The poultry industry is emerging as the world's largest market. The total poultry in the country is 851.81 million in 2019, increased by 16.8% over previous censusas reported by Basic Animal Husbandry Statistics. During the last few decades, there is an emphasis on intensive rearing of poultry. Despite ofsignificant advances, diseases are still a major constraint for profitable poultry production. Infectious and non-infectious diseases take a heavy toll from all types of poultry enterprises. Amongst the various disorders, enteric diseases accounts for high mortality in poultry and the common gastrointestinal tract conditions reported are colibacillosis, salmonellosis, coccidiosis, Ranikhet disease, necrotic enteritis, and fatty liver syndrome¹. Besides, indiscriminate use of antibiotics in the poultry sector is leading to antibiotic drug resistance which is a global concern. There are reports on clear cut and rapid transmission of antimicrobial resistance from food animals to humans². Therefore, this study was designed to observe the prevalence of bacterial diseases in poultry farms, and to assess their antibiotic susceptibility pattern.

Post mortem examination of 84 poultry carcasses obtained from different regions of Southern Rajasthan was conducted in the Department of Veterinary Pathology. Samples were aseptically collected from the liver, intestine, and heart blood. The samples were then processed for isolation and identification of bacteria by the standard procedure of³.The samples (heart blood, liver and intestine) collected during postmortem examination were incubated in Nutrient broth at 37^OC for 24 to 48 h. The growth obtained was then streaked on blood agar (BA) and Mac Conkey's Lactose agar (MLA) and incubated at 37^OC for 24 h. The bacterial growth so obtained was studied for colony characteristics and hemolysis on various agar media as per the standard procedure described by⁴.

For primary identification of bacteria, catalase test and oxidase test were performed. Besides, Indole test, Methyl red test, Voges Proskauer test, Citrate utilization tests were also performed according to the standard procedure described by⁴. Gram's staining of a single pure colony was done for microscopic examination. After isolation, and complete biochemical characterization, the Salmonella and E. coli isolates were sent for serotyping to the National Salmonella and Escherichia center, (NSEC), Central Research Institute, Kasauli (HP), India.

Bacterial isolates obtained in the study were tested for In-vitro drug susceptibility by the disc diffusion method as suggested by⁵. A small amount of test culture was taken in a sterile platinum loop and transferred into a tube of Nutrient broth and then kept in an incubator at 35^OC for 2 to 5 hours. The broth culture was then evenly spread over the surface of Mueller Hinton agar plates. The antibiotic discs of standard concentrations (Ampicillin 10 mcg/disc, Cefixime 5 mcg/ disc, Co-trimoxazole 25 mcg/disc, Gentamicin 10 mcg/ disc, Amoxyclave 30 mcg/disc, Streptomycin 10 mcg/ disc, Tetracycline 30 mcg/disc, Chloramphenicol 30 mcg/ disc, Ciprofloxacin 5 mcg/disc, Cefotaxime 30 mcg/disc, Trimethoprim 5 mcg/disc, Ceftriaxone 10 mcg/disc) were then placed on the agar with a minimum 24 mm distance between two discs. The discs were gently pressed to have uniform close contact with the medium. These plates were then kept at 37^OC for 24 h. The results were recorded as sensitive (S) and resistant (R) on the basis of the zone size interpretation chart, provided by the manufacturer.

The bacteria isolated from the liver, intestine and heart blood of birds during the study period were Escherichia coli (70.31%), Salmonella spp. (12.5%), Staphylococcus aureus (9.37%), Pseudomonas aeruginosa (6.25%) and Klebsiella pneumoniae (1.56%) (Figs. 1, 2 and 3). The necropsy examination revealed that Escherichia coli infected poultry showed presence of fibrin layer on all the visceral organs particularly on heart and liver (Fig. 4). Purulent exudate was observed in the lumen of proventriculus & gizzard. In Salmonellosis, the characteristic lesions in poultry were hepatomegaly and multiple necrotic foci on firm and dark red liver.

Spleen showed presence of small and grayish white necrotic foci. In heart, haemorrhages were evident and white nodular growths were seen on myocardium. Gross lesions observed in Pseudomonas aeruginosa infection were congestion in trachea, lungs, heart and intestines. Few necrotic foci on liver and mild fibrinous perihepatitis and pericarditis, and catarrhal enteritis ina few cases were seen. Infection of Klebsiella pneumonia revealed hepatomegaly along with multiple pale hard necrotic areas in the liver and heart, necrotic area in spleen and kidney, severe congestion & haemorrhages were noted in the large intestine & cloaca. In Staphylococcus aureus infection, haemorrhages and congestion were noted throughout the gastrointestinal tract and liver.

The results of serotyping revealed that predominant serotype of E. coli isolated was O83 (45.83%) followed by O120 (12.5%), O149 (8.33%), O11 (4.16%), O134 (4.16%), O7 (4.16%), O157 (4.16%), O9 (4.16%), rough (4.16%) and untypable (8.33%). E. coli serotypes O157 and O149 were found associated as a mixed infection with Salmonella spp. E. coli serotypes O83 and O149 were found associated with P.aeruginosa infection. E. coli serotypes O83 and O120 were found associated with S.aureus. E. coli infection was also found along with parasitic infection (roundworm and tapeworm).

Salmonella spp. were isolated from a total of 12.5% of cases. The result of the serotyping of Salmonella samples revealed three different serotypes viz. S. Typhimurium, S. Welteverden, S. Linderburg. However, Staphylococcus aureus was isolated from 9.37% of cases. P. aeruginosa was isolated from 6.25% of cases. K. pneumoniae was reported from 1.56% of cases and identified based on culture characteristics and biochemical tests. Besides, K. pneumoniae was found along with infection of S. Typhimurium and parasitic infection (roundworm and tapeworm).

Antibiotic susceptibility tests revealed a varying degree of sensitivity to the chemotherapeutic agents (Table 1). The resistance of E. coli is seen against ampicillin, Co-Trimoxazole, tetracycline and cefotaxime although ciprofloxacin is still showing 50% sensitivity. The antibiotic susceptibility results of Salmonella spp. revealed sensitivity to most of the antibiotics tested except to Co-Trimoxazole and 50% to both Tetracyclin and Cefotaxime.

In most of the reports, E. coli is the most predominant bacteria isolated from poultry^6-9. O83, O149, and O120 were also predominant serotypes isolated from northern India indicating a prevalence of the similar types of serotypes in northern and western India¹⁰, ¹¹. However, in addition to these, other serotypes (O1, O22, O37, O114, O118, O78, O75, O2, O6, and O111) were also isolated from north India¹¹, ¹². It is observed that E. coli serotype O9 is prevalent in Southern Rajasthan as well as in Odisha and West Bengal indicating its countrywide presence¹³, ¹⁴. The major concern is the presence of E. coli O157 isolate as causes severe disease in humans. The vast variation in other E. coli serotypes may be due to variation in geographical area, climate and host and managemental procedures practiced in these areas.

It has been reported that 17.78% of the flocks tested from seven states of India were positive for Salmonella sps.¹⁵. These were identified as S. Gallinarum and S. Pullorum. Highest seroprevalence of salmonellosis is reported from Karnataka state (21.73%), while the lowest from Haryana (8.86%)¹⁶. However, a lower incidence of salmonellosis (4.90% and 6.1%) was reported in West Bengal, India¹⁷, ¹⁸. This indicated that salmonellosis was more prevalent in the southern states of India as compared to the other parts of the country. Serotypes of Salmonella identified in the present study were Salmonella Typhimurium, S. Linderburg, and S. Weltevreden. S. Typhimurium has been reported by other workers from different parts of India and is one of the commonest serotypes isolated in India^17,19,20. S. enterica serovar Weltevreden is associated with the outbreak of foodborne gastroenteritis in humans reported from Mangalore, Kolkata, Pune^21-23 and even from Reunion island, France²⁴. There is increasing occurrence of Non-Typhoidal Salmonella infections in humans due to S . Typhimurium and S. Weltevreden²⁵and so there is urgent need to control these infections in poultry to reduce foodborne infections in humans. This suggests that strict biosecurity measures must be taken to reduce the occurrence of foodborne pathogens. S . Weltevreden is capable of persisting for long periods in soil and thus it is important to treat contaminated poultry manure²⁶.

The prevalence of S. aureus in Haryana (North India) is reported to be 5.63%²⁷ whereas 82% in coastal Andra Pradesh (South India)²⁸. This indicates that the prevalence of S. aureus infection is lower in northern and western India as compared to Southern India. The prevalence of P. aeruginosa and K. pneumoniae noted was 6.25% and 1.56%, respectively. Similarly, other workers also reported a low incidence of these bacteria in poultry farms located in North India¹⁰, ²⁷.

The resistance of E. coli to antibiotics is also observed in other parts of the world like California²⁸, Italy²⁹ and Bangladesh³⁰, and India³¹ suggesting that it's a worldwide public health issue. However,sensitivity to ceftriaxone was previously reported higher as compared to the present study indicating that E. coli may become resistant to this drug soon¹⁰. Low levels of resistance to gentamicin (12%) are observed in Iran³² while in Tanzania, highest resistance is reported against Co-trimoxazole (65.8%) whereas Gentamicin was found sensitive (69.3%)³³. Gentamicin is also reported to be highly sensitive in the years 2014 and 2015, whereas, in the present study, Gentamicin was found resistant to 75.87% of E. coli isolates showing the emergence of E. coli resistant to Gentamicin³⁴. Moreover, antibiotic resistance reported in areas of Maharashtra, India is more as compared to the present study³⁵. As per literature there is an increased incidence of E. coli resistant to Oxytetracycline and Fluoroquinolones in South East Asian Countries³⁶. The increasing incidence of antibiotic resistance may include inappropriate and/or excessive use of antimicrobials. This suggests the need for judicious use of antibiotics in poultry.

The antibiotic susceptibility results of Salmonella spp. showed contrast to the results reported by other workers who observed sensitivity to cefotaxime and resistance to ciprofloxacin in Haryana state which may be due to the differences in the use of antibiotics in different regions and environmental conditions³⁷. Similarly, high sensitivity to chloramphenicol and resistance to tetracycline²⁰ whereas it is observed that Non-Typhoidal Salmonella isolates in Vietnam were resistant (20-40%) against tetracycline, chloramphenicol, sulfamethoxazole-trimethoprim, and ampicillin³⁸. In contrast to the results of the present study, some workers reported the resistance of Salmonella isolated from backyard poultry in West Bengal towards chloramphenicol, ciprofloxacin, gentamicin, and oxytetracycline¹⁸. This suggests the need for good managemental practices at farms and restriction of indiscriminate use of antibiotics in poultry. This variation in susceptibility of the bacteria to the same antibiotic in different areas of the country as well as the world suggests that there is a need to use area-specific and sensitive antibiotics.

The sensitivity patterns of K. pneumonia and P. aeruginosa indicates that with time the resistance of these bacteria is increasing towards antibiotics because those antibiotic agents which were earlier showing sensitivity are now 100% resistant⁸, ²⁷.

None of the antibiotics were 100% sensitive to S. aureus. More or less similar sensitivity patterns have been reported by other workers^39-41. The rapid increase in antibiotic resistance might be due to the misuse of antibiotics in poultry farms. The other risk factors could be over-prescribing of antibiotics, unnecessary use of antibiotics for growth and poor hygiene and sanitation practices.

It is therefore concluded that the majority of bacterial isolates were sensitive to Cefixime, Amikacin, Ceftriaxone and Cefotaxime. So, these drugs may be used as the drug of choice against these bacterial isolates. There is a need to implement better management practices and adhere to strict biosecurity measures along with the prudent use of antibiotics to minimize disease occurrence and consequent economic losses.

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