Characterization of Plasmid-Mediated AmpC and Carbapenemases among Iranain Nosocomial Isolates of Klebsiella pneumoniae Using Phenotyping and Genotyping Methods

Objectives: Plasmid-mediated AmpC β-lactamases (PMABLs) and carbapenemases are emerging groups of antimicrobial-resistance determinants. The aims of the study were to evaluate the occurrence of PMABLs and carbapenemases in clinical isolates of Klebsiella pneumoniae and compare the test performance of various phenotypic methods for detection of these enzymes in Iran. Methods: A total of 100 K. pneumoniae isolates were collected from clinical specimens obtained in Valiasr Hospital. AmpC production in all isolates was determined using the AmpC disk test, the cephamycin Hodge test, the AmpC Etest, and the boronic acid combined-disk test. In addition, carbapenemase production was determined using the modified Hodge test, the EDTA disk synergy test, and the boronic acid combined-disk test. The performances of various phenotypic methods were evaluated by the comparison of their results with polymerase chain reaction (PCR) method as the gold standard. Results: Of the 100 isolates, 19 (19%) were demonstrated to harbor the

Distribution of staphylococcal cassette chromosome mec types among methicillin-resistant coagulase negative staphylococci in central Iran

Background and Objectives: Methicillin-resistant coagulase-negative staphylococci (MR-CoNS) are important nosocomial pathogens. They may serve as a reservoir of SCCmec, the genomic island encoding amongst other methicillin resistance. This study was designed to determine the distribution of different SCCmec types from MR-CoNS isolated from clinical specimens in a tertiary hospital in central Iran, having high frequency of nosocomial methicillin-resistant staphylococcal infections. Materials and Methods: We evaluated isolates from patients attending the Vali-Asr Hospital located in the center of Iran, from February to December 2012. Multiplex PCR was performed for SCCmec typing. For isolates in which SCCmec could not be typed directly, additional ccr and mec complex analyses were performed. Results: Totally, 70 MR-CoNS isolates, comprising of 47 S. epidermidis strains (67%), 10 S. saprophyticus (14.3%), 9 S. hemolyticus (13%) and 4 S. lugdunensis (5.7%) were identified. Thirty-nine were characterized as type IVa 19 (27%), type III 11 (16%), type II 7 (10%) and type V 2 (3%). Only 20 isolates (28.6%) carried the ccr complex, while the current methods could not characterize the 11 remaining isolates. Conclusion: A high level of SCCmec genetic diversity was found among MR-CoNS isolates. MR-CoNS may act as a reservoir of SCCmec IV for MRSA. This issue should be taken into consideration seriously

Molecular characterization of clindamycin constitutive and inducible Resistance Staphylococcus aureus strains’ isolated from nose of carriers

Background: Increasing frequency of Staphylococcus aureus infections and changes in antimicrobial resistance pattern have led to renewed interest in the use of lincosamide– streptogramin B (MLSB) antibiotics for treatment of infections. Since no study has focused on the molecular epidemiology of community -acquired staphylococcus aureus isolates in Iran, the aim of this study was to determine the molecular typing and prevalence of the macrolides-lincosamides-streptogramins B (MLSB) resistance in community associated s.aureus isolated from healthy students at Arak university of Medical sciences. Material and Methods: 568 healthy students from Arak university of Medical sciences were subjected to this study. All samples were subjected to S. aureus–specific isolation procedures. D test was performed to determine various phenotypes as well as spa typing done for molecular typing of these strains. Results: Of 568 the 84 community acquired Staphylococcus aureus, six (7%) were Methiclicin resistant Staphylococcus aureus (CA-MRSA) and 78(93%) were Methicillin sensitive Staphylococcus aureus (CA-MSSA) of the 84 s.aureus strains, eight (9.5%) showed constitutive resistance with spa type t660, t701, t304, t5598, t012, t3204, t084 and t1944. Two strains (2.5%) demonstrated inducible resistance with spa type t9024, t077, two strains (2.5%) were D test negative with spa type t084 and t1149. 72(85.5%) strains. Illustrated susceptible Phenotype. Among CA-MRSA isolates, two strains had constitutive resistance and four remaining CA-MRSA had susceptible phenotype Conclusion: The result of this study indicates that in community associated s.aureus strains, constitutive MLSB resistance rate is higher than the rate of inducible resistance. Presence of inducible resistance to clindamycin in CA-MRSA strains, warrants that D test should be performed to detect this type of resistance. All isolates with inducible and constitutive resistance and D zone negative strains had different molecular typings