Cephalosporin resistance in Klebsiella pneumoniae from Nova Scotia, Canada

Identification of Arg32Ser, His92Tyr and Leu147Phe novel mutations in chromosomally mediated β-lactamase SHV and in silico characterization to understand their substrate activity imparting resistance

The emergence of β-lactam resistance is yearning for clinical significance in Enterobacteriaceae, which are categorized under global priority pathogen lists by the World Health Organization. Likewise, the prevalence of numerous β-lactamase enzymes, mutational propensity in such bacteria, and their role in accelerating resistance is still a major concern. Thus, the present work intends to characterize the β-lactamase producing bacteria isolated from acute diarrheal patients to understand their chromosomally acquired resistance pattern through molecular characterization and in silico approaches. The current study highlights the first identified Escherichia fergusonii and Escherichia marmotae species and their β-lactamase encoding genes, blaOKP-A, blaNDM and blaOXA from the unexplored Enterobacteriaceae family from North East India. First-ever reported point mutations such as Arg32Ser, His92Tyr, and Leu147Phe were observed in BlaSHV protein of two Klebsiella pneumoniae isolates S-35 and S-46. In molecular docking, non-catalytic site H-bond interactions of Arg 218, Ala 223, Asn 128, Ser 126, Gln 95, Asp 100, Tyr 101, Ser 102, Ala 274 with a low binding affinity towards BlaSHV was found. This correlates with the high imipenem, ceftazidime, cefuroxime, ceftriaxone, and cefpodoxime resistance in Klebsiella pneumoniae S-35 with the complementary effect of mutations Arg32Ser and Leu147Phe. Besides, the role of His92Tyr mutation in controlling the resistance in Klebsiella pneumoniae S-46 is also illustrated. Thus, our study highlights the novel mutations of β-lactamase and its clinical importance with altered resistance profiles. This could be useful to design better therapeutics and to readjust antibiotic treatment regimes against them and control to grow more resistance under selective pressure.Communicated by Ramaswamy H. Sarma.

Molecular characterization of plasmid-mediated AmpC beta-lactamase- and extended-spectrum beta-lactamase-producing Escherichia coli and Klebsiella pneumoniae among corvids (Corvus brachyrhynchos and Corvus corax) roosting in Canada

This study evaluated the carriage of AmpC and extended-spectrum beta-lactamase (ESBL) genes and associated plasmids in faecal bacteria of Canadian corvids. Faecal samples from 449 birds in five roosting sites across Canada were analyzed using selective media, screening for AmpC and ESBL genes by PCR, and sequencing. Genomic relatedness was determined by PFGE and MLST. Plasmid mobility was studied by conjugation and transformation experiments, followed by plasmid typing. In total, 96 (21%, n = 449) cefotaxime-resistant Escherichia coli and three (0.7%) Klebsiella pneumoniae isolates were identified. ESBL genes blaCTX-M-1 (n = 3), blaCTX-M-14 (n = 2), blaCTX-M-32 (n = 2) and blaCTX-M-124 (n = 1) were detected in eight E. coli isolates, whereas blaSHV-2 (2) was found in two K. pneumoniae. E. coli isolates contained blaCMY-2 (n = 83) and blaCMY-42 (n = 1). The high genetic diversity of the isolates and presence of clinically important E. coli ST69 (n = 1), ST117 (n = 7) and ST131 (n = 1) was revealed. AmpC genes were predominantly carried by plasmids of incompatibility groups I1 (45 plasmids), A/C (10) and K (7). The plasmid IncI1/ST12 was most common and found in diverse E. coli STs in all sites. Highly diverse E. coli isolates containing AmpC and ESBL genes, including clinically important clones and emerging plasmids, are in circulation throughout Canadian wildlife.

ESBLs: A Clear and Present Danger?

Extended spectrum β-lactamases (ESBLs) are enzymes produced by a variety of Gram negative bacteria which confer an increased resistance to commonly used antibiotics. They are a worrying global public health issue as infections caused by such enzyme-producing organisms are associated with a higher morbidity and mortality and greater fiscal burden. Coupled with increasing prevalence rates worldwide and an ever diminishing supply in the antibiotic armamentarium, these enzymes represent a clear and present danger to public health. This article aims to give an overview of the current situation regarding ESBLs, with a focus on the epidemiology and management of such infections.

Comparative evaluation of a chromogenic agar medium, the modified Hodge test, and a battery of meropenem-inhibitor discs for detection of carbapenemase activity in Enterobacteriaceae

Three phenotypic methods (modified Hodge test, chromogenic agar, and meropenem discs combined with specific inhibitors) used for the detection of carbapenemase activity were tested on a panel of characterized Enterobacteriaceae expressing various β-lactamase mechanisms. Overall, the meropenem-plus-inhibitor approach was more sensitive and specific than the other methods, despite its limitation of being unable to detect class D carbapenemases.

Phenotypic and genotypic characterization of β-lactam resistance in Klebsiella pneumoniae isolated from swine

Little is known about the antimicrobial resistance mechanisms in Klebsiella pneumoniae from swine in China. Thus, this paper aims to demonstrate the β-lactam resistance phenotypes and genotypes of K. pneumoniae isolates from swine in southwestern China, detect possible new β-lactamase variants, and determine whether or not the variants differ in their antibiotic resistance. Isolates from 58 unrelated diseased swine were collected from 61 pig farms in southwestern China from 2007 to 2009. Among the 58 isolates, 75.8-100% were resistant to β-lactam, 62.0-68.97% to fluoroquinolone, 44.8-46.55% to aminoglycoside, and 8.62-17.24% to β-lactam inhibitors. PCR amplification and DNA sequencing showed that bla(TEM-1) was detected in 100% (n=58) of the isolates, bla(SHV) in 82.76% (n=48), bla(CTX-M) in 39.66% (n=23), and bla(OKP) in 17.24% (n=10). The bla(SHV) types included bla(SHV-1), bla(SHV-11), bla(SHV-12), and bla(SHV-27). None of the isolates harbored bla(KPC), bla(LEN), or bla(GES) gene. Four novel variants (bla(OKP-A-13), bla(OKP-A-14), bla(OKP-A-15), and bla(OKP-A-16)) were identified among the 10 OKP β-lactamase-producing K. pneumoniae isolates resistant to ampicillin, amoxicillin, oxacillin, cefalexin, and cefadroxil. Plasmid analysis and PCR amplification indicated that bla(TEM-1) genes were detected in the total plasmid. Molecular typing by pulsed-field gel electrophoresis revealed the presence of 10 distinct pulsotypes of OKP producer isolates. Plasmid DNA digested with XbaI yielded two to six bands of ca. 0.15-30 kb. Transformants of the 10 OKP producer isolates showed no differences in their antibiotic susceptibility, except for the pulsotype B transformant, which carried bla(CTX-M). In China, β-lactam resistance appeared to be common among K. pneumoniae isolates from swine, suggesting that K. pneumoniae may be a reservoir for the dissemination of β-lactam resistance among Chinese pig farms.

Genetic diversity of genes encoding OKP and LEN beta-lactamases produced by clinical Klebsiella pneumoniae strains in Portugal

Of the 308 clinical Klebsiella pneumoniae strains collected in 21 Portuguese health institutions, 11 encoded for LEN and 9 for OKP enzymes; of these, 15 were new enzymes. Ninety-one percent of LEN and all OKP producer strains were resistant to amoxicillin. We demonstrate that these beta-lactamase were highly diverse.

Contribution of fucose-containing capsules in Klebsiella pneumoniae to bacterial virulence in mice

Bacterium Klebsiella pneumoniae (KP) contains a prominent capsule. Clinical infections usually are associated with pneumonia or urinary tract infection (UTI). Emerging evidence implicates KP in severe liver abscess especially in diabetic patients. The goal of this study was to investigate the capsular polysaccharides from KP of liver abscess (hepatic-KP) and of UTI-KP. The composition of capsular polysaccharides was analyzed by capillary high-performance liquid chromatography (HPLC, Dionex system). The terminal sugars were assayed by binding ability to lectins. The results showed that the capsule of a hepatic KP (KpL1) from a diabetic patient contained fucose, while the capsule from UTI-KP (KpU1) did not. The absence of fucose was verified by the absence of detectable polymerase chain reaction (PCR) fragment for fucose synthesis genes, gmd and wcaG in KpU1. Mice infected with the KpL1 showed high fatality, whereas those infected with the KpU1 showed high survival rate. The KpL1 capsule was reactive to lectins AAA and AAL, which detect fucose, while the KpU1 capsule was reactive to lectin GNA, which detects mannose. Phagocytosis experiment in mouse peritoneal cavity indicated that the peritoneal macrophages could interact with KpU1, while rare association of KpL1 with macrophages was observed. This study revealed that different polysaccharides were displayed on the bacterial capsules of virulent KpL1 as compared with the less virulent KpU1. Interaction of KpU1 with mice peritoneal macrophages was more prominent than that of KpL1. The possession of fucose might contribute to KpL1 virulence by avoiding phagocytosis since fucose on bacteria had been implicated in immune evasion.