Correspondence infection control policies and the predominant type of van gene. In our practice, a negative real-time PCR result was used to exclude VRE colonization and all real-time PCR positive cases required confirmation by subculture before aggressive infection control measures were undertaken.
Acknowledgements We thank Goh Hoei Thein, Michelle Tan and Tiong Swee Choo for their technical assistance.
Transparency declarations None to declare.
References
Journal of Antimicrobial Chemotherapy doi:10.1093/jac/dkm139 Advance Access publication 22 May 2007
Providencia stuartii with VIM-1 metallo-b-lactamase V. Miriagou1, L. S. Tzouvelekis2*, K. Flevari3, M. Tsakiri4 and E. E. Douzinas3 1
Laboratory of Bacteriology, Hellenic Pasteur Institute, Athens, Greece; 2Department of Microbiology, Medical School, University of Athens, Athens, Greece; 3Intensive Care Unit, ‘Eugenidion’ General Hospital, Athens, Greece and 4Microbiology Laboratory, ‘Eugenidion’ General Hospital, Athens, Greece Keywords: P. stuartii, carbapenems, resistance, MBLs *Corresponding author. Tel: þ30-210-7462152; Fax: þ30-2107462010; E-mail:
[email protected] Sir, Providencia stuartii is a frequent cause of urinary tract infections in hospitalized and nursing home patients with long-term indwelling urinary catheters. Also, this opportunistic pathogen is occasionally implicated in other types of hospital-acquired infections. Clinical strains of P. stuartii are commonly resistant to aminopenicillins and early generation cephalosporins due to production of an inherent cephalosporinase. Furthermore, they can acquire plasmids encoding class A extended-spectrum b-lactamases (ESBLs) such as TEM, CTX-M and VEB
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1. Young HL, Ballard SA, Roffey P et al. Direct detection of vanB2 using the Roche LightCycler vanA/B detection assay to indicate vancomycin-resistant enterococcal carriage—sensitive but not specific. J Antimicrob Chemother 2007; 59: 809– 10. 2. Koh TH, Hsu LY, Chiu LL et al. Emergence of epidemic clones of vancomycin-resistant Enterococcus faecium in Singapore. J Hosp Infect 2006; 63: 234–6. 3. Ballard SA, Grabsch EA, Johnson PDR et al. Comparison of three PCR primer sets for the identification of vanB gene carriage in feces and correlation with carriage of vancomycin-resistant enterococci: interference by vanB-containing anaerobic bacilli. Antimicrob Agents Chemother 2005; 49: 77– 81.
conferring resistance to newer cephalosporins.1 – 3 In this study, a ceftazidime-resistant strain of P. stuartii producing VIM-1 metallo-b-lactamase (MBL) is described. blaVIM-1 was carried by a self-transferable plasmid. P. stuartii 323/07 was derived from a patient in the ICU of ‘Eugenidion’ General Hospital in Athens. The patient (male, 72 years old) was intubated due to severe ischaemic stroke of the left brain hemisphere and was requiring mechanical ventilation since 10 October 2006. He was transferred to our ICU on 19 October with a lung infection due to aspiration pneumonia. After being stabilized, a new septic event with fever, purulent secretions and haemodynamic instability emerged on 19 January 2007, while on treatment with meropenem and linezolid. Cultures of blood and bronchial secretions yielded both Pseudomonas aeruginosa and Acinetobacter baumannii, and antimicrobial treatment was switched to ceftazidime and colistin with no clinical improvement. A multiresistant but ciprofloxacin-susceptible strain of P. stuartii was isolated from bronchial secretions on 29 January and colistin was replaced by ciprofloxacin. The latter regimen was apparently effective, resulting in a significant clinical improvement within 1 week. MICs of b-lactams were determined by an agar dilution technique. Susceptibility status to non-b-lactams drugs was assessed by a disc diffusion method. P. stuartii 323/07 exhibited resistance or decreased susceptibility to penicillins, penicillin/ inhibitor combinations, ceftazidime and cefotaxime. MICs of carbapenems, aztreonam and cefepime were within the susceptibility range (Table 1). The strain was also resistant to gentamicin, tobramycin, netilmicin, co-trimoxazole, tetracycline and chloramphenicol. Amikacin and fluorinated quinolones were active against P. stuartii 323/07. The strain was negative for ESBL production in the double disc synergy test. Also, addition of either Ro 48-1220 or clavulanic acid did not reduce the MIC of ceftazidime (Table 1), indicating that the observed phenotype was not due to production of an ESBL or a cephalosporinase. However, P. stuartii 323/07 was positive in the double disc test based on synergy between imipenem and EDTA. PCR assays using total bacterial DNA as template and primers specific for blaVIM-1 were positive. Isoelectric focusing of b-lactamases showed that P. stuartii 323/ 07 produced an enzyme with a pI of 5.1, similar to that of VIM-1. A b-lactamase with an apparent pI of 8.5 was also detected. This was probably the chromosomal AmpC of P. stuartii. Conjugal transfer of resistance to b-lactam antibiotics to an Escherichia coli K12 recipient strain highly resistant to rifampicin was carried out in mixed broth cultures and selection on media containing rifampicin and ampicillin. Resistance to b-lactams as well as aminoglycosides and co-trimoxazole was readily transferred at a frequency of 1024 transconjugants per donor cell. E. coli transconjugants were positive for blaVIM-1 by PCR. Agarose gel electrophoresis of plasmid DNA preparations from P. stuartii 323/07 and an E. coli transconjugant indicated transfer of a single plasmid (pPS-v1) of 60 kb that was positive for blaVIM-1 in hybridization experiments performed as described previously.4 PCR mapping was carried out using combinations of oligonucleotide primers specific for the 50 and 30 conserved sequences of class 1 integrons as well as blaVIM-1 and various resistance genes. These experiments showed that blaVIM-1 was the first gene cassette of an integron that also contained—from 50 to 30 —aacA4, dhfrI, aadA and sulI, similar to In-e541 described previously in Klebsiella pneumoniae and E. coli (GenBank accession no. AY339625).5 pPS-v1 belonged to the incompatibility (Inc)
Correspondence Table 1. Antibiotic resistance phenotypes of P. stuartii 323/07 and an E. coli transconjugant clone MICs (mg/L) for Antibiotic Ampicillin Amoxicillin/CLAa Piperacillin Piperacillin/TAZb Ceftazidime Ceftazidime/CLAa Ceftazidime/Ro 48-1220c Cefotaxime Cefepime Aztreonam Imipenem Meropenem
P. stuartii 323/07
E. coli (pPS-v1)
E. coli K12
.128 .128 64 32 64 64 64 32 1 0.25 1 0.5
.128 .128 64 32 .128 — — 64 2 ,0.12 2 0.5
2 1 0.5 0.5 0.25 — — ,0.12 ,0.12 ,0.12 ,0.12 ,0.12
CLA, clavulanic acid (2 mg/L). TAZ, tazobactam (4 mg/L). c Inhibitor at a concentration of 4 mg/L. b
group N as determined by a PCR-based Inc-typing method. It also exhibited a PstI-generated restriction profile similar to that of a group of IncN blaVIM-1-carrying plasmids that have been spread mainly among K. pneumoniae (data not shown).6 The higher resistance levels to various b-lactams, including imipenem, of the E. coli transconjugant clones when compared with P. stuartii 323/07 (Table 1) suggested differences in the production of VIM-1. To validate this hypothesis, hydrolytic activities of bacterial cell extracts against imipenem were determined by spectrophotometry. Extracts from E. coli ( pPS-v1) expressed approximately 5-fold higher activity than P. stuartii 323/07 that was consistent with the b-lactam MIC differences. Additionally, transconjugants were resistant to amikacin, whereas P. stuartii 323/07 appeared susceptible to this drug, probably indicating differences also in the expression of the aacA4 gene cassette. To the best of our knowledge, this is the first description of a P. stuartii strain producing a VIM-type MBL. This finding underscores the ongoing spread of VIM-1 in the flora of Greek hospitals as well as the important role of IncN, blaVIM-1-carrying plasmids in this process.
4. Loli A, Tzouvelekis LS, Tzelepi E et al. Sources of diversity of carbapenem resistance levels in Klebsiella pneumoniae carrying blaVIM-1. J Antimicrob Chemother 2007; 57: 669–72. 5. Miriagou V, Carattoli A, Tzelepi E et al. IS26-associated In4-type integrons forming multiresistant loci in enterobacterial plasmids. Antimicrob Agents Chemother 2005; 49: 3541–3. 6. Carattoli A, Miriagou V, Bertini A et al. Replicon typing of plasmids encoding resistance to b-lactams. Emerg Infect Dis 2006; 12: 1145–8.
Journal of Antimicrobial Chemotherapy doi:10.1093/jac/dkm121 Advance Access publication 4 May 2007
Glutathione-mediated augmentation of b-lactam antibacterial activity against Escherichia coli Manish Goswami and Narendra Jawali* Molecular Biology Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400085, India
Transparency declarations Keywords: antioxidants, ascorbic acid, protection, susceptibility None to declare. *Corresponding author. Tel: þ91-22-25595078; Fax: þ91-2225505326; E-mail:
[email protected]
References 1. Tumbarello M, Citton R, Spanu T et al. ESBL-producing multidrug-resistant Providencia stuartii infections in a university hospital. J Antimicrob Chemother 2004; 53: 277–82. 2. Quinteros M, Radice M, Gardella N et al. Extended-spectrum b-lactamases in Enterobacteriaceae in Buenos Aires, Argentina, public hospitals. Antimicrob Agents Chemother 2003; 47: 2864–7. 3. Aubert D, Naas T, Lartigue M-F et al. Novel genetic structure associated with an extended-spectrum b-lactamase blaVEB gene in a Providencia stuartii clinical isolate from Algeria. Antimicrob Agents Chemother 2005; 49: 3590– 2.
Sir, We have previously established that antioxidants such as glutathione and ascorbic acid protect Escherichia coli against the antibacterial activity of fluoroquinolone and aminoglycoside groups of antibiotics.1,2 However, the mechanism by which the antioxidant-mediated protection is brought about against these two classes of antibiotics is not the same since our data signified that, unlike ciprofloxacin, reduced streptomycin susceptibility of E. coli cells is not due to antioxidant-mediated scavenging of reactive oxygen species.2 Here we report the effect of
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a
