Comparison of effects of sublethal microwave radiation and conventional heating on the metabolic activity of Staphylococcus aureus.

Abstract

This study was conducted in an attempt to characterize some of the effects of sublethal microwave radiation on cells of Staphylococcus aureus. Cultures were exposed to microwave radiation for 10, 20, 30, and 40 s. The effects of a conventional heat treatment were also compared by placing flasks containing cultures in a boiling water bath for the amount of time required to reach temperatures equivalent to those found in cultures exposed to microwave radiation. Control, microwave-treated, and conventionally heat-treated cultures were centrifuged, pellets were resuspended in distilled water, and the resulting suspensions were passed through a French pressure cell. Cell lysates and walls were then isolated and assayed for enzymatic activity. Thermonuclease production was also determined at various levels of exposure of cells to microwave radiation. Activities of malate and alpha-ketoglutarate dehydrogenases, cytochrome oxidase, and cytoplasmic adenosine triphosphatase were higher in microwave-treated cells than in control cells. Membrane adenosine triphosphatase, alkaline phosphatase, and lactate dehydrogenase activities were unaffected when cells were exposed to microwave radiation. The activity of glucose-6-phosphate dehydrogenase was decreased by exposure of cells to microwave radiation. In conventionally heated cells, activities of glucose-6-phosphate and malate dehydrogenases and cytoplasmic adenosine triphosphatase increased activities of alpha-ketoglutarate and lactate dehydrogenases decreased, and alkaline phosphatase activity remained unaffected. Increased levels of thermonuclease activity were observed when cells were exposed to microwave radiation for 10 or 20 s. Data indicate that microwave radiation affects S. aureus in a manner which cannot be explained solely by thermal effects.

AI evidence extraction

Main findings

Compared with controls, microwave-exposed S. aureus showed higher activities of malate and alpha-ketoglutarate dehydrogenases, cytochrome oxidase, and cytoplasmic ATPase; membrane ATPase, alkaline phosphatase, and lactate dehydrogenase were unaffected; and glucose-6-phosphate dehydrogenase activity decreased. Conventional heating to equivalent temperatures produced a different pattern of enzyme activity changes. Thermonuclease activity increased after 10 or 20 s microwave exposure, and the authors state the effects could not be explained solely by thermal effects.

Outcomes measured

• Enzymatic activity in cell lysates/walls (malate dehydrogenase, alpha-ketoglutarate dehydrogenase, cytochrome oxidase, cytoplasmic ATPase, membrane ATPase, alkaline phosphatase, lactate dehydrogenase, glucose-6-phosphate dehydrogenase)
• Thermonuclease production/activity

Limitations

• Frequency and dosimetry (e.g., SAR/power density) not reported in abstract
• Sample size and replication not reported in abstract
• Short exposure durations only (seconds)
• In vitro bacterial culture model; generalizability to other organisms/conditions unclear from abstract

{
    "study_type": "other",
    "exposure": {
        "band": "microwave",
        "source": null,
        "frequency_mhz": null,
        "sar_wkg": null,
        "duration": "10, 20, 30, and 40 s"
    },
    "population": "Staphylococcus aureus cultures",
    "sample_size": null,
    "outcomes": [
        "Enzymatic activity in cell lysates/walls (malate dehydrogenase, alpha-ketoglutarate dehydrogenase, cytochrome oxidase, cytoplasmic ATPase, membrane ATPase, alkaline phosphatase, lactate dehydrogenase, glucose-6-phosphate dehydrogenase)",
        "Thermonuclease production/activity"
    ],
    "main_findings": "Compared with controls, microwave-exposed S. aureus showed higher activities of malate and alpha-ketoglutarate dehydrogenases, cytochrome oxidase, and cytoplasmic ATPase; membrane ATPase, alkaline phosphatase, and lactate dehydrogenase were unaffected; and glucose-6-phosphate dehydrogenase activity decreased. Conventional heating to equivalent temperatures produced a different pattern of enzyme activity changes. Thermonuclease activity increased after 10 or 20 s microwave exposure, and the authors state the effects could not be explained solely by thermal effects.",
    "effect_direction": "mixed",
    "limitations": [
        "Frequency and dosimetry (e.g., SAR/power density) not reported in abstract",
        "Sample size and replication not reported in abstract",
        "Short exposure durations only (seconds)",
        "In vitro bacterial culture model; generalizability to other organisms/conditions unclear from abstract"
    ],
    "evidence_strength": "low",
    "confidence": 0.7399999999999999911182158029987476766109466552734375,
    "peer_reviewed_likely": "yes",
    "keywords": [
        "microwave radiation",
        "sublethal exposure",
        "conventional heating",
        "thermal vs non-thermal effects",
        "Staphylococcus aureus",
        "metabolic activity",
        "enzyme activity",
        "thermonuclease"
    ],
    "suggested_hubs": []
}

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