信息。
