Stenotrophomonas (Xanthomonas) maltophilia is inherently resistant to multiple antimicrobial agents. In order to investigate the in vitro potential of combinations of antimicrobial agents, we obtained 230 epidemiologically unrelated clinical isolates from seven hospitals across Canada and from Northwestern Memorial Hospital in Chicago. Ticarcillin-clavulanate combined with ciprofloxacin or trimethoprim-sulfamethoxazole were assayed for synergy against 31 ticarcillin-resistant strains of S. maltophilia by using microtiter checkerboard panels and against 20 strains by using time-kill methodology. The combination of ciprofloxacin with ceftazidime was also evaluated by time-kill studies. Ticarcillin-clavulanate plus trimethoprim-sulfamethoxazole demonstrated synergy by checkerboard panels, with fractional inhibitory concentration indices ranging from 0.033 to 0.49, and by time-kill studies for all 20 strains tested. Synergy between ticarcillin-clavulanate plus ciprofloxacin was found by the checkerboard method for 24 of 31 strains (77%), with fractional inhibitory concentration indices ranging from 0.188 to 0.75. A correlation between synergy by the checkerboard method and the reference time-kill study method was not observed for ticarcillin-clavulanate plus ciprofloxacin, with results for 3 of 10 strains being nonconcordant. Synergy with both ticarcillin-clavulanate plus ciprofloxacin and ceftazidime plus ciprofloxacin by the time-kill method was found to correlate with ciprofloxacin MICs of <32 g/ml and zone diameters of >15 mm on Mueller-Hinton agar. Evaluation of these combinations in vivo may be warranted.Stenotrophomonas (Xanthomonas) maltophilia is an aerobic, gram-negative bacillus which has been isolated from humans, animals, food, pharmaceuticals, and various environmental sources. Because of the low level of pathogenicity and limited invasiveness of S. maltophilia, serious community-acquired infection is infrequent (12, 18). However, significant morbidity and mortality are widely recognized among neutropenic, immunocompromised, and debilitated patients, in whom this organism may become disseminated and result in life-threatening disease (12,18,23,27,37).The antimicrobial resistance of S. maltophilia is attributed to low outer membrane permeability (9,14,15,20,21,39) and the unusual production of multiple chromosomally mediated, broad-spectrum ␤-lactamases, among which are L1 and L2 (1,10,14,15,29,30,32,33). L1 and related ␤-lactamases are group 3 metallopenicillinases and carbapenemases (1,7,15,20,30,33), while L2 and related ␤-lactamases are group 2e cephalosporinases capable of hydrolyzing penicillins and monobactams (1,7,15,20,29,32). All ␤-lactamases are induced synchronously, indicating an apparent overlap of regulatory systems (1,22,30).In vitro susceptibility testing of S. maltophilia is problematic, and results obtained by such tests should be interpreted with caution (1,6,10,13,16,21,38). The National Committee for Clinical Laboratory Standards (NCCLS) (26) currently recommends broth or agar dilu...

The incidence of methicillin-resistant Staphylococcus aureus (MRSA) has been increasing in many Canadian hospitals over the past few years. Some strains may be considered 'epidemic', in that they are clinically or epidemiologically significant, and have been identified in patients from multiple hospitals and geographic regions across the country. This paper describes phenotypic and genotypic characteristics of four epidemic MRSA strains in Canada and proposes standardized nomenclature. Key Words: Methicillin-resistant Staphylococcus aureus Caractérisation et suggestion de nomenclature des souches épidémiques de MRSA au CanadaRésumé : L'incidence des infections causées par des souches de Staphylococcus aureus méthicillino-résitantes (ou MRSA, pour methicillin-resistant Staphylococcus aureus) est à la hausse dans de nombreux hôpitaux canadiens depuis quelques années. Certaines souches seraient même considérées « épidémiques », en ce sens qu'elles sont importantes sur les plans clinique ou épi-démiologique et qu'elles ont été signalées chez des patients de plusieurs hôpitaux de différentes régions du pays. Cet article porte sur les caractéristiques de quatre souches épidémiques de MRSA sur le plan du phénotype et du génotype signalées au Canada et propose une nomenclature standardisée.

Objective: Several mechanisms account for carbapenem resistance in Pseudomonas (P) aeruginosa which is an emerging problem at a tertiary care hospital (TCH) in Jamaica. The observed pattern of carbapenem resistance that results from efflux mechanisms is unique because it is specific to meropenem (MEM). An investigation of efflux as a mechanism of carbapenem resistance was needed as the information obtained could inform therapeutic and infection control strategies. Methods: At the Microbiology Laboratory of a TCH in Jamaica, from May 2009 to March 2011, of 105 multidrug-resistant Gram-negative bacilli isolated from clinical specimens submitted for routine identification and susceptibility testing, all the MEM-resistant P aeruginosa isolates (a total of 10) were selected. They were tested for efflux using the efflux inhibitor phenylalanine-arginine-β-naphthylamide (PAβN) in a method described by Giske et al in 2008. Results: This study detected evidence of MEM efflux in 80% of MEM-resistant P aeruginosa implicated in nosocomial infections at this TCH in Jamaica, using the PAβN inhibition assay. Meropenem-efflux-positive isolates belonged to two unrelated chromosomal lineages. Conclusion: These results underscored the need for improved surveillance and control to prevent this mechanism from emerging in further P aeruginosa strains.

No abstract

Objective: The global problem of resistance to carbapenem antibiotics, through the production of carbapenemases by clinically significant bacteria, continues to increase while options for antibiotic therapy remain limited. It is important to determine the mechanism of carbapenem resistance in the multidrug resistant (MDR) Acinetobacter spp. isolated at a tertiary care hospital, Jamaica (TCHJ) because of the implications for therapy which is the goal of this study. Methodology: 82 MDR Acinetobacter spp collected at a TCHJ were identified as potential carbapenemase producers during routine susceptibility testing for a one year period from May 2009 to April 2010. These isolates were subjected to phenotypic and genotypic tests for carbapenemase detection using the modified Hodge test and PCR respectively. Multiplex PCR for OXA-23,-24,-51,-58 was performed and PFGE was used to determine if carbapenemase-positive isolates were related. Results: PCR for OXA-carbapenemases found 13 blaOXA-24, two blaOXA-23 and one blaOXA-58, establishing a prevalence of 19.5%. PFGE results showed that Acinetobacter spp sharing phenotypic and genotypic similarites were clonally related. Conclusions: Carbapenemase production was found to be a cause of antibiotic resistance in MDR Acinetobacter spp. isolates at a TCHJ. These isolates were thought to have been derived from an outbreak or endemic strain whose presence is likely to significantly impact patient management and antibiotic policy.