Invasive burden

The human body contains numerous microorganisms, the so-called microbiota that outnumbers human cells. The human nasal passage is one of the primary habitats for microflora as well as pathogenic agents. The nasal passage of the human nostrils leads to the nasopharynx and the upper back part of the throat. The microbial communities inhabiting the nasal passages of humans colonize soon after the birth and distinctly changes over the lifespan of an individual with high inter-individual variations. During a human lifetime, the bacterial colonization of the human nasal cavities and its variations are affected by various factors, including the development of the immunity, hormonal changes, and age. Other affecting factors include environmental variations, e.g., temperature, humidity, pollution, and airborne microbes [1]. In children, a very complex community of bacteria inhabit the nasal passages. Identification of composition and dynamics of these bacteria can provide more insights into the basis of respiratory diseases [2]. Many works have demonstrated that the structure of pediatric bacterial microbiota of the nose is affected by acute respiratory tract infections (ARIs). Some studies have also reported that bacterial flora of the nasal cavities plays a vital role in regulating various immune responses in humans [3]. The interaction between bacterial species in nasal passages and the host include mutualism, commensalism, and pathogenic associations [4]. The most common species of nasal microflora comprise Staphylococcus aureus, Staphylococcus epidermidis, Streptococcus pneumoniae, Micrococcus luteus, Haemophilus influenzae, Proteus vulgaris, Proteus mirabilis, and Bacillus sp. [2, 3]. The members of the genus Staphylococcus are among the common bacteria inhabiting the nasal passages of children and S. aureus, S. epidermidis, and S. hominis are among the most prevalent species. These Gram-positive bacteria are catalase positive, non-motile, and facultative anaerobes. They cause acute to severe infections, such as serious skin infections, pimples, boils, carditis, meningitis, septicemia, arthritis, endocarditis, abscess, osteomyelitis, central venous catheter-associated bacteremia, pneumonia, and ventilator-associated pneumonia. These bacteria produce the enzyme coagulase and are characterized as pathogenic or relatively pathogenic bacteria [5]. Pathogenic strains of the genus Staphylococcus such as S. aureus are usually coagulase-positive. The coagulasenegative strains, e.g., S. epidermidis, are mostly less invasive. However, they are progressively considered pathogens Introduction: Staphylococcus is a genus of pathogenic bacteria, which asymptomatically colonizes the upper respiratory tract of the human. The incidence of invasive Staphylococcal infections and the disease burden are high among children in South Asia, including Pakistan. This study aims to determine the nasal colonization and antimicrobial susceptibility pattern of Staphylococcus species isolated from preschool children in Lahore, Pakistan. Methods: A community-based study was conducted in two camps named Shah Di Khui and Jeevan Haana in Lahore city. A total of 100 nasal samples, were collected from preschool children from lower-middle-class families during January to March 2018. Species identification was performed using the coagulase test, catalase test, and Gram staining. Also, a 370 bp fragment of the tuf gene was targetted using specific primers for the genus Staphylococcus. Antibiotic resistance pattern of the isolates was defined by an antibiotic susceptibility test using a series of antibiotic discs. Results: The results of this study indicated the presence of Staphylococcus species, mainly Staphylococcus aureus in more than 85% of the children. PCR amplification of tuf gene confirmed the identity of the S. aureus isolates from the nasal cultures. Many showed resistance to more than two broad-spectrum antibiotics. Conclusion: The prevalence of nasal colonization of S. aureus was more than 85% among preschool children. Most of the isolates were resistant to β-lactam antibiotics.