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Colistin is one of the last-resort therapeutic agents to combat multidrug-resistant Gramnegative bacteria (GNB) including Klebsiella pneumoniae. Although it happens rarely, resistance to colistin has been reported for several GNB. A total of 20 colistin resistant (col-R) and three colistin susceptible (col-S) clinical isolates of K. pneumoniae were studied to explore the underlying mechanisms of colistin resistance. The presence of plasmid encoded resistance genes, mcr-1, mcr-2, mcr-3, and mcr-4 genes were examined by PCR. The nucleotide sequences of pmrA, pmrB, phoP, phoQ, and mgrB genes were determined. To evaluate the association between colistin resistance and upregulation of pmrHFIJKLM and pmrCAB operons, transcriptional level of the pmrK and pmrC genes encoding for lipopolysaccharide target modifying enzymes was quantified by RT-qPCR analysis. None of the plasmid encoded resistance genes were detected in the studied isolates. Inactivation of MgrB due to nonsense mutations and insertion of IS elements was observed in 15 col-R isolates (75%). IS elements (IS5-like and IS1-like families) most commonly targeted the coding region and in one case the promoter region of the mgrB. Complementation with wild-type MgrB restored colistin susceptibility in isolates with altered mgrB. All col-R isolates lacked any genetic alterations in the pmrA, phoP, and phoQ genes and substitutions identified in the pmrB were not found to be involved in resistance conferring determined by complementation assay. Colistin resistance linked with upregulation of pmrHFIJKLM and pmrCAB operons with the pmrK and pmrC being overexpressed in 20 and 11 col-R isolates, respectively. Our results demonstrated that MgrB alterations are the major mechanisms contributing to colistin resistance in the tested K. pneumoniae isolates from Iran. [ABSTRACT FROM AUTHOR]

Infectious diseases caused by clinically important Mycobacteria continue to be an important public health problem worldwide primarily due to emergence of drug resistance crisis. In recent years, the control of tuberculosis (TB), the disease caused by Mycobacterium tuberculosis (MTB), is hampered by the emergence of multidrug resistance (MDR), defined as resistance to at least isoniazid (INH) and rifampicin (RIF), two key drugs in the treatment of the disease. Despite the availability of curative anti-TB therapy, inappropriate and inadequate treatment has allowed MTB to acquire resistance to the most important anti-TB drugs. Likewise, for most mycobacteria other than MTB, the outcome of drug treatment is poor and is likely related to the high levels of antibiotic resistance. Thus, a better knowledge of the underlying mechanisms of drug resistance in mycobacteria could aid not only to select the best therapeutic options but also to develop novel drugs that can overwhelm the existing resistance mechanisms. In this article, we review the distinctive mechanisms of antibiotic resistance in mycobacteria. [ABSTRACT FROM AUTHOR]

Objectives Multidrug-resistant tuberculosis (MDR-TB) is a global problem that many countries are challenged with. Rapid and accurate detection of MDR-TB is critical for appropriate treatment and controlling of TB. The aim of the present study was to evaluate the TaqMan allelic discrimination without minor groove binder (MGB) as a rapid, efficient, and low-cost method for detection of drug resistant strains of Mycobacterium tuberculosis . Methods A total of 112 M. tuberculosis isolates from cases with diagnosed TB were subjected to drug susceptibility testing (DST), using the proportion method. Resistant isolates were tested for characterization of mutations in the rpoB and KatG genes by TaqMan genotyping. Results Of 112 M. tuberculosis isolates for which DST was performed, three, one, and two isolates were MDR, rifampin (RIF) resistant, and isoniazid (INH) resistant, respectively. According to the threshold cycle (Ct) and curve pattern of mutants, TaqMan probes detect all of the mutations in the analyzed genes ( katG 315, AGC→ACC, rpoB 531, TCG→TTG, and rpoB 531, TCG→TGG). Conclusion The present study suggests that drug-resistant strains of M. tuberculosis can be detected by pattern’s curve or Ct with TaqMan probes without MGB in real-time polymerase chain reaction (PCR). [ABSTRACT FROM AUTHOR]

Seven hundred and fifty nonreplicated clinical isolates of Pseudomonas aeruginosa were collected from five hospitals during March 2007 to May 2009. Forty-one isolates (5.46%) were characterized as multidrug-resistant P. aeruginosa (MDRPA). PCR assays were used to detect class 1 integrons. Amplifications of internal variable regions (IVRs) of class 1 integrons revealed three different arrays (0.8, 1.3, and 1.7 kb) with different distributions in clinical isolates. The amplified IVRs were sequenced and three gene cassette arrays including aadB (0.8 kb), aadA6–orfD (1.3 kb), and blaOXA10 –aacA4 (1.7 kb) were identified. In conclusion, we confirmed the high prevalence of class 1 integons with limited diversity of gene cassette arrays in MDRPA clinical isolates found from five hospitals. This is the first report showing gene cassette contents of class 1 integrons in P. aeruginosa isolates in Iran. [ABSTRACT FROM AUTHOR]

Background and Aim: There are geographical variations in Helicobacter pylori virulence genes; cagA, cagE, vacA and oipA. The present study compared the distribution of these genotypes in major ethnic groups residing in Tehran, Iran and their association with clinical outcomes. Methods: A total of 124 H. pylori-positive patients living in Tehran were enrolled in this study. The ethnic distribution was 74 Persians, 33 Turks and 17 other ethnics including Kurds, Lurs, Afghanis and Arabs. The presence of the cagA, cagE and oipA genes and vacA alleles (signal [s] and middle [m] region) were determined by polymerase chain reaction (PCR) from H. pylori DNA. Results: The cagA-positive status was predominant in all three ethnic groups (e.g. 65% in Persians and 73% in Turks). In contrast, the cagE-positive status was less than half in Persians (47%) and Turks (30%), whereas it was 77% in other ethnicities ( P = 0.008). The predominant vacA genotypes were s1 and m1 in all three ethnic groups (e.g. 68% in Persians and 70% in Turks were s1). There was no significant association between cagA and cagE status or vacA genotypes and clinical outcomes. The oipA-positive strains were more common in non-ulcer dyspepsia (NUD) (63%) than in peptic ulcer patients (15%) ( P = 0.001) in Persians, but the association was not observed in other ethnic groups. Conclusion: There are some differences in the H. pylori genotypes among the ethnic groups in Iran. However, none of these markers seemed to be clinically helpful in predicting the clinical presentation of a H. pylori infection in Iran. [ABSTRACT FROM AUTHOR]

Nocardia ignorata, which was first described in 2001, is a rare human pathogen. We report a case of pulmonary nocardiosis caused by this bacterium in a 55-year-old man from Iran. The patient, a gardener, had frequent exposure to soil and may have acquired the infection from that source. [ABSTRACT FROM AUTHOR]