False extended-spectrum beta-lactamase detection in Acinetobacter spp. due to intrinsic susceptibility to clavulanic acid

In vitro and in vivo evaluation of two combined β-lactamase inhibitors against carbapenem-resistant Acinetobacter baumannii

The objective of this study was to evaluate the in vitro and in vivo efficacy of clavulanic acid (C/A) in combination with tazobactam against clinical strains of carbapenem-resistant Acinetobacter baumannii. The MIC of 24 clinical strains of A. baumannii was determined, and a checkerboard assay and time-kill curve analysis were performed in selected strains to determine the synergy between C/A and tazobactam. The efficacy of C/A in monotherapy and in combination with tazobactam was evaluated in vitro in cell culture experiments and in a murine peritoneal sepsis model. The C/A and C/A plus tazobactam MIC50 were 128 and <1 mg/L, respectively. The checkerboard assay showed that tazobactam (4 and 8 mg/L) demonstrated synergy with C/A against A. baumannii Ab40, an OXA-24 producer strain, and Ab293, a lacking OXA β-lactamase strain. The time-kill curve assay showed both bactericidal and synergistic effects against Ab40 and Ab293, with C/A 1xMIC and tazobactam (4 and 8 mg/L) at 24 h. In the murine peritoneal sepsis model with Ab293 strain, the combination of C/A and tazobactam reduced bacterial loads in tissues and blood by 2 and 4 log10 CFU/g or mL compared with C/A alone. Combining C/A with tazobactam could be considered as a potential alternative strategy to treat A. baumannii in some cases, and future work with more strains is needed to confirm this possibility.

Reporting antimicrobial susceptibilities and resistance phenotypes in Acinetobacter spp: a nationwide proficiency study

Objectives

To evaluate the proficiency of Spanish microbiology laboratories with respect to the antimicrobial susceptibility testing (AST) of Acinetobacter spp.

Methods

Eight Acinetobacter spp. with different resistance mechanisms were sent to 48 Spanish centres which were asked to report: (i) the AST system used; (ii) MICs; (iii) breakpoints used (CLSI versus EUCAST); (iv) clinical category; and (v) resistance mechanisms inferred. Minor, major and very major errors (mE, ME and VME, respectively) were determined.

Results

The greatest percentages of discrepancies were: (i) by AST method: 18.5% Etest, 14.3% Vitek 2 and Sensititre; (ii) by breakpoints: 20.5% (CLSI) and 10.8% (EUCAST); and (iii) by antimicrobial agent: ampicillin/sulbactam (56.2% CLSI), minocycline (40.7% CLSI), tobramycin (38.7% CLSI, 16.8% EUCAST), imipenem (27.8% CLSI, 30.0% EUCAST) and meropenem (25.4% CLSI, 20.8% EUCAST). Categorical error rates: (i) by AST method ranged from 30.0% (Phoenix) to 100% (Sensititre and disc diffusion) for mE, 0.0% (Etest, Sensititre, disc diffusion) to 40% (Phoenix) for ME, and 0.0% (Sensititre and disc diffusion) to 30% (Phoenix) for VME; (ii) by breakpoints: mE (80.1% CLSI, 58.4% EUCAST), ME (3.5% CLSI, 12.4% EUCAST) and VME (16.4% CLSI, 29.2% EUCAST); and (iii) by antimicrobial agent: mE (100% levofloxacin/CLSI, 100% levofloxacin and meropenem/EUCAST), ME (35.3% colistin/CLSI, 25.0% colistin/EUCAST) and VME (64.7% colistin/CLSI, 86.7% gentamicin/EUCAST).

Conclusions

Clinical microbiology laboratories must improve their ability to determine antimicrobial susceptibilities of Acinetobacter spp. isolates. Higher discrepancies using CLSI when compared with EUCAST are mainly due to mE and to a much lesser extent to ME or VME.

Reporting identification of Acinetobacter spp genomic species: A nationwide proficiency study in Spain

Acinetobacter baumannii is the most important genomic species of Acinetobacter from a clinical and epidemiological point of view. Nevertheless, genomic species other than A. baumannii are increasingly recognized as nosocomial pathogens. Molecular methods of identification (genotypic and proteomic assays) are more accurate and reliable and have greater discriminatory power than phenotypic methods. Eleven genomic species of Acinetobacter spp. (8 A. baumannii, 1 A. pittii, 1 A. nosocomialis and 1 A. lwoffii) with different antimicrobial resistance phenotypes and mechanisms of resistance to antimicrobial agents were sent to 48 participating Spanish centers to evaluate their ability for correct identification at the genomic species level. Identification of the genomic species was performed at the two Clinical Microbiology reference laboratories (Hospital Universitario Virgen Macarena, Seville, Spain; and Complejo Hospitalario Universitario de A Coruña, A Coruña, Spain) by partial DNA sequencing of the rpoB gene and MALDI-TOF. The mean percentage of agreement was 76.1%. Fifty percent of CC-01 (A. pittii) and 50% of CC-02 (A. nosocomialis) identification results were reported as A. baumannii. Discrepancies by type of systems used for identification were: MicroScan WA (51.1%), Vitek 2 (19.5%), MALDI-TOF (18.0%), Phoenix (4.5%), Wider (3.8%) and API 20 NE (3.0%). In conclusion, clinical microbiology laboratories must improve their ability to correctly identify the most prevalent non A. baumannii genomic species.

Superbugs in the supermarket? Assessing the rate of contamination with third-generation cephalosporin-resistant gram-negative bacteria in fresh Australian pork and chicken

Background

Antibiotic misuse in food-producing animals is potentially associated with human acquisition of multidrug-resistant (MDR; resistance to ≥ 3 drug classes) bacteria via the food chain. We aimed to determine if MDR Gram-negative (GNB) organisms are present in fresh Australian chicken and pork products.

Methods

We sampled raw, chicken drumsticks (CD) and pork ribs (PR) from 30 local supermarkets/butchers across Melbourne on two occasions. Specimens were sub-cultured onto selective media for third-generation cephalosporin-resistant (3GCR) GNBs, with species identification and antibiotic susceptibility determined for all unique colonies. Isolates were assessed by PCR for SHV, TEM, CTX-M, AmpC and carbapenemase genes (encoding IMP, VIM, KPC, OXA-48, NDM).

Results

From 120 specimens (60 CD, 60 PR), 112 (93%) grew a 3GCR-GNB (n = 164 isolates; 86 CD, 78 PR); common species were Acinetobacter baumannii (37%), Pseudomonas aeruginosa (13%) and Serratia fonticola (12%), but only one E. coli isolate. Fifty-nine (36%) had evidence of 3GCR alone, 93/163 (57%) displayed 3GCR plus resistance to one additional antibiotic class, and 9/163 (6%) were 3GCR plus resistance to two additional classes. Of 158 DNA specimens, all were negative for ESBL/carbapenemase genes, except 23 (15%) which were positive for AmpC, with 22/23 considered to be inherently chromosomal, but the sole E. coli isolate contained a plasmid-mediated CMY-2 AmpC.

Conclusions

We found low rates of MDR-GNBs in Australian chicken and pork meat, but potential 3GCR-GNBs are common (93% specimens). Testing programs that only assess for E. coli are likely to severely underestimate the diversity of 3GCR organisms in fresh meat.

Genomic and physiological characterization of a laboratory-isolated Acinetobacter schindleri ACE strain that quickly and efficiently catabolizes acetate

An Acinetobacter strain, designated ACE, was isolated in the laboratory. Phylogenetic tests and average nucleotide identity value comparisons suggested that ACE belongs to the species Acinetobacterschindleri. We report for the first time the complete genome sequence of an A. schindleri strain, which consists of a single circular chromosome of 3 001 209 bp with an overall DNA G+C content of 42.9 mol% and six plasmids that account for 266 844 bp of extrachromosomal material. The presence or absence of genes related to carbon catabolism and antibiotic resistance were in agreement with the phenotypic characterization of ACE. This strain grew faster and with a higher biomass yield on acetate than the reference strain Acinetobacter baylyi ADP1. However, ACE did not use aromatic compounds and was unable to grow on common carbon sources, such as glucose, xylose, glycerol or citrate. The gluconeogenic and the catechol pathways are complete in ACE, but compounds that are converted to protocatechuate did not sustain growth since some genes of this pathway are missing. Likewise, this strain could not grow on glucose because it lacks the genes of the Entner-Doudoroff pathway. Minimal inhibitory concentration data showed that ACE was susceptible to most of the antimicrobial agents recommended for the clinical treatment of Acinetobacter spp. Some genes related to a possible human-microbe interaction were found in the ACE genome. ACE is likely to have a low pathogenic risk, as is the case with other A. schindleri strains. These results provide a valuable reference for broadening the knowledge of the biology of Acinetobacter.

Emerging threat of multidrug resistant bugs--Acinetobacter calcoaceticus baumannii complex and methicillin resistant Staphylococcus aureus

Background

Infections caused by bacteria such as multidrug resistant (MDR) Acinetobacter spp. and methicillin-resistant Staphylococcus aureus (MRSA) constitute a worldwide pandemic. Without gathering information about these strains, we cannot reduce the morbidity and mortality due to infections caused by these notorious bugs.

Methods

This study was conducted to identify the status of MDR Acinetobacter spp. and MRSA in a tertiary care centre of Nepal. Sputum, endotracheal aspirate and bronchial washing specimens were collected and processed from patients suspected of lower respiratory tract infection following standard microbiological methods recommended by the American Society for Microbiology (ASM). Double disk synergy test method was employed for the detection of extended-spectrum beta-lactamase (ESBL) in Acinetobacter isolates. Methicillin resistance in S. aureus was confirmed by using cefoxitin and oxacillin disks.

Results

Different genomespecies of Acinetobacter were isolated; these consisted of Acinetobacter calcoaceticus baumannii complex and A. lwoffii. Around 95% of Acinetobacter isolates were MDR, while 12.9% were ESBL-producer. Of the total 33 isolates of S. aureus, 26 (78.8%) were MDR and 14 (42.4%) were methicillin resistant.

Conclusions

A large number of MDR Acinetobacter spp. and MRSA has been noted in this study. The condition is worsened by the emergence of ESBL producing Acinetobacter spp. Hence, judicious use of antimicrobials is mandatory in clinical settings. Moreover, there should be vigilant surveillance of resistant clones in laboratories.

In vitro activity and in vivo efficacy of clavulanic acid against Acinetobacter baumannii

Clavulanic acid (CLA) exhibits low MICs against some Acinetobacter baumannii strains. The present study evaluates the efficacy of CLA in a murine model of A. baumannii pneumonia. For this purpose, two clinical strains, Ab11 and Ab51, were used; CLA MICs for these strains were 2 and 4 mg/liter, respectively, and the imipenem (IPM) MIC was 0.5 mg/liter for both. A pneumonia model in C57BL/6 mice was used. The CLA dosage (13 mg/kg of body weight given intraperitoneally) was chosen to reach a maximum concentration of the drug in serum similar to that in humans and a time during which the serum CLA concentration remained above the MIC equivalent to 40% of the interval between doses. Six groups (n = 15) were inoculated with Ab11 or Ab51 and were allocated to IPM or CLA therapy or to the untreated control group. In time-kill experiments, CLA was bactericidal only against Ab11 whereas IPM was bactericidal against both strains. CLA and IPM both decreased bacterial concentrations in lungs, 1.78 and 2.47 log10 CFU/g (P < or = 0.001), respectively, in the experiments with Ab11 and 2.42 and 2.28 log10 CFU/g (P < or = 0.001), respectively, with Ab51. IPM significantly increased the sterility of blood cultures over that for the controls with both strains (P < or = 0.005); CLA had the same effect with Ab51 (P < 0.005) but not with Ab11 (P = 0.07). For the first time, we suggest that CLA may be used for the treatment of experimental severe A. baumannii infections.