Minocycline--an old drug for a new century: emphasis on methicillin-resistant Staphylococcus aureus (MRSA) and Acinetobacter baumannii

Evaluation of minocycline susceptibility of methicillin-resistant Staphylococcus pseudintermedius

Methicillin-resistant Staphylococcus pseudintermedius (MRSP) is an increasingly important cause of opportunistic infections in dogs and cats. Treatment options are often limited because of the high level of antimicrobial resistance. Doxycycline resistance is common, but variable mechanisms of doxycycline resistance exist, with some conferring resistance to doxycycline but not minocycline. However, there has been limited study of minocycline susceptibility in clinical MRSP isolates nor has the association of susceptibility and clonal complex been clearly established. The objective of this study was to evaluate the susceptibility of MRSP to tetracycline, doxycycline and minocycline, to determine the prevalence of tet(M) and tet(K) and to evaluate the impact of strain on minocycline susceptibility. One hundred seven MRSP isolates from dogs from Canada and the US were included; 79 from clinical infections and 28 from colonization sites. Thirty-nine (36%) isolates were susceptible to tetracycline, 41 (38%) to doxycycline and 70 (65%) to minocycline. Two main dru types, dt9a and dt11a, were present. When tetracycline or doxycycline resistant, dru type dt9a and related strains predominantly harboured tet(K) and were susceptible to minocycline. In contrast, dt11a and related strains tended to harbour tet(M), which confers resistance to all three tetracyclines. Minocycline might be a treatment option for some MRSP infections, even those that are doxycycline resistant; however, interpretive breakpoints may need to be re-assessed. Study of the pharmacokinetics and clinical efficacy of minocycline in dogs and cats is warranted.

In vitro activity of minocycline alone and in combination with cefoperazone-sulbactam against carbapenem-resistant Acinetobacter baumannii

The aim of this study was to investigate the in vitro activity of minocycline combined with cefoperazone-sulbactam against carbapenem-resistant Acinetobacter baumannii (CRAB). A total of 53 nonduplicate CRAB were collected from inpatients of intensive care units in three hospitals in China from February 2009 to August 2011. Minimum inhibitory concentrations were determined by the broth microdilution method. The checkerboard method was used to determine whether combinations of the two agents act synergistically. Among the 53 A. baumannii, 64.2% of the isolates were susceptible to amikacin and 69.8% were susceptible to cefoperazone-sulbactam. More than 80% of isolates were resistant to the other agents and no isolates were found resistant to polymyxin B and minocycline. The combination of minocycline and cefoperazone-sulbactam demonstrated synergism in 39 isolates, partial synergism in 11 isolates, and indifference in 3 isolates. No antagonistic interactions were observed. Our study demonstrated that minocycline has good activity against CRAB and the combination of minocycline with cefoperazone-sulbactam had significant synergistic activity against these strains in vitro. The combination of minocycline and cefoperazone-sulbactam may be an alternative option for the treatment of infections caused by CRAB.

Simulated antibiotic exposures in an in vitro hollow-fiber infection model influence toxin gene expression and production in community-associated methicillin-resistant Staphylococcus aureus strain MW2

Community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) strain MW2 harbors a plethora of toxins to mediate its virulence. However, toxin expression and regulation with simulated clinical antimicrobial exposures are unclear. This study evaluated these relationships using an in vitro pharmacodynamic hollow-fiber infection model. Clinical doses of clindamycin, linezolid, minocycline, trimethoprim-sulfamethoxazole (SXT), and vancomycin were simulated over 72 h against MW2 in the hollow fiber model. Expression levels of lukSF-PV and enterotoxin genes sec4, sek, seq, and sel2 were quantified by real-time PCR. Panton-Valentine leukocidin (PVL) was quantified by enzyme-linked immunosorbent assay (ELISA), and cytotoxicity was determined on polymorphonuclear cells (PMNs). Vancomycin produced the maximum MW2 killing (2.53 log(10) CFU/ml) after the first dose, but the greatest sustained killing over 72 h occurred with linezolid and clindamycin. Vancomycin and minocycline induced gene upregulation from 0 to 8 h, followed by downregulation for the remaining simulation period. Clindamycin decreased gene expression in the first 24 h, followed by moderate increases (2.5-fold) thereafter. Linezolid increased gene expression 11.4- to 200.4-fold but inhibited PVL production (0.6 ± 0.3 versus 5.9 ± 0.2 μg/ml, linezolid versus control at 72 h; P < 0.05). Similar effects on PVL production occurred with clindamycin and minocycline. SXT increased PVL production at 48 h (2.8-fold) and 72 h (4.9-fold) of treatment (P < 0.05), resulting in increased PVL cytotoxicity on PMNs. Linezolid, clindamycin, and minocycline were the most effective agents on decreasing the virulence potential in CA-MRSA, notably after 8 h of treatment. SXT had minimal effects on toxin gene regulation, but it increased production and cytotoxicity of PVL toxin in the model and may enhance virulence when it is used to treat severe infections.

Activities of colistin- and minocycline-based combinations against extensive drug resistant Acinetobacter baumannii isolates from intensive care unit patients

BACKGROUND

Extensive drug resistance of Acinetobacter baumannii is a serious problem in the clinical setting. It is therefore important to find active antibiotic combinations that could be effective in the treatment of infections caused by this problematic 'superbug'. In this study, we analyzed the in vitro activities of three colistin-based combinations and a minocycline-based combination against clinically isolated extensive drug resistant Acinetobacter baumannii (XDR-AB) strains.

METHODS

Fourteen XDR-AB clinical isolates were collected. The clonotypes were determined by polymerase chain reaction-based fingerprinting. Susceptibility testing was carried out according to the standards of the Clinical and Laboratory Standards Institute. Activities of drug combinations were investigated against four selected strains and analyzed by mean survival time over 12 hours (MST12 h) in a time-kill study.

RESULTS

The time-kill studies indicated that the minimum inhibitory concentration (MIC) of colistin (0.5 or 0.25 μg/mL) completely killed all strains at 2 to 4 hours, but 0.5×MIC colistin showed no bactericidal activity. Meropenem (8 μg/mL), minocycline (1 μg/mL) or rifampicin (0.06 μg/mL) did not show bactericidal activity. However, combinations of colistin at 0.5×MIC (0.25 or 0.125 μg/mL) with each of the above were synergistic and shown bactericidal activities against all test isolates. A combination of meropenem (16 μg/mL) with minocycline (0.5×MIC, 4 or 2 μg/mL) was synergitic to all test isolates, but neither showed bactericidal activity alone. The MST12 h values of drug combinations (either colistin- or minocycline-based combinations) were significantly shorter than those of the single drugs (p<0.01).

CONCLUSIONS

This study indicates that combinations of colistin/meropenem, colistin/rifampicin, colistin/minocycline and minocycline/meropenem are synergistic in vitro against XDR-AB strains.

Activities of colistin- and minocycline-based combinations against extensive drug resistant Acinetobacter baumannii isolates from intensive care unit patients

Background

Extensive drug resistance of Acinetobacter baumannii is a serious problem in the clinical setting. It is therefore important to find active antibiotic combinations that could be effective in the treatment of infections caused by this problematic 'superbug'. In this study, we analyzed the in vitro activities of three colistin-based combinations and a minocycline-based combination against clinically isolated extensive drug resistant Acinetobacter baumannii (XDR-AB) strains.

Methods

Fourteen XDR-AB clinical isolates were collected. The clonotypes were determined by polymerase chain reaction-based fingerprinting. Susceptibility testing was carried out according to the standards of the Clinical and Laboratory Standards Institute. Activities of drug combinations were investigated against four selected strains and analyzed by mean survival time over 12 hours (MST_{12 h}) in a time-kill study.

Results

The time-kill studies indicated that the minimum inhibitory concentration (MIC) of colistin (0.5 or 0.25 μg/mL) completely killed all strains at 2 to 4 hours, but 0.5×MIC colistin showed no bactericidal activity. Meropenem (8 μg/mL), minocycline (1 μg/mL) or rifampicin (0.06 μg/mL) did not show bactericidal activity. However, combinations of colistin at 0.5×MIC (0.25 or 0.125 μg/mL) with each of the above were synergistic and shown bactericidal activities against all test isolates. A combination of meropenem (16 μg/mL) with minocycline (0.5×MIC, 4 or 2 μg/mL) was synergitic to all test isolates, but neither showed bactericidal activity alone. The MST_{12 h} values of drug combinations (either colistin- or minocycline-based combinations) were significantly shorter than those of the single drugs (p < 0.01).

Conclusions

This study indicates that combinations of colistin/meropenem, colistin/rifampicin, colistin/minocycline and minocycline/meropenem are synergistic in vitro against XDR-AB strains.

Confronting multidrug-resistant Acinetobacter baumannii: a review

Multidrug-resistant Acinetobacter baumannii (MDR-AB) infections are difficult to treat owing to the extremely limited armamentarium. The present review reports all available treatment options against MDR-AB, including single molecules, combination schemes, and alternative modes of antimicrobial administration. Additionally, a group of recently reported peptides with anti-MDR-AB activity is described.

Detection of KPC in Acinetobacter spp. in Puerto Rico

During an island-wide PCR-based surveillance study of beta-lactam resistance in multidrug-resistant (MDR) Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, and Acinetobacter calcoaceticus-baumannii complex isolates obtained from 17 different hospitals, 10 KPC-positive Acinetobacter isolates were identified. DNA sequencing of the bla(KPC) gene identified KPC-2, -3, and -4 and a novel variant, KPC-10. This is the first report of a KPC-type beta-lactamase identified in Acinetobacter species.