Abstract
Resistance to antibiotics, biofilm formation and the presence of virulence factors play important roles in increased mortality associated with infection by staphylococci. The macrolide lincosamide streptogramin B (MLSB) family of antibiotics is commonly used to treat infections by methicillin-resistant isolates. Clinical failure of clindamycin therapy has been reported due to multiple mechanisms that confer resistance to MLSB. This study aims to find the incidence of different phenotypes of MLSB resistance and biofilm production among staphylococci. A total of 375 staphylococci were isolated from different clinical samples, received from two tertiary care hospitals in Nepal. Methicillin resistance was detected by cefoxitin disc diffusion method and inducible clindamycin resistance by D test, according to CLSI guidelines. Biofilm formation was detected by the tissue culture plate method and PCR was used to detect ica genes. Of the total staphylococci isolates, 161 (42.9%) were Staphylococcus aureus, with 131 (81.4%) methicillin-resistant strains, and 214 (57.1%) isolates were coagulase-negative staphylococci, with 143 (66.8%) methicillin-resistant strains. The overall prevalence of constitutive MLSB (cMLSB) and inducible MLSB (iMLSB) phenotypes was 77 (20.5%) and 87 (23.2%), respectively. Both iMLSB and cMLSB phenotypes predominated in methicillin-resistant isolates. The tissue culture plate method detected biofilm formation in 174 (46.4%) isolates and ica genes in 86 (22.9%) isolates. Among biofilm producing isolates, cMLSB and iMLSB phenotypes were 35 (20.1%) and 27 (15.5%), respectively. The cMLSB and iMLSB were 11 (12.8%) and 19 (22.1%), respectively, in isolates possessing ica genes. Clindamycin resistance in the form of cMLSB and iMLSB, especially among MRSA, emphasizes the need for routine D tests to be performed in the lab.
Highlights
Staphylococcus aureus (S. aureus) and coagulase-negative staphylococci (CNS) are recognized as common causes of nosocomial and community-acquired infections worldwide
Among 375 staphylococcal isolates, 131 (34.9%) and 143 (38.1%) isolates were identified as methicillin-resistant S. aureus (MRSA) and methicillin-resistant CNS (MRCNS) by cefoxitin disc diffusion assay, respectively (Table 1)
Staphylococci are emerging as a major health problem due to multidrug resistance and biofilm formation
Summary
Staphylococcus aureus (S. aureus) and coagulase-negative staphylococci (CNS) are recognized as common causes of nosocomial and community-acquired infections worldwide. They cause a broad spectrum of diseases from mild skin and soft tissue infections to lifethreatening sepsis, pneumonia, endocarditis and deep-seated abscesses [1,2]. In addition to extracellular toxins and surface structures that are effective in the induction and continuance of infection in the host, the ability to form biofilm is an important complicating factor associated with many chronic infections [3]. Biofilms are communities of bacteria, immobilized by an extracellular polymeric matrix, which can bind to biotic and abiotic surfaces. Bacteria, protected by biofilm, are resistant to host defense mechanisms and to standard antibiotic therapy [4,5]
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