NEOMYCIN-RESISTANT STAPHYLOCOCCUS AUREUS IN A BURNS UNIT

Topical (local) antibiotics for respiratory infections with sore throat: An antibiotic stewardship perspective

WHAT IS KNOWN AND OBJECTIVE

The overuse and misuse of antibiotics, especially for viral, and self-limiting, respiratory tract infections such as sore throat, increases the risk of the development and spread of antimicrobial resistance within communities. Up to 80% of sore throat cases have a viral aetiology, and even when the infection is bacterial, most cases resolve without antibiotics. However, antibiotics are still frequently and often inappropriately prescribed for the treatment of sore throat. Furthermore, topical (local) antibiotics for treatment of sore throat are widely available over the counter. The objective of this systematic review was to establish the evidence for the benefits, risk of harm and antimicrobial resistance associated with topical (local) antibiotics used for patients with sore throat.

METHODS

Eligible studies included those in patients with sore throat of any aetiology receiving the topical (local) antibiotics tyrothricin, bacitracin, gramicidin or neomycin where the antibiotic was topically/locally applied via the nasal cavity or throat. Nasal applications were included as these are occasionally used to treat upper respiratory tract infections that may involve sore throat. There was no restriction or requirement regarding comparator. The outcomes of interest included efficacy, safety, and in vitro culture and antimicrobial resistance data.

RESULTS AND DISCUSSION

This systematic review found sparse and mainly poor-quality evidence relating to the use of topical (local) antibiotics for sore throat, and it was not possible to establish the benefits, risk of harm or impact of use on antimicrobial resistance.

WHAT IS NEW AND CONCLUSIONS

Further research is necessary to ascertain the risks and benefits of topical (local) antibiotics, their contribution to antimicrobial resistance and the risk of harm. We do, however, question whether it is appropriate and rational to use topical (local) antibiotics for the treatment of sore throat caused by respiratory tract infections in the absence of robust evidence.

Genetic pathway in acquisition and loss of vancomycin resistance in a methicillin resistant Staphylococcus aureus (MRSA) strain of clonal type USA300

An isolate of the methicillin-resistant Staphylococcus aureus (MRSA) clone USA300 with reduced susceptibility to vancomycin (SG-R) (i.e, vancomycin-intermediate S. aureus, VISA) and its susceptible “parental” strain (SG-S) were recovered from a patient at the end and at the beginning of an unsuccessful vancomycin therapy. The VISA phenotype was unstable in vitro generating a susceptible revertant strain (SG-rev). The availability of these 3 isogenic strains allowed us to explore genetic correlates of antibiotic resistance as it emerged in vivo. Compared to the susceptible isolate, both the VISA and revertant strains carried the same point mutations in yycH, vraG, yvqF and lspA genes and a substantial deletion within an intergenic region. The revertant strain carried a single additional frameshift mutation in vraS which is part of two component regulatory system VraSR. VISA isolate SG-R showed complex alterations in phenotype: decreased susceptibility to other antibiotics, slow autolysis, abnormal cell division and increased thickness of cell wall. There was also altered expression of 239 genes including down-regulation of major virulence determinants. All phenotypic properties and gene expression profile returned to parental levels in the revertant strain. Introduction of wild type yvqF on a multicopy plasmid into the VISA strain caused loss of resistance along with loss of all the associated phenotypic changes. Introduction of the wild type vraSR into the revertant strain caused recovery of VISA type resistance. The yvqF/vraSR operon seems to function as an on/off switch: mutation in yvqF in strain SG-R turns on the vraSR system, which leads to increase in vancomycin resistance and down-regulation of virulence determinants. Mutation in vraS in the revertant strain turns off this regulatory system accompanied by loss of resistance and normal expression of virulence genes. Down-regulation of virulence genes may provide VISA strains with a “stealth” strategy to evade detection by the host immune system.

The extensive use of antibiotics has led to the selection of methicillin-resistant S. aureus (MRSA) strains that are resistant to most antimicrobial agents and a treatment of choice against such strains is vancomycin. However, during the last decade reports of treatment failure with vancomycin non-susceptible MRSA (e.g., vancomycin intermediate S. aureus, VISA) began to appear in the clinical setting. In this paper we analyze the mechanism of resistance in a VISA strain that belongs to the epidemic and highly virulent MRSA clone USA300. We had 3 isogenic isolates available for analysis: the vancomycin susceptible parental strain recovered from the patient before the onset of therapy; the VISA strain recovered at the time of clinical treatment failure and a susceptible revertant of the VISA strain acquired during in vitro passage. We identified genetic differences among the three strains through whole genome sequencing. In this strain, the key genetic change responsible for vancomycin resistance was in the functionally connected yvqF/vraSR - two component sensory regulatory system involved with the control of cell wall metabolism of the bacteria. The same genetic change also caused repression of virulence related properties which may help the resistant bacteria to evade the host immune system.

Genetics of antimicrobial resistance in Staphylococcus aureus

Strains of Staphylococcus aureus that are resistant to multiple antimicrobial compounds, including most available classes of antibiotics and some antiseptics, are a major threat to patient care owing to their stubborn intransigence to chemotherapy and disinfection. This reality has stimulated extensive efforts to understand the genetic nature of the determinants encoding antimicrobial resistance, together with the mechanisms by which these determinants evolve over time and are spread within bacterial populations. Such studies have benefited from the application of molecular genetics and in recent years, the sequencing of over a dozen complete staphylococcal genomes. It is now evident that the evolution of multiresistance is driven by the acquisition of discrete preformed antimicrobial resistance genes that are exchanged between organisms via horizontal gene transfer. Nonetheless, chromosomal mutation is the catalyst of novel resistance determinants and is likely to have an enhanced influence with the ongoing introduction of synthetic antibiotics.

Antimicrobial resistance of Staphylococcus aureus: genetic basis

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Stability of aminoglycoside resistance in vitro in gentamicin-resistant Staphylococcus aureus

Stability of aminoglycoside resistance has been investigated in 20 strains of Staphylococcus aureus resistant to gentamicin (16 strains were also resistant to methicillin). In view of previous reports that incubation at elevated temperatures can hasten the loss of unstable antibiotic resistance, we passaged strains daily in a liquid medium for 24 days at 43 degrees C. The nine strains which were resistant to neomycin kept their aminoglycoside resistance virtually intact, whereas most of the other 11 strains (sensitive to neomycin) lost almost all their resistance to gentamicin and kanamycin after 5 days. It thus appears that the stability of aminoglycoside resistances in Staph. aureus is closely linked to the resistance of the strains to neomycin. This finding has important possible consequences in terms of the advisability of the clinical usage of preparations containing neomycin or framycetin for topical application and bowel sterilization.

Gentamicin-resistant Staphylococcus aureus strains isolated in Denmark in 1979

In 1979 seven gentamicin (G)-resistant (res.) Staphylococcus aureus strains caused epidemic episodes in eight Danish hospitals. Furthermore, a total of 37 resistant strains were isolated from separate incidents. All the G-res. strains were resistant to kanamycin, sisomicin and tobramycin, five to amikacin and two to cephalothin. None were resistant to netilmicin. Twelve out of the total of 44 strains were multiply-res. (resistant to penicillin, streptomycin and tetracyclines), and 10 of these were also resistant to methicillin (M). All phage groups/complexes were represented, group III by 13, and the 83A complex by seven strains. Multiply-res. strains, resistant to both M and G were all resistant to mercury, but sensitive to arsenate, whereas such strains resistant to either M or G usually have been found resistant to both metals. Twenty-three strains lost resistance to G upon storage, among them only one multiply-res. Loss of resistance did not influence the metal resistance pattern. From one patient only, the various isolates (nine) differed in respect to bacteriological properties. It was concluded, however, that they all were descendants of the same unstable strain. In the majority of the cases treatment with G had preceded isolation of the resistant strain.

Gentamicin treatment associated with later nosocomial gentamicin-resistant Serratia marcescens infections

During a hospital epidemic of infections with gentamicin-resistant Serratia marcescens (GRS), we studied the relation between receiving antibiotics and acquiring GRS. In a five-month period, 22 patients acquired GRS, whereas 18 patients acquired gentamicin-sensitive Serratia (GSS). When compared with patients with nosocomial GSS infection, patients with nosocomial GRS had been in the hospital (p = 0.04) and the intensive care unit (p = 0.003) longer before infection and more had received gentamicin (p = 0.001) or ampicillin (p = 0.02) before infection. To control for the influence of underlying disease, we matched all 12 ICU patients with GRS infection and 12 patients without GRS infection for underlying illness and duration of intensive care. Use of any antibiotic (p = 0.04), or a combination of gentamicin plus ampicillin or cephalosporin (p = 0.047) was more common among patients with GRS infection. The hospital had not significantly increased the use of aminoglycosides from the previous year. We conclude that for the individual patient antimicrobial therapy, especially with gentamicin or ampicillin, creates a risk for later infection by GRS that is independent of the severity of the underlying illness.

An outbreak of infection caused by a gentamicin-resistant Staphylococcus aureus

An outbreak of infection caused by a strain of Staphylococcus aureus resistant to gentamicin and tobramycin and other antibiotics occurred in two wards in a hospital. Eight patients were colonized, of whom six had clinical infections. Previous administration of gentamicin appeared to predispose the patients to infection with the strain. Restriction of the use of gentamicin and tobramycin is essential to preserve their value in serious infections.

Antibiotic-resistant Staphylococcus aureus in dermatology and burn wards

Staphylococcus aureus isolated between 1967 and 1975 from the nose and skin lesions of patients in dermatology wards and from the burns of patients in a burns unit in Birmingham showed a high incidence of multiple antibiotic-resistant strains in both environments. Over 20% of the strains isolated from patients on admission to the dermatology wards were multiresistant. Resistance to benzylpenicillin, tetracycline, erythromycin, and fusidic acid was common in the dermatology wards; a smaller proportion of strains were resistant to lincomycin, and few (since 1972 none) were resistant to methicillin; resistance to novobiocin and chloramphenicol was uncommon. In the burns unit, fusidic acid resistance was uncommon, but resistance to benzylpenicillin, tetracycline, erythromycin, novobiocin, neomycin, methicilin, and lincomycin was common. Several of the antibiotics to which resistance was common in the burns unit were rarely if ever used there; strains resistant to these antibiotics probably remained common in the ward through the frequent use of other antibiotics, especially erythromycin, to which these strains were also resistant.

Genetic basis, epidemiology, and future significance of antibiotic resistance in Staphylococcus aureus: a review

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Stability of neomycin resistance in Staphylococcus aureus

A strain of Staphylococcus aureus isolated from the skin of a subject with eczema showed a loss in resistance to neomycin and tetracycline after treatment with neomycin was stopped. Seven out of 22 strains of neomycin-resistant Staph. aureus showed a loss in resistance to neomycin and streptomycin after storage in nutrient broth for 14 days at room temperature, and it seems probable that resistance in these unstable strains was controlled by extrachromosomal elements or plasmids. Strains of phage types 84/85 and 29/77 and related types were frequently isolated in general hospital wards and showed no loss in resistance on similar storage in nutrient broth. Five of the neomycin-unstable strains were isolated from patients with eczematous lesions. Multiple-resistant and antibiotic-sensitive strains of Staph. aureus of similar phage type were isolated from patients in a ward for patients with skin disease, and the possibility of transfer of resistance in vivo is discussed.

Binding of neomycin and analogues by fatty acids in vitro

Neomycin forms insoluble complexes with long-chain fatty acids in vitro. This reduces the diffusion of neomycin but does not directly neutralize its antibiotic activity. Possible effects in vivo are discussed.

Wound infections acquired from a disperser of an unusual strain of Staphylococcus aureus

Seven post-operative wounds were infected with a strain of Staphylococcus aureus, probably acquired from a theatre orderly who suffered from a dry generalized eczema. The orderly was a nasal and heavy skin carrier, and was shown to be a disperser of the epidemic strain. Infection was probably acquired from airborne contamination in the operating theatre, since the orderly did not scrub-up. The epidemic strain (phage type 80/81 at 1,000 routine test dilution) was sensitive to penicillin and resistant to tetracycline and novobiocin. Neomycin resistance was variable. This strain was found to lose resistance to neomycin when subcultured in the absence of the antibiotic.

Antiseptic and aseptic prophylaxis for burns: use of silver nitrate and of isolators

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Cultural characters of a newly recognized group of hospital staphylococci

Members of a newly recognized group of hospital staphylococci, which are believed to have arisen from 83A staphylococci by lysogenization, differ from them in several cultural characters. Some but not all of these characters appear to be determined by the carriage of phage.