Antimicrobial susceptibility patterns and macrolide resistance genes of beta-hemolytic viridans group streptococci in a tertiary Korean hospital

Recent development and fighting strategies for lincosamide antibiotic resistance

SUMMARYLincosamides constitute an important class of antibiotics used against a wide range of pathogens, including methicillin-resistant Staphylococcus aureus. However, due to the misuse of lincosamide and co-selection pressure, the resistance to lincosamide has become a serious concern. It is urgently needed to carefully understand the phenomenon and mechanism of lincosamide resistance to effectively prevent and control lincosamide resistance. To date, six mobile lincosamide resistance classes, including lnu, cfr, erm, vga, lsa, and sal, have been identified. These lincosamide resistance genes are frequently found on mobile genetic elements (MGEs), such as plasmids, transposons, integrative and conjugative elements, genomic islands, and prophages. Additionally, MGEs harbor the genes that confer resistance not only to antimicrobial agents of other classes but also to metals and biocides. The ultimate purpose of discovering and summarizing bacterial resistance is to prevent, control, and combat resistance effectively. This review highlights four promising strategies, including chemical modification of antibiotics, the development of antimicrobial peptides, the initiation of bacterial self-destruct program, and antimicrobial stewardship, to fight against resistance and safeguard global health.

Incidence of macrolide-lincosamide-streptogramin B resistance amongst beta-haemolytic streptococci in The Gambia

Background

In West Africa, penicillin, macrolide and lincosamide resistance among beta-haemolytic streptococci (BHS) isolates has rarely been described. However, such data are critical to detect and track the emergence of antibiotic resistance.

Methods

Beta-haemolytic streptococci were cultured from clinical specimens from patients attending the clinic at the Medical Research Council Unit The Gambia (n = 217) and kept at −70 °C. Of these, 186 were revived and tested for penicillin susceptibility by disc diffusion and E-test methods, and the D-test for determination of constitutive and inducible macrolide–lincosamide (MLS_B) resistance phenotypes.

Results

The majority of BHS isolates from infections were group A streptococci (GAS) (126/186, 67.7%). Of these, 16% were from invasive disease (30/186). Other BHS isolated included lancefield groups B (19, 10.2%); C (9/186, 4.8%), D (3/186, 1.6%), F (5/186, 2.7%), G (16/186, 8.6%) and non-typeable (8/186, 4.3%). Prevalence of BHS isolated from blood cultures ranges from 0% (2005) to 0.5% (2010). Most (85, 45.7%) of the isolates were from wound infections. Of the 186 BHS isolates, none was resistant to penicillin and 14 (6.1%) were resistant to erythromycin. Of these, 8 (4.3%) demonstrated constitutive MLS_B resistance, and 5 (2.7%) were inducible MLS_B resistant. All the inducible MLS_B isolates were GAS, and majority of the constitutive MLS_B isolates (6/8, 75.0%) were non-GAS.

Conclusions

Beta-haemolytic streptococci, predominantly GAS are associated with a wide range of infections in The Gambia. It is reassuring that macrolide and lincosamide resistance is relatively low. However, monitoring of MLS_B resistance is necessary with the global spread of resistant BHS strains.

Evaluation of the MicroScan MICroSTREP plus antimicrobial panel for testing β-hemolytic streptococci and viridans group streptococci

BACKGROUND

In order to determine the clinical usefulness of the MicroScan (Siemens Healthcare Diagnostics, USA) MICroSTREP plus antimicrobial panel (MICroSTREP) for testing antimicrobial susceptibility of β-hemolytic streptococci (BHS) and viridans group streptococci (VGS), we compared the accuracy of MICroSTREP with that of the CLSI reference method.

METHODS

Seventy-five BHS and 59 VGS isolates were tested for antimicrobial susceptibility to ampicillin, penicillin, cefotaxime, meropenem, erythromycin, clindamycin, levofloxacin, and vancomycin by using MICroSTREP and the CLSI agar dilution method.

RESULTS

The overall essential agreement with regard to minimum inhibitory concentrations (MICs) (within ±1 double dilution) between MICroSTREP and the CLSI reference method was 98.2%, and categorical agreement (CA) was 96.9%. For the BHS isolates, the CA for erythromycin was 96.0%, whereas that for cefotaxime, meropenem, levofloxacin, and vancomycin (for ampicillin, penicillin, and clindamycin; 98.7%) was 100%. For the VGS isolates, the CA for penicillin was 84.7% and that for erythromycin, clindamycin, and vancomycin (for meropenem, 86.5%; for ampicillin, 88.1%; and for cefotaxime and levofloxacin, 96.6%) was 100%. All categorical errors of penicillin and ampicillin in the VGS isolates were minor.

CONCLUSIONS

The accuracy of MICroSTREP is comparable to that of the CLSI reference method, suggesting that this panel can be effective for testing antimicrobial susceptibility of BHS and VGS.

Evidence-based guidelines for empirical therapy of neutropenic fever in Korea

Neutrophils play an important role in immunological function. Neutropenic patients are vulnerable to infection, and except fever is present, inflammatory reactions are scarce in many cases. Additionally, because infections can worsen rapidly, early evaluation and treatments are especially important in febrile neutropenic patients. In cases in which febrile neutropenia is anticipated due to anticancer chemotherapy, antibiotic prophylaxis can be used, based on the risk of infection. Antifungal prophylaxis may also be considered if long-term neutropenia or mucosal damage is expected. When fever is observed in patients suspected to have neutropenia, an adequate physical examination and blood and sputum cultures should be performed. Initial antibiotics should be chosen by considering the risk of complications following the infection; if the risk is low, oral antibiotics can be used. For initial intravenous antibiotics, monotherapy with a broad-spectrum antibiotic or combination therapy with two antibiotics is recommended. At 3-5 days after beginning the initial antibiotic therapy, the condition of the patient is assessed again to determine whether the fever has subsided or symptoms have worsened. If the patient's condition has improved, intravenous antibiotics can be replaced with oral antibiotics; if the condition has deteriorated, a change of antibiotics or addition of antifungal agents should be considered. If the causative microorganism is identified, initial antimicrobial or antifungal agents should be changed accordingly. When the cause is not detected, the initial agents should continue to be used until the neutrophil count recovers.

Antimicrobial resistance in group B streptococcus: the Australian experience

Intrapartum chemoprophylaxis for pregnant group B streptococcus (GBS) carriers reduces vertical transmission, with a resultant decrease in neonatal as well as maternal morbidity from invasive GBS infection. Current Australian guidelines recommend penicillin for intrapartum prophylaxis of GBS carriers, with erythromycin or clindamycin for those with a β-lactam allergy. Recent reports globally suggest that resistance to erythromycin and clindamycin may be increasing; hence, a study was undertaken to promote an evidence base for local clinical guidelines. Samples collected for standardized susceptibility testing included 1160 invasive GBS isolates (264 isolates retrospectively from 1982 to 2001 and prospectively from 2002 to 2006, plus 896 prospectively collected colonizing GBS isolates gathered over a 12 month period from 2005 to 2006) from 16 laboratories around Australia. All isolates displaying phenotypic macrolide or lincosamide resistance were subsequently genotyped. No isolates showed reduced susceptibility to penicillin or vancomycin. Of the invasive isolates, 6.4 % demonstrated phenotypic erythromycin resistance and 4.2 % were clindamycin resistant. Of the erythromycin-resistant isolates, 53 % showed cross-resistance to clindamycin. Very similar results were found in colonizing specimens. There was no statistically significant change in macrolide-resistance rates over the two study periods 1982-2001 and 2002-2006. Genotyping for macrolide and lincosamide-resistant isolates was largely consistent with phenotype. These findings suggest that penicillin therapy remains an appropriate first-line antibiotic choice for intrapartum GBS chemoprophylaxis, with erythromycin and/or clindamycin resistance being low in the Australian population. It would, nevertheless, be appropriate for laboratories screening for GBS in obstetric patients to consider macrolide sensitivity testing, particularly for those with β-lactam allergy, to ensure appropriate chemoprophylaxis.