Staphylococcus aureus small colony variants in diabetic foot infections

Abstract

BackgroundStaphylococcus aureus (S. aureus) is one of the major pathogens causing chronic infections. The ability of S. aureus to acquire resistance to a diverse range of antimicrobial compounds results in limited treatment options, particularly in methicillin-resistant S. aureus (MRSA). A mechanism by which S. aureus develops reduced susceptibility to antimicrobials is through the formation of small colony variants (SCVs). Infections by SCVs of S. aureus are an upcoming problem due to difficulties in laboratory diagnosis and resistance to antimicrobial therapy.MethodsA prospective study was performed on 120 patients diagnosed with both type 2 diabetes mellitus and infected diabetic foot ulcers. The study was carried out from July 2012 to December 2013 in Hospital General de Mexico. The samples were cultured in blood agar, mannitol salt agar, and MacConkey agar media, and incubated at 37°C in aerobic conditions.ResultsWe describe the first known cases of diabetic foot infections caused by MRSA-SCVs in patients diagnosed with type 2 diabetes mellitus and infected diabetic foot ulcers. In all of our cases, the patients had not received any form of gentamicin therapy.ConclusionsThe antibiotic therapy commonly used in diabetic patients with infected diabetic foot ulcers fails in the case of MRSA-SCVs because the intracellular location protects S. aureus-SCVs from the host's defenses and also helps them resist antibiotics. The cases studied in this article add to the spectrum of persistent and relapsing infections attributed to MRSA-SCVs and emphasizes that these variants may also play a relevant role in diabetic foot infections.

Clinical and surgical characteristics of infected diabetic foot ulcers in a tertiary hospital of Mexico

“…Moreover, this infection and inflammation could be a result of a failure in the immune system’s response, a decrease in the peripheral circulation to the extremities, or a high level of glucose in blood. This has also been reported in other studies, where leukocytosis is considered a risk factor of amputation of lower extremities [40–43]. Also, infection and inflammation could play a role in the development of a peripheral arterial disease (PAD), aggravating the patient’s condition [44].…”

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“…[14] According to foreign authors, the level of S. aureus resistance to oxacillin ranged from 0% of resistant strains isolated from patients undergoing treatment of diabetic foot syndrome in the surgical department of Ouagadougou hospital (Burkina Faso) up to 100% resistance in strains isolated from patients, undergoing treatment at the central hospital in Mexico City (Table 1). [18,19] The same trend was observed among strains of coagulasenegative staphylococci. In patients with I and II Grade, it was allocated 25% and 30.4% methicillin-resistant strains, respectively, with Grade III and IV were verified 54.5% and 66.6% of strains resistant to oxacillin, respectively.…”

Clinical Significance and Pathogenesis of Staphylococcal Small Colony Variants in Persistent Infections

“…Basically, a given SCV isolate mirrors the genetically encoded resistance pattern of its parental strain. Thus, ␤-lactamase-producing SCVs and mecA-based MRSA-SCVs have been described repeatedly (31,63,92,(186)(187)(188). However, in addition to and beyond these classical mechanisms of antibiotic resistance described for staphylococci, the SCV phenotype is viewed as a prime example of the expression of phenotypic resistance, often also called functional resistance.…”

“…In several cases, methicillin-resistant SCVs have been isolated from infection or colonization, sometimes without response to the given antibiotics, even if they tested susceptible in vitro (89,92,187,188,202). If an MRSA-SCV infection has to be treated, the administration of glycopeptides represents a therapeutic option.…”