Abstract
Staphylococcus aureus is one of the major causes of nosocomial infections. This organism produces powerful toxins and cause superficial lesions, systemic infections, and several toxemic syndromes. A total of 109 S. aureus strains isolated from a variety of infections like ocular diseases, wound infection, and sputum were included in the study. Minimum inhibitory concentration (MIC) was determined against 8 antimicrobials. PCR determined the presence of 16S rRNA, nuc, mecA, czrC, qacA/B, pvl, and toxin genes in S. aureus isolates. Pulse-field gel electrophoresis (PFGE), multi-locus sequence typing (MLST), SCCmec, spa-, and agr-typing and serotyping determined the diversity among them. All isolates of S. aureus were resistant to two or more than two antibiotics and generated 32 resistance patterns. These isolates were positive for 16S rRNA and S. aureus-specific nuc gene, but showed variable results for mecA, czrC, and qacA/B and pvl genes. Of the 32 methicillin-resistant S. aureus (MRSA), 13 strains carried SCCmec type V, seven type IV, two type III, and nine carried unreported type UT6. Of the 109 strains, 98.2% were positive for hlg, 94.5% for hla, 86.2% for sei, 73.3% for efb, 70.6% for cna, 30.2% for sea, and 12.8% for sec genes. Serotypes VII and VI were prevalent among S. aureus strains. PFGE analysis grouped the 109 strains into 77 clusters. MLST classified the strains into 33 sequence types (ST) and eight clonal complexes (CCs) of which 12 were singletons, and two belong to new allelic profiles. Isolates showed 46 spa-types that included two new spa-types designated as t14911 and t14912. MRSA and methicillin-susceptible S. aureus (MSSA) isolates were diverse in terms of antibiotic resistance pattern, toxin genotypes, SCCmec types, serotypes and PFGE, MLST, and spa-types. However, few isolates from eye infection and wound infection belong to CC239, ST239, and spa-type t037/t657. The study thus suggests that S. aureus strains are multidrug resistant, virulent, and diverse irrespective of sources and place of isolation. These findings necessitate the continuous surveillance of multidrug-resistant and virulent S. aureus and monitoring of the transmission of infection.
Highlights
Staphylococcus aureus commensal to human skin and mucous membranes could cause nosocomial (Lindsay and Holden, 2004) and systemic infections (Jarraud et al, 2002)
Thirty-one of 109 (29.4%) methicillin-resistant strains were positive for the methicillin resistance (mecA) gene, and 77 (70.6%) methicillin sensitive isolates were negative for the mecA gene
We found a good correlation between oxacillin resistance and the presence of the mecA gene
Summary
Staphylococcus aureus commensal to human skin and mucous membranes could cause nosocomial (Lindsay and Holden, 2004) and systemic infections (Jarraud et al, 2002). The isolation of methicillin-resistant S. aureus (MRSA) from ocular infections varies from 3 to 30% in a hospital in India and other countries (Shanmuganathan et al, 2005; Freidlin et al, 2007). MRSA isolated from conjunctivitis in Nigeria belonging to ST88 and SCCmec type IV were positive for pvl gene (Ghebremedhin et al, 2009). Pvl gene positive methicillin-susceptible S. aureus (MSSA) strains belonged to ST30 (D’Souza et al, 2010). S. aureus carrying the pvl gene and belonging to ST239, ST5, and ST88 was reported from a teaching hospital in China (Liu et al, 2009). MSSA belonging to ST121 and spa-type 287 isolated from community-acquired pneumonia in young patients carried the virulence genes (cna and bbp) and pvl (Baranovich et al, 2010). Multidrug-resistant isolates belonging to ST239 and SCCmec type III were slowly replaced by multidrugsusceptible ST22 (SCCmec type IV) and ST772 (SCCmec type V) in hospitals (D’Souza et al, 2010)
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