There are currently no standardized phenotypic methods for the screening and detection of AmpC enzymes. This study aimed to evaluate different methods to detect AmpC enzymes in Escherichia coli, Klebsiella spp., and Proteus spp., comparing the results from two disk-based methods and an agar dilution method. AmpC activity was determined for 255 clinical isolates by use of a three-dimensional enzyme assay combined with a multiplex PCR assay for plasmid-borne ampC genes. These results were compared against a disk-based inhibitor assay using various combinations of cefpodoxime and cefoxitin as antibiotic substrates and boronic acid or cloxacillin as an AmpC inhibitor. The presence of enzyme induction by disk approximation was evaluated using imipenem, cefoxitin, and amoxicillin-clavulanate as inducing agents against ceftazidime. Finally, an agar dilution assay was performed, using cefoxitin with and without added cloxacillin. AmpC activity was present in 49.8% of test isolates, 93.7% of which were positive for plasmid-borne ampC genes. CIT-like enzymes were predominant in E. coli, and DHA-like enzymes were predominant in Klebsiella spp. The disk-based inhibitor tests performed better than the agar dilution assay, while detection of AmpC by disk induction had a poor sensitivity. The cefoxitin-cloxacillin disk combination provided the best overall performance, with a sensitivity and specificity of 95%. This study confirmed the accuracy of disk-based inhibitor screening for AmpC enzymes, which proved reliable at detecting CIT-and DHA-like plasmid-borne ampC genes. The methods are simple enough for introduction into clinical microbiology laboratories.

Disc susceptibility testing methods are unreliable at detecting colistin resistance. Dilution methods should be the method of choice for susceptibility testing of colistin.

The combination of colistin and minocycline was found to be bactericidal and synergistic against A. baumannii by time-kill methods. There was no agreement between time-kill and Etest methods for synergy testing.

No abstract

Aero-tolerant Actinomyces spp. are an under-recognised cause of cutaneous infections, in part because identification using conventional phenotypic methods is difficult and may be inaccurate. Matrix-assisted laser desorption ionisation time-of-flight mass spectrometry (MALDI-TOF MS) is a promising new technique for bacterial identification, but with limited data on the identification of aero-tolerant Actinomyces spp. This study evaluated the accuracy of a phenotypic biochemical kit, MALDI-TOF MS and genotypic identification methods for the identification of this problematic group of organisms. Thirty aero-tolerant Actinomyces spp. were isolated from soft-tissue infections over a 2-year period. Species identification was performed by 16 s rRNA sequencing and genotypic results were compared with results obtained by API Coryne and MALDI-TOF MS. There was poor agreement between API Coryne and genotypic identification, with only 33% of isolates correctly identified to the species level. MALDI-TOF MS correctly identified 97% of isolates to the species level, with 33% of identifications achieved with high confidence scores. MALDI-TOF MS is a promising new tool for the identification of aero-tolerant Actinomyces spp., but improvement of the database is required in order to increase the confidence level of identification.

In our study population, pneumonia and PLA were the most common sources of community-acquired bacteremia. Hypermucoviscosity, rmpA, aerobactin, and serotype K1 could be useful laboratory markers to alert clinicians to arrange abdominal imaging to detect liver abscess.

Various studies have documented a shift in species distribution in Candida bloodstream infections (BSI), but there are little data from Southeast Asia. This study was performed to determine the species epidemiology and antifungal susceptibilities of Candida species BSI in Singapore. Candida spp. from BSI were collected from a tertiary and secondary referral hospital, and an obstetrics/paediatric hospital over a 3-year period. The most common isolates were Candida albicans (36%), Candida tropicalis (27%), Candida glabrata (16%) and Candida parapsilosis (16%). Candida parapsilosis and C. albicans were predominant in the paediatric hospital, and C. albicans and C. tropicalis predominant in the other two institutions. Candida tropicalis temporarily replaced C. albicans as the predominant strain from BSI in 2006. Overall, 87.3% of Candida isolates were susceptible to fluconazole, and 10.4% classified as susceptible-dose-dependent. Fluconazole resistance was detected in C. tropicalis (3.6%), C. parapsilosis (2.1%) and C. glabrata (4.0%). Candida albicans is the predominant species isolated from BSI in Singapore. However, non-albicans species accounted for nearly two-thirds of all cases of candidaemia and the relative increase in C. tropicalis infections deserves further investigation. Resistance to fluconazole was uncommon.

Lowe et al. (1) recently reported the failure of the Vitek 2 system (bioMérieux) to correctly identify Burkholderia pseudomallei. They also warned that thoughtless reliance on automation runs the risk that incorrectly identified organisms may be reported without question.We recently had the opportunity to evaluate the new Phoenix (BD) automated identification and susceptibility testing system. Because melioidosis is an important infection in our region, we also tested strains of B. pseudomallei even though this organism is not in the Phoenix database.Forty-seven nonduplicate strains of B. pseudomallei were used. The strains were all isolated from patients with compatible clinical histories. The strains were identified on the basis of their characteristic colony morphology on sheep blood agar and Ashdown's medium, bipolar staining of gram-negative rods, oxidase positivity, resistance to aminoglycosides and polymyxin B, and amino acid decarboxylase and dihydrolase reactions. All were identified by the API 20NE test (bioMérieux) as B. pseudomallei, except one that was identified as Chromobacterium violaceum. The 16S rRNA gene sequence of this isolate was identical to that of B. pseudomallei.The NMIC/ID-4 card was used in accordance with the manufacturer's instructions. The results are shown in Table 1. The majority of B. pseudomallei strains were identified as Burkholderia cepacia. We were unable to discern a characteristic pattern of test results that would discriminate between the two species.Although B. pseudomallei is not in the Phoenix database, we felt it was important to evaluate how the system identified this organism, as the characteristic colony morphology may only become apparent after more than 24 h of incubation. It is therefore not improbable that an attempt may be made to identify an unknown strain by using the Phoenix system if B. pseudomallei is not suspected in the first place. Laboratories that use the BD Phoenix system should be aware that it will identify B. pseudomallei as B. cepacia with a high confidence value (95 to 99%).The Phoenix and NMIC/ID-4 cards were kindly provided by BD.