Frequent detection of plasmid-mediated quinolone resistance (qnr) genes in multidrug-resistant Enterobacteriaceae blood isolates, Hong Kong

Transferable Mechanisms of Quinolone Resistance from 1998 Onward

While the description of resistance to quinolones is almost as old as these antimicrobial agents themselves, transferable mechanisms of quinolone resistance (TMQR) remained absent from the scenario for more than 36 years, appearing first as sporadic events and afterward as epidemics. In 1998, the first TMQR was soundly described, that is, QnrA. The presence of QnrA was almost anecdotal for years, but in the middle of the first decade of the 21st century, there was an explosion of TMQR descriptions, which definitively changed the epidemiology of quinolone resistance. Currently, 3 different clinically relevant mechanisms of quinolone resistance are encoded within mobile elements: (i) target protection, which is mediated by 7 different families of Qnr (QnrA, QnrB, QnrC, QnrD, QnrE, QnrS, and QnrVC), which overall account for more than 100 recognized alleles; (ii) antibiotic efflux, which is mediated by 2 main transferable efflux pumps (QepA and OqxAB), which together account for more than 30 alleles, and a series of other efflux pumps (e.g., QacBIII), which at present have been sporadically described; and (iii) antibiotic modification, which is mediated by the enzymes AAC(6')Ib-cr, from which different alleles have been claimed, as well as CrpP, a newly described phosphorylase.

Treatment of Infections Caused by Extended-Spectrum-Beta-Lactamase-, AmpC-, and Carbapenemase-Producing Enterobacteriaceae

Therapy of invasive infections due to multidrug-resistant Enterobacteriaceae (MDR-E) is challenging, and some of the few active drugs are not available in many countries. For extended-spectrum β-lactamase and AmpC producers, carbapenems are the drugs of choice, but alternatives are needed because the rate of carbapenem resistance is rising. Potential active drugs include classic and newer β-lactam-β-lactamase inhibitor combinations, cephamycins, temocillin, aminoglycosides, tigecycline, fosfomycin, and, rarely, fluoroquinolones or trimethoprim-sulfamethoxazole. These drugs might be considered in some specific situations. AmpC producers are resistant to cephamycins, but cefepime is an option. In the case of carbapenemase-producing Enterobacteriaceae (CPE), only some "second-line" drugs, such as polymyxins, tigecycline, aminoglycosides, and fosfomycin, may be active; double carbapenems can also be considered in specific situations. Combination therapy is associated with better outcomes for high-risk patients, such as those in septic shock or with pneumonia. Ceftazidime-avibactam was recently approved and is active against KPC and OXA-48 producers; the available experience is scarce but promising, although development of resistance is a concern. New drugs active against some CPE isolates are in different stages of development, including meropenem-vaborbactam, imipenem-relebactam, plazomicin, cefiderocol, eravacycline, and aztreonam-avibactam. Overall, therapy of MDR-E infection must be individualized according to the susceptibility profile, type, and severity of infection and the features of the patient.

High morbidity and mortality of Clostridium difficile infection and its associations with ribotype 002 in Hong Kong

OBJECTIVES

We aim to study the disease burden, risk factors and severity of Clostridium difficile infection (CDI) in Hong Kong.

METHODS

We conducted a prospective, case-control study in three acute-care hospitals in Hong Kong. Adult inpatients who developed CDI diarrhoea confirmed by PCR (n = 139) were compared with the non-CDI controls (n = 114). Ribotyping of isolates and antimicrobial susceptibility testing were performed.

RESULTS

The estimated crude annual incidence of CDI was 23-33/100,000 population, and 133-207/100,000 population among those aged ≥65 years. The mean age of CDI patients was 71.5. Nursing home care, recent hospitalization, antibiotics exposure (adjusted OR 3.0, 95% CI 1.3-7.1) and proton-pump inhibitors use (adjusted OR 2.2, 95% CI 1.2-3.9) were risk factors. Severe CDI occurred in 41.7%. Overall mortality was 16.5% (among severe CDI, 26.5%). The commonest ribotypes were 002 (22.8%), 014 (14.1%), 012 and 046; ribotype 027 was absent. Ribotype 002 was associated with fluoroquinolone resistance and higher mortality (47.6% vs. 12.7%; adjusted HR 2.8, 95% CI 1.1-7.0).

CONCLUSIONS

Our findings show high morbidity and mortality of CDI in the older adults, and identify ribotype 002 as a possible virulent strain causing serious infections in this cohort.

Differential expression of virulence genes and role of gyrA mutations in quinolone resistant and susceptible strains of Salmonella Weltevreden and Newport isolated from seafood

AIMS

To investigate the differential expression of virulence genes and role of gyrA mutations in quinolone resistant and susceptible strains of Salmonella isolated from seafood.

METHODS AND RESULTS

Forty Salmonella isolates from seafood were tested for antibiotic sensitivity. Minimal inhibitory concentration (MIC) was determined and two nalidixic acid-resistant isolates, viz Salmonella Weltevreden (SW9) and Salmonella Newport (SN36) were selected for identifying the mechanism of resistance. SW9 showed mutation in the gyrA gene at codon 83 (Ser to Tyr) while SN36 presented at codon 87 (Asp to Asn). Experimental induction of resistance to a sensitive Salm. Newport (SN71) showed point mutation at codon 87 (Asp to Gly) in the gyrA gene, and was designated SN71R. All the isolates resistant to nalidixic acid had a single mutation at different positions in the gyrA gene. However, induction of resistance to a sensitive Salm. Weltevreden (SW30) was exceptional in that it did not show any mutation in the gyrA region. Use of Phe-Arg-β-naphthylamide (PAβN) also could not reduce MIC below the Clinical and Laboratory Standards Institute guidelines revealing the absence of efflux mediated resistance. Thus, the resistance mechanism in SW30R is unknown. The growth rate of quinolone resistant isolates was slower than the susceptible ones. The resistant isolates showed decreased epithelial cell invasion and intracellular replication. The mRNA expression levels of some of the genes were significantly (P < 0·005) reduced in SN71R compared to the sensitive strain (SN71).

CONCLUSIONS

Nalidixic acid-resistant Salmonella strains are associated with lower virulence and pathogenicity than the sensitive strains.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study provided valuable information on the difference in the growth, cytotoxicity, infectivity and expression of virulence genes in resistant and susceptible strains. Furthermore, the gyrA mutation was shown to be the main mechanism of quinolone resistance in Salmonella other than the overexpression of efflux pumps or the presence of plasmid mediated quinolone resistance genes.

Once-daily, oral levofloxacin monotherapy for low-risk neutropenic fever in cancer patients: a pilot study in China

This pilot study assesses the safety and efficacy of once-daily, oral levofloxacin monotherapy in Chinese patients with low-risk febrile neutropenia. In this prospective, single-arm, open-label, multicenter clinical trial, 46 adult Chinese patients with solid tumors and low-risk febrile neutropenia were included. Patients received oral levofloxacin monotherapy (500 mg orally/day) until day 12, followed by 7 days of follow-up (day 19). Body temperature was measured three times per day. On days 2, 3, 5-7, 9, 12, and 19, disease symptoms and vital signs were recorded, adverse drug reactions were assessed, and blood samples were collected to determine the whole-blood cell count and the absolute neutrophil count. Blood cultures and chest radiographs were performed simultaneously until negative results were found. Oral levofloxacin was effective and well tolerated in 97.6% of patients irrespective of the cancer type and cause of fever. Body temperature began to decline in 24.4, 68.3, and 90.2% of patients, respectively, at 12, 24, and 48 h after initiating levofloxacin therapy. On days 5 and 7, 95.1 and 97.6% of the patients had complete defervescence, respectively. The median time for absolute neutrophil count recovery to at least 1500/mm after initiation of treatment was 3 days. Only one patient reported mild diarrhea. This pilot study showed that oral levofloxacin quickly and effectively reduced fever, initiated neutrophil recovery, and was well tolerated in Chinese low-risk febrile neutropenic patients with solid tumors. Further study is needed to compare patient data of levofloxacin with the standard amoxicillin/ciprofloxacin protocol in this population for both safety and efficacy.

Extended-spectrum β-lactamases in Enterobacteriaceae isolated in Brazil carry distinct types of plasmid-mediated quinolone resistance genes

One hundred and six nalidixic acid-resistant Enterobacteriaceae isolates from two Brazilian hospitals isolated from June to October 2010 were evaluated to characterize the co-existence of plasmid-mediated quinolone resistant (PMQR) and extended-spectrum β-lactamase (ESBL) determinants. The qnr genetic environment was determined by PCR and sequencing. Conjugation and hybridization experiments determined whether qnr-carrying plasmids were self-transferable. The aac(6')-Ib-cr and qepA genes were also screened. Thirteen qnr-like genes (12.3 %) were identified, with qnrB1 the most common, followed by qnrS1, qnrB2 and qnrB19. No qnrA, qnrC, qnrD or qepA determinant was detected. All qnr-positive strains possessed chromosomal substitutions in gyrase- and topoisomerase-encoding genes and four harboured a aac(6')-Ib-cr gene. The co-production of blaCTX-M was observed in ten qnr-positive strains. These results indicate the dissemination of PMQR genes shown in clinical isolates from Brazil, and their co-existence with ESBL genes emphasizes the complexity of plasmid-mediated resistance determinants among Enterobacteriaceae.