GENERAL AND FOOD MICROBIOLOGY PART I - L. V. Krasnikova - 2016

11. INVESTIGATION OF INDOOR AIR MICROFLORA

Objective: to study the Methods of MICROBIOLOGICAL ANALYSIS OF indoor air.

Equipment and Reagents: Krotov apparatus, sterile Petri dishes, nutrient media – meat-peptone Agar, wort agar.

The air in production areas of food Processing facilities can become a source of raw material and finished product contamination by foreign microorganisms. Typically, the air contains various micrococci, sarcinae, non-spore-forming rods, Yeasts, bacterial spores, and Molds, and pathogenic microorganisms may also be present.

During microbiological analysis, the total microbial count per 1 m³ of air is determined, along with the presence of mold Fungi and, if necessary, sanitary-indicative microorganism groups: hemolytic streptococcus (inoculation on Blood agar) and Staphylococcus aureus (inoculation on yolk-salt agar).

Various methods are used to determine the microbial count in the air. The sedimentation and aspiration methods are the most common ones.

11.1. Sedimentation Method

The sedimentation method (Koch's method) is based on the deposition of dust particles and droplets along with microorganisms onto The surface of a nutrient medium in open Petri dishes. Indoor air monitoring is performed as follows. Two sterile Petri dishes are prepared. One of them is filled with molten meat-peptone agar (MPA), and the other with wort agar (WA). After the agar solidifies, the dishes are brought into the room under study, the lids are opened and shifted to the edges so that the entire surface of the nutrient medium is completely exposed. The dishes are left open for 5, 10, or 15 minutes, depending on the degree of air contamination. Then the dishes are covered, inverted upside down, and placed in a thermostat.

Caution! If the dishes are not inverted, Condensation Water released from the agar medium will drip from the inner side of the lid onto the medium surface and blur the microbial colonies.

The dishes with MPA are incubated at 37 °C for 24 hours, and the dishes with WA at 30 °C for 48 hours.

To determine the number of microorganisms in 1 m³ of air, V. L. Omelyansky's formula is used, according to which as many microorganisms settle onto the surface of a dish with an area of 100 cm² within 5 minutes as are contained in 10 dm³ of air:

X = а • 100 • 5 • 100/ST,

where a is the number of colonies grown on the dish; 100 is the conversion factor for the dish area to 100 cm²; 5 is the exposure time according to Omelyansky, min; 100 is the conversion factor to 1 m³ of air; S is the area of the Petri dish (78.5 cm²); T is the exposure time of the open dish, min.

11.2. Aspiration Method

The aspiration method (Krotov's method) is based on The Use of a slit sampler designed by Yu. A. Krotov. The device, housed in a portable case, consists of a sampling unit where a lidless Petri dish is placed on a special platform, an electric motor, a fan, and a rotameter. The fan, rotating at 4–5 thousand rpm, draws in air, and the air jet impacts the surface of the nutrient medium in the Petri dish, leaving microorganisms on it. The air exits the device through the rotameter. To ensure an even DISTRIBUTION OF MICROORGANISMS on the medium surface, the disk with the dish rotates at 60 rpm. The air sampling rate is 25 dm³/min. When determining the total bacterial count, the volume of sampled air must be 100 dm³. The inoculated dishes are removed from the apparatus, covered with lids, placed in a thermostat at 37 °C for 24 hours, then removed and left at room Temperature for 24 hours. The number of grown colonies is counted, and the count is recalculated per 1 m³ of air:

X = а/1000 • V,

where a is the number of colonies grown on the dish; V is the volume of air sampled through the device; 1000 is the target air volume, dm³.

In addition to quantitative data, a qualitative characterization of the air microflora is provided. For this purpose, the bacterial colonies grown on the Petri dishes are described, and microscopic preparations from these colonies are prepared. Bacterial colonies are described as specified in section 5.3.

The test results are presented in a table in the form of Table 11.1, and microscopic preparations of the colonies are sketched in the notebook.

Class="center">Table 11.1. Study of the Morphology of bacterial colonies grown on MPA

Mold fungi grown in the Petri dish with wort agar are examined visually and under a Microscope using an 8x objective lens. Using the mold descriptions provided in Section 5, their genus is identified.

The sanitary condition of the test room air is assessed in accordance with sanitary standards and regulations. Table 11.2 shows a fragment of the sanitary and microbiological control logbook form for food processing facilities.

Table 11.2. Sanitary and microbiological control at the facility

Using the data presented in Table 11.2, evaluate and conclude on the microbiological purity of the air in the inspected facility.

Review Questions

1. What methods are used to perform microbiological analysis of indoor air?

2. What are the Criteria for the sanitary assessment of air in food industry production facilities?

3. Which microorganisms are most frequently found in indoor air?