BSAC standardized disc susceptibility testing method (version 3)

Characterization of the newly isolated phage Y3Z against multi-drug resistant Cutibacterium acnes

Cutibacterium acnes (C. acnes) is a symbiotic bacterium that plays an important role in the formation of acn e inflammatory lesions. As a common component of the acne microbiome, C. acnes phages have the potential to make a significant contribution to treating antibiotic-resistant strains of C. acnes. However, little is known about their genetic composition and diversity. In this study, a new lytic phage, Y3Z, infecting C. acne, was isolated and characterized. Electron microscopy analysis revealed this phage is a siphovirus. Phage Y3Z is composed of 29,160 bp with a GC content of 56.32%. The genome contains 40 open reading frames, 17 of which had assigned functions, while no virulence-related genes, antibiotic resistance genes or tRNA were identified. The one-step growth curve showed the burst size was 30 PFU (plaque-forming unit)/cell. And it exhibited tolerance over a broad range of pH and temperature ranges. Phage Y3Z could infect and lyse all C. acnes isolates tested, though the host range of PA6 was restricted to C. acnes. Based on the phylogenetic and comparative genomic analyses, Y3Z may represent a new siphovirus infecting C. acnes. Characterization of Y3Z will enrich our knowledge about the diversity of C. acnes phages and provide a potential arsenal for thetreatment of acne infection.

Essential oil of Mentha suaveolens Ehrh., composition and antibacterial activity against bacterial fish pathogens

In this study, it was determinated the essential oil of cultivated apple mint, Mentha suaveolens Ehrh. composition and in vitro antibacterial activity of against 11 fish pathogen bacteria including Gram-positive (Staphylococcus warneri, Staphylococcus sp., Lactococcus garvieae, Vagococus salmoninarum) and Gram-negative (Aeromonas hydrophila, Aeromonas sobria Aeromonas cavieae, Vibrio anguillarum, Pseudomonas aeroginosa, Yersinia ruckeri, Edwardsiella tarda) by using agar diffusion assay. The main component of M. suaveolence oil was obtained as piperitenone oxide. The essential oil exhibited strong inhibitory activity such as inhibition zone sizes: 30-50mm at 250-1000 µL mL-1 concentrations against V. anguillarum; 16-20mm at 31.25-125 µL mL-1 concentrations against P. aeroginosa; 15-18mm at 500-1000 µL mL-1 concentrations against A. sobria. However, it was found to be moderately effective against E. tarda (8-15 mm), Y. ruckeri (9-12mm), S. warneri (9-10mm), V. salmoninarum (9mm) and Staphylococcus sp. (8-9mm). The essential oil showed weak inhibitory activity against A. cavieae (5-8), A. hydrophila (6-7mm), L. garvieae (5-7mm). Thus, effect of essential oil of M. suaveolens on immune response and disease resistance against Vibrio anguillarum, A. sobria and P. aeroginosa should be investigated in vivo in cultured fish species in future studies.

Phenotypic and Genotypic Characterization of Carbapenem-Resistant Gram-Negative Bacilli Pathogens from Hospitals in Ghana

In Ghana, surveillance efforts on antibiotic resistance so far have not covered carbapenem resistance. In this study, our aim was to apply phenotypic and genotypic methods to identify and characterize carbapenem-resistant (CR) Gram-negative bacteria from the hospital environment in Ghana. A collection of 3840 isolates of Gram-negative bacilli infections from various clinical specimens was screened for carbapenem resistance by disc diffusion for imipenem, meropenem, and doripenem. Minimum Inhibitory Concentration (MIC) of the CR isolates was determined by E-test for the three carbapenems. All the CR isolates were further screened for carbapenemase activity by modified Hodge and boronic acid disc synergy tests. The CR isolates were investigated for the presence of carbapenemase and extended-spectrum beta-lactamase genes by PCR and confirmed by sequencing. The overall prevalence of CR isolates was 2.9% (111/3840). Based on the disc diffusion test, prevalence of resistance to carbapenems were doripenem (75%), imipenem (66.7%), and meropenem (58%). The highest measurable MIC levels (≥32 μg/mL) were observed in 56.8% of CR isolates with the nonfermenters, Pseudomonas aeruginosa (24.3%) and Acinetobacter species (18.9%), disproportionately represented. Phenotypic identification of carbapenamase activity occurred in 18.9% of the CR isolates by the modified Hodge test and 2.7% by Boronic acid disc synergy test; 21.6% exhibited carbapenemase production by both methods. All the CR isolates carried ESBL genes (blaTEM and blaSHV), whereas 23.4% were carriers of carbapenemase genes, of which 14.4% were blaNDM-1, 7.2% blaVIM-1, and 1.8% blaOXA-48. Phylogenetically, the CR isolates were diverse and showed limited relatedness to isolates from other geographical regions.

EVALUATION OF ANTIBACTERIAL, ANTITUMOR, ANTIOXIDANT ACTIVITIES AND PHENOLIC CONSTITUENTS OF FIELD-GROWN AND IN VITRO-GROWN LYSIMACHIA VULGARIS L

BACKGROUND

Lysimachia vulgaris L. (Yellow loosestrife) is a medicinal plant in the family Myrsinaceae. It has been used in the treatment of fever, ulcer, diarrhea and wounds in folk medicine. It has also analgesic, expectorant, astringent and anti-inflammatory activities. Two different sources of the plant (field-grown and in vitro-grown) were used to evaluate the biological activities (antibacterial, antitumor and antioxidant) of L. vulgaris. In vitro-grown plant materials were collected from L. vulgaris plants that were previously regenerated in our laboratory.

MATERIALS AND METHODS

Plant materials were extracted with water, ethanol and acetone. For antibacterial test, disc diffusion method and 10 different pathogenic bacteria were used. Antioxidant activity was indicated by using DPPH method. The total phenol amount by using Folin-Ciocaltaeu method and the total flavonoid amount by using aluminum chloride (AlCl₃) colorimetric method were determined.

RESULTS

Generally, yellow loosestrife extracts demonstrated antibacterial activity against Gram-positive bacteria (Staphylococcus aureus, S. epidermidis and Streptococcus pyogenes). Strong antitumor activity of yellow loosestrife was observed via potato disc diffusion bioassay. Nine different phenolics were also determined and compared by using High-Performance Liquid Chromatography (HPLC).

CONCLUSION

Future investigations should be focused on fractionation of the extracts to identify active components for biological activity.

Point prevalence of hospital-acquired infections in two teaching hospitals of Amhara region in Ethiopia

Purpose

Hospital-acquired infection (HAI) is a major safety issue affecting the quality of care of hundreds of millions of patients every year, in both developed and developing countries, including Ethiopia. In Ethiopia, there is no comprehensive research that presents the whole picture of HAIs in hospitals. The objective of this study was to examine the nature and extent of HAIs in Ethiopia.

Methods

A repeated cross-sectional study was conducted in two teaching hospitals. All eligible inpatients admitted for at least 48 hours on the day of the survey were included. The survey was conducted in dry and wet seasons of Ethiopia, that is, in March to April and July 2015. Physicians and nurses collected the data according to the Centers for Disease Control and Prevention definition of HAIs. Coded and cleaned data were transferred to SPSS 21 and STATA 13 for analysis. Univariate and multivariable logistic regression analyses were used to examine the prevalence of HAIs and relationship between explanatory and outcome variables.

Results

A total of 908 patients were included in this survey, the median age of the patients was 27 years (interquartile range: 16–40 years). A total of 650 (71.6%) patients received antimicrobials during the survey. There were 135 patients with HAI, with a mean prevalence of 14.9% (95% confidence interval 12.7–17.1). Culture results showed that Klebsiella spp. (22.44%) and Staphylococcus aureus (20.4%) were the most commonly isolated HAI-causing pathogens in these hospitals. The association of patient age and hospital type with the occurrence of HAI was statistically significant.

Conclusion

It was observed that the prevalence of HAI was high in the teaching hospitals. Surgical site infections and pneumonia were the most common types of HAIs. Hospital management should give more attention to promoting infection prevention practice for better control of HAIs in teaching hospitals.

Screening for antibacterial activity of some Turkish plants against fish pathogens: a possible alternative in the treatment of bacterial infections

The antibacterial activity of ethanolic and aqueous crude extracts from 36 plants in Turkey, including seven endemic species, against fish pathogens was studied using the disc diffusion assay. The extract that was most active against all microbial strains, except Aeromonas salmonicida, was that of Dorycnium pentaphyllum. Some of the extracts also showed a very broad spectrum of potent antimicrobial activity. The extract of Anemone nemorosa showed the highest antimicrobial activity against Vibrio anguillarum. V. anguillarum, a Gram-negative bacterium, appeared to be the most susceptible to the plant extracts used in this experiment. To the best of our knowledge, this is the first report on the antimicrobial activity of 11 of the studied plants. The preliminary screening assay indicated that some of the Turkish plants with antibacterial properties may offer alternative therapeutic agents against bacterial infections in aquaculture industry.

Extraction, characterization and biological studies of phytochemicals from Mammea suriga

The present work involves extraction of phytochemicals from the root bark of a well-known Indian traditional medicinal plant, viz. Mammea suriga, with various solvents and evaluation of their in vitro antimicrobial and antioxidant activities using standard methods. The phytochemical analysis indicates the presence of some interesting secondary metabolites like flavonoids, cardiac glycosides, alkaloids, saponins and tannins in the extracts. Also, the solvent extracts displayed promising antimicrobial activity against Staphylococcus aureus, Bacillus subtilis and Cryptococcus neoformans with inhibition zone in a range of 20-33 mm. Further, results of their antioxidant screening revealed that aqueous extract (with IC₅₀ values of 111.51±1.03 and 31.05±0.92 μg/mL in total reducing power assay and DPHH radical scavenging assay, respectively) and ethanolic extract (with IC₅₀ values of 128.00±1.01 and 33.25±0.89 μg/mL in total reducing power assay and DPHH radical scavenging assay, respectively) were better antioxidants than standard ascorbic acid. Interestingly, FT-IR analysis of each extract established the presence of various biologically active functional groups in it.

In vitro antibacterial and antitumor activities of some medicinal plant extracts, growing in Turkey

OBJECTIVE

To investigate antibacterial and antitumor activities of 51 different extracts prepared with 3 types of solvents (water, ethanol and methanol) of 16 different plant species (Ajuga reptans (A. reptans) L., Phlomis pungens (P. pungens) Willd., Marrubium astracanicum (M. astracanicum) Jacq., Nepeta nuda (N. nuda) L., Stachys annua (S. annua) L., Genista lydia (G. lydia) Boiss., Nuphar lutea (N. lutea) L., Nymphaea alba (N. alba) L., Vinca minor (V. minor) L., Stellaria media (S. media) L., Capsella bursa-pastoris (C. bursa-pastoris) L., Galium spurium (G. spurium) L., Onosma heterophyllum (O. heterophyllum) Griseb., Reseda luteola (R. luteola) L., Viburnum lantana (V. lantana) L. and Mercurialis annua (M. annua) L.) grown in Turkey was conducted.

METHODS

Antibacterial activity was evaluated with 10 bacteria including Streptococcus pyogenes (S. pyogenes), Staphylococcus aureus (S. aureus), Staphylococcus epidermidis (S. epidermidis), Escheria coli (E. coli), Pseudomonas aeruginosa (P. aeruginosa), Salmonella typhimurium (S. typhimurium), Serratia marcescens (S. marcescens), Proteus vulgaris (P. vulgaris), Enterobacter cloacae (E. cloacea), and Klebsiella pneumoniae (K. pneumoniae) by using disc diffusion method. Antitumor activity was evaluated with Agrobacterium tumefaciens (A. tumefaciens)-induced potato disc tumor assay.

RESULTS

Best antibacterial activity was obtained with ethanolic extract of P. pungens against S. pyogenes. Ethanolic and methanolic extract of N. alba and ethanolic extract of G. lydia also showed strong antibacterial activities. Results indicated that alcoholic extracts especially ethanolic extracts exhibited strong antibacterial activity against both gram-positive and gram-negative bacteria. Best antitumor activity was obtained with methanolic extracts of N. alba and V. lantana (100% tumor inhibition). Ethanolic extract of N. alba, alcoholic extracts of N. lutea, A. reptans and V. minor flowers, methanolic extracts of G. lydia and O. heterophyllum and ethanolic extract of V. lantana and aqueous extract of V. minor leaves exhibited strong tumor inhibitions.

CONCLUSIONS

In near future works, identification of active components can be studied for plant extracts having strong bioactivity.

Phosphoethanolamine modification of lipid A in colistin-resistant variants of Acinetobacter baumannii mediated by the pmrAB two-component regulatory system

Colistin resistance is rare in Acinetobacter baumannii, and little is known about its mechanism. We investigated the role of PmrCAB in this trait, using (i) resistant and susceptible clinical strains, (ii) laboratory-selected mutants of the type strain ATCC 19606 and of the clinical isolate ABRIM, and (iii) a susceptible/resistant pair of isogenic clinical isolates, Ab15/133 and Ab15/132, isolated from the same patient. pmrAB sequences in all the colistin-susceptible isolates were identical to reference sequences, whereas resistant clinical isolates harbored one or two amino acid replacements variously located in PmrB. Single substitutions in PmrB were also found in resistant mutants of strains ATCC 19606 and ABRIM and in the resistant clinical isolate Ab15/132. No mutations in PmrA or PmrC were found. Reverse transcriptase (RT)-PCR identified increased expression of pmrA (4- to 13-fold), pmrB (2- to 7-fold), and pmrC (1- to 3-fold) in resistant versus susceptible organisms. Matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectrometry showed the addition of phosphoethanolamine to the hepta-acylated form of lipid A in the resistant variants and in strain ATCC 19606 grown under low-Mg(2+) induction conditions. pmrB gene knockout mutants of the colistin-resistant ATCC 19606 derivative showed >100-fold increased susceptibility to colistin and 5-fold decreased expression of pmrC; they also lacked the addition of phosphoethanolamine to lipid A. We conclude that the development of a moderate level of colistin resistance in A. baumannii requires distinct genetic events, including (i) at least one point mutation in pmrB, (ii) upregulation of pmrAB, and (iii) expression of pmrC, which lead to addition of phosphoethanolamine to lipid A.

Effects of gender and seasonal variation on the prevalence of bacterial septicemia among young children in benin city, Nigeria

Aim

To determine the effects of gender and seasonal variations on the prevalence of bacterial septicaemia among children 5 years and younger, and to identify the bacterial agents responsible for septicaemia and their antibiotic susceptibility profiles.

Methods

Blood was collected from 1,724 children (967 males and 757 females) aged 1 day to 5 years with clinical signs and symptoms of septicaemia. This study was carried out from 1 January to 31 December 2007 at the University of Benin Teaching Hospital, Benin City, Nigeria. The blood samples were processed to diagnose bacterial septicaemia. Bacterial isolates were identified and susceptibility test was performed using standard techniques.

Results

An overall prevalence of 22.10% of confirmed bacterial septicaemia was observed in this study. Generally, gender and seasonal variations did not significantly affect the prevalence of bacterial septicaemia, though females (50.57%) during the dry season had significantly (p < 0.001) higher prevalence than their male counterparts (19.91%). Staphylococcus aureus was the predominant bacterial isolate causing septicaemia in both seasons, while Citrobacter freundii was the least frequent. Pseudomonas aeruginosa was not recovered during the dry season. Most isolates were susceptible to gentamicin and cefuroxime, but only 1.44% of Staphylococcus aureus strains were susceptible to ceftriaxone.

Conclusion

Bacterial septicaemia was observed in 22.1% of children 5 years and younger with clinical signs and symptoms of septicaemia. Seasonal variation did not affect the prevalence. Effect of gender was only noticed in the dry season, where females had a higher prevalence than males. Gentamicin and cefuroxime were the most active antibacterial agents. Rational use of antibiotics is advocated.

Antimicrobial susceptibility of Neisseria gonorrhoeae strains isolated in 2004-2006 in Bangui, Central African Republic; Yaoundé, Cameroon; Antananarivo, Madagascar; and Ho Chi Minh Ville and Nha Trang, Vietnam

GOAL

To investigate the in vitro antimicrobial susceptibility of Neisseria gonorrhoeae strains isolated in 2004 and 2005 in Bangui, Central African Republic; Yaoundé, Cameroon; Antananarivo, Madagascar; and Ho Chi Minh Ville and Nha Trang, Vietnam.

STUDY DESIGN

Antimicrobial susceptibility testing was performed by both disk diffusion and agar dilution methods according to Clinical and Laboratory Standards Institute (CLSI) recommendations. Minimum inhibitory concentrations (MICs) to 5 antimicrobials (penicillin G, ceftriaxone, ciprofloxacin, spectinomycin, and tetracycline) were determined when feasible. Penicillinase-producing N. gonorrhoeae (PPNG) was analyzed by the paper acidometric method (nitrocefin test).

RESULTS

Thirty N. gonorrhoeae isolates from Bangui could be studied, 79 from Yaoundé, 126 from Antananarivo, 56 from Nha Trang, and 126 from Ho Chi Minh Ville in 2004 and 2005. Unfortunately, because of problems of electricity supply, no strains could be recovered for the determination of MICs in Yaoundé, and only 68 strains could be tested in Antananarivo and 121 in Ho Chi Minh Ville. Patterns of resistance were similar in Antananarivo, Bangui, and Yaoundé but different from those observed in Vietnam. Ciprofloxacin was highly effective in Africa, but nearly all strains in Vietnam were resistant to this drug. Overall, ceftriaxon and spectinomycin were the best antibiotics, with one strain resistant to spectinomycin in Antananrivo and one strain resistant to ceftriaxon in Ho Chi Minh Ville.

CONCLUSIONS

Ciprofloxacin remains highly efficient in Madagascar and Central Africa, ceftriaxone and spectinomycin should be used as the first-line antimicrobial agents in treating gonorrhea in Vietnam.

Meticillin-resistant Staphylococcus aureus carriage among district nurse patients and medical admissions in a UK district

We studied the prevalence of meticillin-resistant Staphylococcus aureus (MRSA) carriage in two defined community populations and assessed risk factors associated with MRSA colonization. The study was designed as a population prevalence survey and was carried out in the medical assessment unit (MAU) of the local hospital and the district nurse patient (DNP) population in Huntingdonshire. In all, 162 participants were recruited, 91 were from MAU and 71 from the DNP population. MRSA was found in 21.1% [confidence interval (CI): 11.6-30.4] of the DNP study population and 6.6% (CI 1.5-11.7) of the MAU study population. Factors found to be significantly associated with MRSA colonization were age (76.6 years, P=0.008), presence of wound/ulcer (P=0.012), hospital admission in the past year (P=0.017), past history of MRSA (P<0.001), and antibiotic use in the preceding six months (P=0.016). The only independent predictor for MRSA colonization was found to be past history of MRSA (adjusted odds ratio: 8.53; CI: 2.11-34.43; P=0.003). The DNP population are a significant reservoir for MRSA in the community and policies on screening high-risk patients need to reflect this.

Hemolytic uremic syndrome associated with invasive pneumococcal disease: the United kingdom experience

OBJECTIVE

To describe the presentation, management, and outcome of 43 cases of pneumococcal-associated hemolytic uremic syndrome (P-HUS). An increased incidence of P-HUS has been noted in the United Kingdom between January 1998 and May 2005.

STUDY DESIGN

Cases with microangiopathic hemolytic anemia (Hb <10 g/dL with fragmented RBCs), thrombocytopenia (platelet count < 130 x 10(9)/L), acute renal impairment with oliguria and elevated plasma creatinine for age, confirmed or suspected pneumococcal infection and/or T-activation were included.

RESULTS

The median age at presentation was 13 months (range, 5-39 months). Pneumococcus was identified in 34 of 43 cases; T-activation was identified in 36 of 37 cases. Twelve strains were serotyped: serotypes 3 (n = 2), 6A (n = 2), 12F (n = 1), 14 (n = 1), 19A (n = 6). Empyema was present in 23 of 35 pneumonia cases; 13 cases had confirmed (9) or suspected (4) pneumococcal meningitis; 36 cases required dialysis (median, 10 days; range, 2-240 days). The mortality rate was 11%, comprising 3 cases of meningitis, 1 case of sepsis and 1 case of pulmonary embolism at 8 months follow up while on dialysis. Follow-up data were available for 35 of 38 patients who survived (median follow-up period, 9 months; range, 1-63 months); of these, 10 patients had renal dysfunction, 1 patient was dialysis-dependent, 5 patients had hypertension and 8 patients had at least 1+ proteinuria on urinalysis.

CONCLUSION

P-HUS has increased compared with historic surveys (0/288 in 1985-1988; 8/413 in 1997-2001, 43/315 in 1998-May 2005). Early mortality remains high (8-fold that of VTEC-induced HUS). Ten of 12 strains identified would not be covered by the PCV7 vaccine.

Concentrations in plasma, epithelial lining fluid, alveolar macrophages and bronchial mucosa after a single intravenous dose of 1.6 mg/kg of iclaprim (AR-100) in healthy men

OBJECTIVES

A validated microbiological assay was used to measure concentrations of iclaprim (AR-100) in plasma, bronchial mucosa (BM), alveolar macrophages (AM) and epithelial lining fluid (ELF) after a single 1.6 mg/kg intravenous 60 min iv infusion of iclaprim.

METHODS

Male volunteers were randomly allocated to three nominal sampling time intervals 1-2 h (Group A), 3-4 h (Group B) and 5.5-7.0 h (Group C) after the start of the drug infusion.

RESULTS

Mean iclaprim concentrations in plasma, BM, AM and ELF, respectively, were for Group A 0.59 mg/L (SD 0.18), 0.51 mg/kg (SD 0.17), 24.51 mg/L (SD 21.22) and 12.61 mg/L (SD 7.33); Group B 0.24 mg/L (SD 0.05), 0.35 mg/kg (SD 0.17), 7.16 mg/L (SD 1.91) and 6.38 mg/L (SD 5.17); and Group C 0.14 mg/L (SD 0.05), no detectable level in BM, 5.28 mg/L (SD 2.30) and 2.66 mg/L (SD 2.08).

CONCLUSIONS

Iclaprim concentrations in ELF and AM exceeded the MIC(90) for penicillin-susceptible Streptococcus pneumoniae (MIC90 0.06 mg/L), penicillin-intermediate S. pneumoniae (MIC90 2 mg/L), penicillin-resistant S. pneumoniae (MIC90 4 mg/L) for 7, 7 and 4 h, respectively, and Chlamydia pneumoniae (MIC90 0.5 mg/L) for 7 h. Mean iclaprim concentrations in ELF exceeded the MIC90 for Haemophilus influenzae (MIC90 4 mg/L) and Moraxella catarrhalis (MIC90 8 mg/L) for up to 4 and 2 h, respectively; in AM the MIC90 was exceeded for up to 7 h. Furthermore, the MIC90 for methicillin-resistant Staphylococcus aureus of 0.12 mg/L was exceeded at all sites for up to 7 h. These data suggest that iclaprim reaches lung concentrations that should be effective in the treatment of community-acquired pneumonia.

Antimicrobial resistance in non-typhoidal salmonellas from humans in Northern Ireland, 2001-2003: standardization needed for better epidemiological monitoring

This study investigated the identification and antimicrobial susceptibility testing of Salmonella isolates in Northern Ireland during 2001-2003. All six participating hospital laboratories used similar methods. Identification and antimicrobial resistance of human enteric (n=897) Salmonella isolates were analysed by retrospective collation of laboratory records. Resistance of human Salmonella isolates to nalidixic acid was 16% but resistance to ciprofloxacin or cefotaxime was rare (<1%). Minor inter-laboratory variations in sensitivity testing practices make it difficult to compare antimicrobial sensitivity results reliably and also to monitor for epidemic clones such as S. Typhimurium DT104 with the ACSSuT resistance pattern. The outcome of this study was the adoption of a standardized regional approach to the isolation of salmonella antimicrobial resistance. This should improve epidemiological monitoring of epidemic clones and assure optimum treatment options are available. In cases of treatment failure, MICs to third-generation cephalosporins and ciprofloxacin should be determined.

Development of extended-spectrum activity in TEM beta-lactamases in hyper-mutable, mutS Escherichia coli

TEM-1 and TEM(pUC19)beta-lactamases can gain activity against ceftazidime and other expanded-spectrum cephalosporins via point mutation. The frequency of emergent resistance to ceftazidime at 4 x MIC was elevated >or= 250-fold in hyper-mutable, MutS-deficient Escherichia coli harbouring these beta-lactamase genes on high- or low-copy plasmids. Moreover, although ceftazidime-resistant mutants, or those with reduced susceptibility, were selected in both the wild-type and mutS hosts, many more mutants in the mutS host showed ceftazidimase-type extended-spectrum beta-lactamase (ESBL) activity. This correlated with a G-A point mutation at position 484 in the bla(TEM-1) and bla(TEM-pUC19) genes, conferring the Arg164His amino-acid substitution found in the TEM-29 ESBL. Non-ESBL mutants lacked changes in bla(TEM).

Development of high-level ceftazidime resistance via single-base substitutions of blaCTX-M-3 in hyper-mutable Escherichia coli

Mutations can increase the ceftazidimase activity of CTX-M-3 beta-lactamase, as seen with its widespread variant CTX-M-15. This study compared the frequencies of emerging ceftazidime resistance in isogenic wild-type and hyper-mutable mutS CTX-M-3-producing Escherichia coli strains, and sequenced the mutant bla(CTX-M) alleles selected. Ceftazidime resistance emerged more readily in the hyper-mutable background than in the wild-type strain. All selected CTX-M mutants, in both the wild-type and the mutS derivatives, had single amino-acid changes at position 167, including a novel Pro167Gln substitution. These data emphasise the potential for further diversification of CTX-M enzymes.

Guidelines for the laboratory diagnosis and susceptibility testing of methicillin-resistant Staphylococcus aureus (MRSA)

These evidence-based guidelines have been produced after a literature review of the laboratory diagnosis and susceptibility testing of methicillin-resistant Staphylococcus aureus (MRSA). We have considered the detection of MRSA in screening samples and the detection of reduced susceptibility to glycopeptides in S. aureus. Recommendations are given for the identification of S. aureus and for suitable methods of susceptibility testing and screening for MRSA and for S. aureus with reduced susceptibility to glycopeptides. These guidelines indicate what tests should be used but not when the tests are applicable, as aspects of this are dealt with in guidelines on control of MRSA. There are currently several developments in screening media and molecular methods. It is likely that some of our recommendations will require modification as the new methods become available.

Effect of medium type, age and aeration on the MICs of tigecycline and classical tetracyclines

BACKGROUND

Tigecycline is a minocycline derivative, belonging to a chemical class prone to oxidation and to medium-related effects on susceptibility. We therefore studied the effect of medium type and age on the tigecycline MICs found in broth and on agar by the Clinical Laboratory Standards Institute and British Society for Applied Chemotherapy methods.

METHODS

MICs of tigecycline, minocycline and tetracycline were determined for 96 non-fastidious bacteria and 20 streptococci using Mueller-Hinton broth (MHB), Mueller-Hinton agar (MHA), Iso-Sensitest broth (ISB) and Iso-Sensitest agar (ISA) as: (i) freshly-prepared media; (ii) fresh media but with the antibiotic added 1 day before inoculation and (iii) media stored for 7 days before antibiotic addition and use.

RESULTS

MICs of tigecycline in fresh MHB were up to two doubling dilutions higher than on or in MHA, ISA or ISB. Media with tigecycline or classical tetracyclines added a day before use gave raised MICs, though rarely by more than one dilution. MICs of tigecycline (less so classical tetracyclines) were increased in 7-day-old MHB or ISB, even though the antibiotic was freshly added. This latter effect was greatest for the most susceptible strains and was absent or much reduced for organisms with MICs > or = 8 mg/L; it did not occur in the corresponding agar dilution tests. Addition of blood to MHB largely abrogated the effect, as did steaming the broth before adding the antibiotic.

CONCLUSIONS

The raised MICs of tigecycline in aged broth probably reflect inactivation by dissolved oxygen. This accords with the lack of any MIC increase in newly-steamed (i.e. degassed) MHB or on aged agar (which is melted at 100 degrees C before use). Blood, which also abrogated the effect, may increase reducing capacity, protecting the tigecycline. At a practical level, broth MIC determinations for tigecycline should always employ fresh media.

Molecular epidemiology of antimicrobial-resistant commensal Escherichia coli strains in a cohort of newborn calves

Pulsed-field gel electrophoresis (PFGE) was used to investigate the dissemination and diversity of ampicillin-resistant (Amp(r)) and nalidixic acid-resistant (Nal(r)) commensal Escherichia coli strains in a cohort of 48 newborn calves. Calves were sampled weekly from birth for up to 21 weeks and a single resistant isolate selected from positive samples for genotyping and further phenotypic characterization. The Amp(r) population showed the greatest diversity, with a total of 56 different genotype patterns identified, of which 5 predominated, while the Nal(r) population appeared to be largely clonal, with over 97% of isolates belonging to just two different PFGE patterns. Distinct temporal trends were identified in the distribution of several Amp(r) genotypes across the cohort, with certain patterns predominating at different points in the study. Cumulative recognition of new Amp(r) genotypes within the cohort was biphasic, with a turning point coinciding with the housing of the cohort midway through the study, suggesting that colonizing strains were from an environmental source on the farm. Multiply resistant isolates dominated the collection, with >95% of isolates showing resistance to at least two additional antimicrobials. Carriage of resistance to streptomycin, sulfamethoxazole, and tetracycline was the most common combination, found across several different genotypes, suggesting the possible spread of a common resistance element across multiple strains. The proportion of Amp(r) isolates carrying sulfamethoxazole resistance increased significantly over the study period (P < 0.05), coinciding with a decline in the most common genotype pattern. These data indicate that calves were colonized by a succession of multiply resistant strains, with a probable environmental source, that disseminated through the cohort over time.

High prevalence of the plasmid-mediated quinolone resistance determinant qnrA in multidrug-resistant Enterobacteriaceae from blood cultures in Liverpool, UK

OBJECTIVES

To determine the prevalence of the plasmid-mediated quinolone resistance qnrA gene in a selected collection of blood culture isolates of Enterobacteriaceae resistant to both ciprofloxacin and cefotaxime.

METHODS

Over a 29 month period, a total of 47 non-repetitive isolates of Enterobacteriaceae resistant to both ciprofloxacin and cefotaxime were identified. Isolates were screened for the presence of the qnrA gene, class I integrons and bla(ESBL) by PCR. Transferability was examined by conjugation with the sodium azide-resistant Escherichia coli J53. All qnrA-positive isolates were examined for DNA-relatedness by PFGE.

RESULTS

A total of 15 of the 47 test isolates (32%) were positive for the qnrA gene, and included single isolates of E. coli and Citrobacter freundii, 4 Klebsiella pneumoniae and 9 Enterobacter cloacae. All 15 qnrA-positive isolates carried class 1 integrons, and 11 the extended-spectrum beta-lactamase gene bla(SHV-12). By PFGE two K. pneumoniae and three E. cloacae, respectively, were considered clonally but not temporally related. Plasmid transfer of quinolone resistance was only achieved with single isolates of K. pneumoniae and E. cloacae. Both plasmids carried class 1 integrons with a pSAL-1-like gene cassette arrangement intl1-aadA2-qacEDelta-sul1.

CONCLUSIONS

In this selected group of ciprofloxacin- and cefotaxime-resistant bacteria, carriage of the qnrA gene was high (32%). This compares with <2.0% as demonstrated in worldwide studies of laboratory collections of ciprofloxacin-resistant bacteria. The majority of qnrA-positive isolates in our study originated from high-dependency care units within our hospital, but were shown not to be clonal by PFGE. This is the first report of qnrA-positive Enterobacteriaceae in the United Kingdom.

Résistance de bas niveau aux fluoroquinolones par surexpression de l'efflux chez Pseudomonas aeruginosa : conséquences thérapeutiques et détection au laboratoire

The aim of this study was (i) to assess the impact of stable overproduction of efflux systems MexAB-OprM and MexXY-OprM on the bacteriostatic activities of fluoroquinolones in clinical Pseudomonas aeruginosa strains and (ii) to find a convenient test for screening isolates with a low level resistance to fluoroquinolones. The minimal inhibitory concentrations (MICs) of ciprofloxacin and levofloxacin were determined for clinical isolates of P. aeruginosa overexpressing MexAB-OprM or MexXY-OprM. Efflux pumps derepression was associated with a modest two- to fourfold increase in resistance to the tested fluoroquinolones. Clinical significance of low level resistance conferred by the efflux mechanism was evaluated with a Monte Carlo simulation with various fluoroquinolone regimens. With this model, low levels of resistance to ciprofloxacin (MIC > or =0.25 mg/L) or levofloxacin (MIC > or =1 mg/L) such as those due to overproduced MexAB-OprM or MexXY-OprM were predicted to result in poor clinical outcomes. Altogether these data strongly suggest that when derepressed MexAB-OprM or MexXY-OprM provides P. aeruginosa with a resistance that may be sufficient to impair the efficacy of single therapy with highly potent fluoroquinolones such as ciprofloxacin and levofloxacin. Routine detection of clinical strains that displayed low-level resistance to fluoroquinolones with a Mueller Hinton agar containing 0.20 mg/L of ciprofloxacin will help clinician in his therapeutical choice.

Susceptibility to moxifloxacin of pneumococci isolated in English hospitals participating in the European Antimicrobial Resistance Surveillance System (EARSS) in 2003

Susceptibility to moxifloxacin, penicillin and erythromycin was determined for 592 invasive Streptococcus pneumoniae collected from 20 English hospitals participating in the European Antimicrobial Resistance Surveillance System (EARSS) during 2003. Resistance to moxifloxacin, penicillin and erythromycin was observed in 0.8%, 5.4% and 13% of the isolates, respectively. These results show that the large majority of pneumococci were susceptible to moxifloxacin in 2003, the year when it was licensed for clinical use in the UK.

The relationship between primary care antibiotic prescribing and bacterial resistance in adults in the community: a controlled observational study using individual patient data

OBJECTIVES

To examine the relationship between primary care prescribed antibiotics and the development of antibiotic resistance in perineal flora contaminating unselected urinary isolates from a large sample of asymptomatic adults representative of the general community.

PATIENTS AND METHODS

Escherichia coli isolates contaminating urine samples were obtained from asymptomatic adults aged >16 years registered with general practices in the former Avon and Gloucestershire health authority areas. Data on antibiotic exposure during the 12 months prior to providing the urine samples were collected from the primary care electronic and paper medical records. The main outcome measure was resistance to amoxicillin or trimethoprim or both.

RESULTS

Two thousand nine hundred and forty-three adults submitted urine samples. Susceptibility among E. coli isolates and antibiotic prescribing data were available from 618 patients. We found no evidence of an association between resistance and patients' exposure to any antibiotic prescribed in primary care in the previous 12 months [adjusted odds ratio (OR) 1.12, 95% confidence interval 0.77-1.65, P = 0.52]. Secondary analyses demonstrated greater resistance in patients exposed to antibiotics within 2 months (adjusted OR 1.95, 1.08-3.49, P = 0.03), a dose-response relationship to increasing exposure to trimethoprim in the previous 12 months (adjusted OR 1.01, 1.01-1.02, P = 0.001) and that individuals who had been prescribed any beta-lactam antibiotic in the previous 12 months had amoxicillin MICs more than twice (adjusted 95% CI 1.23-3.31, P = 0.009) that of those who had not been prescribed any beta-lactams.

CONCLUSIONS

Whether or not adults receive a prescription for any antibiotic during a 12 month period does not appear to influence the antimicrobial resistance of perineal flora. However, the temporal and dose-response relationships found may be suggestive of a causative association and should be the focus of further research.

Bacteriostatic and bactericidal activities of eight fluoroquinolones against MexAB-OprM-overproducing clinical strains of Pseudomonas aeruginosa

OBJECTIVES

To assess the impact of stable overproduction of efflux system MexAB-OprM on the bacteriostatic and bactericidal activities of fluoroquinolones against clinical Pseudomonas aeruginosa strains.

METHODS

The minimal inhibitory concentrations (MICs) and the minimal bactericidal concentrations (MBCs) of eight fluoroquinolones (pefloxacin, norfloxacin, ofloxacin, moxifloxacin, levofloxacin, ciprofloxacin, trovafloxacin and grepafloxacin) were determined for nine post-therapy resistant isolates of P. aeruginosa overexpressing MexAB-OprM. Clinical significance of low-level resistance conferred by the efflux mechanism was evaluated with a Monte Carlo simulation.

RESULTS

Compared with their pre-therapy susceptible counterparts, seven out of the nine post-therapy efflux mutants exhibited a modest two- to eight-fold increase in resistance to all the fluoroquinolones tested. Interestingly, stronger variations in resistance (up to 64-fold) were observed in two other mutants, one of which had acquired a GyrB target mutation in addition to efflux under chemotherapy. Time-kill experiments showed that MexAB-OprM up-regulation did not confer tolerance to fluoroquinolones as the ratio of MBC to MIC was less than 4 for most of the strains. To gain an insight into the clinical significance of resistance conferred by MexAB-OprM, a Monte Carlo simulation was conducted with various fluoroquinolone regimens. With this model, low levels of resistance to ciprofloxacin (MIC > or = 0.25 mg/L) or levofloxacin (MIC > or = 1 mg/L), such as those due to overproduced MexAB-OprM, were predicted to result in poor clinical outcomes.

CONCLUSIONS

Altogether, these data strongly suggest that when derepressed, MexAB-OprM provides P. aeruginosa with a resistance that may be sufficient to impair the efficacy of single therapy with highly potent fluoroquinolones, such as ciprofloxacin and ofloxacin.

Antimicrobial susceptibility of community-acquired respiratory tract pathogens in the UK during 2002/3 determined locally and centrally by BSAC methods

OBJECTIVES

To determine the antimicrobial susceptibility of Haemophilus influenzae, Moraxella catarrhalis and Streptococcus pneumoniae causing community-acquired lower respiratory tract infection in the UK during 2002/2003 and to compare susceptibilities determined locally by disc diffusion with agar dilution MICs determined at a central laboratory.

METHODS

H. influenzae, M. catarrhalis and S. pneumoniae were isolated in 30 laboratories and susceptibility determined locally by the BSAC standardized disc diffusion method. At a central laboratory, isolates were re-identified, tested for beta-lactamase production (H. influenzae and M. catarrhalis only) and MICs determined using the BSAC agar dilution method.

RESULTS

Five hundred and eighty-one H. influenzae, 269 M. catarrhalis and 519 S. pneumoniae were collected. Over 93% of M. catarrhalis and nearly 15% of H. influenzae were beta-lactamase positive rendering these sub-populations resistant to aminopenicillins. Overall, the antibacterial susceptibility rates for the isolates were high. However, macrolides showed poor activity against H. influenzae (0.86-1.38% susceptible by disc or MIC methods) and, compared with other antimicrobials, against S. pneumoniae (approximately 88% susceptible). Between 84% and 95% of H. influenzae, M. catarrhalis and S. pneumoniae were susceptible to cefuroxime but all isolates were susceptible to cefotaxime. Eighty-five percent of H. influenzae were susceptible to trimethoprim. The fluoroquinolones were very active against the isolates, with moxifloxacin showing lower MICs than levofloxacin against S. pneumoniae. Susceptibility determined locally by disc diffusion was in general agreement with that determined centrally by agar dilution MIC testing. However, there was one inconsistency with H. influenzae where disc diffusion indicated 22.9% and 46.8% resistance to clarithromycin and erythromycin, respectively but by MIC, only 0.9% and 6.9% were resistant, respectively.

CONCLUSIONS

Rates of resistance within community-acquired respiratory tract isolates were relatively low in the UK, in agreement with other studies. Moxifloxacin was the only antibacterial with over 99% isolates susceptible for each of the three pathogens investigated where breakpoints are available. The comparison between disc susceptibility testing and MIC determination using BSAC methods indicated generally good correlation but has highlighted a methodological problem with macrolides against H. influenzae in particular.

Outbreak of carbapenem-resistant Pseudomonas aeruginosa producing VIM-8, a novel metallo-beta-lactamase, in a tertiary care center in Cali, Colombia

The prevalence of imipenem resistance among Pseudomonas aeruginosa isolates at a 195-bed tertiary care medical center in Cali, Colombia, rose from 2% in 1996 to 28% in 1997 and to over 40% in 2003. Many isolates showed high-level multiresistance, and phenotypic characterization suggested the spread of a predominant strain with minor variants. Sixty-six resistant isolates collected between February 1999 and July 2003 from hospitalized patients (n = 54) and environmental samples (n = 12) were subjected to a fuller analysis. Genetic fingerprints were compared by pulsed-field gel electrophoresis (PFGE) of SpeI-digested genomic DNA, and bla(IMP) and bla(VIM) genes were sought by PCR. PFGE and serotyping indicated that 52 of the 66 isolates belonged to a single strain, with 82% similarity; the PFGE pattern for this organism was designated pattern A. Two further pairs of isolates represented single strains; the remaining nine isolates were unique, and in the case of one isolate, no satisfactory PFGE profile could be obtained. The pattern A isolates were mostly of serotype O12 and were highly resistant to imipenem (MICs, 32 to >256 microg/ml), with this resistance decreased eightfold or more in the presence of EDTA. They yielded amplicons with bla(VIM)-specific primers, and sequencing of DNA from a representative isolate revealed bla(VIM-8), a novel allele with three polymorphisms compared with the sequence of bla(VIM-2). Two of these nucleotide changes were silent, but the third determined a Thr139Ala substitution. Only 4 of 13 resistant isolates (2 clinical isolates and 2 environmental isolates) assigned to other PFGE types carried bla(VIM) alleles, whereas the others were less multiresistant and mostly had lower levels of imipenem resistance (MICs, < or =32 microg/ml) which was not significantly reduced by EDTA. No bla(IMP) alleles were detected. During 2003, when the environmental study was undertaken, serotype O12 isolates with bla(VIM) were recovered from sinks and stethoscopes in the most-affected units, although not from the hands of staff; the problem declined once these reservoirs were disinfected and hygienic precautions were reinforced.

Surveillance of linezolid resistance in Germany, 2001–2002

A surveillance study was performed throughout Germany from November 2001 to June 2002 to assess the prevalence of linezolid-resistant isolates among Gram-positive bacteria from routine susceptibility data and to compare the in-vitro activity of linezolid to that of other antibacterial agents. Each of 86 laboratories provided routine susceptibility data for 100 consecutive isolates. Most laboratories (c. 60%) used the disk diffusion test. Laboratories were also requested to send a representative sample of their isolates, as well as all isolates reported as intermediate or resistant to linezolid, to a reference laboratory for MIC determination. Susceptibility data for 8594 isolates were evaluated. Sites of infection were skin and soft tissue (29.9%), upper and lower respiratory tract (19.1%), foreign body or catheter (10.5%), or urinary tract (9.8%). Routine linezolid susceptibility data were reported for 6433 isolates. The prevalence of linezolid resistance, as reported to the clinician, was 0.4% in Staphylococcus aureus, 0.3% in Staphylococcus epidermidis, 2.9% in Enterococcus faecalis, 2.3% in Enterococcus faecium, 1.4% in Streptococcus pyogenes and 2.9% in Streptococcus agalactiae. Linezolid resistance was not detected in Streptococcus pneumoniae or in viridans group streptococci. Sixty-nine of 115 isolates reported as intermediate or resistant to linezolid were retested, but none was resistant to linezolid. Linezolid exhibited excellent in-vitro activity against representative isolates of the six most frequently encountered species (MIC90, 1-2 mg/L). The prevalence of resistance to linezolid was very low in Germany. Organisms reported as linezolid-resistant should be retested, either in the same laboratory with an alternative method or in a reference laboratory.

Resistance determinants in strains of Clostridium difficile from two geographically distinct populations

Ninety-three clinical isolates of Clostridium difficile, comprising 65 from Royal Gwent Hospital, Newport and 28 from Southmead Hospital, Bristol were examined to determine the prevalence of genes coding for macrolide resistance and to explore differences in susceptibility patterns. Antibiogram testing produced similar results for both sets of strains with respect to amoxicillin, tetracycline, erythromycin and cefotaxime. Results differed for rifampicin, where 53% of the Bristol isolates were resistant, compared with 3% of the Newport isolates. Clindamycin disc susceptibility testing produced similar resistance rates. However, clindamycin MIC determinations revealed that 53% of the Bristol strains exhibited high-level resistance (MIC > 256 mg/L), whereas strains from Newport had clindamycin MICs ranging from 0.25 to 3mg/L. erm (B) was present in 15 of the strains from Bristol and in none of the Newport strains. erm (F) and erm (Q) were not detected in either population. The two geographically distinct populations of C. difficile differed considerably in their susceptibility to antibiotics. The possibility that C. difficile may serve as a conservator for resistant determinants subsequent to exposure to antimicrobial agents, has important implications for infection control.

Community and hospital spread of Escherichia coli producing CTX-M extended-spectrum β-lactamases in the UK

OBJECTIVES

During 2003, the Health Protection Agency's Antibiotic Resistance Monitoring and Reference Laboratory began to receive isolates of Escherichia coli for confirmation of extended-spectrum beta-lactamase production with a phenotype implying a CTX-M-type beta-lactamase, i.e. MICs of cefotaxime > or = 8-fold higher than MICs of ceftazidime. Many were referred as being from community patients. We examined 291 CTX-M-producing isolates from the UK and investigated the genetic basis of their phenotype.

METHODS

PCR was used to detect alleles encoding CTX-M enzymes and to assign these to their blaCTX-M phylogenetic groups. Selected alleles were sequenced. Producers were compared by analysis of banding patterns generated by pulsed-field gel electrophoresis of XbaI-digested genomic DNA. MICs were determined by an agar dilution method or by Etest.

RESULTS

Of 291 CTX-M-producing E. coli isolates studied from 42 UK centres, 70 (24%) were reportedly from community patients, many of whom had only limited recent hospital contact. Community isolates were referred by 12 centres. Two hundred and seventy-nine (95.9%) producers contained genes encoding group 1 CTX-M enzymes and 12 contained blaCTX-M-9-like alleles. An epidemic CTX-M-15-producing strain was identified, with 110 community and inpatient isolates referred from six centres. Representatives of four other major strains also produced CTX-M-15, as did several sporadic isolates examined. Most producers were multi-resistant to fluoroquinolones, trimethoprim, tetracycline and aminoglycosides as well as to non-carbapenem beta-lactams.

CONCLUSIONS

CTX-M-producing E. coli are a rapidly developing problem in the UK, with CTX-M-15 particularly common. The diversity of producers and geographical scatter of referring laboratories indicates wide dissemination of blaCTX-M genes. Because of the public health implications, including for the treatment of community-acquired urinary tract infections, the spread of these strains--and CTX-M-15 beta-lactamase in particular--merits close monitoring.

Activity of dalbavancin against staphylococci and streptococci, assessed by BSAC and NCCLS agar dilution methods

BACKGROUND

Dalbavancin is a long-half-life (9-12 days) glycopeptide, now in Phase 3 development. Its pharmacokinetics may facilitate home intravenous therapy, early discharge and long prophylaxis.

METHODS

Dalbavancin and comparators were tested in vitro against staphylococci and streptococci to determine (i) activity and (ii) the comparability of agar dilution MICs by the BSAC and the NCCLS methods. The test panels comprised 92-93 isolates each of Staphylococcus aureus, coagulase-negative staphylococci (CoNS) and 'viridans' streptococci, chosen for epidemiological diversity and to over-represent strains resistant to conventional agents, including teicoplanin.

RESULTS

Dalbavancin MICs by the BSAC and NCCLS methods generally were identical, or else those by the BSAC method were two-fold lower. In both cases the MIC distributions of dalbavancin within species groups were unimodal, with peaks at 0.25, 0.12/0.25 and 0.12 mg/L for S. aureus, CoNS and viridans streptococci, respectively. MIC differences between the BSAC and NCCLS methods were similarly small for other glycopeptides and, generally, non-glycopeptides. Dalbavancin MICs were mostly two- to 16-fold below those of vancomycin and dalbavancin-like vancomycin-remained highly active against teicoplanin-non-susceptible staphylococci.

CONCLUSIONS

Dalbavancin has good activity versus streptococci and staphylococci, including teicoplanin-resistant strains. MICs by BSAC and NCCLS agar dilution methods were comparable to each other; slightly lower MIC values, nevertheless, have been recorded by broth microdilution.