Instability and linkage of silver resistance, lactose fermentation, and colony structure in Enterobacter cloacae from burn wounds.

Abstract

SYNOPSIS A strain of Enterobacter cloacae from a burn wound has displayed unstable resistance to silver nitrate and a linkage of this characteristic to that for rapid lactose fermentation and mucoid colony structure. Attempts to demonstrate transferability of these unstable determinants gave negative results.The use of silver preparations for topical antimicrobial therapy in the Burns Unit of this Hospital has prompted routine screening of bacterial isolates for resistance to this metal.During some early tests in this project two strains of Enterobacter cloacae were isolated which displayed high but unstable resistance to silver nitrate. Each was isolated from a different patient in the Burns Unit.The two strains differed in that in one of them (Z173) silver resistance was linked to rapid lactose fermentation and to mucoid colony structure. In the other (Z147), the progeny were homogeneously slow lactose fermenters and yielded non-mucoid colonies. These features seemed of sufficient interest to warrant being recorded and the present paper is concerned mainly with the evidence for the instability and linkage of the characters in Z173. MethodsCultures were grown in nutrient broth (Oxoid No. 2) and colonies were screened for lactose fermentation on MacConkey agar (Oxoid No. 2). Screening of colonies for resistance to silver nitrate (40 ,ug/ml) and measurement of minimum inhibitory concentrations of the compound was done with a salt-free agar medium (McHugh et al, 1975).Experiments to detect transfer of silver resistance were conducted in Brain Heart Infusion Broth (Difco) using as a recipient a strain of Escherichia coli (M2243) which was ONPG negative, resistant to Received for publication 11 November 1975 nalidixic acid, and auxotrophic for histidine and several other amino acids.Organisms were preserved by drying and were stored in air for short-term and in vacuo for longterm maintenance (Annear and Grubb, 1973). ResultsA colony of Z173 was checked for silver resistance, cultured in broth, and spread on a MacConkey plate which was incubated at 30°C for 20 hours. The majority of the resulting colonies were bright red, indicating rapid lactose fermentation, and were mucoid in texture; the remainder were pale pink, non-mucoid, and smaller than the rapid lactose fermenters. The pale pink colonies assumed a deeper red after several days of further incubation and were shown to be ONPG positive as were the rapid fermenters. Single colonies of the rapid fermenters were transferred to tubes of broth which were cultured at 30°C. The cultures were sampled periodically and spread for the single colonies on MacConkey plates. During a period of 10 days the fraction of rapid lactose fermenters fell from a level of approximately 90% to one of <1%.Screening of the colonies on silver plates by multipoint replication (Annear and Grubb, 1972) during these experiments revealed a firm linkage of silver resistance with rapid lactose fermentation and mucoid colony structure. No exceptions were found in tests with 500 colonies of e...

Diversity of silver resistance genes in IncH incompatibility group plasmids

“…These resistances are selected frequently when metal salts are used as antiseptics. Ag + -resistant bacteria have been reported periodically from sources such as hospitals and burn wounds where silver toxicity might be expected to select for resistance (Annear et al, 1976 ;Bridges et al, 1979 ;Hendry & Stewart, 1979 ;McHugh et al, 1975 ;Pruitt et al, 1998). The physiological, biochemical and molecular basis of bacterial Ag + resistance were not described prior to our studies .…”

Subtractive Hybridization Yields a Silver Resistance Determinant Unique to Nosocomial Pathogens in the Enterobacter cloacae Complex

“…Since the late 1960s, when silver compounds were routinely applied to burn wounds (e.g., silver sulfadiazine in Flamazine), mortality rates rapidly reduced to about 1/4 (35). A decade later, a series of studies reported silver resistance in Enterobacteriaceae and nonfermenters (3,6,20,33). Since that time, an increasing number of outbreaks due to silver-resistant strains of Enterobacteriaceae have been reported.…”

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“…(1,4). Staplz.ylococeus aureus türlerinin yapısındaki penisilinaz plazmidlcri antiman, arsenik, bizmut, kadmiyum, kurşun, civa ve çinko bileşiklerine karşı da mikroorganizmanın direnç göstermesini sağlamaktadır.…”