Leading article

Vancomycin-resistant leuconostocs, lactobacilli and now pediococci

Pediococcus spp. have been reported to cause infections in patients with underlying conditions. However, the pathogenicity of this bacteria is unclear. Herein, we describe the first case of Pediococcus acidilactici bacteremia, which occurred in a 16-year-old male with dasatinib-induced hemorrhagic colitis during maintenance therapy for leukemia and resolved without antibiotic treatment. P. acidilactici bacteremia might be self-limiting, even in immunocompromised patients receiving chemotherapy.

“…Antibiotic resistance-when bacteria change and antibiotics fail-is happening right now, across the world…without urgent action we are heading for a post antibiotic era in which common infections and minor injuries can once again kill” (World Health Organization, April 2014). In this dramatic scenario, we are presenting this short review on lipoglycopeptides, potent inhibitors of cell wall biosynthesis that are derived from natural sources, as a contribution to up-to-grade the state-of-the-art in the battle against the bacteria resistance. The first compound introduced in the clinical practice was vancomycin, which still is widely used for the treatment of multidrug-resistant infections sustained by Gram-positive strains and also for the treatment of Clostridium difficile-associated diarrhea, a life-threatening infection. In the last 20 years, several products, which are semisynthetic derivatives of the vancomycin core structure have reached the market, in particular, telavancin, oritavancin, and dalbavancin. In this review, we would like to highlight the chemical and biological properties of these drugs and compare their profile from a medicinal chemistry perspective.

A case of bacteremia caused by Pediococcus acidilactici occurring in a patient with metastatic adenocarcinoma of the gallbladder is described. The bacteremia persisted despite an antimicrobial regimen of vancomycin, ciprofloxacin, metronidazole, and caspofungin. Within 36 h of switching the vancomycin to daptomycin (6 mg/kg per day), the bacteremia resolved and the patient improved clinically. Previous reports of human pediococcal infection are also reviewed.

This chapter discusses the resistance to glycopeptide antibiotics. The history of glycopeptides represents a perfect example of the various circumstances that provoke medical and scientific interest in an antibiotic. Because of the increased isolation of Staphylococcus aureus strains resistant against antibiotics, such as erythromycin, tetracycline and penicillin in the early 1950s, a large-scale screening program aimed at the identification of antibiotics with high anti-staphylococcal activity was initiated. Vancomycin was soon introduced clinically; however, problems with toxicity and the introduction of β-lactamase-resistant penicillins in the early 1960s caused a decline in the use of vancomycin. The appearance of methicillin-resistant staphylococci and other, multiply resistant Gram-positive organisms revived interest in glycopeptide antibiotics especially since improved purification procedures largely reduced early toxicity problems of vancomycin. The emergence of resistance to glycopeptide antibiotics in staphylococci and enterococci confronts scientists with a bacterial defence mechanism that is unexpected, and had been considered to be highly improbable.

Two selective agar media for Leuconostoc enumeration and/or isolation were obtained by adding Vancomycin to MRS or NL media. Under the conditions described, Leuconostoc strains were able to grow on these media, while Lactococcus strains do not. Comparison of colony counts showed no difference with the MRS medium. Enumeration of Leuconostoc mesenteroides subsp. cremoris in mixed culture with Lactococcus strains was performed successfully using these media. In a milk medium, mixed cultures with lac⁺ prt⁺ strains of Lactococcus· showed a rapid decrease of the proportion of Leuconostoc strain in the total bacterial population.

Intraperitoneal vancomycin is used in the treatment of peritonitis in patients undergoing continuous ambulatory peritoneal dialysis (CAPD). We describe the emergence of low-level glycopeptide-resistance in five Gram-positive species over a one-year period. Isolation of these organisms was associated with vancomycin treatment failure in four patients who had had numerous episodes of peritonitis. Clinicians and microbiologists should be aware that repeated administration of glycopeptides to such patients might lead to the emergence of organisms resistant to these antibiotics.