Adherence of non-enteropathogenic Escherichia coli to HeLa cells.

Three hundred and nine strains of Escherichia coli isolated from infants and children with diarrhoea but not belonging to any recognised classes of diarrhoeagenic E. coli were investigated for their ability to adhere to HeLa cells in the presence of D-mannose. An enteroadherent-aggregative pattern (EAgg) was observed in 32.03%, localised adherence (LA) in 4.5%, diffuse adherence (DA) in 5.8%, and LA/DA and EAgg/LA in 1.9% and 1.2% of the isolates respectively. The results obtained with 100 control isolates were: EAgg 17%, LA 2%, DA 2%, LA/DA 2%, EAgg/LA 6% and DA/EAgg 1%. No adherence was manifested by 168 (54.36%) of 309 diarrhoeal isolates and 70% of the 100 control isolates. The results of this study showed that amongst non-enteropathogenic E. coli, strains exhibiting the EAgg pattern are significantly associated with diarrhoea (p < 0.005). Most of these strains showed a pattern of multiple drug resistance.

In vitro adhesion and invasion of Salmonella enterica serovar Havana.

A total of 132 isolates of the Havana serovar of Salmonela enterica were studied for their adhesion to and invasion of Hela cells in the presence of D-mannose. A total of 124 (93.9%) isolates were adherent, and 51% of these were invasive. Of these 124 strains 82 (66%) adhered to HeLa cells with a pattern typical for enteroaggregative (EAgg) Escherichia coli whereas the remaining 34% adhered in a non-aggregative (non-EAgg) pattern. Of the 82 strains showing the EAgg pattern 60% were invasive whereas only 33% of the 49 non-EAgg isolates invaded HeLa cells (P < 0.01). The action of mannose-sensitive type 1 pili was inhibited by the addition of D-mannose. Therefore we conclude that type 1 pili are not important in adhesion and invasion of Havana.

The use of biochemical fingerprinting, phage typing and antimicrobial-susceptibility testing in the detection of epidemic strains of Salmonella of serotype Typhimurium in Iran.

A collection of 86 strains of Salmonella of serotype Typhimurium isolated from children with gastroenteritis in Tehran, Iran was examined for biochemical phenotype, phage type and antibiotic-resistance pattern. Twenty-seven biochemical phenotypes (BPTs), 14 discrete phage types (PTs) and 18 resistotypes (RTs) were identified. Fifty-three strains (62%) belonged to two major and probably related BPTs, whereas the other 33 isolates belonged to less common BPTs. The two predominant BPTs contained 26 strains of the same PT and 23 strains of the same RT. Different PTs and RTs of strains with similar BPT were sometimes observed, possibly reflecting antibiotic pressures in Iran. These results suggest that two major "clones" of Typhimurium strains are particularly common in Iran and, although each method alone adequately detected these and other less common "clones", biochemical fingerprinting provided additional information about relationships among strains.

Application of biochemical fingerprinting to the investigation of clonal groups of Salmonella of serotype Havana.

A computerised typing method based on biochemical fingerprinting was used to investigate biochemical phenotypes (BPTs) among 70 strains of Salmonella of serotype Havana isolated from human cases of gastroenteritis in Iran and other parts of the world. A total of 16 BPTs comprising five common and 11 single phenotypes was identified. The most frequently found BPT contained 24 isolates from Iran and nine from other countries. Three common BPTs with two, seven and 15 isolates were found among Iranian strains only and one common BPT with two isolates was found among non-Iranian strains only. Antibiotic-resistance patterns and virulence properties of strains from these common BPTs suggested that they might be unique clones. Forty-two Iranian isolates shared multi-resistance to between three and seven antibiotics. In contrast, none of the isolates from other countries was resistant to antibiotics. Furthermore, 43 Iranian isolates showed mannose-resistant adhesion to HeLa cells and 24 of them possessed an aerobactin-mediated iron-uptake system, whereas none of the isolates from other countries possessed any of these virulence properties. These findings suggest that four unique clones of Salmonella Havana with different BPTs and virulence properties are common in Iran; two particular clones were responsible for a majority of Havana infections there. However, the most prevalent BPT found among Iranian strains was also common in strains from other countries. It is concluded that biochemical fingerprinting, as used in this study, is a reliable method for identifying clonal groups of Havana strains. The method is reproducible, easy to perform and can be used alone, or in combination with other typing methods, in epidemiological studies of serotype Havana.

Occurrence of colonization factor antigens I & II in enterotoxigenic Escherichia coli associated diarrhoea in Iran & correlation with severity of disease.

The occurrence of colonization factor antigens I and II (CFA/I and II) and type 1 somatic pili was investigated in 197 enterotoxigenic Esch. coli (ETEC) isolated from 197 patients of diarrhoea (aged under 3 yr) during February 1985 to March 1986 in Tehran, Iran. Among ETEC strains, 154 strains were heat-stable enterotoxin (ST) producers, 27 strains were heat-labile enterotoxin (LT) producers, and 16 strains produced both toxins. Sixty five (33%) strains showed mannose-resistant haemagglutination (MRHA) of human and/or bovine erythrocytes; of these, 51 (86%) strains were positive for CFA/I and II. Seventy one (36%) strains also exhibited type 1 somatic pili. CFA/I was found in 4 (15%) LT producing, 24 (16%) ST producing, and 2 (13%) LT/ST producing strains. In contrast, CFA/II was only found in ST producing strains (17 strains) and those producing both toxins (4 strains). Patients having CFAs-positive ETEC strains had a significantly (P less than 0.001) higher number of stool evacuation per day and a longer duration of diarrhoea than those having CFAs-negative strains. Fifty nine patients had mixed infections of ETEC strains and other enteropathogens. CFA/I or II (CFAs)-positive and CFAs-negative ETEC strains were found in 17 and 42 patients with mixed infections respectively. The mean number of stool evacuations per day was much higher in patients with ETEC and rotavirus than those with only ETEC infection (P less than 0.001). However, severity of the disease was not affected by the presence or absence of CFA/I or II in ETEC strains found in these patients.

Aetiological studies of diarrhoeal diseases in infants and young children in Iran.

The aetiology of diarrhoeal diseases was investigated among 715 patients admitted to four Children's Hospitals in Tehran, during February 1986 to March 1987, and also among 443 patients attending the central Out-Patient Clinic in Sanandaj, State of Kordestan, during October 1986. Enteropathogenic Escherichia coli (EPEC) were the most common pathogens found in both areas. Almost 26.7% of the patients in Tehran and 20.1% of the patients in Sanandaj were infected with EPEC. Enterotoxigenic E. coli (ETEC) were the next most frequent groups found (17.1% both in Tehran and Sanandaj), with heat-stable enterotoxin (ST)-producing strains being dominant. Of 122 ETEC strains isolated in Tehran, 94 (77%) strains produced ST, 15 (12.3%) strains produced heat-labile enterotoxin (LT) and 13 (10.7%) strains produced both LT and ST. Almost the same pattern of toxigenicity was observed among ETEC strains isolated in Sanadaj. Of the 76 ETEC strains isolated in this area, 70 (92.1%) strains were ST producers, followed by those producing both LT and ST (five strains) and LT only (one strain). One strain of enteroinvasive E. coli (EIEC) was also isolated from a patient in Tehran. The rates of salmonella and shigella isolation were 8.8 and 5.7% in Tehran and 3.8 and 4% in Sanandaj respectively. Enterohaemorrhagic E. coli, Vibrio cholerae and V. parahemolyticus were not isolated but a mixture of two or more pathogens was found in 59 patients (8.2%) in Tehran and in 20 patients (4.5%) in Sanandaj. These findings suggest that diarrhoegenic E. coli are the most important cause of diarrhoeal diseases in infants and young children in these areas in Iran.

Antimicrobial drug resistance and resistance factor transfer among clinical isolates of salmonellae in Iran.

508 salmonella strains isolated during 1983-1986 in Tehran, Iran from cases of diarrhoea in children less than 5 were tested for sensitivity to 10 antimicrobial drugs and their ability to transfer the resistance determinants. Salmonella typhimurium and S. havana were most common (45.7% and 30.9%, respectively) followed by S. typhi (2.9%) and S. larochelle (2.4%). The antimicrobial agents used were chloramphenicol (C), gentamicin (G), tetracycline (T), ampicillin (A), cephalothin (Cf), trimethoprim-sulfamethoxazole (SXT), kanamycin (K), nalidixic acid (Na), streptomycin (S), and furoxone (F). 91% of the salmonellae isolates contained resistance determinants, of which 89.6% were resistant to more than one agent. Strains resistant to 4-7 drugs comprised 85.6% of the total isolates. Ampicillin resistance was found in 85.4% and nalidixic acid in 2.7%. 58 different patterns of resistance to the antimicrobial agents used were observed, of which C/T/A/SXT/K/S and C/T/A/SXT/K/S/Cf were the most frequently encountered. 71.9% of the resistant strains contained transferable resistance factors and S. typhimurium had the highest rate of transfer (80.8%). Resistance to chloramphenicol had the highest rate of transfer among the agents used (77.4%) and streptomycin the lowest (20.0%). The pattern most frequently transferred was C/T/A/SXT/K (41.9%).