Xiaogang Xu

Since the discovery of qnrA in 1998, two additional qnr genes, qnrB and qnrS, have been described. These three plasmid-mediated genes contribute to quinolone resistance in gram-negative pathogens worldwide. A clinical strain of Proteus mirabilis was isolated from an outpatient with a urinary tract infection and was susceptible to most antimicrobials but resistant to ampicillin, sulfamethoxazole, and trimethoprim. Plasmid pHS10, harbored by this strain, was transferred to azide-resistant Escherichia coli J53 by conjugation. A transconjugant with pHS10 had low-level quinolone resistance but was negative by PCR for the known qnr genes, aac(6')-Ib-cr and qepA. The ciprofloxacin MIC for the clinical strain and a J53/pHS10 transconjugant was 0.25 microg/ml, representing an increase of 32-fold relative to that for the recipient, J53. The plasmid was digested with HindIII, and a 4.4-kb DNA fragment containing the new gene was cloned into pUC18 and transformed into E. coli TOP10. Sequencing showed that the responsible 666-bp gene, designated qnrC, encoded a 221-amino-acid protein, QnrC, which shared 64%, 42%, 59%, and 43% amino acid identity with QnrA1, QnrB1, QnrS1, and QnrD, respectively. Upstream of qnrC there existed a new IS3 family insertion sequence, ISPmi1, which encoded a frameshifted transposase. qnrC could not be detected by PCR, however, in 2,020 strains of Enterobacteriaceae. A new quinolone resistance gene, qnrC, was thus characterized from plasmid pHS10 carried by a clinical isolate of P. mirabilis.

Since glycopeptide-resistant enterococci (GRE) were reported in 1988, they have appeared in hospitals worldwide. Seven van gene cluster types (vanA, vanB, vanC, vanD, vanE, vanG, and vanL) are currently known. We investigated a clinical strain of Enterococcus faecium Efm-HS0661 that was isolated in 2006 from an inpatient with intra-abdominal infection in Shanghai. It was resistant to most antimicrobials, including vancomycin (MIC, >256 μg/ml) and teicoplanin (MIC, 96 μg/ml). Glycopeptide resistance could be transferred to E. faecium BM4105RF by conjugation. The donor and its transconjugant were negative by PCR for the known van genes. By cloning and primer walk sequencing, we discovered a novel van gene cluster, designated vanM. The vanM ligase gene was 1,032-bp in length and encoded a 343-amino-acid protein that shared 79.9, 70.8, 66.3, and 78.8% amino acid identity with VanA, VanB, VanD, and VanF, respectively. Although the vanM DNA sequence was closest to vanA, the organization of the vanM gene cluster was most similar to that of vanD. Upstream from the vanM cluster was an IS1216-like element, which may play a role in the dissemination of this resistance determinant. Liquid chromatography-mass spectrometry analysis of peptidoglycan precursors extracted from the VanM-type strain Efm-HS0661 treated with vancomycin or teicoplanin revealed a modified precursor (UDP-N-acetylmuramic acid [MurNAc]-tetrapeptide-D-Lac), indicating that VanM, like VanA, confers glycopeptide resistance by the inducible synthesis of precursor ending in D-Ala-D-Lac.

Three kinds of plasmid-mediated quinolone resistance (PMQR) determinants have been discovered and have been shown to be widely distributed among clinical isolates: qnr genes, aac(6')-Ib-cr, and qepA. Few data on the prevalence of these determinants in strains from animals are available. The presence of PMQR genes in isolates from animals was determined by PCR amplification and DNA sequencing. The production of extended-spectrum beta-lactamases (ESBLs) and AmpC beta-lactamases in the strains was detected, and their genotypes were determined. The genetic environment of PMQR determinants in selected plasmids was analyzed. All samples of ceftiofur-resistant (MICs > or = 8 microg/ml) isolates of the family Enterobacteriaceae were selected from 36 companion animals and 65 food-producing animals in Guangdong Province, China, between November 2003 and April 2007, including 89 Escherichia coli isolates, 9 Klebsiella pneumoniae isolates, and isolates of three other genera. A total of 68.3% (69/101) of the isolates produced ESBLs and/or AmpC beta-lactamases, mainly those of the CTX-M and CMY types. Of the 101 strains, PMQR determinants were present in 35 (34.7%) isolates, with qnr, aac(6')-Ib-cr, and qepA detected alone or in combination in 8 (7.9%), 19 (18.8%), and 16 (15.8%) strains, respectively. The qnr genes detected included one qnrB4 gene, four qnrB6 genes, and three qnrS1 genes. Five strains were positive for both aac(6')-Ib-cr and qepA, while one strain was positive for qnrS1, aac(6')-Ib-cr, and qepA. qnrB6 was flanked by two copies of ISCR1 with an intervening dfr gene downstream and sul1 and qacEDelta1 genes upstream. In another plasmid, aac(6')-Ib-cr followed intI1 and arr-3 was downstream. PMQR determinants are highly prevalent in ceftiofur-resistant Enterobacteriaceae strains isolated from animals in China. This is the first report of the occurrence of PMQR determinants among isolates from companion animals.

BACKGROUND: Carbapenem-resistant Klebsiella pneumoniae (CRKP) has become a threat to public health, most notably as a superbug causing nosocomial infections. Patients in the intensive care unit (ICU) are at increased risk of hospital-acquired K pneumoniae infection, especially CRKP. This study was conducted to investigate the frequency of gastrointestinal and nasopharyngeal K pneumoniae colonization and its contribution to infections in ICU patients. METHODS: A 3-month prospective cohort study was performed in which 243 ICU patients were screened for intestinal and nasopharyngeal carriage of K pneumoniae at admission and once per week thereafter. The colonization and clinical infection isolates were analyzed by antimicrobial susceptibility testing to identify CRKP and were characterized by multilocus sequence typing (MLST) and whole-genome sequencing combined with epidemiological data to investigate the resistance mechanisms and assess the possible transmitted infection. RESULTS: Twenty-eight percent (68 of 243) of patients tested positive for carriage of K pneumoniae immediately upon admission to ICU, 54% (37 of 68) of which were nonduplicate CRKP isolates. Patients with carbapenem-susceptible K pneumoniae (CSKP) colonization at admission were more likely to acquire CRKP colonization during the ICU stay compared with patients without K pneumoniae colonization at admission. The incidence of subsequent CRKP infection in the baseline CSKP (32.3%, 10 of 31) and CRKP (45.9%, 17 of 37) carrier group was significantly higher than that of the baseline non-KP carrier group (8.6%, 15 of 175). The risk factors associated with acquired CRKP colonization during the ICU stay among negative CRKP colonization at admission included previous exposure to carbapenem, tigecycline or β-lactam/β-lactamases inhibitor, and invasive processes or surgical operations. Sixty-four percent (27 of 42) of patients with K pneumoniae infection were colonized by clonally related K pneumoniae strains according to enterobacterial repetitive intergenic consensus sequence-polymerase chain reaction analysis. ST11 (72%, 53 of 74) was the most predominant MLST type of clonally related CRKP isolate colonizing these patients, followed by ST15 (26%, 19 of 74). CONCLUSIONS: The colonization of K pneumoniae may increase the incidence of corresponding K pneumoniae infection in critically ill patients in the ICU. High prevalence of ST11 CRKP (due to blaKPC-2) carriage and infection in ICU was observed.

Fifty-three Mycoplasma pneumoniae strains were isolated from pediatric patients in Shanghai, China, from October 2005 to February 2008. Of 53 clinical isolates, 44 (83%) were resistant to erythromycin (MICs of >128 microg/ml for all 44 strains), azithromycin, and clarithromycin. All macrolide-resistant M. pneumoniae strains harbored an A-to-G transition mutation at position 2063 in 23S rRNA genes. Forty-five (85%) clinical isolates were classified into the P1 gene restriction fragment length polymorphism type I, and six (11%) were type II.