We have characterized S. aureus isolates from different cities in India, which belong to a wide variety of STs from healthy carriers and individuals with simple to complicated diseases. Even in a small number of isolates (68), there were 15 different STs (including the two isolates resembling S. aureus from animal origin) and MSSA isolates were the most diverse. Among the MRSA isolates, the predominant ST were 22, 772, 672, 8 and 30. ST672 is a new emerging clone with only two isolates reported from Australia and U.S. While EMRSA-15 (ST22) appeared as a major clone in Indian hospitals with SCCmec type IV element, ST772, 672 and 8 are emerging as SCCmec type V. It is evident from our studies that at least two different types of SCCmec type V elements exist in isolates belonging to three distinct STs.
The most obvious bias in the study is the limited number of isolates collected, but our results are in part concordant with those in the literature: the two major MRSA STs (STs22 and STs772) reported earlier in India [9
]. Many of the other MSSA and two of the MRSA STs are being reported for the first time.
The antibiotic sensitivity data (not shown) indicates that majority of carrier MSSA were sensitive to all five tested antibiotics. Antibiotic resistant determinants were found mainly in carrier and disease MRSA isolates, but few ST22 carrier and disease MSSA isolates also had resistance determinants for gentamicin and /or erythromycin. For few MRSA isolates (STs 22, 772, 672, and 8) containing the mec
A gene, MICs for oxacillin and cefoxitin were 4–8 and 8-16
μg/ml respectively while for most other isolates the corresponding values were 8–16 and 16-32
μg/ml (data not shown). We considered these isolates as methicillin resistant as the patient treatment with oxacillin would select for resistance in a heterogeneous population containing the mecA
gene. Similar MRSA isolates of ST59 background were found in Taiwan [16
] and CC5 lineage in Switzerland among injection drug users. One of the Swiss isolates of CC5 (ZH47) has been reported to have low MIC for oxacillin and sequenced to contain a composite SCCmec
cassette with ZH47 region containing a second ccrC
. Our isolates of ST772 and ST672 with low level of oxacillin resistance also contain the second ccrC
region. The low level of resistance has been attributed to mutations in the mecA
promoter region [17
EMRSA-15 (ST22) has been reported to be replacing HA-MRSA in hospitals in many countries - Germany, Portugal, Singapore, to name just a few [18
]. In 2003 when we had collected MRSA isolates from Indian hospitals [7
], majority of them belonged to ST239 with SCCmec
type III or IIIA; ST22 now made up 28% of the total in the present collection. A study from Mumbai, India, with larger sample numbers, from a tertiary care hospital also indicates that EMRSA-15 is replacing type III SCCmec
containing isolates [11
ST772 (CC1) has been reported from India, Bangladesh and Malaysia [9
]. Our ST772 isolates and that from Bangladesh have agr
type II while CC1 isolates from Malaysia, Australia and U.S. have been reported to be agr
type III. Aires de Sousa et al., have reported three sequence types (ST188, ST573, ST1) belonging to CC1, as agr
types I, II, and III respectively in a survey of isolates from Portuguese hospitals and community [21
]. CC1 lineage itself seems to be changing from an independent founder to a sub-founder and CC15 is evolving as the founder strain from the eBURST analysis (Figure ). ST573 appears to be the link between the founder and sub-founder clones. CC1 appears to be evolving along with the agr
locus rapidly with numerous recombinations which is unusual, as agr
types are usually uniform in a CC.
ST672 has not been reported from any of the Asian countries till now. The MLST data base reports one isolate from Australia and one from U.S. It appears important to determine if this clone will persist as a minor clone or not. ST772 and ST672 MRSA isolates carried the same composite type V SCCmec elements unlike the ones carried by ST1208 isolates (Table ). Among the numerous results obtained by the microarrays, collagen binding adhesion (cna) was absent in ST672 and present in 772 (raw data of microarray provided). The capsular polysaccharide types 8 and 5 were present in ST672 and 772 respectively.
The large diversity in the STs present in the MSSA isolates confirmed the highly diverse MSSA population reported from Shanghai, China, recently which included ST5, 6, 7, 30 and 121 isolates along with others [22
]. The probability of MSSA conversion to MRSA is perhaps high in India with the over use of antibiotics and its spread due to inadequate hygienic practices.
High prevalence of PVL
among the Indian MSSA and MRSA isolates is unlike the situation in Bangladesh, and Indonesia where only MSSA isolates contain PVL [12
]. This indicates a possibility of PVL
positive MSSA acquiring SCCmec
elements to become PVL
positive MRSA although this needs to be confirmed. A combination of PVLegc
along with other entero-toxins could increase the severity of diseases caused by S. aureus
although the role of PVL
and other toxins is not completely elucidated [24
]. There were no differences in the presence of the different virulence factors we characterized among the carrier isolates or the patient isolates.